Appropriate Sanitation Alternatives /9 g A Planning and Design Manual John M. Kalbermatten * DeAnne S. Julius * Charles G. Gunnerson * D. Duncan Mara World Bank Studies in Water SuD DXv and Sanitation 2 Appropriate Sanitation Alternatives A Planning and Design Manual WOR1LID BANK STUIDIE-S IN W'AT'E1R SUPPLY AND SANITATION 2 I Appropriate Sanitation Alternatives A Planning and Design Manual John M. Kalbermatten, DeAnne S. Julius, Charles G. Gunnerson, and D. Duncan Mara Published for The World Bank The Johns Hopkins University Press Baltimore and London Copyright © 1982 by the International Bank for Reconstruction and Development / THE WORLD BANK 1818 H Street, N.W., Washington, D.C. 20433, U.S.A. All rights reserved Manufactured in the United States of America The Johns Hopkins University Press Baltimore, Maryland 21218, U.S.A. The views and interpretations in this book are the authors' and should not be attributed to the World Bank. to its affiliated organizations, or to any individual acting in their behalf. EDITOR James McEuen PRODUCTION Virginia deHaven Hitchcock FIGURES Pensri Kimpitak BOOK DESIGN Brian J. Svikhart COVER DESIGN George Parakamannil Library of Congress Cataloging in Publication Data Main entry under title: Appropriate sanitation alternatives. (World Bank studies in water supply and sanitation; 2) Bibliography: p. Includes index. 1. Underdeveloped areas-Sanitary engineering. I. Kalbermatten, John M. II. Series. TD353.A64 1982 628.1'09172'4 82-13098 ISBN 0-8018-2584-9 (v. 2: pbk.) Contents Foreword ix Part Two. Sanitation Program Planning Preface xi 5. Comparison of Sanitation Technologies 39 Water Supply Service Levels 39 Acronyms and Abbreviations xiii Soil Conditions 42 Housing Density 42 1. An Overview 3 Costs 43 Dimensions of the Problem 3 Other Factors 44 The Constraints 4 Environmental Factors Affecting Choice of Incremental Sanitation 4 Technology 45 Sanitation Program Planning 5 Institutional Constraints 45 6. Selection of Sanitation Technologies 46 Part One. Socioeconotic Aspects Selection Algorithms 46 of Sanitation Program Planning Postselection Questions 51 7. Sanitation Upgrading Sequences 52 2. Health Aspects of Sanitation 11 Composting Toilets 52 A Southeast Asian Family 11 Three-Stage Septic Tanks 52 A North African Family 13 Vault Toilets 52 Excreted Infections 15 Vatriles 52 Environmental Classification of Excreted viP Latrines and ROEC'S 55 Infections 17 plets S o Health Benefits of Sanitation Sample Staged Solutions 55 Improvements 20 Excreted Infections and Children 21 Part Three. Sanitation Technology Options Groundwater Pollution from On-site 8. Latrine and Toilet Superstructures 61 Excreta Disposal 21 9. Latrine and Toilet Fixtures 64 3. Community Participation 23 Squatting Plates for vIP Latrines 64 Characteristics of Community Squatting Plates for ROEC's 66 Participation 23 Pedestal Seats for vip Latrines and Institution-Community Linkage 25 ROEC'S 66 Squatting Plates for Composting, PF, and 4. Economic Analysis of Sanitation Vault Toilets 69 Technologies 27 Pedestal Seats for PF and Vault Toilets 72 Economic Costing 27 Financial Costing 31 10. vIP Latrines 73 Costing of Community Support VIDP Latrines 73 Services 32 ROEC'S 77 Appendix. Examples of Economic Pit Design 77 Costing 32 Factors Affecting Suitability 81 v vi 11. Composting Toilets 83 Bibliography 153 Continuous Composting Toilets 83 Index 157 Batch Composting Toilets 83 Vault Design 87 Factors Affecting Suitability 88 Figures 12. PF Toilets 89 1-1. Recommended Structure of Feasibility PF Toilet Design 89 Studies for Sanitation Program Factors Affecting Suitability 91 Planning 6 Sewered PF Systems 91 5-1. Gereric Classification of Sanitation 13. Aquaprivies 94 Systems 40 Technical Appropriateness 94 6-1. First-stage Algorithm for Selection of Self-topping or Sullage Aquaprivy 99 Sanitation Technology 47 Tank Design 99 6-2. Second-stage Algorithm for Selection of Factors Affecting Suitability 100 Sanitation Technology 48 6-3. Third-stage Algorithm for Selection of 14. Septic Tanks, Soakaways, and Drainfields 101 Sanitation Technology 49 Effluent Disposal 101 Technical Appropriateness 104 7-1. Potential Sanitation Sequences 53 Factors Affecting Suitability 107 7-2. Sample Sanitation Sequences 54 15. Conventional Sewerage 109 8-1. Alternative Materials for Latrine Excreta Disposal 109 Superstructures 62 Sewage Collection 109 9-1. Concrete Squatting Plate 65 16. Small-bore Sewers 114 9-2. Tanzanian "Flap-trap" Design for VIP Technical Appropriateness 114 Latrines and DVC Toilets 66 Design Criteria 114 9-3. Pedestal Seats for Dry Latrines and Chute Designs for ROEC'S 67 17. Bucket Latrines 116 9-4. Water-seal Squatting Plate for PF Toilets Located Immediately above the Pit 68 18. Vault and Cartage Systems 118 9-5. Galvanized Sheet-metal Water-seal Unit for Designs Crieteria 118tability 120 PF Toilets Located Immediately above the Factors Affecting Suitability 120 Pit 69 19. Communal Sanitation Facilities 122 9-6. Plastic or Fiberglass Water-seal Toilet 70 Effluent Disposal 122 9-7. PF Units for Displaced Pits 71 Design Criteria 122 10-1. Conventional Unimproved Pit Latrine 74 20. Disposal and Treatment of Sullage 125 10-2. VIP Latrine 75 Sullage Volume and BOD 125 10-3. VIPD Latrine 76 Health Aspects 126 10-4. ROEC 78 Design Criteria 126 10-5. Alternative Pit Designs 80 21. Off-site Treatment 128 11-1. "Multrum" Continuous-composting Waste Stabilization Ponds 128 Toilet 84 Night-Soil Treatment Ponds 133 11-2. DVC Toilet Used in Vietnam 85 Thermophilic Composting 133 11-3. DVC Toilets 86 Appendix. Examples of Waste Treatment 12-1. Alternative Designs for PF Toilets 90 Calcualtions 135 12-2. PF Toilet-Septic-tank Systems 92 22. Resource Recovery 145 13-1. Conventional Aquaprivy 95 Agricultural Reuse 145 13-2. Formal Equivalence of Sullage Aquaprivy to Aquacultural Reuse 148 VIP Latrine with Separate Sullage Biogas Production 151 Soakaway or to PF Toilet 96 Social, Institutional, and Economic Aspects 13-3. Formal Equivalence of Sewered Aquaprivy of Reuse 151 to Sewered PF Toilet 97 vii 13-4. Improved Sewered Aquaprivy with Sullage Tables Disposal 98 2-1. Viral, Bacterial, and Protozoan Pathogens 14-1. Schematic of Conventional Septic Found in Excreta 12 Tank 102 2-2. Helminthic Pathogens Found in Feces 13 14-2. Alternative Septic Tank Designs 103 2-3. Environmental Classification of Excreted 14-3. Schematic of Soakaway 104 Infections 18 14-4. Drainfield for Septic Tank Effluent 105 4-1. Annual Economic Costs of a Ventilated 14-5. Evapotranspiration Mounds 106 Improved Pit (vip) Latrine 33 15-1. Influence of Time and Temperature on 4-2. Shadow-priced Collection and Treatment Selected Pathogens in Night Soil and Costs of a Conventional Sewerage Scheme Sludge 112 Constructed over Five Years 33 4-3. Costs and Wastewater Flows for 17-1. Bucket Latrine and Cartage 117 Conventional Sewerage Scheme 34 4-4. Present Values (pv) of Costs and 18-1. Alternative Designs for Vault Toilets 119 Wastewater Flows for Conventional 19-1. Schematic of a Communal Sanitation Sewerage Scheme 34 Facility 123 5-1. Descriptive Comparison of Sanitation 20-1. Improved Stormwater Channels for Drainage Technologies 41 of Sullage 127 5-2. Summary of Annual Economic Costs per Household 43 21-1. Stabilization Pond Layout and Details 129 6-1. Critical Information Needed for Selection 21-2. Inlet Structures for Stabilization and Design of Sanitation Systems N0 Ponds 130anDeinoSaiainSsms5 21-3. Alternative Interpond Connections 131 7-1. Costs of Sample Sanitation Sequences 56 21-4. Outlet Structures for Stabilization 14-1. Minimum Required Distances from Various Ponds 132 21-5. Beltsville Agricultural Research Center Physical Features for Septic Tanks and (BARC) System for High-rate Thermophilic Soakaways Located in Common Well- Composting 134 developed Soils 104 21-6. Alternative Flow Diagrams for Composting 16-1. Slopes and Capacities of Circular Pipes Night Soil by BARC System 138 Flowing Full 115 22-1. Reuse Potential of Wastes 146 21-1. Equipment Needed for Night-Soil 22-2. Schematic of Typical Biogas Digesters 150 Composting 143 I I r I Foreword DESPITE THE IMPRESSIVE LEVEL of economic growth also directed to the impact of water service levels the developing countries as a whole have achieved upon waste disposal options and, where applicable, over the past quarter century, most of the people in to opportunities for recovering some of the costs by these countries do not have a safe water supply or physically recycling the water and fertilizer compo- even rudimentary sanitation. Immediate investment nents of the waste. costs for providing these services at the standards This is the second of a series of volumes which which prevail in developed countries are estimated document the Bank's research findings. Based on at over $800,000 million. Corresponding operating case studies in thirty-nine commuriities around the costs are projected at another $10,000 million per world, it presents to project engineers, analysts, and year. These amounts vastly exceed the resources technicians a planning and design manual for the available for the sector. To help address this problem many sanitation options which are available and ap- a two-year research project to develop more appro- propriate to developing country conditions. Other priate (i.e. lower cost) technologies for water supply volumes in the series include a technical and eco- and waste disposal was undertaken by the World nomic assessment of these sanitation options to plan- Bank in 1976-1978. Meanwhile, the member coun- ning officials and senior policy advisors, and a com- tries of the United Nations have declared the 1980s pilation and synthesis of health and disease factors to be the International Drinking Water Supply and in sanitation system planning and implementation. Sanitation Decade, with the obiective of satisfying Their publication is particularly timely at the begin- for all populations of the globe two of the most basic ning of this decade. More important, if the twin ob- human needs-clean water and the sanitary disposal jectives of economic growth and the eradication of of human wastes. absolute poverty are to be met, the nations of the The Bank's research revealed the technological, world must ensure that everyone has access to safe economic, environmental, and institutional interde- water and adequate sanitation. It is to the sanitation pendence of water supply, sanitation, and health. objective that this volume is dedicated. Waste disposal technologies costing as little as one- tenth the amount of conventional sewerage were WARREN C. BAUM identified. Means to ensure high health and envi- Vice President, Central Projects Staff ronmental benefits were developed. Emphasis was The World Bank ix I I Preface IN 1976 THE WORLD BANK undertook a research pro- sanitation options is included because water use is a ject on appropriate technology for water supply and determinant of wastewater disposal requirements. The waste disposal in developing countries. Emphasis was guidelines, procedures, and technologies contained placed on sanitation and reclamation technologies, in this volume are based upon World Bank studies particularly on ways in which they are affected by in nineteen developing and industrial countries where water service levels and by the ability and willingness local specialists conducted or contributed to the re- of the project beneficiaries to pay for them. In ad- search. Both the research and its application con- dition to the technical and economic factors, assess- tinue to be undertaken by the Bank and others ments were made of environmental, public health, throughout the world. Future research will present institutional, and social constraints. The findings of improvements in resource recovery technologies, such the World Bank research project and other parallel as biogas; information on others, such as marine dis- research activities in the field of low-cost water sup- posal of urban wastes, combined sewers, water-sav- ply and sanitation are presented in the series of pub- ing plumbing fixtures, and small-bore sewer design lications entitled World Bank Studies in Water Supply and operation; and more precise estimates of ma- and Sanitation, of which this is number 2. Other vol- terials and construction requirements on both per umes in this series are: capita and population-density bases. Number 1. John M. Kalbermatten, DeAnne S. This manual is intended both for professionally Julius, and Charles G. Gunnerson, Appropriate trained project engineers and scientists and for tech- Sanitation Alternatives: A Technical and Economic nicians and field workers who are familiar with the Appraisal geographical and cultural conditions of the project Number 3. Richard G. Feachem, David J. Brad- areas to which they are assigned. The reason for ley, Hemda Garelick, and D. Duncan Mara, San- emphasis on this familiarity is clear: it is upon the itation and Disease: Health Aspects of Exereta and observations, interpretations, and communications Wastewater Management of staff in the field that the ultimate success of san- itation programs depends; technical and economic A series of related monographs entitled Appropriate analyses must incorporate recommendations from Technology for Water Supply and Sanitation is avail- knowledgeable field specialists. able from the World Bank. Additional volumes and The findings and recommendations of this report occasional papers will be published as ongoing re- are based on surveys of relevant literature (Ryb- search is completed. czynski, Polprasert, and McGarry 1978; Kuhlthau It is the purpose of this manual to provide early 1980), an evaluation of sociocultural aspects (El- dissemination of research results to field workers, to mendorf and Buckles 1980), detailed field studies summarize selected portions of the other publica- (Kuhlthau 1980; Feachem, Mara. and Iwugo 1980; tions that are needed for sanitation program plan- Elmendorf 1980; Lauria and others 1980), and the ning, and to describe engineering details of alter- personal observations, experience, and advice of col- native sanitation technologies and the means by which leagues in the World Bank and other institutions. the technologies can be upgraded. Although the de- Because the list of contributors is so large, only a sign of water supply systems is not discussed at length, few can be mentioned. We wish to acknowledge in information on water service levels corresponding to particular the support given to this project by Yves xi xii Rovani. director of the Bank's Energy Department, giene (London). who have generously contributed and the valuable review and direction provided by help and advice and have allowed us to abstract and the Bank staff serving on the steering committee for quote some of their own publications. the project: Edward Jaycox, Arthur Bruestle, Wil- The reports could not have been produced without liam Cosgrove, Frederick Hotes. Douglas Keare, Jo- the dedication and cooperation of the secretarial staff, hannes Linn, Richard Middleton, Ragnar Overby, Margaret Koilpillai, Julia Ben Ezra, and Susan Pur- Alistair Stone, and Charles Weiss; Michael McGarry cell, and the editorial assistance of research assistant and Witold Rybczinski of the International Devel- David Dalmat. Their work is gratefully acknowl- opment Research Centre (Ottawa) were generous in edged. their advice on specific issues. The contributions of consultants conducting field studies and providing specialized reports are acknowledged in the mono- JOHN M. KALBERMATTEN graphs to which they have contributed. DEANNE S. JULIUS Special thanks are due to Richard Feachem and CHARLES G. GUNNERSON David Bradley of the Ross Institute of Tropical Hy- D. DUNCAN MARA Acronyms and Abbreviations AIC Average incremental cost PF Pour-flush (toilet) BARC Beltsville Agricultural Research Center PV Present value (U.S. Department of Agriculture, Beltsville, Pvc Polyvinyl chloride Maryland, U.S.A.) ROEC Reed Odorless Earth Closet BOD Biochemical oxygen demand UNC Units of national currency BOD5 Five-day BOD (by the standard test) VIDP Ventilated improved double-pit (latrine) CRF Capital (or annuity) recovery factor V1P Ventilated improved pit (latrine) DVc Double-vault composting (toilet) xiii Appropriate Sanitation Alternatives A Planning and Design Manual I I I I I I 1 An Overview A READILY AVAILABLE SUPPLY of safe water and ulation in developing countries have adequate sani- the sanitary disposal of human wastes are essential, tation services; that is, about 630 million out of 1.7 although not the only, ingredients of a healthy, pro- billion people.2 Population growth over the span of ductive life.' Water that is not safe for human con- the International Drinking Water Supply and Sani- sumption can spread disease; water that is not readily tation Decade (1981-90) will add another 700 million accessible takes up the productive time and energy people who will have to be provided with some of the water carrier-usually women or children; in- means of sanitation if the goals of the Decade-ad- adequate facilities for excreta disposal reduce the equate water supply and sanitation for all people- potential benefits of a safe water supply by trans- are to be achieved. A similar number of people. mitting pathogens from infected to healthy persons. about 2 billion, will require water supply by the same Over fifty infections can be transferred from a dis- date. Thus, roughly half the world's present total eased person to a healthy one by various direct or population of just over 4 billion people have to be indirect routes involving excreta. Coupled with mal- provided with water and sanitation services to meet nutrition, these excreta-related diseases take a dreadful the Decade's targets; that is. approximately half a toll in developing countries, especially among chil- million people per day for the next twelve years. dren. For example, in one Middle Eastern country, One of the fundamental problems in any attempt half of the children born alive die before reaching to provide the necessary sanitation services is their the age of five as a result of the combined effects of cost. General estimates based on existing per capita disease and malnutrition; in contrast, only 2 percent costs indicate that around $800 billion would be re- of children born in the United Kingdom die before quired to provide water supply and conventional sew- reaching their fifth birthday. erage for everyone.3 Per capita investment costs for Invariably it is the poor who suffer the most from sewerage range from $150 to $650, which is totally the absence of safe water and sanitation, because beyond the ability of the intended beneficiaries to they lack not only the means to provide for such pay: some I billion of these unserved people have facilities but also information on how to minimize per capita incomes of less than $200 per year: more the ill effects of the unsanitary conditions in which than half have incomes below $100 per year. they live. As a result, the debilitating effects of un- In industrialized countries, the standard solution hygienic living conditions lower the productive po- for the sanitary disposal of human excreta is water- tential of the very people who can least afford it. borne sewerage. Users and responsible agencies have come to view the flush toilet as the absolutely es- sential part of an adequate solution to the problem of excreta disposal. This method, however, was de- Dimensions of the Problem signed to maximize user convenience rather than health benefits, an objective that may be important To understand the magnitude of the problem, it in developed countries but has a lower priority in is only necessary to consider data collected by the developing countries. In fact, conventional sewerage World Health Organization in preparation for the is the result of slow development over decades, even United Nations Water Conference that took place centuries, from the pit latrine to the flush toilet, and in Mar del Plata, Argentina, in the spring of 1977. the present standard of convenience has been achieved These figures show that only 32 percent of the pop- at substantial economic and environmental costs. 3 4 OVERVIEW The problem facing developing countries is a fa- ments. The lesson commonly (but erroneously) miliar one: high expectations coupled with limited drawn from the historical development of sanitation resources. Decisionmakers in these countries are technology is that the many less costly alternatives asked to achieve the standards of convenience ob- formerly used should be abandoned rather than im- served in the industrialized world. Given the backiog proved. Therefore, few serious attempts have been in service, the massive size of sewerage investments, made to design and implement satisfactory low-cost and the demands on financial resources by other sec- sanitation technologies. The implementation of such tors, they do not have the funds to realize this goal. alternatives is complicated by the need to provide Sewerage could be provided for a few, but at the for community participation in both the design and expense of the vast majority of the population. As operating stages of the projects. Few engineers are a consequence, many developing countries have aware of the need to consider the sociocultural as- taken no steps at all toward improving sanitation. pects of excreta disposal, and fewer still are com- The very magnitude of the task has effectively dis- petent to work with a community to determine the couraged action. technology most compatible with its specific needs At the present time the first priority of excreta and resources. disposal programs in developing countries should be Given these constraints, it is not surprising that the improvement of human health; that is, the ac- sanitation service levels in developing countries have complishment of a significant reduction in the trans- remained low. A major effort is needed to identify mission of excreta-related diseases. This health ob- and develop alternative sanitation technologies ap- jective can be fully achieved by sanitation technologies propriate to local conditions in developing countries that are much less costly than sewerage. The goals and designed to improve health rather than raise for the Decade of the 1980s intentionally do not spec- standards of user convenience. Clearly the solutions ify sewerage, but call for the sanitary disposal of must be affordable to the user and reflect community excreta, leaving the disposal method to the discretion preferences if they are to find acceptance. of individual governments. Similarly, Decade targets include an adequate supply of safe water, without specifying the methods to be used to achieve the Incremental Sanitation goal. To provide as many people as possible with safe water and sanitation is to find technologies An examination of how conventional waterborne which can achieve these objectives with the resources sewerage came about reveals three facts very clearly. available. First, excreta disposal went through many stages be- fore sewerage. Second, existing systems were im- proved and new solutions devised whenever the old The Constraints solution was no longer satisfactory. Third, improve- ments were implemented over a long period of time The primary constraints to the successful provision as funds became available to meet conditions of of sanitation facilities in developing countries are the crowding and demands for convenience. Sewerage lack of funds, the lack of trained personnel, and the was not a grand design implemented in one giant lack of knowledge about acceptable alternative tech- step, but the end result of a long series of progres- nologies. Where high-cost systems developed in in- sively more technologically sophisticated solutions. dustrialized countries have been used to solve waste For example, the collection of night soil from bucket disposal problems in developing countries, access to latrines in eighteenth century London was a step to- the facilities has been limited to the higher income ward reducing gross urban pollution. This was fol- groups, who are the only ones able to afford them. lowed by piped water supplies and the development Little official attention has been paid to the use of of combined sewerage, then separate sanitary sew- low-cost sanitation facilities to provide health ben- erage, and eventually sewage treatment prior to river efits to the majority of the population. This situation discharge. This particular series of improvements exists because officials and engineers in developing spanned over 100 years-a time frame necessitated and developed countries alike are neither trained nor by historical constraints in science, technology, and experienced in the consideration or design of alter- capital. Present levels of knowledge enable sanita- native sanitation systems or in the evaluation of the tion planners to select from a wider range of options effects of these alternatives on health. Waterborne and to design a sequence of incremental sanitation sewerage is designed to satisfy convenience and improvements. The choice of proceeding with se- local environmental, rather than health, require- quential improvements is the user's, who also decides OVERVIEW 5 the time frame over which improvements are to be selves, of course, are interrelated. A technology may made and higher levels of convenience achieved in fail technically if the users' social preferences militate step with his increasing income. Most important, a against its proper maintenance. The economic cost user can start with a basic low-cost facility without of a system is heavily dependent upon social factors. the need to wait for greater income, knowing that such as labor productivity, as well as on technical he will have a choice to provide for greater conve- parameters. Because it is operationally difficult to nience when he has the funds and wishes to do so use simultaneous (or even iterative) decision pro- at some future date. cesses, a step-by-step approach with feedback across disciplines is suggested. For simplicity it is assumed that separate individ- Sanitation Program Planning uals or groups are responsible for each part, although in practice responsibilities may overlap. In stage 1 Sanitation program planning is the process by each specialist collects the information necessary to which the most appropriate sanitation technology for make his respective exclusion tests. For the engineer. a given community is identified, designed, and im- public health specialist, and behavioral scientist4 this plemented. The most appropriate technology is de- data collection would usually take place in the com- fined as the one that provides the most socially and munity to be served. The economist would talk with environmentally acceptable level of service at the both government and municipal officials to obtain least economic cost. the information necessary to calculate shadow rates The process of selecting the appropriate technol- and to obtain information on the financial resources ogy begins with an examination of all of the alter- likely to be available. The behavioral scientist would natives available for improving sanitation; these are consult with and survey the potential user and com- described in Part Two of this book. Theie will usually munity groups. Then, in stage 2, the engineer and be some technologies that can be readily excluded sociologist apply the information they have collected for technical or social reasons. For example, septic to arrive at preliminary lists of technically and so- tanks with large drainfields would be technically in- cially feasible alternatives. The public health spe- appropriate for a site with a high population density cialist relates the most important health problems to or with bedrock near the ground surface. Similarly, any relevant environmental factors involving water. a composting latrine would be socially inappropriate excreta, or both. In the third stage the economist for people who have strong cultural objections to the prepares economic cost estimates for those technol- sight or handling of excreta. Once these exclusions ogies that have passed the technical and social tests have been made, cost estimates are prepared for the and selects the least-cost alternative for each tech- remaining technologies. These estimates should re- nology option. At the fourth stage the engineer pre- flect real resource cost to the economy, and, as de- pares final designs for these remaining choices. The scribed in chapter 4, this may involve making ad- social information collected in stage 1 should be used justments in market prices to counteract economic in this process to determine the siting of the latrine distortions or to reflect development goals such as on the plot, the size of the superstructure, the ma- employment creation. Since the benefits of various terials to be used for the seat or slab, and other sanitation technologies cannot be quantified, the details that may have low technical and economic health specialist must identify those environmental importance but make a major difference in the way factors in the community that act as disease vehicles the technology is accepted and used in the commu- and recommend improvements that can help prevent nity. The designs should also incorporate features disease transmission. The final step in identifying the necessary to maximize the health benefits from each most appropriate sanitation technology rests with the technology. Final designs are turned over to the intended beneficiaries. Those alternatives that have economist in the fifth stage so that financial costs can survived technical, social, economic, and health tests be determined, including how much the user would are presented to the community with their attached be asked to pay for construction and maintenance financial price tags, and the users themselves decide of each alternative. In the last stage the behavioral what they are willing to pay for. An algorithm for scientist presents and explains the alternatives, their technology selection that incorporates economic, so- financial costs, and their future upgrading possibili- cial, health, and technical criteria is presented in ties to the community for final selection. The form chapter 6. that this community participation takes will vary Figure 1-1 shows how the various checks are ac- greatly from country to country; its important ele- tually coordinated in practice. The checks them- ments are discussed in chapter 3. Figure 1-1. Recommended Structure of Feasibility Studies for Sanitation Program Planning Sanitary Engineer and Economist Behavioral Scientist Community Public Health Specialist Examine physical and Consults with cotmmunity A on Stage I environmental conditions Collects to collect information Apraties an and establish community macroemonomi on exi stintgpr-acu.ces pracetice.san health profile if)mto andprrecs preferences Stage 2 technically and medically Ident~fies econotmic Lits sociallyv andc atage 2 hindenlternativecdst // \ constraints and limits institutionally feasible alternatives \ /a.Sible alternanvweS ---------- ___ r-/----T -------------- Prepares short list Identifies comnzunity's Stage 3 of feasible alternatives contribution and level -. Advises of af.fordability Prepare final de.sign Agrees on typ zia vaouts Stage 4 and estimate unit cost and local communitty Advises of feasible alternati ves \/ participation \~~~~~ / Prepares financial costing Stage 5 of feasible alternative systems Stage 6 | Community selects S preferred alternative OVERVIEW 7 As part of the sanitation planning process, the ex- of whether and when to proceed to the next higher isting or likely future pattern of domestic water use level of convenience. Yet we believe that the plan- should be ascertained so that the most appropriate ning format discussed above has a far greater chance method of sullage disposal can be selected. This is of achieving operational success because the most particularly important in the case of properties with appropriate sanitation technology is drawn from a a multiple tap level of water supply service, since wider range of alternatives, imposes the least cost large wastewater flows may, according to conven- burden on the economy, maximizes the health ben- tional wisdom, preclude the consideration of tech- efits obtainable, and is selected after extensive in- nologies other than sewerage or, in low-density teraction with the intended beneficiaries. Because areas, septic tanks with soakaways. It is not neces- incremental sanitation systems are so much less ex- sary, however, either for reasons of health or user pensive than sewerage (both in initial investment and convenience, for domestic water consumption to ex- total discounted cost), many more people can be ceed 100 liters per capita daily.5 The use of low-vol- provided with satisfactory excreta disposal facilities ume cistern-flush toilets and various simple and in- for the same amount of money, and these facilities expensive devices for reducing the rate of water flow can be upgraded as more money becomes available from taps and showerheads (described in the appen- in the future. Given the huge service backlog and dix of chapter 4) can achieve substantial savings in the severe investment capital constraints in devel- water consumption without any decrease in user con- oping countries, incremental sanitation may be the venience or any required change in personal washing only, as well as the best, way to meet the sanitation habits. These savings can be as high as 75 percent goals of the International Drinking Water Supply in high-water-pressure areas and 30 to 50 percent in and Sanitation Decade. low-pressure areas. If wastewater flows can be re- duced by these means, then the options for sanitation facilities are much broader than only conventional Notes to Chapter 1 sewerage. In addition, separation of toilet wastes from other wastewater by simple modifications in 1. For a more detailed discussion of the issues in this chapter. see chapters 1 and 2 of Kalbermatten. Julius. and Gunnerson household plumbing, coupled with improved designs (1982). of septic tank filters (see chapter 14), may make 2. One billion is equivalent to one thousand million. nonsewered options more widely feasible. 3. All dollar figures in this manual are 1978 U.S. dollars. The framework suggested in this chapter for the 4. The term "behavioral scientist" is used to describe a person identification of the most appropriate sanitation skilled in assessing communitv needs, preferences. and processes. The person's training may be in anthropology, communications. technology takes more engineering time and analysis geography, sociology, or psychology, or it may come from a wide than that of traditional feasibility analysis. It also variety of education and experience. requires the recruitment of staff in other disciplines, 5. Where water has to be carried, 20 liters per capita daily is such as behavioral scientists. In addition, the concept considered a minimum acceptable level to provide all the health of incremental sanitation requires municipal activity benefits of a safe water supply. With closer standpipe spacing and yard hydrants, consumption rises typically to 50 and, with house in sanitation programs to be spread over a consid- connections, to 100 liters per capita daily. At the higher levels of erably longer time because the user has the option consumption, off-site disposal of sullage becomes necessary. I I Part One Socioeconomic Aspects of Sanitation Program Planning I I 2 Health Aspects of Sanitation IMPROVED HEALTH is normally considered one of the cholera epidemic that swept through the area the principal benefits of improved sanitation.' Ex- four years ago. creta contain a wide variety of human pathogens It is particularly difficult to control excreta in this (tables 2-1 and 2-2), and the removal of these path- damp environment; most feces are deposited not far ogens from the immediate environment, which is from the house, and the younger children urinate in achieved by proper sanitation, can have a dramatic the canals nearby. Some years ago a government effect on community health. Prior or concurrent im- campaign was mounted to provide pit latrines, and provements in water supply and solid waste collec- one was dug near the family's house. They used it tion services and a vigorous and sustained campaign for a while, but in the monsoon season the pit flooded of community education in hygiene are ordinarily and a large quantity of fecal material was spread required, however, before all the health benefits of around the house. It was around that time that the a sanitation improvement program can be realized. cholera epidemic occurred, and its sad consequences In this chapter a recently developed environmental for the family, together with the unpleasant mess, classification of excreta-related infections is pre- discouraged them from using the pit latrine again. sented, and the likely health benefits of sanitation The next government recommendation was to build improvements are discussed. Particular emphasis is a concrete aquaprivy extending well above the placed on the effects on children, who are in many ground to avoid the flood problem, but the family ways the most vulnerable to excreta-related infec- could not afford this and went back to defecating tions. First, however, two illustrative sketches that around the home during the day. Nocturnal excreta describe the effects of poor sanitation on two families were collected in a bucket and deposited in a nearby living in different parts of the world are presented fishpond. to help the reader visualize the poor health and san- How has this situation affected the family's health? itation status of the urban and rural poor throughout All the children get diarrhea several times a year, as the world. do the parents from time to time. The worst occasion was when two girls, both under three years of age, got it at the same time. The younger one seemed A Southeast Asian Family just to shrivel up overnight, and she died the next day. Her death may have been attributable to ro- In high-rainfall areas of Southeast Asia with a per- tavirus infection, but the reason that this infection ennially hot climate and where irrigated rice is the should more often be lethal in the tropics than it is main cereal crop, the health hazards from excreta in temperate countries is unclear. Certainly the poor are diverse. They may be illustrated by the following sanitary facilities were a factor, particularly in com- case history, which is a composite of several real sites bination with the malnutrition that is so ubiquitous and people. A family lives in a palm-roofed, wooden during the weaning period in communities such as house surrounded by rice fields and small irrigation this one. Most of the diarrheas are sudden attacks channels, one of which, flowing near the house, acts that produce watery stools, but last year the grand- as the domestic water supply. There are four children mother, who shares the house with the family, was in the family; the mother has had six babies but one one of several people in the village who suffered an died following a sudden attack of diarrhea at the age attack of a more painful diarrhea, which produced of fifteen months, and a child of school age died in blood in the feces and from which she nearly died. 11 12 SOCIOECONOMIC ASPECTS Table 2-1. Viral, Bacterial, and Protozoan Pathogens Found in Excreta Biological group and organism Disease, Reservoir Viruses CoxsackieviTus Various Man Echovirus Various Man Hepatitis A virus Infectious hepatitis Man Poliovirus Poliomyelitis Man Rotavirus Gastroenteritis in children ? Bacteria Campylobacter species Diarrhea in children Animals and man Pathogenic Escherichia coli Gastroenteritis Man Salmonella typhi Typhoid fever Man S. paratyphi Paratyphoid fever Man Other salmonellac Food poisoning Man and animals Shigella species Bacillary dysentery Man Vibrio cholerae Cholera Man Other vibrios Diarrhea Man Yersinia species Yersiniosis Animals and man Protozoa Balantidium coli Mild diarrhea Man and animals Entamoeba histolytica Amebic dysentery and liver abscess Man Giardia lamblia Diarrhea and malabsorption Man Source: Feachem and others (forthcoming). a. In all diseases listed, a symptomless carrier state exists. Medicine from the dispensary 6.5 kilometers away ily has in large numbers is Fasciolopsis buski, ac- seemed to help her begin to recover, but even so she quired from eating aquatic vegetables in an uncooked remained ill for weeks. The attack was from bacillary state. Neither of these parasites has catastrophic re- dysentery, though it would have been difficult with- sults, but their diversion of food from their human out laboratory tests to be sure it was not from ame- hosts and their other insidious effects make life less biasis. satisfactory than it otherwise might be. The family All these were dramatic illnesses, but the family also suffers from many other intestinal worms oc- has several more insidious health problems of which curring in even greater numbers and causing more they are barely aware. The eldest son has not grown illness. (These are discussed below in relation to an- properly; although he is twenty-three, he looks as if other family.) he were in his early teens. His belly is always grossly A nonintestinal infection is also associated with swollen, and the dispensary attendant can feel his the family's problems of excreta disposal. Within the hard liver and spleen under the tight skin. These pit latrines that have been flooded and abandoned, physical effects are from schistosomiasis, which is the fecal liquid is colonized by larvae of a mosquito spread from one person to another through a tiny known as Culex pipiens.2 When the adult females of snail living in the damp grass beside the canals as this mosquito bite the members of the household, well as in the water itself. Several of the family are they are able to transmit the larvae of a parasitic infected, but only this boy has obvious symptoms, worm that then inhabits the tissues under the skin although the father suffers from elephantiasis, a non- of the legs and elsewhere. In particular, these worms intestinal infection described below. inhabit the lymph nodes and block the flow of lymph, With so much water around, fish is an acceptable causing a disease known as bancroftian filariasis or and available food item, sometimes cooked but often elephantiasis. As a consequence, the tissues become pickled in vinegar. A proportion of these fish are swollen from the accumulation of lymph, and in some grown in ponds that are fertilized with human feces, of the people a massive elephantiasis results. The and this practice has caused some of the family to father is troubled by this in his right leg, which is so become infected with the helminth (parasitic worm) swollen that he cannot work in the fields as well as Clonorchis sinensis. Another helminth that the fam- he could before. HEALTH ASPECTS 13 Table 2-2. Helminthic Pathogens Found in Feces Pathogen Common name Disease Transmission Distribution Ancylostoma duodenale Hookworm Hookworm Man-soil-man Mainly in warm wet infection climates Ascaris lumbricoides Roundworm Ascariasis Man-soil--->man Worldwide Clonorchis sinensis Chinese liver fluke Clonorchiasis Animal or man-aquatic Southeast Asia snail-fish-man Diphyllobothrium Fish tapeworm Diphyllobothriasis Man or animal- Widely distributed foci. latum copepod-fish-man mainly temperate regions Enterobius vermicularis Pinworm Enterobiasis Man-man Worldwide Fasciola hepatica Sheep liver fluke Fascioliasis Sheep-aquatic Worldwide in sheep- and snail--aquatic cattle-raising areas vegetationman Fasciolopsis buski Giant intestinal fluke Fasciolopsiasis Man or pig--aquatic Southeast Asia. mainly snail-aquatic China vegetation--man Gastrodiscoides - Gastrodiscoidiasis Pig-aquatic India. Bangladesh, hominis snail--aquatic Vietnam. Philippines vegetation-man Heterophyes - Heterophyiasis Dog or cat--.brackish- Middle East, southern heterophyes water snail--brackish- Europe, Asia water fish-man Hymenolepis species Dwarf tapeworm Hymenolepiasis Man or rodent-man Worldwide Metagonimus - Metagonimiasis Dog or cat---aquatic Japan. Korea. China, island yokogawai snail-freshwater of Taiwan. Siberia fish-man (U.S.S.R. ) Necator americanus Hookworm Hookworm Man-soil-man Mainly in warm wet infection climates Opisthorchis felineus Cat liver fluke Opisthorchiasis Animal-aquatic U.S.S.R.. Thailand 0. viverrini snail-fish-man Paragonimus Lung fluke Paragonimiasis Pig, man, dog. cat, or Southeast Asia, scattered westerinani other animal-aquatic foci in Africa and South snail-crab or America crayfish-nman Schistosoma Schistosome; bilharzia Schistosomiasis: Man--aquatic snail-man Africa, Middle East, India haemalobium bilharziasis S. japonicum Animals and Southeast Asia man-snail-+man S. mansoni Man-aquatic snail--man Africa. Arab Middle East, Central and South America Strongyloides stercoralis Threadworm Strongyloidiasis Man-rman (?) Mainly in warm wet (dog-man) climates Taenia saginata Beef tapeworm Taeniasis Man-cow-rman Worldwide T. solium Pork tapeworm Taeniasis Man-pig--man, or Worldwide man-man Trichuris trichiura Whipworm Trichuriasis Man-soilt-man Worldwide -Not applicable. Source: Feachem and others (forthcoming). tropics. In the winter it is quite cold, though the summer temperatures are at least as high as in the A North African Family Asian village just described. The houses cluster to- gether on a mound rising up from the irrigated areas The North African village is quite different in gen- around. This irrigation, however, is by water brought eral appearance, but behind this difference there are from afar by great rivers, not by heavv rainfall. The certain similarities in disease problems. The village ground is baked hard where it has not recently been is a cluster of mud-brick houses situated in the sub- irrigated. Within the village the streets are narrow; 14 SOCIOECONOMIC ASPECTS they are not made up or paved, and large quantities then one of the younger children passes one in his of debris lie around. stools. This excites a little comment, but there is not One family in this village consists of parents with obvious illness except for pain in the abdomen; as three children and some elderly relatives. There is always, it is difficult to ascribe this to a particular again the sad story of some children dying from diar- cause. What is certain is that the worms are absorbing rheal disease; in tropical areas diarrheal disease a good deal of the nutrients intended for the children, (alone or in combination with other diseases) is al- and there is also a risk that the worms will get stuck most invariably the principal cause of child mortality. in the narrowest part of the intestine and block it, There are some exceptions in areas where the very a condition requiring a surgeon's attention. The fam- high incidence of malaria makes this the greater ily is well aware of this problem and has visited the threat, but in these areas the overall death rate is dispensary to get medicine on frequent occasions. even higher. Unfortunately, in the absence of better methods of As in Asia, we find problems of schistosomiasis disposing of excreta, the infection comes back every and of elephantiasis. These are of a somewhat dif- few months. The adults seem to have become some- ferent type from the Asian forms but nevertheless what immune to the infection, and the children carry create disability in similar ways. In addition to in- the brunt of the disease. testinal schistosomiasis, two of the younger children What arrangements are made for excreta disposal have a urinary variety and are passing blood in their here? A bore-hole latrine was made for each family urine every day. This looks more serious than it is; to use, but it filled up quickly and was so unpleasant in fact, the blood loss is not great. Nevertheless, the that no one wanted to use it. In any case, it was near children suffer pain and the inconvenience of having the house, and the family spends much of the day to get up frequently to pass urine at night. in the fields working on rice and other crops. It would The helminths associated with fish and water be a quite unreasonable waste of their time, or so plants that troubled the previous family are absent they feel, to come all the way back to the home from this one, but when we look at the family's feces merely to defecate. It is also more convenient to under the microscope we find the eggs of Ancylos- defecate in the field because the family's religion toma duodenale (hookworm), Ascaris lumbricoides insists that they wash the anus after defecation, and (roundworm), and Trichuris trichiura (whipworm) there is no water readily available for this purpose in large numbers. The hookworm eggs are particu- within the compound. Because of these varying sites larly numerous. Infection has been contracted by the for defecation, eggs of Ascaris and Trichuris are family's wandering about with bare feet on land that spread rather widely throughout the environment. has been used for defecation and has been kept moist They are extremely resistant, even to the harsh cli- enough by nearby drains and canals for the larval mate of this part of the world, and find their way worms to develop in the soil. The worms live in the onto vegetables, which are eaten raw. They also oc- small intestine and attach themselves to the inside cur in the mud and sand of the compound, from walls of the intestinal tract. They suck blood, which which they are readily picked up by the hands of is used for their growth and for the production of crawling babies. their eggs, but they are very messy feeders and large Another intestinal worm of some importance is amounts of blood pass straight through their bodies the beef tapeworm (Taeniasaginata).This is acquired and are lost into the intestine. As a result the blood by eating undercooked beef, which can occur when losses from this infection are very heavy. The hook- meat is roasted in a large piece. The adult tapeworm worms are particularly numerous in the mother of matures in the intestines of the family, and it too the family, and her blood loss is twice as heavy as competes for nutrients with its hosts. Its eggs, often that from menstruation. Since her diet is not partic- in the swollen segments of the tapeworm, are shed ularly rich in iron, she has consequently become very in large numbers when a whole segment of tapeworm anemic and is unable to work nearly as much as a wriggles out of the anus. These tapeworm segments fit person. The same applies to one of the children may be ingested by browsing cattle and undergo fur- of the familv: his abdomen is swollen, he cannot run ther development within the muscles of the cow. The fast to keep up with the other children, and his con- family's religion prohibits the eating of pork, and so dition gives the family considerable cause for anxiety. they are spared infection by pork tapeworm (Taenia If he were to catch some other infection in addition solium), which has as one of its possible hazards the to hookworm, he might well lose his life. larvae's developing in human muscles. All the family have roundworms. These are very All these helminthic infections are long lasting and large (over 100 millimeters long), and every now and sap the strength, so that it is not easy to attribute HEALTH ASPECTS 15 specific damage to their presence, except in the case in themselves (flies, cockroaches, mosquitoes); they of hookworm. They are all infections that tend to be may transmit excreted pathogens mechanically, either underrated because of their widespread nature and on their bodies or in their intestinal tracts (cock- insidious, drawn-out course. By contrast, the family roaches and flies); or they may be vectors for path- also suffers from several acute infections-not only ogens that circulate in the blood (mosquitoes). diarrheas, which have been discussed already, but Where flies or cockroaches are acting as vehicles for also typhoid and hepatitis. The incidence of typhoid the transmission of excreted pathogens, this repre- in the village is very high. This is for several reasons, sents a particular instance of the many ways in which not least of which are the defective arrangements for excreted pathogens may pass from anus to mouth. excreta disposal. In addition, the complication of In considering the transmission of excreted infec- schistosomiasis in the inhabitants leads to a very tions, the distinction between the state of being in- drawn-out course of the typhoid, and up to one in fected and the state of being diseased must be kept every twenty-five people may become a typhoid car- in mind. Very often the most important section of rier in some of these villages. This incidence is an the population involved in transmitting an infection order of magnitude or more higher than is found shows little or no sign of disease; conversely, indi- elsewhere. The upshot is that typhoid is extremely viduals with advanced states of disease may be of common, no less severe than elsewhere, and an ap- little or no importance in transmission. A good ex- preciable cause of mortality. Hepatitis, too, occurs ample of this distinction occurs in schistosomiasis, frequently. In the younger children it rarely gives in which as much as 80 percent of the total egg output rise to serious symptoms, but in adults the patient in feces and urine reaching water from a human pop- may have to take to his bed for weeks or months, ulation may be produced by children five to fifteen and acute illness leading to death is not unknown. years old; many of these children will show minimal One feature that emerges with particular strength signs of disease. Conversely, adults with terminal from this account of a family in North Africa is the disease conditions may produce few or no viable extent to which it shares the fecal health problems eggs. of the family in Southeast Asia. Indeed, unlike many If an excreted infection is to spread. an infective other patterns of disease, there is a sameness about dose of the relevant agent has to pass from the ex- the bulk of the serious, frequently transmitted, ex- creta of a case, carrier, or reservoir of infection to creted infections that cannot be avoided. There are the mouth or some other portal of entry of a sus- certainly infections that are peculiar to particular lo- ceptible person. Spread will depend upon the num- calities, but the pattern of diarrheal disease. enteric bers of pathogens excreted (excreted load), upon fever, numerous viral infections, and the intestinal how these numbers change during the particular worms is repeated throughout the world. Cholera is transmission route or life cycle, and upon the dose the only excreta-related disease of major importance required to infect a new individual. Infective dose that has a variable and patchy distribution. is in turn related to the susceptibility of the new host. Three critical factors govern the probability that, for a given transmission route, the excreted pathogens Excreted Infections from one host will form an infective dose for another. These are latency, persistence, and multiplication. As these examples illustrate, excreta are related Diagrammatically, we can represent the concepts to human disease in two ways. First, the agents of thus: manv important infections escape from the body in excreta and may eventually reach other people. EXCRETED latency INFECTIVE These are called the excreted infections. In some LOAD persistence . cases the reservoir of infection is almost entirely in multiplication animals other than man. These reservoirs are not These concepts are discussed in turn. considered here because such infections cannot be controlled through changes in human excreta dis- Excreted load posal practices. A number of infections for which both men and other animals serve as a reservoir are There is wide variation in the concentration of included, however. pathogens passed by an infected person. For in- The second way in which excreta relate to human stance, a person infected by a small number of ne- disease is by their disposal, which can encourage the matode worms may be passing a few eggs per gram breeding of insects. These insects may be a nuisance of feces, whereas a cholera carrier may be excreting 16 SOCIOECONOMIC ASPECTS more than 108 Vibrio cholerae per gram, and a patient most waste treatment processes and during the reuse may pass 10'3 vibrios per day. of excreta. Where large numbers of organisms are being A pathogen that persists outside the body for only passed in the feces, they can give rise to high con- a very short time needs to find a new susceptible host centrations in sewage. Thus, even in Engiand, where rapidly. Hence, transmission cannot follow a long water use is relatively high and salmonellosis rela- route through sewage works and the final effluent tively rare, raw sewage may contain 104 Salmonella disposal site back to man but, rather, will occur per liter. At these concentrations, removal efficien- within the family by transfer from one member to cies of 99 percent in conventional sewage treatment another as a consequence of poor personal hygiene. works will still leave 102 pathogenic organisms per More persistent organisms can readily give rise to liter in the effluent, and their implications for health new cases of disease farther afield, and as survival will depend upon their ultimate disposal, their ability increases, so also must concern for the ultimate dis- to survive or multiply, and the infective dose re- posal of the excreta. In addition, pathogens that tend quired. to persist in the general environment will require more elaborate processes if they are to be inactivated LSatency in a sewage works. Methods of sequestering them- for example, by sedimentation into a sludge that re- Latency is the interval between the excretion of ceives special treatment-are often needed. a pathogen and its becoming infective to a new host. Although it is easy to measure persistence or vi- Some organisms, including all excreted viruses, bac- ability of pathogenic organisms by laboratory meth- teria, and protozoa, have no latent period and are ods, to interpret such results it is necessary to know immediately infectious when the excreta are passed. how many are being shed in the excreta (which is The requirements for the safe disposal of excreta relatively easy to determine) and the infective doses containing these agents are far more stringent than for man (which is extremely difficult to discover). for those helminthic infections in which there is a prolonged latent period. In particular, infections that M have a considerable latent period are largely risk free ultiplication even where night soil is being carted by vacuum Under some conditions certain pathogens will mul- truck, whereas the others constitute a major health tiply in the environment. Thus, originally low num- hazard in fresh night soil. Therefore, in the classi- bers can be multiplied to produce a potentially in- fication presented below, the first two categories, in fective dose. Multiplication can take the form of which no latency is observed, are separated from the reproduction by bacteria in a favorable environment remaining categories, where a definite latent period (for example, Salmonella on food), or of the multi- occurs. plication by trematode worms in their molluscan in- Among the helminthic infections, only three have termediate hosts. eggs or larvae that may be immediately infectious to Among the helminths transmitted by excreta, all man when passed in the feces. These are Enterobius the trematodes infecting man undergo multiplication vermicularis, Hymenolepis nana, and, sometimes, in aquatic snails. This introduces a prolonged latent Strongyloides stercoralis. The remaining excreted period of a month or more while development is helminths all have a distinct latent period, either taking place in the snail, followed by an output of because the eggs must develop into an infectious up to several thousand larvae into the environment stage in the physical environment outside the body for each egg that reaches a snail. or because the parasite has one or more intermediate hosts through which it must pass in order to complete Infective dose its life cycle. In principle, from a knowledge of the output of Persistence pathogens in the excreta of those infected, the mean infective dose, and the extractive efficiency of the Persistence, or survival, of the pathogen in the excreta treatment process, it would be a matter of environment is a measure of how quickly it dies after simple calculation to assess risk. The real world is it has been passed in the feces. It is the single prop- much less predictable than this because of the vari- erty most indicative of the fecal hazard in that a very able infective dose of most pathogens and the uneven persistent pathogen will create a risk throughout distribution of infection in the environment. While HEALTH ASPECTS 17 the minimal infective dose for some diseases may be cautions to prevent, so that in practice improved san- a single organism, or very few, the doses required itation increases the disease problem by deferring in most bacterial infections are much higher. Data infection to an age where its clinical course is more bearing on this are very hard to acquire, since they severe. involve administering a known dose of a pathogen The prevalence of disease among juveniles makes to a volunteer. Information is scanty, and generally this group the main sources of infection, the acute concerned with doses required to infect at a single need for better community excreta disposal is there- exposure a very large proportion (say half) of those fore among young children, the group perhaps least exposed, rather than a minute proportion. The vol- inclined to use any facilities that may be available. unteers have usually been well-nourished adults from nonendemic areas. Such results therefore have to be applied with considerable caution (if, indeed, they Nonhuman hosts can be applied at all) in estimating doses that would Some excreted diseases (for example, shigellosis) cause disease in a small proportion of, say, malnour- are infections exclusively or almost exclusively of ished children continuously exposed to infection. man; it is then the control of human excreta that is important in preventing transmission. Many, how- Host response ever, involve other animals either as alternatives to man as host or as hosts of other stages in the path- This is important in determining the result of an ogen's life cycle. In the first case, where wild or individual's receiving a given dose of an infectious domestic vertebrate animals act as alternative hosts agent. In particular, acquired immunity and the re- (such infections are called zoonoses), control of hu- lation of age to pathology are important for pre- man excreta is not likely to suffice for complete pre- dicting the effects of sanitation improvements. In vention of the infection. In the second case, some general the balance between exposure to infection excreted helminthic infections have intermediate and a host's response to it will determine the pattern aquatic hosts. These infections will therefore be con- of excreta-related disease. If transmission, creating trolled if: exposure to a particular infection, is low, then few people will have encountered the infection; most will m Excreta are prevented from reaching the inter- be susceptible. If a sudden increase in transmission mediate host of the disease occurs, it will affect all age groups in X The intermediate hosts are controlled epidemic form. Improvements in sanitation will have * People do not eat the intermediate host un- a great effect under these circumstances by reducing cooked or do not have contact with the water the likelihood of an epidemic and, should one occur, in which the intermediate host lives (depending its magnitude. on its particular life cycle). By contrast, if transmission is very high, all the people will be repeatedly exposed to the infection and first acquire it in childhood. Subsequent expo- Environmental Classification sures may be without effect if long-lasting immunity of Excreted Infections is acquired from the first attack. Alternatively, im- munity may be cumulative from a series of attacks. The lists of human pathogens in excreta given in The infection will always be present and is described tables 2-1 and 2-2 are useful only to the degree they as endemic. Under these conditions much transmis- show the wide variety of excreta-related pathogens sion is ineffective because of human acquired im- and the membership of pathogens in one of four munity, and reduced transmission as a result of im- groups of organisms: viruses, bacteria, protozoa, and proved sanitation will only delay the date of infection helminths. It is essentially a biological classification. till later in life. Extensive sanitary improvements will To the sanitation program planner it is interesting, either render the infection rare or, if the disease but not very helpful. An environmental classifica- originally were highly transmitted, make it an adult tion, which groups excreted pathogens according to disease. An example of the first case is typhoid, common transmission characteristics, is much more which can be completely prevented in the community helpful in predicting the health effects of sanitation by adequate management of excreta and of water improvements and in understanding the health as- supplies. An example of the second is poliomyelitis pects of excreta and sewage treatment and reuse virus infection, which requires extreme hygienic pre- processes. The environmental classification (table 2- 18 SOCIOECONOMIC ASPECTS Table 2-3. Environmental Classification of Excreted Infections Category and Environmental epidemiological transmission Major control feature Disease focus measure i. Nonlatent; low infective Amebiasis Personal Domestic water supply dose Balantidiasis Domestic Health education Enterobiasis Improved housing Enteroviral infection, Provision of toilets Giardiasis Hymenolepiasis Infectious hepatitis Rotaviral infection t. Nonlatent; medium or Campylobacter Personal Domestic water supply high infective dose; infection Domestic Health education moderately persistent; Cholera Water Improved housing able to multiply Pathogenic Crops Provision of toilets Escherichia Treatment of excreta before coli infection discharge or reuse Salmonellosis Shigellosis Typhoid Yersiniosis i. Latent and persistent: no Ascariasis Yard Provision of toilets intermediate host Hookworm infectionb Field Treatment of excreta before Strongyloidiasis Crops land application Trichuriasis iv. Latent and persistent; cow Taeniasis Yard Provision of toilets or pig as intermediate Field Treatment of excreta before host Fodder land application Cooking; meat inspection v. Latent and persistent, Clonorchiasis Water Provision of toilets aquatic intermediate Diphyllobothriasis Treatment of excreta before host(s) Fascioliasis discharge Fasciolopsiasis Control of animal reservoirs Gastrodiscoidiasis Cooking Heterophyiasis Metagonimiasis Paragonimiasis Schistosomiasis vi. Excreta-related insect Bancroftian filariasis Various fecally contaminated Identification and elimination vectors (transmitted by Culex sites in which insects breed of suitable insect breeding pipiens) and all infections sites in i-v for which flies and cockroaches can be vectors~ Source: Feachem and others (forthcoming). a. Includes polio-, echo-, and coxsackieviral infections: poliomyelitis; viral meningitis; diarrheal, respiratory, and other diseases (see Feachem and others, chapter 1). b. Ancylostoma duodenale and AVecator americanus. c. Culex pipiens is a complex of mosquito species and subspecies. The principal tropical species, and the vector of filariasis in those tropical areas where the infection is transmitted by Culex, is Culex quinquefasciatus (previously also known as Culex pipiens fatigans, C. p. quinquefasciatus. or C. fatigans). See map 19 in Kalbermatten. Julius, and Gunnerson (1982) for distribution of the complex. 3) developed in Feachem and others (forthcoming) spread from person to person wherever personal and distinguishes six categories of excreted pathogens. domestic hygiene are poor. Therefore, it is likely that changes in excreta disposal technology will have little if any effect on the incidence of these infections if Category X the technological changes are unaccompanied by These are the infections that have a low infective sweeping changes in hygiene, which may well require dose (less than 100 organisms) and are infective im- major improvements in water supply and housing, mediately on excretion. These infections are easily as well as major efforts in health education. The HEALTH ASPECTS 19 important aspect of excreta disposal for the control The criteria chosen to separate the pathogens of of these infections is the provision of a hygienic toilet categories I and ii are infective dose and "length" of any kind in or near the home so that people have of the environmental cycle, since the objective of somewhere to deposit their excreta. What subse- environmental classification is to predict the efficacy quently happens to the excreta (how wastes are trans- of sanitation improvements as a control measure. ported, treated, and reused) is of less importance The reason these pathogens do not form distinct because most transmission will occur in the home. groups is the variable persistence of the organisms. Although transmission can, and does, occur by com- The extreme category-I pathogen, which has a low plex routes, most transmission is directly person-to- infective dose and is environmentallv fragile, will person, and therefore the provision of hygienic toi- clearly tend to be spread in an intrafamilial or other lets alone will have a negligible effect. The control close pattern and depend for its control more on measures appropriate to categories I and Hi, however, personal hygiene than on sanitation. A low infective merge into each other and really form a continuum dose in an environmentallv persistent organism, (see below). In particular, the parasitic protozoa however, will lead to an infection very difficult to share some features of each group. The extreme ex- control either by sanitation or by personal and do- ample of a category-I pathogen is the pinworm, En- mestic hygiene. Many viruses fall into this category terobius vermicularis, whose sticky eggs are laid by and pose major problems of control so that induced emerging females on the anal skin so that autoinfec- resistance by immunization may be the best ap- tion is predominantly by way of scratching fingers proach. as discussed above for poliomvelitis. In cat- and not by eggs in the feces. At the other extreme, egory ii the role of sanitation improvements is to Giardia lamlblia has been associated with well-doc- reduce the efficacy of the longer cycles (this would umented waterborne diarrheal outbreaks, and there- have less overall benefit in the case of category-i fore is presumably in part subject to control by ex- pathogens, where these longer cycles are of little creta management. significance). Category ni Category Iii The infections in this category are all bacterial. This category contains the soil-transmitted hel- They have medium or high infective doses (>104) minths. They are both latent and persistent. Their and therefore are less likely than category-i infec- transmission has little or nothing to do with personal tions to be transmitted by direct person-to-person hygiene. since the helminth eggs are not immediatelv contact. The pathogens in this category are persistent infective to man. Domestic hygiene is relevant only and can multiply. so that even the small numbers insofar as food preparation must be adequate to de- remaining a few weeks after excretion can, if they stroy any infective stages present on food. and la- find a suitable substrate (such as food), multiply to trines must be maintained in a tolerable state of form an infective dose. Person-to-person routes are cleanliness so that eggs do not remain on the sur- important but so too are other routes with longer roundings for the days or weeks of their latent pe- environmental cycles, such as the contamination of riod. If ova are not deposited on soil or other suitable water sources or crops with fecal material. development sites, transmission will not occur. The control measures listed under category i in Therefore, any kind of latrine that contains or re- table 2-3 are important (namely, water supply, hous- moves excreta and does not permit the contamina- ing, health education, and the provision of hygienic tion of the floor, yard, or fields will limit transmis- latrines), but so also are waste treatment and reuse sion. Because persistence is so long. it is not sufficient practices. Changes in excreta disposal and treatment to stop fresh feces from reaching the yard or fields. practices alone may reduce the incidence of cholera, Any fecal product that has not been adequately typhoid, amebiasis, certain shigelloses, and infec- treated must not reach the soil. Therefore, in soci- tions due to Balan tidiumn coli and species of Hvmeni- eties that reuse their excreta on the land, effective olepis and Yersinia, but such changes are unlikelv to treatment (for example, storage of excreta for at least be effective against enteroviral infections, salmonel- a year) is vital before reuse. loses (other than typhoid), and infections due to S/ti- gel/a sonnei, Giardia, Enterobiuls, and enteropatho- genic Escherichia coli. since these latter pathogens Category IV are still commonly transmitted within affluent com- This category contains only the beef and pork munities in industrialized countries. tapeworms (Taenia saginata and T. solium, respec- 20 SOCIOECONOMIC ASPECTS tively). Any system that prevents untreated excreta cause filariasis. The other two groups, flies and cock- from being eaten by cattle and pigs will control trans- roaches, proliferate where feces are exposed. Both mission of these infections. Cattle are likely to be have been shown to carry large numbers and a wide infected in fields treated with raw sewage or sludge. variety of excreted pathogens on their feet and in They may also eat feces deposited in cowsheds. Pigs their intestinal tracts, but their importance in actually are likely to become infected by eating human feces, spreading disease from person to person is in fact a practice common in areas where swine are em- controversial, though their nuisance value is great. ployed as scavengers. Therefore the provision of toi- Flies have been implicated, however, in the spread lets of any kind to which cattle and pigs do not have of eye infections and infected skin lesions. access and the treatment of all wastes before land The implied control measure is to prevent access application are the necessary control methods. It is of the insects to excreta. This can be achieved by also necessary to prevent birds, especially gulls, from many sanitation improvements of differing sophis- feeding on trickling filters and sludge drying beds tication. In general, the simpler the facility, the more and subsequently depositing tapeworm ova in their care is needed to maintain it insect-free. droppings on pastures. Personal and domestic clean- liness are irrelevant, except in the use of toilets. Health Benefits of Sanitation Improvements Category v These are the water-based helminths that need one The theoretical potential for control of excreted or more aquatic hosts to complete their life cycles. infections by sanitation improvements alone and by Control is achieved by preventing untreated excreta personal hygiene improvements alone, by environ- or sewage from reaching water in which these inter- mental category of infection, is: mediate hosts live. Thus, any land application system Sanitation Personal or any dry composting system will reduce transmis- alone hygiene sion. There are two complications. First, in all cases alone except Schistosoma mansoni and S. haematobium, I Nligible Great except i~~~~~~~~~~~~~~~i Slight to moderate Moderate animals are an important reservoir of infection. In Great Negligible Therefore, any control measures restricted to human iv Great Negligible excreta can have only a partial effect. Second, in the v Moderate Negligible case of S. haematobium it is the disposal of urine that vi Slight to moderate Negligible is of importance, and this is far more difficult to Table 2-3 gives additional control measures for control than the disposal of feces. Because multipli- categories I through vi. The outstanding difference cation takes place in the intermediate hosts (except is between categories I and iI together, which depend in the case of the fish tapeworm, Diphyllobothrium so strongly on personal and domestic hygiene, and latum), one egg can give rise to many infective larvae. the other categories, which do not. Category-i and A thousandfold multiplication is not uncommon. -ii infections are thus much more likely to be con- Therefore, effective transmission may be maintained trolled if water availability is improved concurrently at very low contamination levels, and the require- with sanitation and if an effective and sustained pro- ments of adequate excreta disposal, in terms of the gram of hygiene education is organized. If improve- percentage of all feces reaching the toilet, are very ments are made only in the water supply, there will exacting. be some reduction in the incidence of category-i and -ii infections, but the full health benefits of the water Category Vi supply improvements will not be realized until ex- creta disposal improvements are made as well. This category is reserved for excreted infections If one considers the changes necessary to control that are, or can be, spread by excreta-related insect category-il and -iv infections, they are relatively vectors. The most important and ubiquitous of these straightforward: the provision of toilets that people vectors are mosquitoes, flies, and cockroaches. of all ages will use and keep clean and the effective Among the mosquitoes there is one cosmopolitan treatment of excreta and sewage prior to discharge tropical species, Culex quinquefasciatus, which pref- or reuse. The reason why the literature on the effects erentially breeds in highly contaminated water and of latrine programs often does not show a marked is medically important as a vector of the worms that decrease in the incidence of category-ll through -Vi HEALTH ASPECTS 21 infections is because, although latrines were built, government and other concerned agencies respond they were typically not kept clean and often not used to this situation through health education of parents at all by children or by adults when working in the to encourage a belief that the stools of young children fields. are dangerous and require hygienic disposal. Al- Sanitation improvements are thus necessary but though the problem is primarily connected with pa- in themselves are not sufficient for the control of rental attitudes and behavior, the provision of some excreted infections. Without them, excreted infec- form of toilet for the disposal of children's stools tions can never be controlled. But other comple- and, perhaps more important, a convenient water mentary inputs, such as improved water supplies and supply will greatly assist child hygiene. sustained hygiene education programs, are essential Children over three years old are capable of using for success. In some cases, the provision of sanitation a toilet if one of suitable design is available. Children improvements and these complementary inputs for in the age range of three to twelve frequently do not the urban and rural poor may necessitate major so- use toilets, even where they are available, because: cial and economic changes. * They find it inconvenient and are not encour- aged to use them by adults * They are afraid of falling down the hole or of Excreted Infections and Children being attacked by domestic animals or rodents that may live next to the latrine Many of the excreted infections have a markedly c They cannot, because the toilet is physically too nonuniform distribution of prevalence among differ- big for them ent age groups. Although all of them are found * They are prevented from doing so by adults who among people of all ages, many are concentrated in do not want children "messing up their nice particular age groups. Many are primarily infections clean toilet." of childhood, or they afflict children as well as adults; relatively few are restricted to adults only. This has As with the very young children, it is of vital im- great relevance for disease control through sanitation portance that the stools of these children are hy- improvements, especially in areas where infant and gienically disposed of because some of them will be child mortality is high. rich in pathogens. The solution lies in a combination In all societies children below the age of about of the provision of a toilet that children are happy three years will defecate whenever and wherever to use and hygiene education for the parents so that they feel the need. A proportion of these children they compel their children to do so. Education at will be excreting substantial quantities of pathogens. school can also be effective, and it is vitally important In some societies the stools of these children are that all schools have well-maintained latrines of a reg,arded as relatively inoffensive, and the children good design so that the children may learn from pos- are allowed to defecate anywhere in or near the itive experience (but this will be of little benefit with- house. In this case it is highly likely that these stools out reinforcement from the parents and the availa- will play a significant role in transmitting infection bility of a toilet in the home) to other children and adults. For example, habits of children that determine the degree of soil pollution in the yard and around the house will largely deter- Groundwater Pollution mine the prevalence and intensity of ascariasis in the from On-site Excreta Disposal household. In contrast, in some other societies stren- uous efforts are made to control and manage the On-site disposal of human waste presents a poten- stools of young children, either by making them wear tial hazard of groundwater contamination and, thus. diapers or by cleaning up their stools wherever they disease transmission from the disposal site through are observed. Either of these reactions will have an groundwater to users of well water. Contaminants important controlling influence on the intrafamilial are pathogens (bacteria, viruses, protozoa, hel- transmission of excreted pathogens. minths) and inorganics (principally chlorides and, in Between these two extremes there is a whole range areas where baby formulas replace breastfeeding. of intermediate behavioral patterns with regard to nitrates). the reaction of adults to the stools of young children. The severity of contamination and the distance In most poor communities the picture is closer to the pollutants travel depend on factors such as soil type first example than to the second. It is important that and porosity, distance to and type of underlying rock, 22 SOCIOECONOMIC ASPECTS groundwater level and hydraulics, composition of tity and quality. Such studies, and necessary correc- waste (presence and characteristics of contami- tive measures, are beyond the topic of this manual. nants), natural contaminant removal processes (fil- Qualified professionals should be consulted. tration, dispersion, sorption), distance to surface The inorganic pollutant of concern is nitrate, which water, and the like. The effects on people depend occurs in groundwater as a result of natural and man- on the type of water service (individual shallow or made pollution. Nitrates do not appear to affect deep wells, piped systems and their water sources), adults even at levels far higher than those specified climate, and so forth. in the World Health Organization (wHo) drinking Clearlv, the most serious problem exists where a water standards, but bottle-fed infants contract latrine penetrates the groundwater that provides methemoglobinemia at nitrate levels considerably drinking water through shallow wells located nearby. below the wHo standard. As a consequence, it is In such a situation, vault latrines should be used or suggested that where groundwater contains more the water piped to standpipes from a protected well. than 10 milligrams per liter of nitrate nitrogen and The most favorable situation exists where the water where the local water supply is used in preparing supply is already a piped system, latrines do not reach infant formulas, the local health officer be consulted groundwater. and soil porosity is low. to determine the possible effect on infants. Where It is not possible to establish detailed, universally infants are bottle fed, acidified milk powder or other valid guidelines for horizontal and vertical separation nutritional changes are available to cure or prevent of latrines, drainfields, and wells. Much further work methemoglobinemia. is required to determine the travel distance and sur- vival of pathogens entering the soil through latrines. It is clear, however, that the greater the groundwater Notes to Chapter 2 abstraction, the more porous or fissured the soil, the greater the distance should be between a latrine and 1. Much of this chapter is taken from Feachem and others a well. It is generally accepted practice to keep a (1980): for a more thorough examination of the issues discussed. minimum distance of 10 meters between latrine and see Feachem and others (forthcoming). well in loam or sandy silt soils. Where wells are 2. Culex pipiens is a complex of mosquito species and subspe- cies. The principal vector of filariasis (elephantiasis) in the tropical equipped with mechanical pumps and supply a large areas in which the disease occurs is Culex quinquefasciatus (pre- number of people, a groundwater study should in- viously also known as Culex pipiens fatigans, C.p. quinquefascia- vestigate and subsequently monitor both water quan- tus. or C. fatigans). .3 Community Participation THIS CHAPTER is concerned with the individual that the supporting agency has to provide are the household and community aspects of sanitation pro- purchase and delivery of materials, water resource gram planning.' Failure to involve the community surveys, drilling of wells, and the like. that is intended to benefit will almost certainly result A discussion of institutional and organizational in failure of the project. For example, government managements needed to support the community par- efforts, extending from 1930 to 1944 and repeated ticipation is beyond the scope of this manual. Those in 1958 and 1974. that tried to impose latrines on a interested will find the details in a companion voiume Central American village had by 1977 a success rate (Kalbermatten, Julius. and Gunnerson 1982). of only 11 percent. In contrast, two villages in the same country responded to their own leaders with such enthusiasm that 65 and 85 percent of the vil- Characteristics of lagers now use self-built latrines. At the other end ra ei o of the scale, both an East Asian and a West African Community Participation city spent considerable sums to construct sewers that . . . are largelv unused because the intended beneficiaries six phases. The first three should be undertaken at have chosen not to connect to them. the very beginning of project development (they are Although it is true that possibilities and ap- p o proaches fo communitv . . re difren part of stage 1 in figure 1-1), the fourth toward the proaches for community participation ar end of the selection phase (stage 6 of figure 1-1). and for villages and cities, personal contacts and dlalogue the final two depend upon technical requirements are important in both. The long-range objective of .. . . . . l ~~~~and opportunity patterns. In the first phase unstruc- communitv participation in sanitation program plan- community prcaotured interviews are conducted with a few local lead- ning is to ensure that the technology selected matches the refeence andresorceconsrains ofthe en- ers (such as political officials, religious leaders, and the preferences and resource constraints of the ben- sho eces n ml ubro oshls .. . .~~~~hoseodes school teachers) and a small number of households. eficiaries. The Lechnology must satisfv h The purpose of these preliminary interviews is to needs at a cost they are willing to pay. To this end, it is necessary that the considerations and practices idkely to determine the engineering design and ac- presented in this chapter be applied by people who .. . . . . . ~~~~~~~ceptance criteria listed below. In this phase it is es- are familiar with tried social science techniques and I who haeacutrld to tsential to determine what kind of description or who havendad cultural bcgonsilrtthtf model of a technology is needed for the householders the intended users. .' Community participation alone is not sufficient for to understand it. A socially acceptable glossarv of the successful design and implementation of a sani- terms relating to defecation also must be prepared tation program. Institutiona supportso that local sensitivities and taboos may be pro- ation program. 'nsttutiona support by gove tected, and local communication channels and ment-national, state, and local-is needed to sup- boundaries should be defined. In the second phase ply technical expertise and support services not a community questionnaire is designed and tested available in the community. For example, the com- munity worker conducting interviews and the tech- . . . nician designing and supervising installation of fa- elicit include: cilities are generally employees of the institution * The desire of the community for sanitation and responsible for sanitation in the area. Other services water supply improvements. expressed as will- 23 24 SOCIOECONOMIC ASPECTS ingness to contribute to the costs through cash who are most concerned about sanitation. If, for ex- contributions, labor and materials, Or both ample, land tenure or employment is found to be a * Preference for private or communal latrines (for problem during unstructured parts of an interview, example, do the latter represent alternatives to sanitation problems will get little attention from the defiling orthodox Buddhist households or do householder. This in turn may indicate little preoc- they lead to crowding and quarreling?) cupation with sanitation within the community and * Health, sickness, and nuisance as they are per- augur ill for any eventual program. ceived to be affected by water supply and san- After the formal interviews, the responses should itation practices be evaluated by the program's behavioral scientist. * Attitudes toward convenience as measured by This information is then used by the engineer and latrine or standpipe location, abundance or ca- economist to develop a list of socially acceptable, pacity of water supply systems, and reliability technically feasible, least-cost alternatives. of service In the fourth phase, a meeting should be held be- * Preferences for color, taste, odor, temperature, tween the program's behavioral scientist and the and the like in water quality community or its representatives at which the former * Aesthetic features of sanitation alternatives presents the alternative technologies and their costs. such as superstructure color and materials or Photographs and other visual aids, working models, squatting plate design visits to other communities, or a combination of * Attitudes toward visibility, means of removal, these should be used, particularly in areas where and so forth, of stabilized wastes, and toward written communication is not common. The benefits conservation, reuse, or reclamation (biogas, fer- of each service level and the manner in which each tilizer, aquaculture, stock and garden watering, alternative can be upgraded should be presented. At and the like) of wastes a follow-up meeting conducted at an early date, a • Importance attached to local autonomy that technology option or options should be selected. If might be lost if a higher authority were to as- necessary, limited demonstration projects may be sume part or all of the responsibility for funding, built and operated. In any event, community choice fee collection, construction, operation, and and willingness to pay should be determined as soon maintenance of the improved facilities as possible. * Community or peer pressure for joining and If a significant proportion of the community pop- supporting "unity and progress" groups and the ulation (say, 50 percent) is not interested in coop- like erating in a sanitation project by the end of the com- * Confidence in local or visiting political and tech- munity participation and assessment program, it will nical authorities. ordinarily be better to shift the project and resources to another community. Two additional warnings are Other factors about which information is essential in order. First, important differences between com- for design or implementation include land tenure and munity preference and design or service level, whether the customary manner in which local committees are for higher or lower levels of service, are seldom re- formed. solved by more education or information. Second, In the third phase, structured interviews are con- schemes that depend on wealthier individuals' in- ducted using the questionnaire developed (and mod- voluntarily supporting sanitation services for others ified if necessary) in the second phase. At least thirty ordinarily do not work. For example, wealthy home- households should make up the sample to be inter- owners are not likely to abandon operating septic viewed, and care must be taken to ensure that they tanks and pay high sewer connection charges so that are representative of the social and income groups poor neighborhoods can be served by the same sewer of the community; information gained in the unstruc- system. tured, preliminary interviews usually can be used to The fifth phase occurs either in parallel with the select representative households. technology selection or as a result of it. The com- Interviews should include women because they are munity will have to organize the implementation and both knowledgeable about water use and responsible subsequent operation and maintenance of the facil- for training children in personal hygiene and sani- ities to be constructed. If there is a formal organi- tation. It should always be remembered by the in- zational structure in the community, it may be used terviewer that the most reliable comprehensive an- to organize project implementation and operation. swers to questions on sanitation will come from those If no structure exists, special arrangements will have COMMUNITY PARTICIPATION 25 to be made for the project. These can vary from the selection of a local craftsman to check a piece of equipment periodically to the hiring of full-time staff Institution-Community Linkage to operate and maintain a communal facility. Just as in the selection of the technology, the type of or- Many aspects of community participation in san- ganizational arrangement should be a community itation program development depend upon and in- decision. fluence institutional structures. Although it has been Construction work should be performed with the assumed that the necessary institutional support ex- assistance of the technician of the technical support ists, it may be useful to conclude this chapter with agency, but under local leadership if possible. It is a simplified description of the institutional steps re- important that the community ensures that some of quired to facilitate and support involvement of the its members are trained by the technician during this community: process. ome r f * Establish a support unit for water supply and Some requirements for a successful construction sanitation in existing regional agencies or form program are the selection of sites for communal and an ind exist regioa agencies or rm private facilities; the purchase of materials not avail- aepen de support uni The staf ll re- able in the community; the distribution of materials r needed to construct individual facilities; prompt de- clude engineers, hydrogeologists. a behavioral livery by the community of materials provided in lieu scientist, an economist, accountants, plumbers, of cash contributions; organization of work parties mechanics, electricians, well drillers, purchasing and maintenance of records of time, cash, or mate- agents, and health educators. rals provintenae by rcordsuofttime,es casuppy or m - eEstablish design and operating standards and rials provided by community members; supply of village selection and priority criteria, conduct technical assistance for the construction and initial . . operation of the facilities; and external input from .specializedttaks isch ga yoeoaogialsur- the echica supor agncy veys, management training, operating assist- the techical support agency. ance, and the like. Phase six is the operation and maintenance of the i Train community workers in low-cost water sup- facilities. In the case of communal systems, this in- ply and sanitation technology., hygiene promo- volves regular operation, maintenance, occasional tion, and community organization. repairs, and the collection of funds to pay for recur- .Train community workers in health care and rent expenses. In addition, performance should be nutrition monitored by the technical agency, in collaboration oCanvass and organize selected communities. with the community, and information disseminated g to ote comnte so tha lesn lere fro Plan, design, and implement prototype projects to complete the training of communitv workers. the success or failure in one can be used in the design and implementation of programs in others. The pro- gram should also include exchange visits by those nated areas to canvass and organize communi- responsible for operation and maintenance in various ties. communities and, if systcms are large or sophisti o* Assist communities in constructing facilities. communities and, if.systemsarelargeorp * Maintain a limited number of community work- cated enough, the training of local personnel at re- ers as roving operation and maintenance advis- gional agency headquarters. Any training not accom- ers and monitors for completed projects. Assign plished during phases four and five should take place and monito forkcoplted pres Assig now, and the relation between the operators and the othe rommunity w erewiarea h technician should be established. The latter should succes tectsscanbe treplicated . . 1 . . ~~~~~~* Provide technical assistance through a support make periodic visits to the community to help solve unit. Maintain a stock of spare parts adminis- minor problems, provide routine technical assist- tered bv the support unit. ance, order spare parts, and mobilize additional sup- . Monitor the operation and quality of service. port if major problems arise. Regular visits should disseminate information and provide continu- be made at short intervals in the beginning and at . . least once a month after the community has become ous training programs for community workers familiar with the tasks of operating the facilities. and local staff. Provision also should be made for rapid contact in In summary, the degree of community participa- cases of emergency (failure of equipment, suspected tion and willingness to pay for improved service lev- water contamination, and the like). els by contributions of money, labor, or materials 26 SOCIOECONOMIC ASPECTS depends fundamentally upon household income tev- sibility of people accepted by the community: these els and perceived needs. Whether a feasibility study tasks are too important to be entrusted to strangers. results in a project that properly meets the needs of the community depends on the accuracy, complete- ness, and timeliness of information exchanged be- Note to Chapter 3 tween the residents and those who are conducting the feasibility study. The analysis of social factors 1. For a more thorough discussion of these issucs, see Kalber- and conduct of the interviews should be the respon- matten, Julius, and Gunnerson (1982). 4 Economic Analysis of Sanitation Technologies ONCE THE TECHNOLOGIES that are technically in- opportunity cost to the national economv of pro- feasible for the site being considered have been elim- ducing that service. Three principles must be fol- inated by the project engineer, it is necessary to rank lowed in preparing estimates: the remaining technically feasible technologies by * All relevant costs must be included. some meaningful scale so that the most appropriate * Each cost must be properly evaluated. one may be selected.' Implicit in this is the need for a common basis for the objective comparison of the ologesumus be foal cost ent. remaining technologies that reflects both the positive n and negative consequences of adopting each of them. The first principle of economic costing is that all Ideally. a cost-benefit analysis should be used to costs to the economy, regardless of who incurs them. rank alternatives, but, as is true of many public serv- should be included. In comparing the costs of dif- ices, it is impossible to quantifv most of the benefits ferent sanitation technologies, too often only those (such as those of improved health and user conven- costs met by the administrative (usually municipal ience) of a sanitation system. In general, there is no or state) authority are considered in the cost com- completely satisfactory way to get around this diffi- parison. The costs borne by the household or the culty. Only in the case of mutually exclusive alter- costs of complementary services (for example, water natives with identical benefits should one always se- for flushing) are often ignored. In the analysis of the lect the one with the least cost. Where there are financial implication for the authority of alternative differences in the levels of service provided by the technologies, such a comparison would be appro- various alternatives, the least-cost choice will not priate. For an economiZic comparison, however (that necessarily be the one that is economically optimal. is, for the determination of the least-cost technoloav For this reason a least-cost comparison will not nor- with respect to the national economy). it is necessary mally provide sufficient information to select the to include all costs attributable to a given alternative most appropriate sanitation technology. Nonethe- irrespective of whether they are borne bv the house- less, if properly applied, it will provide a reasonably hold, the administrative authoritv. the national gov- objective basis for comparison that reflects the cost ernment, or whomever. Some financial costs should tradeoffs corresponding to different levels of service. be excluded from the economic comparison. Ex- Once comparable cost data have been developed, amples of costs that should be ignored are subsidies the users or their community representatives can and taxes, since these represent a transfer of money make their own determination of how much they are within the economy rather than a cost to it. willing to pay to obtain various standards of service. The determination of which costs to include should rest on a comparison of the situation over time both with and without the project. This is not the same Economic Costing as a simple "before and after" comparison. Rather than using the status quo as the "without" scenario, The basic purpose behind the economic costing of it is essential to estimate how the current situation sanitation technologies (or the economic costing of would improve or deteriorate over the project period any other development activity) is to give policy- if the project were not to be undertaken. In addition. makers a basis for their decisions by providing a price a broad enough view of the project must be taken tag for a given level of service that represents the so that all relevant costs will be included. For ex- 27 28 SOCIOECONOMIC ASPECTS ample, a cost that is often ignored when costing sew- is economically overvalued; that is, the paycheck of erage systems is the cost of the additional water that an unskilled laborer is higher than that he would will be required for flushing. receive in the absence of minimum wage legislation. Once the relevant costs have been identified, the Because his economic value is less than his wage, second principle of economic costing concerns the however, employers will be reluctant to hire him. prices that should be used to value these costs. Since Thus, where minimum wages are set above the real the objective of economic costing is to develop fig- productivity of unskilled labor, unemployment gen- ures that reflect the cost to the national economy of erally results (of course, unemployment happens for producing a good or service, the economist is con- other reasons as well). This means that, if a country cerned that unit prices represent the actual resource has a very large pool of unemployed laborers, the endowment of the country. Thus a country with shadow factor for unskilled labor wages might be abundant labor will have relatively inexpensive labor close to zero because there is almost no cost to the costs in terms of the alternative production possibil- national economy that results from employment of ities of its labor. Similarly, a country with scarce such people, since they would otherwise be unem- water resources will have expensive water costs, in ployed and so be producing nothing. On the other the economic sense, regardless of the regulated price hand, if a country has few unemployed unskilled charged to the customer. Only by using prices that workers, then the shadow factor would be 1, as this reflect actual resource scarcities can one ensure that situation is an indication that the market wage fairly the least-cost solution will make the best use of a reflects economic value. Generally the shadow factor country's physical resources. for unskilled labor in developing countries is in the Because governments often have sociopolitical range of 0.5 to 1.0. goals that may be only indirectly related to economic objectives, some market prices may bear little rela- tion to real economic costs. For this reason it is some- Foreign exchange times necessary to adjust market prices in the eco- Many governments do not permit free movement nomic costing exercise so that they represent more of the exchange rate of foreign currency for their accurately "real" unit costs (in the sense of reflecting national currency in the international money mar- the effect of these costs on the national economy). kets. Instead they fix its value, often in terms of the This adjustment of market prices to reflect oppor- currency of a major trading partner such as the tunity costs is sometimes known as "shadow pricing." United Kingdom or Japan. As a result, the currency The calculation of these shadow rates, or conver- is sometimes overvalued; imports thus cost fewer sion factors, is a difficult task that requires intimate units of the national currency than they would if the knowledge of a country's economy. It is rarely (if government allowed the currency to trade freely on ever) worthwhile for an economist or engineer in- the international market, and exports are overpriced volved with sanitation program planning to take the in foreign currency value. Sometimes this same result time to collect data and calculate conversion factors is achieved not by an overvalued domestic currency directly. Rather, he or she should check with the but by a system of import restrictions, export taxes. ministry of planning or economic affairs to see if the or both. The foreign exchange shadow factor is the figures have already been determined. ratio of the shadow exchange rate (what the currency In the economic costing of sanitation technologies would be worth in a freely trading international mar- there are four shadow rates that normally need to ket) to the official exchange rate fixed by the gov- be incorporated in the analysis. These are: ernment; expressed in this way, the shadow factor * The unskilled labor wage shadow factor is thus greater than 1 whenever the local currency * The foreign exchange shadow factor is overvalued or import restrictions are high. Suppose * The opportunitv cost of capital a government fixes its official rate of exchange at 10 * The shadow price of water, land, and other di- units of its national currency (UNC) to the U.S. dol- rect inputs, lar, but that in the free market 15 UNC would be required to purchase one U.S. dollar; the foreign Each is briefly discussed in turn. exchange shadow factor is thus 1.5. Suppose further that a municipality in the same country wishes to Unskilled labor import a night-soil vacuum tanker that has a direct foreign exchange cost at the border of $10,000. It Many governments enact minimum wage legisla- would have to pay only 100,000 UNC for the tanker, tion. The usual effect of this is that unskilled labor but the true economic or "shadowed" cost to the ECONONIIC ANALYSIS 29 country's economy is 1.5 times this amount (that is, described below and shown in the appendix to this 150,000 UNC), and this is the cost that should be used chapter. in evaluating the economic cost of the night-soil col- For most developing countries, where labor is lection system the municipality wishes to adopt. abundant but capital and foreign exchange are scarce, the effect of shadow pricing is to decrease the cost of unskilled labor and to increase the cost of both capital and imported goods. Since shadow This is defined as the marginal productivity of ad- pricing removes distortions attributable to political ditional investment in its best alternative use. It can decisions (for example, minimum wage legislation, also be thought of as the price (or yield) of capital. overvaluation of local currencies, and the provision In countries where capital is abundant, such as the of development capital at low rates of interest), it is industrialized countries of Europe, one expects the extremely valuable in the identification of the most yield on capital to be relatively low. This is because appropriate sanitation technology for the actual re- capital has already been employed in its most pro- sources of the country. An example of the use of ductive uses and is now being substituted for labor shadow pricing in economic costing is given in the or other inputs in less and less profitable areas. In appendix to this chapter. many developing countries, however, capital is a In addition to these adjustments for shadow prices, scarce commodity and therefore has a high oppor- economic costs differ from financial costs in that they tunity cost. A government might decide for socio- are based on incremental future investments rather political reasons to make available loans to house- than average historical investments. This principle holders at a low rate of interest to enable them to rests on the idea that costs already incurred ("sunk" build, say, ventilated improved pit (vIP) latrines. The costs) should be disregarded in making decisions economic cost of this decision is the yield that the about future investments. Thus, in analyzing the real government would have received had it invested its resource cost of a given technology. it is necessary capital in the best alternative way; for example, by to value the components of that technology at their buying shares in a well-managed industrial enter- replacement costs rather than at their actual histor- prise. The opportunity cost of capital is thus ex- ical prices. In the case of sanitation systems, this is pressed as a percentage; in developing countries it particularly important in the costing of water. Be- usually ranges from 8 percent to 15 percent. cause cities develop their least expensive sources of water first, it generally becomes more and more Water, land, and other direct inputs costly (even excluding the effect of inflation) to pro- Water, land, and other direct inputs duce and deliver an additional liter of water as the The prices of some inputs of sanitation systems are city's demand grows. By using the average cost of controlled by governments or incorporate govern- producing today's water, one is often seriously ment subsidies. For example, land for the construc- underestimating the cost of obtaining additional tion of waste stabilization ponds may be owned by water in the future. The decision to install a con- the government because it is near a public airport. ventional sewerage system with high-volume cistern- The government may decide to transfer it to the sew- flush toilets will increase domestic water consump- erage authority for no financial cost. Its economic tion by around 50 to 70 percent. Thus, in calculating cost, however, should be calculated as what it would the costs of such an alternative, it is extremely im- have been worth had it been sold on the market to portant to value properly the cost of the additional a farmer or industry that wished to locate there. water that will be required. The economic cost of Usually a good approximation of this shadow cost this additional water is its average incremental pro- can be obtained by reviewing recent sales records of duction cost; it is not the cost charged to the con- similar land in the area. sumers or its current average production cost. Other prices that may need adjustment to reflect The application of these costing principles to san- real resource costs are those of publicly produced itation program planning presents several difficul- outputs such as water and power. It is usually not ties. The main one is the problem of finding a scaling possible to estimate directly what a free market price variable that allows comparison among diverse tech- would be for these items because the government nologies regardless of their design populations. On- normally has a monopoly in their production. Never- site systems such as improved pit latrines are gen- theless, the shadow price of water or power can be erally designed for a single family or household. The approximated by calculating its average incremental latrine's lifetime or the intervals between fairly major production cost. A good method for doing this is maintenance work, such as desludging. will depend 30 SOCIOECONOMIC ASPECTS on how many people use it. The life of some com- r = opportunity cost of capital in ponents (such as the vent pipe), however, may be percent times 10-2. independent of usage, so that the annuitized per cap- It is essential that all costs used in the equation ita construction cost of a latrine used by six people have been appropriately shadow priced. Note that, will not be the same as that of one used by ten people. for a system that is fully utilized upon construction, For this reason most costs should be calculated on the equation reduces to merely the sum of the an- a per household basis. nuitized capital costs and annual operating and main- It is often difficult to calculate comparable costs tenance costs divided by the design population. when considering low-cost sanitation as an alterna- In practice it is often easier to calculate the AIC tive to sewerage. The low-cost facility is fully used of a sewerage system on a volumetric, rather than almost immediately by its "design population.'" a per capita, basis. The AIC per cubic meter of sewage Many of the components of sewerage, however, ex- is calculated from year-by-year projections of the hibit economies of scale and are therefore sized to total wastewater flow. The resulting volumetric costs meet a design flow that usually does not arise for can then be transformed into per capita (and per many years. With such a facility all the investment household) costs using the per capita wastewater costs are incurred at the beginning of its lifetime, flow. An example is given in the appendix to this whereas the benefits (services) are realized gradually chapter. over time. Just as costs incurred in the future have An additional problem in deriving comparable a lower present value than those incurred today, ben- costs for different sanitation technologies is the dif- efits received in the future are less valuable than fering abilities of the technologies to handle sullage. those received immediately. In the derivation of per With conventional sewerage, most septic tanks and household costs, this means that serving a person pour-flush (PF) and aquaprivy systems. sullage is dis- five years hence is not worth as much as serving the posed of with the excreta and toilet flushwater. With same person now. To divide the cost of a sewerage most of the on-site excreta disposal technologies, system by its design population would greatly un- sullage must be disposed of into surface or piped derstate its real per household cost when compared storm drainage systems or into soakage pits. If storm- with that of a system that is fully used upon com- water drains are present (or would be constructed pletion. anyway), the incremental construction cost if sullage One of the best methods to overcome this problem is to be discharged into them might be very small of the differing capacity utilization rates of different since they are usually designed to handle flood peaks. systems is the average incremental cost (AIC) ap- It would be necessary to include only the cost of any proach. The per capita (or household ) AIC of a sew- special modifications needed to enable the relatively erage system is calculated by dividing the sum of the small volumes of sullage to enter and flow in the present value of construction costs and incremental storm drains without nuisance in the dry seasons, the operating and maintenance costs by the sum of the maintenance costs of ensuring that they are not present value of incremental persons (or households) blocked (and so form breeding grounds for mosqui- served; the appropriate equation is: toes), and the environmental cost of the eventual disposal of the sullage into the receiving watercourse. E (C, t 0, )/(1 + r)'-1 If large amounts of sullage are left to soak into the AIC, = ground, nuisance and possibly health risks may be , N, /(I + r)'-1 created, and these costs should be evaluated and Z = I included. Alternatively, separate disposal of sullage where t time in years may be considered a benefit where populations re- T = design lifetime in years (meas- cycle kitchen and bathwater to irrigate gardens or ured from start of project at t dampen dust. In such a case, the removal of sullage = 0) through the introduction of a sewerage system would C, = construction costs incurred in involve a cost. In any particular case it is best to year t compare alternatives that represent approximately 0, = incremental (from year t = 0) the same benefit levels. Thus, if sewerage (including operation and maintenance sullage collection) is one alternative, the cost of sul- costs incurred in year t lage disposal in, for example, road drains should be N, additional people or house- included in the cost of other sanitation alternatives holds (from year t = 0) served unless the road drains would be built anyway for in year t flood control, in which case it is necessary only to ECONOMIC ANALYSIS 31 include the additional costs incurred as mentioned the original facility (either in total or through a loan above. The guiding principle, again, is to compare at the interest rate that reflects the opportunity cost the conditions with and without the project. of capital) and then pay a periodic sum to cover its In general, the data necessary for the calculation operation and maintenance expenses, if any. In cases of comparable economic costs can be collected fairly such as these, the financial cost would be identical early in the design process, after preliminary designs to the economic cost except for any taxes and shadow have been prepared. This has the advantage of pro- pricing of those inputs that must be purchased in the viding an early warning if, as is frequently the case, market. To the extent that the latter account for a most of the alternative designs are too costly relative significant part of total economic costs, financial to the resources likely to be available. It thus saves costs may be above or below economic costs. the trouble of preparing final designs for those tech- In deriving financial costs in any particular case, nologies that are outside the bounds of affordability. it is necessary to talk with central and local govern- Economic costing should therefore be seen as an ment officials to determine their financial policies early screening of the various sanitation technologies and noneconomic objectives. If the government that have passed the basic tests of technical and social places a high priority on satisfying the basic needs feasibility. of all of its citizens, then it may be willing to subsidize part or all of the construction cost of a simple sani- tation system. The general policy of international Financial Costing lending agencies such as the World Bank is that, if the cost of the minimal sanitation facility necessary The purpose of deriving economic costs is to make to provide adequate health is more than a small part a meaningful least-cost comparison among alterna- of the household income (say, 5 to 10 percent), then tives. Such a comparison is extremely useful to the the central or local government should attempt to planner and policymaker. The consumer, however, subsidize its construction to make it affordable. Any is much more interested in financial costs; that is, operation or maintenance costs should be borne by what he will be asked to pay for the system and how the beneficiary. If, however, some consumers wish the payment will be spread over time. The difficulty to have better or more convenient facilities, they in developing financial costs is that they are entirely should pay the additional cost themselves. Similarly, dependent upon policy variables that can range if more affluent communities decide that, beyond widely. Whereas economic costs are based on the meeting basic health needs, they wish to safeguard physical conditions of the community (for example, the cleanliness of their rivers or general environment its abundance or scarcity of labor, water, and so by building a more expensive sanitation system, they forth) and therefore are quite objective, financial should pay for that system either through direct user costs are entirely subject to interest rate policy, loan charges or through general municipal revenues. maturities, central government subsidies, and the Since the majority of the poorest people in most like. For example, the financial costs of a sanitation countries live in rural areas, it is usually not appro- system for a community can be zero if the central priate to subsidize urban services from central tax government has a policy of paying for them out of revenues. the general tax fund. Thus, financial costs cannot be In general, it is necessary to calculate several sets used to make judgments about least-cost alterna- of financial costs based on different assumptions tives. about municipal or central government subsidies. To promote the economically efficient allocation The first set, which is hereafter called the base fi- of resources, financial costs should of course reflect nancial cost, is that which assumes no financial sub- economic costs as closely as possible, given the gov- sidy. For an on-site system with a short construction ernment's equity goals and the degree of distortion period and little requirement for municipal mainte- in other prices in the economy. This could be ac- nance, the engineer's estimate of construction costs complished with sewerage, for example, bv setting (in market prices) is simply annuitized over the life a surcharge on the connected consumer's water bill of the facility at the prevailing (market) interest rate. that is equal to the AIC of sewerage per cubic meter If self-help labor can be used for part of the con- of water consumed (that is, if 75 percent of water struction, then the cost of hiring that labor should consumption reaches the sewers, the AIC of sewerage be subtracted from the total before annuitizing. To per cubic meter would be multiplied by 0.75 to arrive this annual capital cost must be added any operating at the water surcharge). In the case of most of the and maintenance costs that will be required. Then on-site systems, the consumer would pay to construct this total base financial cost can be compared with 32 SOCIOECONOMIC ASPECTS household incomes to check affordability. If the tech- ting plate), are manufactured locally. Let the costs nology is considered affordable by the target popu- (in units of national currency, UNC) be: lation, then the only financial arrangements that will Local materials 100 LNC be required at the outset are those necessary to aid Imported materials 60 UNC. consumers in securing loans from commercial and public banks. If the technology's base financial cost Assume that skilled labor is used in building the is not affordable by the households to be served, and squatting plate and superstructure and for general if lower-cost solutions are infeasible or unacceptable. supervision, and that unskilled labor is used to ex- then various options involving increased self-help in- cavate the pit, to mix the concrete, and generally to put, deferred or low-interest loans, partial construc- assist the skilled labor. Let the costs be: tion grants, and the like should be used to compute Skilled labor 30 UNC alternative sets of financial costs. Before any of these Unskilled labor 70 UNC. are offered to the consumer, however, it is obviously Assume that the household can be expected to necessary to obtain local government funding to spend 10 UNC per year on minor repairs and cleaning cover the financing gap. materials, that the repairs are done by the house- The development of financial costs is more difficult holder, and that the cleaning material is manufac- for technologies with off-site investments and the tured locally. accompanying need for centralized management and Assume the following: operation. There is a large body of literature on ac- counting svstems for public utility enterprises, and Unskilled labor shadow factor 0.7 the subject cannot be fairly summarized in this brief Foreign exchange s ado atal 12.0 percent chapter. Official rate of exchange per U.S. 2.80 UNC dollar Household size 6 persons. Costing of Community Assume also that the pit latrine is designed to last Support Activities ten years and that no items can be reused at the end The construction cost figures used for both the of that period. economic and financial analyses do not include the cost of community organization, hygiene education Example and technical assistance, and government adminis- An example of costs calculated from these as- trative support, which are not directly related to the sumptions is presented in table 4-1. The following construction of the facilities but which are normally points also apply: provided to complement a water supply or sanitation program. Unless otherwise noted, it is assumed that * The annuity or capital recovery factor (CRF) can assistance provided by government for health edu- most easily be obtained from a book of financial cation and technical assistance is paid for from reg- or compound interest tables or by using a fi- ular budgetary resources. Where additional assist- nancial calculator. It can also be calculated, ance is required, the cost should be estimated and however, from the equation: specific funding arrangements made. Needs for as- r (1 + r)N sistance vary too widely from community to com- CRF - (1 + r)N- munity to permit the estimation of a useful average per capita cost figure. where r = opportunity cost of capital in percent x 10-2 and N = design lifetime in years. Here r = 12 percent and N = ten years, so that the Appendix. Examples CRF is 0.177. of Economic Costing * The annuitized annual cost (in UNC) of each capital item is obtained by multiplying its cost (in UNC) by the CRF and by the appropriate Economic costing of a ventilated improved pit sao atr fay (VIP) latrine shadow factor, if any. * The annual cost in U.S. dollars is calculated by Assume that all materials, except the vent-pipe, converting the shadowed local cost at the official cement, and reinforcing steel (for the concrete squat- rate of exchange. ECONOMIC ANALYSIS 33 Table 4-1. Annual Economic Costs of a Ventilated Improved Pit (vip) Latrine Item Total Lifetime Shadow Adjusted annual cost cost (UNC) (years) factor UNC U.S. dollars Materials Local 100 10 None 17.7 6.3 Imported 60 10 1.3 13.8 4.9 Labor Skilled 30 10 None 5.3 1.9 Unskilled 70 10 0.7 8.7 3.1 Maintenance 10 1 None 10.0 3.6 Total Per household 55.5 19.8 Per capita 9.3 3.3 UNC Units of national currency. twice). All these costs must be shadow priced, and Economic costing of a conventional it is thus necessary to determine separately the costs sewerage scheme of unskilled labor and imported items. These capital costs are then converted to annual costs by multi- Sewerage costs are divided into two types: house- plying by the appropriate CRF as described in the hold costs, and collection and treatment costs previous example. (although collection and treatment costs should be Annual operation and maintenance costs are then calculated separately, for reasons explained below), calculated, using the AIC of water for the unit cost HOUSEHOLD COSTS. These include all the toilet of the flushing water necessary. and plumbing fixtures, the connection to the street COLLECTION AND TREATMENT COSTS. These in- sewer, and the superstructure (in the case of a toilet clude all material and installation (labor) costs for located inside the house, this may be calculated as the sewer network and its appurtenances (such as the toilet floor area times the construction cost per manholes and pumping stations) and for the treat- square meter-excluding from the latter the toilet ment works (including land costs). Capital costs for and plumbing fixtures, to avoid including these collection and treatment should be calculated sepa- rately because they may be incurred at different Table 4-2. Shadow-priced Collection and times during the construction period and may also Treatment Costs of a Conventional Sewerage have different design lifetimes. Scheme Constructed over Five Years Year Total Component incurred cost (UNC) Example Collection Household costs are excluded from the example Sewers, force mains, man- since they are calculated in the same way as those holes 1-5 (evenly) 4,000,000 of the pit latrine. Note that the design lifetime of the Pumping stationsa 5 400,000 household components is not likely to be the same Engineering design 1-2 (evenly) 200.000 as those of the collection system and treatment Operation and maintenanceb Annually 150,000 Treatment works. Land 1 2,000 Assume that the collection netWork and treatment Fencing 3 10,000 works are constructed over a five-year period. As- Engineering design 3 15,000 sume further that the shadowed costs are as listed Treatment works 3-5 (evenly) 900,000 (and incurred in the years stated) in table 4-2. Operation and maintenanceb Annually 100,000 (n nurdi h er ttd ntbe42 Assume also that: the design population is 250,000; a. Includes mechanical and electrical installation. the wastewater flow is 200 liters per capita daily; 50 b. Calculated assuming full capacity, beginning in year 11. percent of the design population is served up (Because of initially incomplete capacity utilization, the costs upon completion of the system in year 5 would be 50 percent of the pletion of construction, increasing linearly to full costs listed, increasing over years 6-10 to the full amounts shown.) utilization by the beginning of the eleventh year from 34 SOCIOECONOMIC ASPECTS Table 4-3. Costs (in Constant Base-year Prices) and Wastewater Flows for Conventional Sewerage Scheme (UNC,) Collection Treatment Wastewater flow Operation and Operation and (thousancds of Year Capital maintenance Capital maintenance cubic meters) 1 90(0,000 2.000 0 0 2 900.0(0 0 0 0 0 3 8(0,000 0 325.000 0 0 4 800.000 0 300,000 0 0 5 1.200,000 0 300,000 ( 0 6 ( 75.000 0 50,000 9,125 7 0 82,000 0 55,000 10,038 8 0 90,000 0 60,000 10,950 9 0 97,500 0 65,000 11,863 1 0 105,000 0 70.000 12,775 11 0 112,500 0 75.000 13,688 12 0 120,000 0 8(.000 14,600 13 ( 127.000 0 85.000 15,513 14 0 135,000 0 90.000 16,425 15 0 142,500 0 95.000 17.338 16 0 150,000 ( 10(.((0 18,250 17 0 150,000 o 10o.((o 18,250 44 0 150,000 0 100,00 18,250 45 0 150.000 0 100,0(( 18,250 Table 4-4. Present Values (Pv) of Costs (in Constant Base-year Prices) and Wastewater Flows for Conventional Sewerage Scheme (UNC) Collection Treatment ___ ___ ___ ___ ___ ___ ___ _ ___ ___ ___ ___ ___ ___ __ W aste w ater flow Operation and Operation and (thousands of Year Capital maintenance Capital maintenance cubic meters) 1 900,000 0 2,000 0 0 2 803,571 0 0 0 0 3 637,755 0 259.088 0 0 4 569,424 0 213,534 0 0 5 762,621 0 190,655 0 0 6 0 42,557 0 28,371 5,177 7 0 41,543 0 27,864 5,085 8 0 40,711 0 27,140 4,953 9 0 39,378 0 26,252 4,791 10 0 37,864 0 25,242 4.606 11 0 36,221 0 24,147 4,407 12 0 34,497 0 22.998 4,197 13 ( 32,597 0 21,817 3,981 14 0 30,938 0 20.625 3,764 15 0 29,158 0 19A438 3,547 16 0 27,404 0 18.269 3,334 17 0 24,468 0 16,312 2.976 44 0 1,147 0 764 139 45 0 1,024 0 682 124 Present value 3,673,371 612,689 665,277 408,702 74,575 of column Note: AIC (average incremental cost) = (3,673,371 + 612,689 + 665,227 + 408,702),'74,575,000 = 0.07 UNC per cubic meter of wastewater. ECONOMIC ANALYSIS 35 completion; the design lifetime of both the collection where C, = cost incurred (or total wastewater system and treatment works is forty years (measured volume produced) in vear t: and r = opportunitv from completion)- and the opportunity cost of capital cost of capital in percent times 10-2. is 12 percent. Note that the costs given in table 4-2 * Calculate the AIC of the collection and treatment are assumed to have been shadow priced already for components by adding together the sums of the unskilled labor and foreign exchange components. Pv of the capital and operation and maintenance Operation and maintenance costs are assumed to costs for both components and then dividing by vary with the population served, being 50 percent of the sum of the Pv of the wastewater volumes as the figures given upon completion. increasing to 1(10 shown in the last line of table 4-4. This gives the percent of the figures by the beginning of the elev- AIC of collection and treatment in UNC per cubic enth year from completion. meter, from which the annual per capita AIC can Given these assumptions, the costing procedure be calculated because the per capita wastewater is: flow is known to be 200 liters per capita daily (73 cubic meters per year). In this example the * Construct a table. similar to table 4-3, in which AIC per cubic meter is 0.072 UNC, or 5.2 UNC all the costs incurred and the total volume (in per capita annually. The total AIC of the whole cubic meters) of wastewater generated in each sewerage scheme in UNC per capita annually is year are entered under the various headings as then obtained by adding in the shadowed annual shown. The effect of inflation should be ignored per capita household capital and operation and in this calculation so that all costs are in constant maintenance costs. This may be expressed in prices. U.S. dollars by converting at the official ex- * As shown in table 4-4, convert these costs and change rate. volumes to their present values (pv) by using a set of financial tables, a financial calculator, or the equation: Note to Chapter 4 V,= C, 1. For a more detailed treatment of the issucs in this chapter. (I + Ot l see Kalbermatten. Julius. and Gunnerson (1982). * l s~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Part Two Sanitation Program Planning I I I 5 Comparison of Sanitation Technologies A VARIETY of sanitation technologies exist. The with the existing level of water supply service and principal ones are shown in figure 5-1. Those con- the community's general socioeconomic status. limit sidered suitable for application in developing coun- the choice of technologies considerably. irrespective tries are described in chapters 8 through 22. of the overall scores achieved in a numerical matrix The most common approach to making compari- comparison of all possible technologies. These fac- sons of sanitation technologies is to define the com- tors and their influence on technology choice are parative criteria and then use some kind of matrix discussed below. that displays the putative performance of each al- ternative in relation to the stated criteria in the man- ner shown in table 5-1. The comparison is purely Water Supply Service Levels descriptive, and no overall ranking or conclusions are attempted. Table 5-1 is essentially a guide for A readily available supply of water is quickly re- nontechnical readers and a convenient summary for flected in the amount used and, hence, in the options professionals. Its most useful function may be to ex- available for its disposal. It has been found that dlude certain technologies in a given situation, rather neighborhood standpipes ordinarily supply 20 to 25 than to select the best. liters per capita daily. When a yard tap is provided. More complex approaches to matrix comparisons water use increases to 50 liters per capita daily, and are possible. For example. each criterion may be when water is supplied through a tap inside the weighted numerically and the degree to which each house, water use becomes 50 to 100 liters per capita technology satisfies each criterion may be assigned daily, which is about the limit for on-site disposal of a score on a numerical scale, so that weighted per- sullage. formance figures can be obtained for each technol- ogy, and the technologies ranked accordingly. This Hand-carried supplies method of technology comparison. which is by im- plication a method of technology selection, has sev- Clearly, ventilated improved pit (v:i) latrines. eral major disadvantages. The ranking depends on Reed Odorless Earth Closets (ROECS), ventilated the weightings given to the performance criteria. and improved double-pit (VIDP) latrines, and double- these weightings contain a strong element of value vault composting (DVC) toilets are possible choices judgment. The value judgments used are generally since they require no water, except for toilet hygiene. those of an "expert group," which does not represent Equally. cistern-flush toilets with either conventional the user population. A different panel of experts sewerage or septic tanks and soakawavs are techni- might well produce different results, and the com- cally infeasible, as are sewered pour-flush (PF) toi- munity members themselves might not only assign lets, since insufficient flows would be generated. The different scores and weighting factors but would principal problem is whether PF toilets and vault toi- probably employ different criteria. Thus, ranking lets (which also have a PF squatting slab) are feasible technologies in this way produces not only a numer- or not. Is sufficient PF water likely to be hand carried ical comparison of spurious precision. but one that into the toilet? Experience with the difficulty of may also be, to the users at least, irrelevant. More- water seal maintenance in conventional aquaprivies over. in any given community there are always basic (chapter 13) suggests not, but user perception of the physical and cultural attributes that, in conjunction need to flush PF toilets is likely to be very high (in 39 Figure 5-1. Generic Classification of Sanitation Systems Sanitation sVstcfll | 0)51-site fIn-sitc r n(Ill-sitc Dry Wet le we()ry 1. Overhung at.imne- S Poiur-ils1- t1 latrine. siko- 14 I. Lo-vohli c-eitetuI- h, 17 ( o)-iixii titl s-w-rage I) Valth and -acumtut tank 2. Trcnch latrie warv sawkaiwtay or sew-r 19 Vmlt. ilttle) renal-ovxl. track. 3 PIllrint 9 '9 latrine. aiutiprivy. sotaki- 15 titw- -olutmtc cistern -luslh. Ca aI 4 Reed Ododrlss E[iIt Closet wit tq-privyi . so:akawaN, or 201. Buketl lI onrn (Rt l ) IlL I, lati,rme, seplic tatik va.ault sewer 21 M-hanical h(tcket lit- 5 Ventilated inprovred pit ( 1i') I . Sullagv filtli. a.qiiapruye 16t I.o -olit ticc tn-fl-sh. latrinnc soakasasa septic tank. soakawv. or ( Hatch.-.t..pi.. tistg latrinc 12 SLulL'g-IIudI. scptic tank. ser 7. ( onrnu1-111- -po'tmlg mom,h- oak-t;kl.y 13.S tkl, 2 3 -45 8 10 1 1 13 Sam s ax 12 -xcepl --nvemiitial cisterlt Push 14 IS, 16 Sanme as c,rrsponding ciifigitafiut ini 8 to 12. 17 Scc standard murnit-ls and 1iti t ccpt f cincd cistcrn ith lo-ol IMO IS 19 20 21 0 Motvcitcnt of liquids: c . movement of stlids, Soarrce: IThe World BHank. Water Su1pple urnd Wile Dii.prrdl. Itelvcrtv n iand 13iasic Needs Serics (Wtashington, I) C: Septrember 1980). Table 5-1. Descriptive Comparisoni of Sanitation Technologies Sanitationi Rural Urban Construction Operating Ease of Self-help Water Required soil Complementarv Reuse Healthi Inistittionlal techniology application application cost cost constructiotn potential requirement conditions off-site investmnentr potetntial benefits requirements Ventilated Suitablc Suitable III I/ I 1. Verv eatsy II Nonc Stabte perimicable soil: None I Griod L improved pit M-densitv except in groundwater at least I (vil) latiitees and areas wet 1or meter below surface' Reed Odorless roscky Earth Closets ground (R(iL s) Pour-flush (Pi Suitable Suitable in L./ 1. L Favy I Watcr near Stable permeablc soui. Nonie I Very good l tirilets M-density itoilet groundwater at least I areas meter below surface' Doubie vault Suitable Suitable in L/ M 1 Very easy It None None (can he built ahiove Nonc t toiid 1. composting (DVC) M density except it wet grounni) toilets areas or rocky ground Sclf-topping Suitalile Suitable ]II L M L Requires If Water nea:r Permeahle soil groundwater Treatment facilitics for M Very gord 1 aquaprivv M-dentits siomc skillcd toilet at least I meter below sludge areas labor surtlace' 441 Septic tank Suitable SuntablL in L' Ii fi Requires 1. Water pipcd to Permcable soil: groutitewater Off-sitc treatment Is1 Very good 1L for rural M-densitv onre skilleil housc and at least I titctcr below facilities for sludge institutions arcis labol toilet surface' Three-stage septic Suitable Suitabic in L Mt 1. Requires H Water near Permeable soil; groundwater Ticatment facilities for M Very go-i 1. tanks M-densitv soli skilled toilet at least I meter below sludge areas lalbI surface' Vault toilet, anid Not suittahle Suittble M If Rcquicr H I (tol viult Waiter ncnir None (can be built above Treatmctit taclitics for H Veiv good VIH cartage ..irne skilled co0isti( tctaion toilet ground) night soil labir Sewered Pr toilets. Not suitable Suitable Ft M Requires 1. Water pipeul ti None Sewers and treattient H Vcry grood Fl septic tanks, skilled tllnIc and facilities aquapTrViCi engitteer/ todet builder Sewerage Not suitabile Sutaile VFi 7i Requircs L Water piped to Nonc Sewers and treatment 11 Very good I-I skilled houuss anid faicilities CneineerC toilet bhuliler Note: L, low; M, medium; H, high: VH, very high. a. On- or off-site sullage disposal facilities are required for tonsewered technologies with water service levels in excess of 51) to 10( lcd, depending onl population density, b. If groundwater is less than I meter below the surfacc, a plitith can bc built. 42 SANITATION PROGRAM PLANNINCG contrast, the water seal in an aquaprivy is almost often to their bases. Soil permeability is important invisible). The inconvenience of carrying PF water for these technologies as well, and also for septic to the toilet might be considered by the users to tank soakaway trenches. In impermeable soils these outweigh the advantages PF toilets have over pit la- technologies are infeasible. Sewerage may be af- trines, and a VIP latrine might well be preferred at fordable by those who could have afforded septic least until the water supply is upgraded, when the tanks, bui often the only alternative is to provide latrine can also be upgraded to a PF toilet (chapter vault toilets and separate sullage disposal facilities. 7). On the other hand, if the PF or vault toilet is to If the groundwater table is within 1 meter of the be located inside the house, social aspirations for an ground surface, viP latrines, ROEC's. and PF toilets 'inside" toilet might outweigh the inconvenience of are of doubtful feasibility. They may be feasible if carrying the PF water. This discussion highlights the the soil is sufficiently permeable that the liquid level need to determine community preferences (chapter in the pit is not less than 0.5 meter below ground 3). level, but the pit may be unstable unless supported Yard taps to its base, and mosquito breeding is likely to be a problem (except in PF toilets). The structure mav be PF toilets and vault toilets are now possible choices, set on a plinth or raised as shown in figure 10-4. For but not cistern-flush toilets. If sullage generation ex- ROE-'s and single-pit vip's, which require large pits. ceeds 50 liters per capita daily. sewered PF toilets pit excavation and lining are likelv to be hazardous also become technically feasible. Direct discharge to and very difficult. sewers is not advisable, however, because the small The presence of rock near the ground surface cre- amount of water needed for a PF toilet is rarely suf- ates difficulties for all technologies affected by soil ficient to carry excreta the distance required. It is conditions. It makes conventional sewera(ge even therefore preferable to connect the PF wall to a small more expensive and PF svstems with small-bore sew- settling tank (usually the existing soakage pit) and ers comparatively more attractive, though still very then to the sewer. The choice between these addi- costly. viP latrines, ROEC'S, and PF toilets become tional possibilities and ViP latrines, ROEC's. and DVC considerablv more expensive. but the temptation to toilets (which are also still technically feasible) de- build pits with an effective life of less than two years pends on other factors discussed later. should be strongly resisted. After two years another pit must be dug, but when it is filled the contents of In-house connections the first may be safely removed because only a few viable Ascaris ova will remain after one year. Social Cistern-flush toilets with conventional sewerage or viable at ovatin excr even Social septic tanks and soakaways are now technically fea- repugnance at excavating execreta even though ex- sible, and the decision of whether to install thIemi creta are a pathogen-free compost. may militate economic and financial one. Communities thmis against these technologies and favor vault toilets, an eooianfiacaon.Cmuiisthat unless pit emptying is a municipal function. value the reuse of excreta and have successfully op- erated DVC toilets or three-stage septic tanks may be reluctant to abandon them and certainly should not be encouraged to do so. Housing Density In very densely populated urban areas, vill latrines Soil Conditions and ROEC's are infeasible. and PF toilets and septic tanks with soakawavs are feasible only under excep- Soil conditions are important for all sanitation tional circumstances. Conventional sewerage, sew- technologies except those that can be completely ered PF systems, and vault toilets are feasible. If site contained above ground level. The only two tech- gradients are steep enough to provide self-cleansing nologies that fall into this category are DVC toilets velocities, PF toilets discharging directly to sewers and vault toilets, although in principle the three-stage without the wastes' first entering a settling tank are septic tank and the conventional septic tank with a also feasible. The choice among these possibilities raised evapotranspiration bed for effluent disposal is decided essentially on economic grounds. although could also be classified as 'above ground" technol- access for service vehicles and sullage disposal facil- ogies. ities is important for vault toilets (and the former Soil stability is important for vip latrines, ROEC'S, also for desludging sewered PF settling tanks). It is and PF toilets. In unstable soils pits must be lined, unlikely that DVC toilets will be feasible because suf- COMPARISON OF TECHNOLOGIES 43 ficient biodegradable waste such as straw may not 5-2, which summarizes costs collected in 1977-78 bv be available and, in any case, the community gen- the World Bank. erally will not have a use for the compost and so will The costs perceived bv the municipality (or other not be motivated to produce it. implementing agency) and by the users are the fi- It is not easy to define at what population density nancial costs that they will have to incur. Munici- on-site systems such as vip latrines, ROEC'S, PF toi- palities may be sophisticated enough to consider fi- lets, and DVC toilets become infeasible. The figure nancial "life cycle" costs (in effect the present value is probably most commonly around 250' to 300 per- of the costs to be incurred bv the municipality itself: sons per hectare, although it depends to some extent these distort the picture by excluding householders' on the type of housing: feasibilitv at higher densities costs and often the cost of flushintg water), but more (up to around 500 to 6(0(0 persons per hectare) may commonly both the institution and the individual are often be possible if double-storied buildings are used: most concerned about the level of the capital and PF toilets may be feasible at even higher densities. operating costs of the recommended program. The main point is to determine. in any given situa- "Lumpiness" of investment is as much a problem in tion, whether or not there is sufficient space on the sanitation as it is in conventional sewerage. Although plot to provide two alternating pit sites that have a a VIP latrine with a large pit and a permanent su- minimum lifetime of two years. Two years is the perstructure may be more economical over its tell- absolute minimum lifetime, as noted above, but the year life, it is not practical for the householder if its minimum desirable lifetime is five years. with ten initial construction requires most of his cash income years being preferred for vip latrines and fifteen to for months. (An exactly analogous situation occurs twenty years for ROEC'S. Even longer lifetimes are in water supply: poor families continue to dependi on found in the Sudan, where pits some 25 meters deep water vendors although. if they could once save up are common. An advantage of ROE c's and PF toilets enough money. thev could have a house connection is that their pits, being completely offset, can be and enjoy a far better service at lower cost.) easily emptied so that it is not essential to provide The objective of the financial feasibility study is two alternating pit sites. Pit contents less than one to identify ways of making the alternative with the year old must be aged or treated beforc rcuse. With lowest economic cost affordable to the recipients. alternating pits. one pit can be rested for sufficient Initially, a very difficult judgment will have to be time (at least one year) for complete pathogen de- made on what proportion of their cash income house- struction so that treatment is not necessarv. holders are able and willing to devote to sanitation, and on the extent to which they can contribute their own labor and materials to reduce capital and op- Costs erating costs. This may need to be decided through pilot studies, which may also be used to develop Clearly. all technologies should be least-cost so- lutions and must be affordable. The decision of which technology to select should be basced on economic Table 5-2. SummarY of Annual Econiomic Costs (rather than financial) costs since these represent the per Household real resource cost to the national economy. Mili- (1978 U.S. dollars) mizing such cost is an economic goal of all counitries. Cost The technology with the lowest economic cost is gen- Sanitation technology' Mean Higihest Lowest erallv the one that shouldl be selectect (although where two technologies hame verv similar economic Pitlatrines.PFtoilets,and Rorcs 28 -5 s DY~C toilets 46 75 2)9 costs, the choice may be largely a matter of judgimient Vault and vacuum collection 104 21(1 26 on nonquantified aspects). If the users are willing to Sewered aquaprivy or PF toilets 159 191 125 pay the full economic cost of a more expensive tech- Flush toilets with septic tanks 233 390 35 nology (so that there is no need for subsidv), they Conventional sewerage 400 641 142 should be free to select that technology. In such a Note: Costs include annuitized capital and annuai operatinlg case, the additional benefits perceived biy the users costs of on-site. collection, and treatment facilities, shadow priced of the more expensive technology outweigh its ad- as appropriate. Sewerage costs are average incremental costs ditional cost to them. An example of total annual (AIC'S). The figures given in this table are taken from a limited number of observations (particularly in the cases of D,C and PF economic (shadow-priced) costs per household of the toilets and sewered aquaprivies): they should therefore be used different technologies may be obtainied fronm table only as an indication of relative costs, not as absolute values. 44 SANITATION PROGRAM PLANNING criteria for deciding on the levels of contribution to be required from participating households. This judgment, when compared with the estimated capital and operating costs of the program. will give guid- Sullage disposal facilities need to be considered ance on how to arrange the program financing. for all technologies except sewered PF toilets and For example, if on the one hand the household cistern-flush toilets with conventional sewerage or contribution is equivalent to the annuitized financial septic tanks and soakaways in regions where water cost of the system., then the alternative is affordable use exceeds, say, 50 liters per capita daily in medium- provided that some means can be found to even out or high-density areas. Off-site night-soil or sewage the lumpiness of the investment. This may be done treatment works are required for vault toilets, sew- by the municipality lending the funds directly to the ered PF toilets, and conventional sewerage systems. users, by the national government channeling funds through the implementing agency, or by anv other Reuse potential means that can be devised to fit the circumstances. The point is that these funds can be in the form of DVC toilets should be provided only where there loans, and in designing the program careful thought is a demand to reuse excreta. Material from latrines should be given to cost recovery mechanisms, the can be applied as fertilizer if the pits from which it treatment of defaulters. and so on. is removed were not used for twelve months or more. If, on the other hand, it is evident that the maxi- Treated sludge from sewered systems requiring pe- mum likely household contribution will not meet the riodic desludging, vault toilets, single-pit PF and vIP annuitized cost of even the cheapest technology, then latrines, and conventional sewerage also can be used there are only two choices: abandon the program in as fertilizer. Night soil and sludges can be digested that particular area or find means of subsidizing it to provide biogas (methane) as well as fertilizer. through other revenues. Subsidies should be gener- Before the predicted benefits from a reuse scheme ated within the community (if possible within the are included in the economic assessment of a tech- sector; for example, from water revenues) because nology, however, the feasibility of the scheme must it is the community that primarily benefits from the be thoroughly and realistically examined, especially improved health of its poorest members. In many in areas where the reuse of excreta is not a traditional small towns in developing countries, however, the practice. tax base is too weak to sustain any further burdens. In such cases the national government may be able to provide subsidies. Before doing so, however, it Sel§f-help potential should carefully consider the opportunity cost of sub- The unskilled labor and some (but not all) of the sidies. Equity questions arise as well: for example, skilled labor required for VIP latrines, ROEC'S, DVC is it appropriate to use funds collected from the entire and PF toilets, and three-stage septic tanks can be country to subsidize residents of a few cities? The provided bv the users. Self-help labor, however, re- sociopolitical goals of the national government often poie yteues efhl ao,hwvr e determinethe financiallfeasibility of thsagvenmnitai n p quires organization and supervision by the local au- determine the financial feasibility of sanitation pro- thority, especially in urban areas. Manv of the labor grams. For example, the government may wish to i decide upon its total budget for sanitation improve- requirements for the on-site portions of the other mendupts anddistributal bt sor asanitualize impero- ctechnologies can be provided by residents. Off-site ments and distribute it so as to equalize per capita construction requires experienced engineers and expellditures; alter.natively, It may wish to spend it skilled builders for design and construction. all m rural areas. In any case, continuing subsidies For the least-cost technology comparison, self- from outside the community for operation and main- help labor should be shadow priced at the oppor- tenance costs are not advisable. tunity cost of unskilled labor during the season when the work will be done. In countries where unskilled labor is inexpensive, the reduction in economic costs Other Factors achieved by the use of self-help labor may not be very great. The householders' involvement in con- In addition to water service levels, soil character- struction, however, may be psychologically advan- istics, housing density, and system costs, several tageous: subsequent toilet maintenance is likely to other factors enter into comparisons of sanitation be of a higher standard because its need and how to technology. do it may be more readily perceived. COMPARISON OF TECHNOLOGIES 45 portant. Soil types reflect long-term effects of cli- Anal cleansing material mate, and potential productivity is a measure of land or aquatic plant growth. Soil and weather yield PF and cistern-flush toilets cannot easily dispose higher productivity in the tropics, where rapid cycling of anal cleansing materials such as maize cobs, of material through the biosphere is a major element stones, and cement-bag paper because these mate- in efficiencies of waste treatment ponds. Distribu- rials can clog the water seal. Aquaprivies (and la- tions of many excreta-related diseases show the en- trines with mechanical seals) are better able than PF vironmental influence of the tropics (the limits of toilets to process these materials, but at greater cost disease spread are based on reported cases where and at higher risk of system malfunction (see chapter absence may be due to the absence of the disease 12). Many communities, however, have a traditional itself or of specialists who can recognize it). practice of not disposing of their anal cleansing ma- In contrast to the regional or global environmental terials in the toilet; for example. the Ashanti people influences, local changes in land use are often the in central Ghana place paper and maize cobs on the limiting factor. especially in urban areas. For ex- ground surface near traditional unimproved pit la- ample, sewered communal latrines would occupy up trines, and in many parts of Brazil even conventional to 3 percent of total land area where population dens- toilet paper is placed in small bins adjacent to cistern- ities are about 1.000 persons per hectare and up to flush toilets. In some communities in Zambia, used 10 percent if shower and laundry facilities are pro- cleansing material is placed in metal cans rather than vided (not including space for clotheslines). Other being flushed into sewered aquaprivies because com- schemes may require even greater percentages of the paratively recent experience has shown the users that available space. blockages otherwise happen. Clearly, these various means of disposal can present serious health hazards and require attention when the public hygiene pro- gram is being designed. The practice of using water Institutional Constraints for anal cleansing presents problems for DVC toilets. which may become too wet for efficient composting. S t m - Sanitation tech nologies may not operate satisfac- torily, even if they are properly designed. because of lack of adequate maintenance (at the user or mu- Environmental Factors Affecting nicipal levels), since the users and some municipal Choice of Technology officials may not be fully aware of the need for main- tenance or may lack the funds or know^-how to pro- Information on the natural physical environment vide it. Thus, user education and institutional de- of an area will often enable one to exclude certain velopment programs will generally form an essential options. Kalbermatten, Julius, and Gunnerson (1982) part of sanitation program planning. Often major have included descriptions of environmental varia- changes are needed in a community's attitude toward bles and their effects in their study (maps 1-19). excreta disposal and environmental sanitation gen- Winter temperatures affect performance of waste erally, and major alterations to the existing municipal treatment ponds, digesters, and biogas units because structure are often required. These changes. espe- each decrease of about 10° Celsius (C), or 18° Fahr- cially those in social attitudes, can be accomplished enheit (F), has the effect of decreasing biochemical only slowvly, which emphasizes the need for a planned reaction rates by about half. The magnitude and rate series of incremental sanitation improvements over of precipitation affects the general levels of flooding, time (see chapters 1 and 20). In addition. pricing runoff, water table, and plant growth. Aridity in- policies for communal sanitation systems must pro- dexes show the ratios of potential evaporation to vide adequate funds for maintenance expenses. If precipitation and indicate climatic zones, particularly community members are able but not willing to pay those subject to desertification, where recovery of the necessary rates on a continuing basis, the system water, fertilizer, and energy from wastes is most im- should not be built. 6 Selection of Sanitation Technologies ONCE DIFFERENT SANITA-TION technologies have eral, the existing household sanitation systems will been compared on a technical basis, the sanitation influence the technology chosen to improve excreta program planner must select from those available the and sullage disposal. In addition. it is important to one most appropriate to the needs and resources of consider the existing or planned sanitationi facilities the community. This selection, which should be in neighboring areas. In this context and in the al- based on a combination of economic, technical, and gorithm, affordability is taken to embrace both eco- social criteria, essentially reduces to the question of nomic and financial affordability at the household. which is the cheapest. technically feasible technology municipal, and national levels. including the question that the users can afford. maintain. and prefer to of subsidies. In any event, the environmental and cheaper alternatives and that the local authoritv is other information listed in table 6-l is essential to institutionally capable of operating. The critical the algorithm. items of information needed for selectioni and design The algorithm commences in figure 6-1 by asking of sanitation systems are indicated in table 6-1 (p. if there is (or is likely to be in the near future) an 50). in-house level of water supply service to the houses under consideration. This is the crucial question bc- cause its answer immediately determines whether Selection Algorithms cistern-flush toilets can be considered. If the houscs do have piped water. if there is a strong social desire Figures 6-1. 6-2. and 6-3 present stages of an al- for cistern-flush toilets. and if thev can be afforded. gorithm that can be used as a guide to the selection the main engineering problems are how to dispose of the most appropriate sanitation technology for any of wastewater from the toilet ("black water") and given community in a developing country. It should from the kitchen, laundry, and bath (sullage or be stressed that the algorithm is meant only as a "graywater"). Septic tanks of either the conventional guide to the decisionmaking process. Its main virtue kind or of the design described in chapter 12 are is that it prompts engineers and planners to ask the preferable to conventional sewerage where they are right sort of questions. which perhaps they would not cheaper, but their technical feasibility depends on otherwise ask: some answers can onlv be obtained the availability and suitabilitv of land for soakawavs from the intended beneficiaries (see chapter 3). Al- and, in medium-density areas especially, on whether though it is believed that the algorithm is directly water use can be reduced to permit ground disposal applicable to most situations encountered in devel- of the effluent. If septic tanks are inappropriate, con- oping countries, there will always be combinations ventional sewerage can be used, provided that it is of circumstances for which the most appropriate op- affordable and that there are no strong environmen- tion is not the one suggested. The algorithm, there- tal reasons to oppose it. If neither septic tanks nor fore, should not be used blindly in place of engi- conventional sewerage is affordable, or if the com- neering judgment, but as a tool to facilitate the munity does not have in-house water supply service, critical appraisal of the various sanitation options, then cistern-flush toilets cannot be used. The com- especially those for the urban and rural poor. munity may have a single yard tap supply or it may The algorithm is most useful when th,ere are no rely on hand-carried water from either public stand- existing sanitation systems other than communal fa- pipes or water vendors. In any case., an essential cilities in the communitv under consideration. In gen- question is whether there is sufficient water to flush 46 SELECTION OF TECHNOLOGIES 47 Figure 6-1. First-stage Algorithm for Selection of Sanitation Technology Start Arc thcre nater tap- No Is the wastewatcr No | Go to s-,coiid t.agc n the houses t. h. flow greater thain . .llrithle rind rmnikc scred'" 50 liters ouillahlc rrd is,n n per captta daiV or Pullw . di.' Ye> Yes Are thcre stron, social odr envirn No Is there a strong Y es mental reaons ihi,t soilpfcne prcclude thc usc tocial preference of concntio nil to rcuse cxcreta.' scwerangc' No No fiu Ih (pi tlltst' I ordableao hcsti IS thest sl No sUfticicntl\ No permc.able tor . o > Are scrs i i es o n-,itc disposl,>, >dfrd 1- s.>c ;,ec f ptcc Ar n r s 'TYes ra the sewers as wel. a te oes ft wa euCn ,tc conSiMPtien Ars c tu g plusi fl, Na he reduced o , that No5 N o pti tpnko de i a ord alnd n s iit v disposal of 10ak., so> ' CPtic t.ank effluent .~ ~~~~~I os pshie.) I ~ Arc wcptvv t;rnk, i h oakaCr , YC' Ar,: septic t ank, cs 'rpli t.,wk, ch>\iperthnl ----- 0- ;ttozrd.hl': mi -, t ,&mk. t, the sewers as well as the toilets. If the wastewater If the quaintitv of water available is not sufficient (sullage plus flushwater) flow is greater than 50 liters for several svstems, the choice lies betwveen thie * ar- per capita dailyv. then a sewered PF svstCm can be ious o n-site excreta disposal tech nolopves. with ap- used, provided it is affordable and there is no social propriate t'acilities provided for the disposal of sul- preference for night soil to be collected separately lage (see chapter 20). The algorithm recomrmences for reuse. in figure 6-2 by asking if household reuse of excreta Figure 6-2. Second-stage Algorithm for Selection of Sanitation Technology Start Is there an assumned Uise Yes Is reuse of liuid preferrd Yes Is sufficient wate Yes Ar he-tg etcYes Trett for compost or stabilized q p a f Three-stage hums by household or j t motttie?tanks affordable? septic tank No No No No tti | ~~~~~~~~~~~~~~~~~~~~~~~Yes Can dotible-vault Yes Yes Is sufficient orgatnic waste eomposting (DVC) toiletS Are DVC toiletS Ye VnC material or ash available? be expected to be affordable? toilets well maintained? No N No |No Are ventilated improved double- Yes VIDP pit (VIDP) latrines latrines affordable? No, Go to third-stage algorithm Figure 6-3. Third-stage Algorithm for Selectioni of Sanitation Technology Start Are plot sizes large N'e5 IN water taible Yes Is sufficienit water Yes Yes Arc local anal Yes Ys p enoug fo " more thnImeter avial o iIs soil sufficientlv cleansing materials Are Pr- toilets P enough ttc'' h~~~~~elo%k gvaiabl fd permeable') suitable for use affordabic" toilets alternating pit gt?s roune" toilets.' with Pi toilets" No Y(soNo No No Can latrine level Are Recd Odorless Yrs o Yes No Can latrine Icvcl _ Earth Closets (Rot YeS Yes R S ROt( s bc raised? preferred over vti affordable' latrines') -VI ~ ~~ ~ ~ ~ ~ ~ ~ NoNonnlni B~~~~~~~~~~~~~~~~~~~~~~N No Yes ;IPiil ff(ir(lable" kullne,~~~~~~si Ciummunal samitation No ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~faicilities 1, the rte eicthe r a l space lor .a pcrinanluln Yes Are io)p Yes ]DPl C1011111-Pil tl) _\ I Ilatrines v ith .i niini[Lllz] "If I affordahie 'Ilatrines \car Mozr.qc per s.,Wlt' Is [here itnhcr .1 yes Ar val tolt e al vsauintipal ir pil- sate ss\stCl1i to l affordable t cinipt\ iiig lt ruincs' Noi Nit Commutniiinal so-aniat ion I'ci lutes 50 SANITATION PROGRAM PLANNI'NG Table 6-1. Critical Information Needed able and willing to reuse the compost in their own for Selection and Design of Sanitation Systems gardens or are able to give or sell it to local farmers. Item Description DVC toilets also require a sufficient and continuous Climatic condi- Temperature rances supply of organic waste materials such as straw and tions Precipitation (including drought or flood pe- a very high level of user care, which often can only riods) be achieved by a vigorous and sustained program of Site conditions Topography user education (the cost of which must be included Geology (including soil stability) in the total cost of the svstem). If all these conditions Hydrogeoloev (including seasonal water table fu n -can be met and if the cost is lower than those of the Vulnerability to flooding alternative on-site disposal technologies. then either Population Number (present and projected) a three-stage septic tank or a DVC toilet is recorn- Density (including growth patterns) mended, as determined bv the algorithm. Housina types (including occupancy rates If DVC toilets and the three-stage septic tank sys- and tenure patterns) tern cannot be used, the choice lies among VIP ta- Health status (of all age groups) Health status (of all age groups) trines, VIDP latrines, ROEC's. PF toilets, vault toilets. Income levels Locally available skills (managerial and tech- and communal sanitation blocks as determined by nica() the algorithm in figure 6-3. If there is space enough Locally available materials and components for two alternating pit sites and if the ground,,atce Municipal services available (including roads, table is at least 1 meter below the ground surface. power) then Environmental Existing water supply service levels (includ- the recommended choice is either VIP latrines. sanitation ing accessibility, reliability. and costs) VIDP latrines. ROECs, or, if there is sufficient watcr Marginal costs of water supply improvements and if the soil is sufficiently permeable. I'F toilets. Existing facilities for excreta disposal, sullage Since the costs of these systems are verv similar, the removal, and storm drahilage choice among them should be left to the communitv. Other environmental problems (such as car- ba *e or animal wastes) There mav often be a strong social preference for E'F bage or animal wastes) Sociocultural People's perceptions of present situation, in- toilets because these can be located inside the house. factors terest in or susceptibility to change PF toilets require water to be hand carried to and. Reasons for acceptance or rejection of amn for user convenience, to be stored in the toilet. This previous upgrading attempts mav be difficult in houses dependent on public stand- Level of hvygene education eiisor r fipes or water vendors and is an essential point to Religious or cultural factors afecting h1 gienc r practices and technology choice discuss with the community or their representatives. Location or use of facilities by both sexes anc In houses with yard taps, a simple upgrading, pro- all age groups cedure. which can be done bv individual household- Attitudes toward resource reclamation ers (but under municipal control). is to pipe water Attitudes toward communal or shared facil- ers (bu under m paltm ontr ities ito the toilet compartment. Institutional Allocation of responsihility: effectiveness of In those urban areas where viP latrines. izoF- s. framework state, local. or municipal institutions in and unsewered PF toilets cannot bc used, the choice providing watcr, sewerage. sanitation, street is between vault toilets and communal facilities. cleaning, drainage, health and education Household vaults are preferable to communal facil- services, housing and urban upgrading ities, but they are more expensive and require access Nore: The priority given various items will vary with the sani- for collection vehicles, which the niunicipalitv must tation options being considered; the list above indicates typical be capable of maintaining. in some very hieh-densitv areas to be investigated bv planners and designers. areas there ma' not be access for even the smallest collection vehicles. In such areas eithcr communal sanitation facilities are necessary or the vaults must be emptied by Inanually operated pumps: thc coIII- munity may prefer vaults so emptied because thc is socially acceptable. If it is. then the choice is be- vault toilet is an in-house facility that has good po- tween three-stace septic tanks and DVC toilets. Reuse tential for upgradino to a sewered PF svstem (see of liquid excreta from three-stage septic tank systems chapter 7). There are. however, some high-denisity is appropriate for rural areas only. whercas DVC toi- and low-income urban areas. such as those built on lets are suitable for urban areas as well. provided tidal mud flats, for which a sewered PF systenm will that there is space for them and that the users are alwavs remain unaffordable. although it may be tech- SELECTION OF TECHNOLOGIES 51 nically feasible, and a communal facility is the only * What are the potential upgrading sequences (see realistic sanitation improvement. Further improve- chapter 7)? What time frame is involved? Is it ment will generally be extremely difficult and often compatible with current housing and water de- impossible both technically and economically unless velopment plans? Are more costly technologies it forms part of an urban renewal scheme involving in the upgrading sequence affordable now? overall housing improvements. * What facilities exist to produce the hardware required for the technology'? If lacking, can they be developed? Are the necessary raw materials Postselection Questions locally available? Can self-help labor be used? Are training programs required? Once a tentative selection of the most appropriate * Can the existing sanitation system, if anv, be technology has been made, several questions should upgraded in any better way than that shown in again be asked as checks: tagora ithm the algorithm? * Is the technology socially acceptable? Is it com- * Is there a neighboring area whose existing or patible with cultural and religious require- planned sanitation system makes a more costly ments? Can it be maintained by the user and, alternative feasible (for example, small sewers if appropriate, by the municipality? Are munic- discharging to an existing sewer system)? ipal support services (for example, education. * What is the potential for reuse? If low, would inspection) required? Can these be made avail- the adoption of a technology with a higher reuse able? potential be economically justifiable? . Is the technology politically acceptable? * If the selected technology cannot process sul- . Are the beneficiaries willing (and able) to pav lage, what facilities for sullage disposal are re- the full cost of the proposed facility? If not, are quired (see chapter 20)? Is the amount of sullage user subsidies (direct grants or 'soft" loans) low enough, or could it be reduced sufficientlv available? Is foreign exchange required? If so. to preclude the need for off-site sullage disposal is it available? facilities? 7 Sanitation Upgrading Sequences THE SELECTION of the technology best suited to ef- anal cleansing materials, or the PF toilet and thence. fect initial improvements in sanitation should also eventually, a sewered PF system. The user may also reflect the future need for incremental improvements wish to make this upgrading of his facility by personal as the users' aspirations and socioeconomic status choice rather than by being forced to do so by chang- rise. This chapter examines the feasibility of sani- ing conditions. tation upgrading sequences with particular reference to incremental improvements in the level of water supply service (which is, of course, a measure of Three-Stage Septic Tanks socioeconomic status). Representative upgrading se- quences are summarized in figure 7-1 and are de- This version of the septic tank is suitable where scribed below. Upgrading is optional and should be PF toilets are installed and excreta reused as fertilizer done only if users' demand and ability to pay for in liquid form (as in many rural areas of China, for additional investments exists or if environmental example). Upgrading would apply only to water sup- conditions (increased population density, and the ply service level, as described above. It is important like) require it. that sullage should not enter the septic tank because the excreta would then become too dilute for eco- nomic cartage to the farm, and the retention time in Composting Toilets the tank would become too short for the required level of pathogen destruction. Consider the DVC toilet in a rural village where If demand for the stabilized liquid excreta (slurrv) water is obtained from surface sources or wells and to be reused as fertilizer falls., it is necessary to alter must be hand drawn and carried. Provided that the the technology rather than upgrade it, although (as toilet functions well and is properly operated and in the case of the DVC) the user may elect to do this that the demand for compost continues, there is no as a personal choice. The easiest modification in rural need to upgrade the toilet. Upgrading of the water areas is subsurface percolation in a septic tank drain- supply from hand carrying to household hand pumps field; sullage may then be added to the third com- or reticulated yard taps, and thence to a fully retic- partment, as described in chapter 14. ulated system with multiple house connections would likely be given priority over improvements in excreta disposal. Vault Toilets If the demand for compost should fall (perhaps because of increased housing density that necessi- The vault toilet and vacuum-truck system is most tates fewer gardens or the introduction of subsidized commonly used in urban areas, requires less space chemical fertilizer distribution) or the toilet does not than any other system, and provides for reclamation function properly (perhaps because of a sudden or of energy (as methane, or biogas) and fertilizers. a gradual unavailability of ash or suitable organic Because the vault satisfactorily stores excreta and waste material), then it would be necessary to alter any PF water, no upgrading is necessary from the (rather than upgrade) the toilet; the most appropri- point of view of excreta disposal. Once the water ate replacement technology will normally be the supply service improves to the multiple tap level. viDP latrine, which would not require a change in however, it may be considered desirable to provide 52 SANITATION UPGRADING SEQUENCES 53 Figure 7-1. Potential Sanitation Sequenices Level of water service San it/aton teclhnology Hand- Yard tap or House carried household pump connection Composting toilets Double-vault Vaults Septic tank (Unlikely) Vault and vacuum truck (Unlikely) Improved pit latrines viP latrine and ViDP latrine O O-O X (Unlikely) ROEC (Unlikely) PF toilet O Sewerage Small-bore sewered PF toilet Q Conventional sewerage or septic tank ( ) O Technically feasible. * Feasible if sufficient pour-flush water will be hand carried. o Technically infeasible. O Feasible if total wastewater flow exceeds 51) liters per capita dailv. 54 SANITATION PROGRAMf PLANNING Figure 7-2. Sample Sanitation Sequences (costs in 1978 U.S. aollars) Total present value Item Year I Year 10 Year 20 / Year 30 economic cost Year 20 Year 30per household over 30-year period a b C Scheme I Construction cost 108 65 905 354 a c Scheme 2 Construction cost 108 915 1,111 Scheme 3 Construction cost 960 1.519 d Scheme 4 Construction cost 978 3.01)0 a VIP latrine. b PF toilct with soakaway. C PF toilet with small-bore sewer (with optional bowl and seat). d Conventional sewerage. SANITATION UPGRADING SEQUENCES 55 drainage systems for sullage disposal. If sewers are As discussed above for vault toilets, the main san- installed, the vault toilet may be converted to a sew- itation improvement is better disposal of sullage by ered PF toilet, as described in chapter 6, by the ad- surface drains or sewers. If sewers are to be used. dition of a small sullage tank adjacent and connected they can also receive the settled flushwater from the to the vault that discharges both settled sullage and original PF pit. The conversion operation is as fol- settled excreta into small-bore sewers. lows: * Build a small single-chamber septic tank close VIP Latrines and ROEC'S to the existing PF pit and discharge all the sullage directly into it (the tank should provide a twelve- Many rural and suburban water and sanitation hour retention time, subject to a minimum projects plan to provide pit latrines and communal working volume of 0.5 cubic meter). hand pumps or public standpipes as the initial imfl- *Connect the existing PF pit to the sullage tank provement. The pit latrine should be either a VIP with 100-millimeter-diameter pipe (the pit out- latrine or ROEC (as described in chapter 10). The let "T" junction should be located as near the subsequent priority for improvement would most top of the pit as technically feasible). likely be upgrading the water supply to yard taps * Connect the sullage tank to the street sewer (the (or household hand pumps where applicable). Both invert of the tank outlet should be a nominal 30 the viP latrines and ROEC'S could then be upgraded millimeters below that of the inlet from the pit to PF toilets. The conversion of a ROEC to a PF tolilet to prevent sullage from flowing into the pit). is very simple and inexpensive: a water-seal squatting plate or pedestal seat (see chapter 12) is installed in If the existing pit has sufficient infiltration capacity place of the ROEC chute, and the existing displaced there will be little or no flow from the pit to the pit used to receive the toilet wastewater. Depending sullage tank. This does not matter. But as the infil- on soil conditions, it may be necessary to add a soak- tration capacity falls, and especially if low-volume age pit to provide more infiltration area for the toilet cistern-flush toilets are installed, the flow will in- flushwater; alternatively, an infiltration trench could crease, and the pit acts as a sealed or seinisealed first be provided. compartment of the two-stage scptic tank described A viP latrine can also be readily converted to a PF in chapter 12 (see also chapter 14). It is essential that toilet by filling in the pit with soil and installing a the sullage tank-the second compartment of the water-seal unit that is connected by a short length two-stage septic tank-is provided so that the small- of pipe to a newlv dug pit. Clearly, this is best done bore sewers do not become blocked. when the pit is close to the end of its life and is most advantageous where the superstructure is not easily dismantled (for example, if it were constructed in Sample Staged Solutions concrete blockwork). With both vip latrines and ROEC S it is helpful if the original design permits easy To demonstrate the feasibilitv of using a staged removal of the squatting plate to facilitate its re- sanitation system, a possible scheme with several placement by a water-seal unit. variations is described, and comparative economic In many areas, especially where water is used for costs are presented. The scheme or its variations anal cleansing, users prefer a PF toilet even though could be started at any stage and terminated at any water has to be carried to the house. In such areas stage, depending on the desires of the users. For a water storage vessel should be provided near the simplicity it is assumed that each stage remains in toilet. service for ten years. when the next stage would be added. The schemes described could be varied sub- PF Toilets stantially without adding greatly to the cost. For ex- ample. to a PF latrine a vault (with vacuum-truck When the water supply is upgraded to the multiple emptying) could be added if housing densitv in- tap level, it is possible to install a low-volume cistern- creases or the soil becomes clogged. Similarly. a com- flush toilet. This is not essential and mav not be posting toilet that already has a watertight vault considered a priority by the users, to whom upgrad- could be converted into a vault toilet or PF privy with ing of the water supply from a single vard tap to a vault. multiple in-house connections usuallv first means As shown in figure 7-2 (scheme 1). the initial san- plumbed kitchens and bathrooms. itation facility would consist of a vip latrine with a 56 SANITATION PROGRAM PLANNING concrete squatting slab and concrete block super- system in year 1. This would have a total PV cost of structure. One such facility in an East African city $1,519 per household over thirty years. The final is used as the basis for the costs shown. Its (unlined) alternative, calculated in the same way and with data pit is about 5.5 meters deep and 1 meter square, and from the same city as the sewered PF for purposes the normal filling time is ten years. Its initial con- of comparison, is the immediate construction of a struction cost is $108, of which the superstructure conventional sewerage system. A five-year construc- accounts for $53. tion period is assumed and the facility is assumed to In year 11 the community water system is upgraded be two-thirds utilized at the end of the five years and from wells or standpipes to yard hydrants, and the fully utilized ten years after completion. Based on dry latrine is converted to a PF latrine by digging a these assumptions, the Pv cost per household over new soakage pit near the superstructure and replac- thirty years is $3,000. This includes the cost of flush- ing the old squatting plate with a bowl and inverted ing water and all regular operating and maintenance siphon. The old pit is filled in prior to placement of costs (as do the costs of the other alternatives). It is the new squatting plate. For estimating purposes it nearly ten times as high as the cost of the first, three- is assumed that the accumulated sludge would be stage scheme and almost twice that of the one-stage removed from the new pit at five-year intervals and sewered PF alternative. composted.2 The cost of trucks and the land and An alternative to this upgrading sequence would equipment for the composting facility are therefore be to move from the ViP latrine to a vault with vac- included in year 15, and the trucks are replaced at uum-truck collection in year 11. Based on costs from five-year intervals thereafter. The operating and such a system in a city on the island of Taiwan, the maintenance costs incurred in years 11-20 also in- total Pv cost per household over thirty years would clude the flushing water for the PF toilet, calculated be $334. If in year 21 it was decided to convert from as 10 liters per capita daily for six persons at $0.35 vacuum collection to a small-bore sewer system (as per cubic meter. described in the previous sequence) the total Pv cost In year 21 the third stage would begin, when the would increase to $411 per household. These costs water service is upgraded to house connections and are summarized in table 7-1, where the figures in a large volume of sullage water has to be disposed of. At this point a new (lined) pit would be dug and the existing bowl and siphon would be connected to Table 7-1. Costs of Sample Sanitation Sequences it. An overflow pipe would connect the pit to a newly (1978 U.S. dollars) constructed small-bore sewer system. This upgrading Total would permit the use of cistern-flush toilets if desired present by the users. Annual collection of sludge would be value (pv) required from the smaller vault. and two trickling Sequence and construction cost cost filter plants would be constructed for treatment of Year 1 Year 11 Year 21 per Year I Year 11 Year 21 household& the vault effluent.3 The combined flushing water and sullage flow from year 21 onwards is taken as 175 1. VIP vc liters per capita daily. (108) (293) 2.vip vc B Comparative economic costs, on a household ba- (108) (293) (907)b 411 sis, were prepared for this scheme and for three vari- 3. viP PF SBS ations (schemes 2-4), including the alternative of (108) (73) (907)h 354 proceeding immediately with the construction of a 4. vip SBS conventional sewerage system. At a discount rate of (108) (907)b 1,111 8 percent, the present value (Pv) of the total cost per (960)h 1.519 household of the three-stage scheme 1 over a thirty- 6. Cs year period is $354. which includes the salvage value (978)h 3,000 of the sewerage system, assumed to have a forty-year VIP, Ventilated improved pit latrine; vc, vault toilet with vac- life. The second variation is a two-stage scheme that uum-truck collection; PF, pour-flush toilet; SBS, small-bore sewer; moves directly from the VIP (installed in year 1) to cs, conventional sewerage. small-bore sewers in year 1 1. The PV cost per house- a. Includes annuitized construction costs and operating and hold over thirty years is $1,111. or more than three maintenance costs for entire thirty-year period. b. Total construction cost divided by design population. Pv cal- times that of the three-stage alternative. The third culated on basis of average incremental cost (AIC), which takes alternative is simply to install a small-bore sewerage into account gradual capacity utilization (see chapter 4). SANITATION UPGRADING SEQUENCES 57 parentheses (from left to right) represent construc- to dispose of sullage, not excreta, and that the elim- tion costs in years 1, 11, and 21. ination or reduction of nonessential water use is thus None of the upgrading sequences discussed above the critical element in an economic solution to san- leads to conventional sewerage. This is not because itation problems. Furthermore, the costs of sewage conventional sewerage schemes should not be built treatment are higher where sullage has been added (they are an excellent form of sanitation for those to sewage. These costs are particularly significant in who have plenty of water and can afford the collec- developing countries, where the increasing compe- tion and increasingly expensive treatment systems). tition for investment funds often limits the amount but because they are not necessary to provide the of resources that can be allocated to the water and highest standard of sanitation. The sewered PF sys- sanitation sector. tem, which can include a low-volume cistern-flush toilet for added user convenience. is a sanitation svs- tem of equally high standard that has two important advantages over conventional sewerage: it is sub- Notes to Chapter 7 stantially cheaper, and it can be reached bv staged t Alternatively-especially where ground conditions make improvement of several different sanitation technol- deep excavation difficult or expensive-two alternating pits may ogies. Thus, sanitation program planners can confi- be constructed, and the squatting plate moved to the second Pt dently select one of these "baseline" technologies in after the first is filled. The full pit can be emptied after one year the knowledge that, as socioeconomic status and sul- and eventually reused, and the excavated material could be used lage flows increase, it can be upgraded in alternative without further treatment. sequences of incremental improvements to a more 2. In some communities, sludge may be buried rathcr than sequenes inrementl impovemens to more composted. technologically sophisticated final system. The im- 3. This option is chosen for illustrative purposes because of portant fact to remember is that sewers are required available cost data from the same East African city. I Part Three Sanitation Technology Options I I i I 8 Latrine and Toilet Superstructures THE FUNCTION of the toilet superstructure is to pro- sufficient. The toilet should be sufficiently shaded, vide privacy and to protect the user and the toilet however, to discourage flies; this is particularly from the weather. Superstructure design requires important in the case of vIP latrines and ROEC'S. assessment of whether separate facilities are required * Walls and roof: These must be weatherproof, for men and women in the same household. Local provide adequate privacy, exclude vermin, and customs and preferences often influence superstruc- be architecturally compatible in external ap- ture location, orientation, shape, construction ma- pearance with the main house. In urban areas terial, design (for example, roof, window details), especially, an L-shaped wall in front of the door and size. Color may strongly influence a house- may be regarded by the community as desirable holder's use and maintenance of the facility. These or essential for privacy. details should be designed in consultation with the A wide variety of materials may be used to con- user. The technical design requirements of the su- struct the superstructure: for example, brick or con- perstructure are relatively straightforward and may crete blocks, with tile, corrugated iron, or asbestos- be stated as follows: cement roof; mud and wattle, bamboo, or palm * Size: The plan area should be at least 0.8 cubic thatch, with palm-thatch roof; ferrocement, sheet meter to provide sufficient space and generally metal, or timber, with corrugated iron or asbestos- not more than 1.5 cubic meters. The roof height cement roof. Some alternatives are illustrated in fig- should be a minimum of 1.8 meters. ure 8-1. The choice depends on cost, availability of * Ventilation: There should be several openings material, and community preferences. The impor- at the top of the walls to dissipate odors and, tant point is that designs meet the criteria in the list in the case of vIP latrines and ROEC's, to provide above. If the superstructure is for a VIP latrine or the through draft required for functioning of the ROEC, it may not be a permanent structure but one vent pipe. These openings should be about 75 that must be dismantled and erected again over or to 100 millimeters by 150 to 200 millimeters in adjacent to the new pit. It should therefore be de- size; often it is convenient to leave an open space signed with this in mind, although this becomes of between the top of the door and the roof. less economic importance as the design life of the pit * The door: This should open outwards to mini- increases. mize the internal floor area. In some societies, Many communities, given the choice, choose in- however, an outward opening door may be cul- side toilets. Only PF and cistern-flush toilets are suit- turally unacceptable, and an open entrance with able for interior locations. If these are not to be a "privacy wall" may be preferred. In either provided initially, it may be sensible to design the case it must be possible to fasten the door from house with a toilet compartment that can be fitted the inside, and it may also be necessary to pro- out at a later date as part of a sanitation upgrading vide an external lock to prevent use by unau- program. thorized persons. At its base the door should be In figure 8-1, several low-cost, easily constructed just clear of the floor to provide complete pri- superstructures are shown. A wide variety of options vacy and to prevent rot of the bottom of the is available to the homeowner, only four of which door planks. are illustrated here. The choice of superstructure * Lighting: Natural light should be available and should reflect the user's personal preferences. 61 62 SANITATION TECHNOLOGY OPTIONS Figure 8-1. Alternative Materials for Latrine Superstructures A. Mud and wattle walls and palm-thatch roof B. Timber walls and corrugated iron or asbestos-cement roof C. Brick walls and tile roof (an alternative D. Rough-cut tree limbs and logs is concrete block walls and corrugated iron or asbestos-cement roof) LATRINE AND TOILET SUPERSTRUCTURES 63 Screen Flat roof 150-mm vent pipe Spiral strutctuire Concrete slab Pit E. Palm-thatch wall and roof covering F. A ventilated pit privv Plan Elevation G. Multiple-compartment pit latrine Sources: For A-E, Wagner and Lanoix (1958); for F. Appropriate Tec70nolo, (1979: Si International Scholarly Book Services. Inc.: used by permission); G is adapted from a design used in Haiti bv the Foundation for Cooperative Housing 9 Latrine and Toilet Fixtures A SUITABLE BASE or foundation for latrine or toilet or rough surfaces that would make its cleaning fixtures is often included in the construction of the difficult and unpleasant. pit or other substructures. Alternatively, the base may be constructed separately of wood or integrally A variety of materials can be used to make the as part of the squatting plate. squatting plate: timber, reinforced concrete, fer- It is essential to determine whether the local pref- rocement, and sulfur cement are usually the cheap- erence is to sit or squat during defecation. If the est, but glass-reinforced plastic, high-density molded wrong facility is chosen, it will have to be converted rubber, or Pvc (polvvinyl chloride) and ceramics can at unnecessary expense; alternatively, it will remain also be used. Cost and aesthetics are the important unused or the superstructure will be used for other criteria, apart from strength and rigidity. A variety purposes such as grain storage. Anal cleansing prac- of finishes can be applied to concrete or ferrocement tices and materials also need to be evaluated; flap- squatting plates (for example, alkali-resistant gloss trap designs, conventional and vIP latrines, ROEC'S paint and polished marble chippings) or the concrete (chapter 10), and aquaprivies can accept rocks, mud itself can be colored. Aesthetic considerations are balls, maize cobs, and other bulky materials that often extremely important to the users and should would clog water seals. never be ignored by engineers and planners; indeed. planners should make a special effort to determine community preferences before the final design stage. Squatting Plates for VP Latrines Figure 9-1 shows a good design for a reinforced Four important design considerations (for further concrete squatting plate. A ferrocement version of Fourils, se i apoertt ds c der this is possible and advantageous, since it need only details, see chapter 10) are: be 18 to 25 millimeters thick, rather than 70 milli- * The opening should be about 400 millimeters meters as shown, with consequent savings in mate- long, to prevent soiling of the squatting plate. rials and weight but with equal strength. The mix and at most 200 millimeters wide, so that chil- specification for ferrocement is: 1 part cement, 2 dren will not fall into the pit. A "keyhole" shape parts medium to coarse sand (sisal and coconut husk is suitable. fibers have also been used as filler), and up to 0.4 * Footrests should be provided as an integral part parts water (the mix should be as dry as possible); of the squatting plate and properly located so reinforcement is provided by two layers of 12-milli- that excreta fall into the pit and not onto the meter-opening chicken wire across the slab. An al- squatting plate itself. ternative ferrocement design with an integral metal * The free distance from the back wall of the su- "flap-trap" has been developed in Tanzania (figure perstructure to the opening in the squatting 9-2). The metal flap-trap is prefabricated from 1- plate should be in the range of 100 to 200 mil- millimeter-thick mild steel sheet and is then galva- limeters; if it is less there is insufficient space. nized. It is not known how successful this design is, and if it is more there is the danger that the rear although a similar design made of aluminum has been part of the squatting plate will be soiled. In gen- successfully used in the Sudan. Figure 9-2 is included eral, the preferred distance is 150 millimeters. to demonstrate the feasibility of developing locally * The squatting plate should have no sharp edges acceptable alternatives. 64 LATRINE AND TOILET FIXTURES 65 Figure 9-1. Concrete Squatting Plate (millimeters) 1,000 b 0-~~~~~~~~~~~~~ aa b 6-mm diameter reinforcing bars Plan I ,180 ,150, L15() 1810 Section a-a j 180 S 1 90 4 Section b-b Source: Adapted from Wagner and Lanoix (1958). 66 SANITATION TECHNOLOGY OPTIONS Figure 9-2. Tanzanian "Flap-trap" Design for vIP Latrines and DVC Toilets (millimeters) 30) 1 6 30 30 ~~~~~~~~500 Plan fT 60s 0 ~~~~~~0 270 Section Side view Front view Note. It is suggested that the flap-trap be made of plastic. Source: Adapted from a drawino by U. Winhlad. Squatting plates should be cast in an oiled timber plate opening. It is possible, but rather difficult, to mold for ease of construction. If the scale of man- cast the chute in ferrocement as an integral part of ufacture is large, a steel mold may be preferable. the squatting plate; in practice it is easier to use metal or Pvc pipe cut to shape. Squatting Plates for ROEC'S Pedestal Seats for vIP Latrines With ROEC'S (for further details, see chapter 10) and ROEC'S it is necessary to provide a steeply (60°) sloping chute The important design criteria (for further details. to direct the excreta into the adjacent offset pit (fig- see chapter 10) are the seat height and the size of ure 9-3). The chute diameter should be from 150 to the opening. For adults a 250-millimeter diameter is 200 millimeters but should be enlarged under the normally suitable. The pedestal riser can be con- squatting plate to attach around the entire squatting structed in brick, concrete blockwork. or wood; in- LATRINE AND TOILET FIXTURES 67 Figure 9-3. Pedestal Seats for DrY Latrines anid Chliute Designis for ROEC'S Hinged cover t~~~~~~~~~~~~~~~~ /S1 To pit _ / / / Pit latrine ; To pit ROEC Superstructure A . .. -J. a < / / Slopin 9 / / ~~~urinal trough Squatting chute Note: The pedestal hole should be 100 millimeters in diameter for use bv children, 201) millimeters for adults. Unsupported fiberglass should not be used in construction. 68 SANITATION TECHNOLOGY OPTIONS Figure 9-4. Water-seal Sqiiottinlg Plate for Pr Toilets Located fminediatel/v above the Pit (nmillimieters) 3A) 30 340) -4~~~~I- 160 ~ 1 I13(0 15 h 31)~~~~~~~~~~~1 Plan of water seal Sectional elevation a a Details of squatting plate 1.(15(1 25-mm dashing - - 60 400''^ 1,056( 6(0-mm-thick ferrocement Section a-a Source: Adapted from Wagner and Lanoix (1958). LATRINE AND TOILET FIXTURES 69 Figure 9-5. Galvanized Sheet-mnetal Water-seail Unit Jor PiF Toilets Located Immediatelv above the Pit (millimeters) 32() 31 5t)(I 3( Plan = 0 ~~~~~~~~~~~650/ r 90 20 Section ternal surfaces of ROEC'S should be smooth and ac- cessible for cleaning. To encourage proper use by children and to prevent their falling into the pit, a Squatting Plates for Composting, PF, second smaller (150-millimeter diameter) seat should and Vault Toilets be provided. This may be a separate seat on the seat cover. A cover should always be provided to mini- Squatting plates for composting toilets are the mize fly access, but it should have several small holes same as those for viP latrines, except that, if urine drilled in it to permit the through draft necessary for is to be excluded. a suitable urine drainage channel odor control in these toilets. Alternative designs are must be provided (see chapter 11, figure 11-1). shown in figure 9-3. In PF and vault toilets, if the squatting plate is 70 SANITATION TECHNOLOGY OPTIONS Figure 9-6. Plastic or Fiberglass Water-seal Toilet (millimcters) =~~~~ l0 At3()~~~~- 40 I= e~~~~~~~~~~~~~~~I Plan 46(1 Water-seal bowl Source: Adapted from Wagner and Lanoix (1958). LATRINE AND TOIIET FIXTURES 71 Figure 9-7. PF Units foir Displacedl Pits (millimeters) A. Cement mortar or ceramic pan 345 1- 495 18 a 23(=S a h fi=-h a 6~~~~~~~~~7 13 Plan of squatting plate (pan) Plan of water-seal unit (trap) > 495 ,1 2- 89345 2308! 1121)l 58 64 122 mm Ot Clement nortar 8 ~~~~~~~~~~~~~~~~~~~~~~~~15'-45' 381 mm of cemcnt mnortr 70 5 7 13 7'6 13 K121 1)S I115 Section a-a Pan Section b-b Pa NI .ort.r-eroilt G-+/ T/ ~~gron 1mg B. Ceramic pedestal 352 .Trap Junction of pan trap 280 51) 300 Side view Top view Sources: A adapted from Wagner and Lanoix (1958): B adapted from ( INHOR (Ceniter for NMultidisciplinary Investigation's in Rural Development), Colombia. 72 SANITATION TECHNOLOGY OPTIONS situated immediately over the pit or vault (for further If the squatting plate is connected to a completely details, see chapters 12 and 18), the design is of the displaced pit or vault, the design is of the type shown type shown in figure 9-4. This unit is most easily in figure 9-7. made from ferrocement or reinforced plastic. An alternative sheet metal design, essentially a PF mod- Pedestal Seats for PF and Vault Toilets ification of the Tanzanian flap-trap described above. is shown in figure 9-5. It is essential that this unit be These are essentially the same design as for cistern- properly and completely galvanized before it is cast flush toilets but with a smaller water seal (generally into the ferrocement slab. Figure 9-6 shows a similar 15 to 20 millimeters) and a smaller exposed surface design that can easily be produced in plastic. When area and volume of water (around 75 square centi- used with ViP latrines, all designs of squatting plates meters and 2 liters, respectively). A low-cost ceramic discharging to the pit should be placed to flush for- design such as that from Colombia (shown in figure ward to avoid erosion of the pit wall. 9-7B) cost about $5 in 1978. 10 VIP Latrines CONVENTIONAL PIT LATRINEs are the most common superstructure odor free. The pit may be provided sanitation facility used in developing countries. In its with removable cover sections to allow desludging. simplest form, a pit latrine has three components: Recent work has indicated that pit ventilation may a pit, a squatting plate (or seat and riser) and foun- also have an important role in reducing fly and mos- dation, and a superstructure. quito breeding. The draft discourages adult flies and A typical arrangement is shown in figure 10-1. The mosquitoes from entering and laying eggs. Never- pit is simply a hole in the ground into which excreta theless. some eggs will be laid and eventuallv adults fall. When the pit is filled to within 1 meter of the will emerge. If the vent pipe is large enough to let surface, the superstructure and squatting plate are light into the pit, and if the superstructure is suffi- removed and the pit filled up with soil. A new pit ciently dark, the adults will try to escape up the vent is then dug nearby. pipe. The vent pipe. however, is covered by a gauze The simple unimproved pit latrine has two major screen so that the flies are prevented from escaping. disadvantages: it usually is malodorous, and flies or and they eventually fall back to die in the pit. mosquitoes readily breed in it, particularly when it Both the vent pipe and the gauze screen must be is filled to within 1 meter of the surface. These un- made from corrosion-resistant materials (for exam- desirable attributes have led to the rejection of the ple, asbestos cement, fiberglass. Pvc). Little detailed pit latrine in favor of other, far more expensive forms work has been done on the design of the vent pipe. of sanitation, but these problems are almost com- At present it is recommended that the pipe diameter pletely absent in vip latrines, VIDP latrines, and should be 75 to 200 millimeters and that it should ROEC'S. It is therefore recommended that unim- extend 300 to 600 millimeters above the roof. Local proved pit latrines of the type shown in figure 10-1 wind patterns and the diurnal variation in ambient no longer be built, and that those that do exist should temperatures affect ventilation efficiency: theoretical be converted. and field work on these aspects is continuing. Recent work has provided designs for pit latrines that are odorless and have minimal fly and mosquito nuisance. VIP latrines (figure 10-2) are a hygienic. VIDP Latrines low-cost, and more acceptable form of sanitation that has only minimal requirements for user care and To eliminate the need to construct very deep pits. municipal involvement. The pit is slightly offset to to preclude the necessity of constructing another la- make room for an external vent pipe. The vent pipe trine once the pit is full, and to facilitate the emptying should be at least 75 millimeters in diameter (ranging of the pit where space for a replacement latrine does up to 200 millimeters); it may be painted black and not exist, a double-pit latrine should be used. A VIDP located on the sunny side of the latrine superstruc- latrine differs in design from the vip latrine only in ture to heat the vent pipe more than the rest of the its having two pits (see figure 10-3). Two pits can be structure and thus augment the updraft. The air in- provided by constructing a separation wall in the vIP side the vent pipe will be aspirated and create an pit or by constructing two separate pits. Each of the updraft and a corresponding downdraft through the two pits should be designed to have an operating life squatting plate. Any odors emanating from the pit of at least one year before it is necessary to seal the contents are expelled via the vent pipe, leaving the pit and switch to the second pit. The VIDP super- 73 74 SANITATION TECHNOLOGY OPTIONS Figure 10-1. Conventional Unimproved Pit Latrine structure and squatting plate arrangements would be (millimeters) similar to that of the DVC toilet (see chapter 11). Regular vIP squatting plates would be used, how- ever, where urine separation is not required. Operation and maintenance of the VIDP is the same for pit emptying as that for the vip. With two pits Open tor available, one pit would be used until full and then ventilation sealed while the second pit is in use. When the latter is almost full, the first pit would be emptied and put back into use once more. By alternating. the two pits can be used indefinitely. Because of the long resi- dence time (a minimum of one year) of the decom- posing excreta in the pit not in use at the time. path- ogenic organisms will have been destroyed by the time the pit needs to be emptied. The excavated humus-like material can be used as a soil conditioner Removable or disposed of without fear of contamination. In permeable soil the liquid fraction of the excreta. Vent hole Base together with the water used for latrine and personal Ground tevel : 2 / cleansing, percolates into the soil and so reduces the volume of excreta in the pit. The solid fraction of the / 4/ ,8<,3Concrctc or \ _ X. >K, 2. tltn . bL ~~~rI Jmrtar or tar 94 L 1~ ~ ~~~~~~~~~~~~~~~~~~~ - ' - - Reo I (i)(le ,0 _t2.()()11oto 4 2.()()() ho 4 3.(i()( mm % _ r _ I()()~~~~~~~10-nim concrete, _ 7 Y ~~~~~~~~~~~~200(-mrm block. or 200(-mm brick liner Section a-a Section b-b (vent not shown) VIP LAT RINES 79 B. Structural details 40)0 a a~~~~~~~Pa 400t Plan Plan of pit collar Vent pipe ISon} Manhole with heavy lid j- jlont, to bh scaled wNith mrn,tar 4 Possible flap-trap < 2.T 2 I0 I I m0 Alternative concrete collar and cover sections for 1,000 x 2.000-mm unlined pit Section a-a 0 ~ ~ ~ ~ ~ ~ ~~i7 7- /X,, .~~~~~~~~~~~~~~~ O h7 I.'t-nmn / / COS er scctiiif 7- / 2 pieces 1 Chicken wire / - tn-mnim dilamceter | 1+25() j0 i jlcinflorcin2 r I tIM 01~~~~~~~~ba oArC ire ceh 7(11)0 711(1 in Cfl lat Fixed lid Removable lid Detail of cover section Note: Pedestal seat with curved chute may be substituted for squatting plate. Construction materials and dinensions for the superstructure may vary according to local practice. The ven should he placed for maximum exposure to sunlight. Source: Adapted from a drawing by U. Winblad. 80 SANITATION TECHNOLOGY OPTIONS Figure 10-5. Alternative Pit Designs (millimeters) 40iJ to 6(X)-MM joints laid v%ith mortar Circular pit with brick lining Round pit with partial Bored pit with concrete lining lining of tree limbs Squatting plate Built-up l _ _ / ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~plinth Ground lcvel Base Ground tf . 7 . C ~~Squatting G. tSroilndl plates ; ,;i ........ Av =A-=X_ > \Concrcte SCledLean concretc On_ coennSeonil backfill brickwork cementPi 9 X ~~~~~~~~~~~~~~~~~brickJ^w,~~~~A n 'S 12 -HU~~~aumltu Dcpi d 9cyv D C) a r _ *Gravel soakawav Decomposn Source: Adapted from a drawing by U. Winblad. Note: This figure has been included because of widespread interest on the part of many development agencies and officials. Recent intensive efforts by Winblad (personal communication 1981) to ensure adequate user operation and maintenance were unsuccessful. The 'multrum" is not recommended for use in developing countries. and 60 percent. This can be achieved in several ways. water; this approach is not applicable in areas where In the Vietnamese DVC toilet (figure 11-2), urine is there is a high groundwater table. In this situation excluded from the vault and either drained to a small the vault must be completely sealed, and moisture gravel soakaway or collected for use as a nitrogenous control depends on the correct addition of absorbent liquid fertilizer. Direct use is not acceptable in areas materials such as dried grass, sawdust, and ashes. where the prevalence of urinary schistosomiasis is The addition of ashes also helps to make the excreta high. In the Botswanan and Tanzanian DVC toilets alkaline and so aids the composting process. The (see figure 11-3), the base of the vault is permeable, moisture problem is exacerbated in areas where permitting infiltration and percolation of urine and water is used for anal cleansing. Figure 11-2. DVC Toilet Used in Vietnam (millimeters) 142(0 Ash 34(1 1 1 54(1 11)11 341) storage Urine area . . z- > , ) outlet Superstructure corner posts Plan a J Bamboo wall cladding Compost rl X I I 111- ,removal jj ~~~~port 250 1(1 14140 72(1 j It 1)1) Section a-a 1,620 (M) 50() 5 (00 l ( !1401 11!40 !, i !'140l Section b-b 85 Figure 11-3. DVC Toilets (millimeters) 75-mm I uniplasticized vent pipe . Removable 690 1.0(0 640 superstructure .-- . _ _ - i~~~~~~~~~~~~~~~~~~~~~ormed fronm . ~ and -alvanized II~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~r- -- - - - millecd stect i I t _ l t ~ Concrete Concrete seat and I ] l l l I | . closure cover access cover covcr I I h ~~~~~to second I ~~~~~~~~~Vault Plan Section Model used in Botswana l ) 137-mlm ferrocemyenit 50~~~~~~~~~~~~~~5 I 1 5)') 45() Plan Section Model used in Tanzania Source: Adapted from a drawing by R. A. Boydell. 86 CO-NPOSTING TOILETS 87 It is important to ensure that only one vault is used by the equation: at a time. In the case of the Vietnamese DX'C toilet. which is provided with two squatting plates. this has V - (1.33) (4 .) P presumably been achieved by a vigorous user edit- ' cation program. In parts of the world where there where P is the number of people using the toilet. are cultural preferences or obligations for one or The factor 1.33 is introduced since the vault is taken more members of a household to use a separate toi- out of service when it is three-quarters full. let, however, several squatting plate locations are indicated. In the Tanzanian DVC' toilet, one squatting plate and a continuous slab are provided within a Materiail antid lcbor requirements singie superstructure, their positions being inter- chaned s neessrv. n te Btswaan esigi, oth Construction material and labor requLiremients are changed as necessary. In the Botswanan design., both generally comparable to those for vIP latrines and the squatting plate and the superstructure are moved ROEC'S providing special care is given to making the into position over the vault in use, while the other t u c is covcredbv a concete slab.vaults weather resistant. Separate urine channels is covered by a concrete slab. nmay be needed to improve nitrogen recovery, reduce supplemental carbon requirements. and reduce moisture content. Vault Design Suitable superstructure and squatting plate designs CoinplemnentartY investments are given in chapters 8 and 9. DVC toilets should be anid water requirements ventilated in the same way as v:iP latrines (chapter Sullage disposal facilities are required (see chapter 10). The correct sizing of the vaults is more difficult. 20 for more detail). since there is little information available. In Viet- A mall qati wie z nam, the volume of each vault is approximatel 0.3of water is required to clen the squatting plate. Onlv the absolute minimum of water cubic meter: it is used by a family of five to ten for should be added to DXC toilets two months. This is equivalent to a minimum design capacitv of 0.18 cubic meter per person a year. In Tanzania. the volume of each vault of experimental Maintenance requirements DVC toilets was 0.6 cubic meter. which served a fam- ilv of four to six for six months. equivalent to a min- Batch composting or DVC toilets require a great imum design capacity of 0.2 cubic meter per person deal of user care and maintenance. Ash and easily a year. The recommended design for future instal- biodegradable organic wastes such as sawdust. grass, lations of DVC toilets in Tanzania. however. has a and vegetable wastes must be added regularly in the working volume of 0.88 cubic meter per vault, equiv- correct quantities (determined by trial and error, alent to a design capacity of 0.3 cubic meter per with seasonal adjustments as required) to maintain person yearly if it is to serve a family of six for six a suitable carbon-nitrogen ratio in the composting months. material. Where such material is not available, com- Alternatively, in areas with a high water table. a posting toilets are not ordinarily recommended. Ash series of shallow vaults- mav be constructed (on a is often added to control odors, moisture, and flies. plinth, if necessary). over which a portable super- Care must be taken to exclude water. Finally, the structure mav be moved on a schedule that ensures vaults must be properly sealed with earth when they that excreta remains sealed for at least one vear he- are three-quarters full, the other vault emptied and fore being removed and used. put into service, and its contents reused on the land. The destruction of all excreted pathogens cannot IDvC toilets are relatively easy to build on a self- be expected to occur within six months at vault tem- help basis, and municipal authorities are generally peratures below 40'C. If the atternating cvcle of vault only required to supervise their desien and construc- usage is increased to one vear, then only a few viable tion and to organize appropriate forms of credit for Ascaris ova will remain. It is therefore recommended the smallholder. A continuing long-termn and vigor- that the vault cvcle be taken as one year and the ous program of user education. howexer. will nor- design capacity as 0.3 cubic meter per person yearly. mally be necessary to ensure that DVC toilets are Then the vault volume V (in cubic meters) is given used correctly. 88 SANITATION TECHNOLOGY OPTIONS negligible if the household removed the compost for its own use. If the municipality collected the compost Factors Affectl[ng Suitabilitv and transported it for use, the operating costs could be significant. DVC toilets are not suitable in areas where: * Sufficient user care cannot be reasonablv ex- pected ~~~~~~~~~~Potential for upgrading and resource recoverv pected * There is insuflicient organic waste material There is usually no need to upgrade DVC toilets. available They can, however, be converted to PF toilets if de- * The users are unwilling to handle the composted sired and if the soil is sufficiently permeable. Their humus conversion to sewered PF toilets is straightforward * There is no local use or market for the humus since they have two vaults. one of which can be used produced. for excreta and the other for sullage. This conversion DVC toilets may be unsuitable in high-density areas mav be necessary if the housing densitv increases . . ~~~~~~~~~~~~~sub~stantiallv so that the land available to the house- where users are not motivated to produce good hu- s o that the lan ailbe to therhouse- mus for agricultural use, or are unable to obtain com- hlers on which they can reuse their excreta de- plementary waste materials to regulate the moisture creases and on-silte sullage dsposal Is therefore no and carbon content of the vault contents, longer possible. DVC toilets are specifically designed for resource recovery. Health aspects Vault ventilation reduces odor and fly nuisance, and if the squatting plate is kept clean, DVC toilets Advantages and disadvantages do not pose significant risks to health. Provided each DVC toilets have the following advantages: vault can store excreta for one year at ambient tem- peratures (see Figure 15-1), the composted humus * The production of a stable, safe humus-a ben- can be safely handled and used on the land because efit particularly in societies where there is a tra- only a few viable Ascaris ova will be present. dition of reusing excreta in agriculture * Minimal water requirements. Costs They have the following disadvantages: The total cost of DVC toilets built as part of pilot * An extremely high degree of user care and mo- projects in Africa ranged from $150 to over $550. It tivation is required for satisfactory operation. is likely, however. i:hat a typical DVC toilet with a L Substantial quantities of biodegradable organic modest superstructure could be built for $100 to matter must be locally available. $300. Operating and maintenance costs would be * They are unsuitable for high-density areas. 12 PF Toilets PF TOILETS have water seals beneath the squatting This PF toilet may be installed inside the house plate or pedestal seat and are available in many dif- since it is free from both odors and fly and mosquito ferent designs. Two basic types are shown in figure nuisance; it therefore obviates the need for a sepa- 12-1: the direct discharge and the offset pit. They rate external superstructure, and it can thus meet can be used for several levels of sanitation service. social aspirations for an "inside" toilet at low cost. Wherever space permits, two pits should be built. When the first pit is full, the PF unit can be connected PF Toilet Design to the second pit. When the second pit is nearly full. the first one can be emptied and the toilet again The first type is a modification of the pit latrine connected to it. A PF toilet with alternating pits can in which the squatting plate is provided with a simple be used almost indefinitely. water seal. Approximately 1 to 2 liters of water (or This second type of PF toilet can also be connected sullage) are poured in by hand to flush the excreta to a septic tank (see chapter 14) and hence to a into the pit. This PF toilet is often used with wet pits soakaway drainfield or sewer as shown in figure 12- since the water seal prevents odor development and 2. Alternative designs for superstructures and squat- mosquito breeding. It is especially suitable where ting plates and designs for pits and soakaways are water is used for anal cleansing. discussed in chapters 8 through 10. The second type of PF toilet, which is widely used in India, Southeast Asia, and some parts of Latin America, is used in combination with a completely Material and labor requirements offset pit. The PF bowl is connected to a short length Material and labor requirements for PF toilets (8 meters maximum) of 100-millimeter-diameter shown in figure 12-1 are similar to those for vip la- pipe that discharges into an adjacent pit. Approxi- trines and ROEC'S (figures 10-2 and 10-4). Rather mately 1 to 2 liters of water are required for each more skill, however, is required to make the water- flush. The slope of the connecting pipe should not seal units, and this would normally be beyond the be less than 1 in 40. scope of individual householders on a self-help basis. The pit is designed as described in chapter 10 for The manufacture of water-seal units is, however. wet ViP latrine pits and is provided with a concrete with experience, not a difficult task and one that or ferrocement cover slab and wall lining as neces- readily lends itself to local enterprise. In areas where sary. Because the digestion of excreta solids proceeds sitting is the preferred position for defecation, the more rapidly in wet than in dry pits, a design capacity "Colombian" pedestal is suitable (see figure 9-7B): of 0.04 cubic meter per person yearly can be used. this too is readily amenable to local enterprise. The volume (V) of pits less than 4 meters deep may be calculated from the equation: Complementary investments V = 1.33 CPN, and water requirements where C = pit design capacity (in cubic meters per Sullage disposal facilities are required for the non- person yearly, or 0.06 for dry pits); P = number of sewered PF toilet (see chapter 20). people using the latrine: and N = number of years Assuming that flushing only takes place when the pit is to be used. stools are passed and that a maximum of three stools 89 90 SANITATION TECHNOLOGY OPTIONS FiguTe 12-1. Alternative Designs for PF Toilets (millimeters) Rock l filling Section a-a Pit I - L ~ ~ ~ ~ ~~_____ _ '---Y" jlunctionl on _ _ ' ' side 2 is blocked \ \ ; 0 when pit I is in use _____________ > ~~~~~~~~Pit 2 Plan Offset-pit design emptving- vault ll_ Direct-discharge design Note: In the offset pit design, the pit is placed at site of YY" junction if ony one pit is installcd. PF TOILETS 9] are passed per person daily, the maximum water re- quirement is 6 liters per capita daily. Advantages and disadvantages The main advantages of unsewered PF toilets are: Maintenance requirements * Possible location inside the house The householder is required to ensure an adequate * No odor or fly and mosquito breeding supply of flushing water throughout the year. Other- * Minimal risks to health wise, the maintenance requirements are as described * Low level of municipal involvement for vip latrines. * Low annual costs * Ease of construction and maintenance * Very high potential for upgrading. Factors Affecting Suitability Their main disadvantages are that they require small In general, PF toilets are subject to the same con- but nonetheless significant amounts of water (3 to straints as vip latrines and ROFc's. They have the 6 liters per capita dailv) and that the pit when filled stra1nts ~ ~ ~ ~ ~ ~ ~ ~~ms be empie orr1e take out'S ofe servic and a new additional constraint of a water requirement of 3 to must be emptied or taken out of service and a new 6 liters per capita daily. one built. They also require separate sullage disposal facilities. They do not accept large bulky items (such as maize cobs, mud balls, and the like) used for anal Health aspects cleansing; user cooperation and instruction are there- If properly used and maintained, toilets are free fore required in areas where this is the practice. from fly and mosquito nuisance and provide health benefits similar to cistern-flush toilets. Sewered PF Systems Costs The sewered PF system is a conceptual develop- rment of the sewered aquaprivy system that not only The cost of the PF toilet is similar to that of the overcomes certain drawbacks inherent in the design vip latrine or ROEC. with the additional cost of the concept of the latter while retaining its inherent water-seal unit. Thus, its total construction cost economic advantages (see chapter 13), but also pro- should be in the range of $75 to $225. Maintenance vides a more technically appropriate sanitation sys- costs of the system would be minimal, but flushing tem in areas where the wastewater flow exceeds the water requirements would probably add $3 to $5 per absorptive capacity of the soil (see chapter 14). The year for the household in water-scarce areas. sewered PF system can be developed from an existing PF pit latrine, or it can be installed as a new facility. There are minor technical differences between these alternatives, and only the latter will be considered PF toilets can be easily upgraded to a low-cost sew- in this section (the former is described in detail in erage system that also accepts sullage. The necessary chapter 16). design modifications are discussed below. Since the The sewered PF toilet system has five parts: manual PF system can also be eventually replaced bv *The PF bowl, with a vent pipe and inspection a low-volume, cistern-flush unit, PF toilets can be fully upgraded to sewered cistern-flush toilets. The chamber draiage rragemets ae dffernt fom hosefor * A short length (8 meters maximum) of 10()-mil- drainage arrangements are different from those for limeter pipe laid at not less than I in 40 conventional sewered cistern-flush toilets, but the i differences are of no importance to the users, who *A small two-compartment septic tank : e~~ A network of small-bore sewers perceive only that thev have a cistern-flush toilet. A sewage dipsallity. - * ~~~~~~~~A sewage disposal facility. The pit contents may be used as humus, as de- scribed for the viP latrine. If only one pit is used. A typical arrangement is shown in diagrammatic however, the material removed from it should be form in figure 12-2. Only excreta and PF water are treated by aerobic composting or by storage (for ex- discharged into the first compartment of the septic ample, burial) for at least a year before reuse to tank and only sullage into the second. The two com- reduce pathogens to an acceptable level. partments are interconnected by a double T-junc- 92 SANITATION TE-CHNOLOGY OPTIONS Figure 12-2. PF Toilet-Septic-tank Systems PF toilet Sullage inlet Septic tank l 'ISoakawa With soakaway PF toilet Sullage inlet Distribution box X U : Septic tank : ... To drainfield __n. Septi :t'.: With distribution box and drainfield rr toilet P F t oil et S u lla g e in le t 1:50 S . / :i . Septic tank Sewer With sewer S Slope. Note: See chapter 14 for d-tails of septic tanks. soakaways. and drainfields. rAin PF TOILETS 93 tion, the invert of which is a nominal 30 millimeters ing of the septic tank is required when the first com- above the invert of the exit pipe of the second com- partment is half full of sludge, which occurs every partment, which is connected to the street sewer. twenty-two months, assuming a sludge accumulation Thus, the contents of the first compartment are able rate of 0.04 cubic meter per person yearly and a to overflow into the second, but sullage cannot enter capacity of 0.15 cubic meter per user. the first compartment. This arrangement effectively Since all but the smallest solids are retained in the eliminates the very high degree of hydraulic distur- septic tank, it is not necessary to ensure self-cleansing bance caused by high sullage flows that, in single- velocities of 1 meter per second in the receiving sew- compartment tanks, would resuspend and prema- ers. Small-bore sewers of 100- to 150-millimeter di- turely flush out some of the settled excreta; it thus ameter can be used, and these can be laid at flat permits a considerably higher retention time for ex- gradients of 1 in 150 to 300. Sullage water ordinarily creta in the tank and hence is able to achieve a sub- carries no solids that could clog sewer pipes. Con- stantially increased destruction of excreted patho- sequently, manholes need only be provided at pipe gens. junctions. Thus, the sewered PF system achieves con- Guidelines for the size of the two-compartment siderable economies in pipe and excavation cost com- septic tanks may be developed as follows. Assuming pared with a conventional sewerage system. Taking a per capita daily production of excreta of 1.5 liters into account these savings, the extra cost of the small and a maximum PF water usage of 6 liters per capita septic tank, the savings in water usage, and the lower daily, the maximum toilet wastewater flow amounts cost of the toilet fixtures, the annual economic cost to 7.5 liters per capita daily. Allowing a mean hy- of a sewered PF system can be expected to be con- draulic residence time of twenty days in the first com- siderably less than that of cistern-flush toilets con- partment is equivalent to a volume requirement of nected to a conventional sewerage system.' In ad- 0.15 cubic meter per user, which compares well with dition, treatment costs will be less because of the the recommendation that the first compartment enhanced pathogen removal and reduction of bio- should be calculated on the basis of 0.15 cubic meter chemical oxygen demand (BOD) (approximately 30 per user, subject to a minimum of 1 cubic meter. The to 50 percent) in the septic tank. flow into the second compartment is the sullage flow and the overflow from the first compartment, or the total wastewater flow. A tank of the minimum rec- tommendedasizew (1.5-cubic-mter wlow k oringi lumre)- 1. The magnitude of cost savings is largely controlled by the ommended size (1.5-cubic-meter working volume) on-site gradient. The sewered PF system is most advantageous in is thus suitable for up to seven users and a water flat areas in which deep excavation and pumping stations would consumption of 140 liters per capita daily. Desludg- be required for conventional sewerage. 13 Aquaprivies THERE ARE THREE TYPES of aquaprivies: the simple capita daily. The soakaway should therefore be de- or conventional aquaprivy. the self-topping or sul- signed on this basis, although it is common to include lage aquaprivy. and the sewered aquaprivv. The sec- a factor of safety so that the design flow would be, ond and third are simple modifications of the first say, 8 liters per capita daily. The sidewall area of the to accept sullage. soakaway should be calculated assuming an infiltra- The conventional aquaprivy toilet (figure 13-1) tion rate of 10 liters per square meter daily (see chap- consists essentially of a squatting plate situated im- ter 14). mediately above a small septic tank that discharges its effluent to an adjacent soakaway. The squatting plate has an integral drop pipe, 100 to 150 millimeters Technical Appropriateness in diameter, the bottom of which is 10 to 15 centi- meters below the water level in the tank. In this Maintenance of the water seal has always been a manner a simple water seal is formed between the problem with conventional aquaprivies. except in squatting plate and the tank contents. To maintain some Islamic communities where the water used for this water seal, which is necessary to prevent fly and anal cleansing is sufficient to maintain the seal. Even odor nuisance in the toilet, it is essential that the there, however, it is necessary for the vault to remain tank be completely watertight and that the toilet user watertight. In many other communities people are add sufficient water to the tank via the drop pipe to either unaware of the importance of maintaining the replace any losses. A superstructure is provided for seal or they dislike being seen carrying water into privacy. and a small vent pipe is normally incorpo- the toilet. If the seal is not regularly maintained. rated in the design to expel the gases produced in there is intense odor release and flx and mosquito the tank. nuisance. The excreta are deposited directly into the tank. The conventional aquaprivy (figure 13-1) suffers where they are decomposed anaerobically in the a major disadvantage: in practice the water seal is same manner as in a septic tank. There is, as with rarely maintained. As a consequence it cannot be septic tanks. a gradual accumulation of sludge (ap- recommended as a viable sanitation option. Al- proximately 0.03 to 0.04 cubic meter per user per though the problem of water-seal maintenance may year), which should be removed when the tank is be overcome in both the sullage and sewered aqua- two-thirds full of sludge. The tank volume is usually privies as shown by figures 13-2 and 13-3, and in spite calculated on the basis of 0.12 cubic meter per user. of the evidence that these two systems have had suc- with a minimum size of 1 cubic meter. Desludging cess (notably in Zambia), the basic design of the is normally required every two to three years. The aquaprivy system is questionable because of the ex- liquid depth in the tank is usually 1.0 to 1.5 meters pensive watertight tank needed to maintain the water for individual households: depths of up to 2 meters seal. Experience has shown that the water seal may have been used in large communal aquaprivies. not always be maintained (usually because of failure The volume of excreta added to the aquaprivy tank or inadequacy of the water supply), so that the sys- is approximately 1.5 liters per capita daily, and the tem suffers a relatively high risk of intermittent mal- water used for "flushing' and maintenance of the function. water seal is about 4.5 liters per capita daily; thus As shown in figure 13-2, the sullage aquaprivy is the aquaprivy effluent flow is around 6 liters per operationally equivalent to either a vIP latrine (or 94 AQUAPRIVIES 95 Figure 13-1. Conventional Aquaprivy (millimeters) -- ~~~~~~~~ ~900 ~t C,77 6 _ to1 soakawav 25-mm I I vent pipe I l I Removable slab I I I l for desludging access Plan 25-mm vent pipe Removable slab for desludging access ('_ _._ ..... X - to soakawav 1,370 10~~~~~~~~~~~~~~ . . - N Section a-a Source: Adapted from Wagner and Lanoix (1958). 96 SANITATION TECHNOLOGY OPTIONS Figure 13-2. Formal Equivalence of Sullage Aquaprivy to VIP Latrine with Separate Sullage Soakaway or to PF Toilet Sullage Wj Excreta Vent Sullage soakaway 11 reI Inseto chme _- . z ]. v~~~~~~PFtoilet _ _ = r _ ~~~~~~~~~~~.:....'. .:.......' :.:.:,. :.:. : . : :,:,:::,:,:': : ---.:.. :-:-:.. -:: :,,, .:.:.:.:.:.:,.:,.:.:',: : .: : .:.: .: . ..:,,:,::: Aquaprivy 9_~Vent Excreta Sullage soakaway _.:.:.:.:.:-.... :- . :, .. . .:-... :..... .................... VIP latrine with separate sullage soakaway Inspection chamber Excreta with vent Sullage soakaway _ "' .......'.'... PF toilet AOUAPRIVIES 97 Figure 13-3. Formal Equivalence of Sewered Aquaprivy to Sewered PF Toilet Sullage lExcreta Vn ' -' .-' - . - ' ', . .. -. ' ,. .: -,: Sewer Sewered aquaprivy Inspection chamber Excreta with vent Sullage Septic tank Sewer Sewered PF toilet ROEC) with an entirely separate soakage pit for sul- nuisance and operational malfunctions. The PF toilet lage disposal or a PF latrine with a completely offset has a much more reliable water seal, does not require pit that can also be used for sullage disposal. Either a watertight pit, can be located inside the house, and alternative costs less than the sullage aquaprivy and is more easily upgraded to a cistern-flush toilet. is superior because of reduced risks of odor and fly The logic of the sewered aquaprivy system is sim- 98 SANITATION TECHNOLOGY OPTIONS Figure 13-4. Improved Sewered Aquaprivy with Sullage Disposal Vent pipe Removable slab a ~~~~~~~~~~~~~~~a Sect ion b-b L t To sewer or +___ _____ soakage pit Plan/section a-a AQUAPRIVIES 99 ilarly questionable. An aquaprivy is sewered not be- cause of any need to transport excreta along sewers. but as a method of sullage disposal in areas where Tank Design the soil cannot accept any or all of the sullage pro- duced. As shown in figure 13-3. the sewered aqua- The principal modification to the standard aqua- privy can be considered as functionally equivalent to privy tank is the addition of a sullage compartment a sewered PF toilet (see chapter 12). The sewered PF provided to avoid hydraulic disturbance of the settled toilet is the superior system for the reasons noted excreta in the main part of the tank. The invert of above: it is also marginally cheaper. the pipe connecting the two compartments is a nom- Thus, aquaprivy systems ordinarily cannot be rec- inal 30 to 50 millimeters below the invert of the ef- ommended as a viable sanitation option since they fluent pipe from the sullage compartment (which can be replaced by technically superior systems at leads to the soakage pit or sewer), so that the sullage lower cost. One important exception to this, how- flow can be used to maintain the water seal in the ever, is found in areas where the common anal main compartment but is unable to resuspend the cleansing materials (such as maize cobs, mud balls, settled excreta. Since the proportion of excreta in and the like) would clog the water seals of PF toilets. the effluent is considerably less than that in the ef- In such cases the improved aquaprivy design shown fluent from conventionally designed aquaprivy tanks. in figure 13-4 should be used. the soakage pit can be smaller as the infiltration rate of the effluent (now mostly sullage) is greater, ap- proximately 30 to 50 liters per square meter of side- Self-topping or Sullage Aquaprivy wall area per day. Thus, sewers may not be required The self-topping or sullage aquaprivy was devel- because soakage pits can be used for much larger oped to overcome the problem of maintenance of wastewater flows. the water seal. In this simple modification of the The tank volume is calculated to provide 0.12 cubic conventional svstem, all the household sullage is meter per user in the settling compartment, which added to the tank; the water seal is thus readily main- should have a minimum size of 1.0 cubic meter. The tained and the sullage is conveniently disposed of. sullage compartment should have a volume of about Although the sullage can be added to the tank via 0.5 cubic meter the drop pipe, it is more common, and for the user more convenient, for it to be added from either a Material and labor requirements sink inside or immediately outside the toilet or from one located in an adjacent sanitation block. Natu- The aquaprivy vault may be constructed of brick, rally. as the volume of water entering and leaving concrete, or concrete block and must be water- the aquaprivv tank is increased by the addition of proofed with a stiff mortar. The smaller units may sullage, the capacity of the soakage pit musi be in- be prefabricated of plastic, if economically feasible. creased to absorb a larger flow. Sullage aquaprivies Self-help labor is suitable for excavation work, but cannot, therefore, be used in areas where the soil is the vault construction requires skilled bricklayers. not suitable for soakaways or where the housing den- sity or water usage is too high to permit subsurface Complementary investments percolation for effluent disposal (unless the aqua- and water requirements privy tank can be connected to a sewer system). Since all but the smallest solids are retained in the aqua- Aquaprivies require sullage piping to the vault and privy tank, the sewers can be of small diameter and effluent piping with either an on-site infiltration fa- laid at the nominal gradients necessary to ensure a cility (drainfield, soakage pit. or the like) or off-site velocity of around 0.3 meter per second rather than sewerage (small-bore or conventional sewers). the self-cleansing velocity of 1 meter per second re- Water required to maintain the water seal depends quired in conventional sewers transporting raw sew- on local climatic conditions. In the sullage aquaprivv, age. Commonly. 100- to 150-millimeter pipes are the amount of sullage water discharged to the privy used at a fall of 1 in 150 to 300. Substantial economies is sufficient to maintain the water seal, provided all in sewer and excavation costs are thus possible, and sullage water is drained to the vault. In practice this sewered aquaprivy systems are therefore consider- means that, wherever sullage water is used to irrigate ably less expensive than conventional sewerage. a garden, self-topping aquaprivies are not recom- 100 SANITATION TECHNOLOGY OPTIONS mended unless water is piped to the house or yard- would be the cost of either the householder's or the or the users are made aware of the need to maintain municipality's emptying the pit every three years. the water seal. Potential for upgrading and resource recovery Maintenance requirements Self-topping aquaprivies can easily be upgraded to Maintenance is simple. The aquaprivv should be low-cost (small-bore) sewerage in the manner de- Mant clean ancthe isasimle. Thesl aquprwoy houd bree scribed for upgrading PF toilets. Similarly, the squat- kept clean and the vault desludged at two- to three- ting plate could be replaced by a cistern-flush unit year intervals. An adequate supply of water is nec- discharging into the vault. essary for "flushing" and to maintain the water seal. Material removed from the pit should be treated by aerobic composting or stored for twelve months before use to lower health risks to an acceptable Factors Affecting Suitability level. Only self-topping aquaprivies should be used and Advantages and disadvantages only where a water seal is desired and users have traditionally used bulky anal cleansing materials that The main advantages of the self-topping aquaprivy would clog a PF toilet. Water is required on-site (yard are: or house connection) to ensure that enough water No danger of clogging by bulky anal cleansin is available to maintain the water seal. materi a material * Possible location inside the house Health aspects and cs* No odor or fly and mosquito breeding * Minimal risks to health Properly used and maintained, the self-topping * Low annual costs aquaprivy provides health benefits equivalent to * Potential for upgrading. those offered by the cistern-flush toilet. The main disadvantages are: Costs of the self-topping aquaprivy can be ex- pected to be higher than either pit latrines or PF * Relatively high costs for on-site disposal toilets because both a pit and a percolation unit are * High level of skill required for construction needed. The range of construction cost may be $150 * Pit emptying requires some municipal involve- to $400. Maintenance costs would be minimal, al- ment though the cost of water could easily reach $5 or * Small but nevertheless significant amounts of more per year in water-scarce areas. Added to this water required. 14 Septic Tanks, Soakaways, and Drainfields SEPTIC TANKS are rectangular chambers, usually desludging operations (which are required when the sited just below ground level, that receive both ex- tank is one-third full of sludge) is readily calculated. creta and flushwater from flush toilets and other Figure 14-2 shows a variety of alternate designs, household wastewater. The mean hydraulic reten- including an experimental septic tank in which an tion time in the tank is usually one to three days. anaerobic upflow filter is substituted for subsurface During this time the solids settle to the bottom of systems for effluent disposal. Reports of initial re- the tank where they can be digested anaerobically, search findings are promising. An eighteen-month and a thick layer of scum is formed at the surface. study showed that, after ninety days' maturing of a Although digestion and volume reduction of the set- 12- to 19-millimeter medium, intermittent flows of tled solids is reasonably effective, some sludge ac- 40 to 60 liters per day and BOD solids removal com- cumulates, and the tank must be desludged at regular parable to or better than those for primary sewage intervals, usually once every one to five years. The treatment were achieved. Further pilot studies may effluent from septic tanks is, from the viewpoint of result in further application of this method. Mean- health, as dangerous as raw sewage and so is ordi- while, anaerobic upflow filters are being used for narily discharged to soakaways or leaching fields; it various domestic and industrial waste applications. should not be discharged to surface drains or water- courses without further treatment. Although septic Effluent Disposal tanks are most commonly used to treat the sewage from individual households, they can be used as a Subsurface disposal into soakage pits or irrigation communal facility for populations up to about 300. in drainfield trenches (soakaways) is the most com- A two-compartment septic tank (figure 14-1) is mon method of disposal of the effluent. The soil must now generally preferred to one with only a single be sufficiently permeable; in impermeable soils compartment because the concentration of sus- either evapotranspiration beds or upflow filters can pended solids in its effluent is considerably lower. be used, although there is little operational experi- The first compartment is usually twice the size of the ence with either of these systems. For large flows, second. The liquid depth is 1 to 2 meters and the waste stabilization ponds may be more suitable (see overall length-to-breadth ratio is 2 or 3 to 1. Expe- chapter 21). rience has shown that, if sufficientlv quiescent con- ditions for effective sedimentation of the sewage sol- Drainfield design ids are to be provided, the liquid retention time The tank effluent is discharged directly to a soak- should be at least twenty-four hours. Two-thirds of away (figure 14-3) or, with larger flows or less perme- the tank volume is normally reserved for the storage able soils, to a number of drainage trenches con- of accumulated sludge and scum, so that the size of nected in series (figure 14-4). Each trench consists the septic tank should be based on three days' re- of open-joint agricultural drainage tiles of 100-mil- tention at start-up; this ensures that there is at least limeter diameter laid on a 1-meter depth of rock fill one day of retention just before each desludging op- (20-millimeter to 50-millimeter grading). The ef- eration. Sludge accumulates at a rate of 0.03 to 0.04 fluent infiltrates into the soil surrounding the trench, cubic meter per person yearly; thus, knowing the the sidewalls of which are smeared and partially number of users, the interval between successive clogged during excavation. Further clogging of the 101 102 SANITATION TECHNOLOGY OPTIONS Figure 14-1. Schematic of Conventional Septic Tank (millimeters) Access openings Inspectin opening Inspection opening near side wall 150-mm diameter 150-mm diameter at least 600-m,m Compartment / / dianmeter baffle Inlet '\;.- Vo ' ^. ,- ,,', ^ , \ . -' w /. .', s 'to, -/ ' . ,\, //. Outlet "T" At least 25 mm Liquid level 20 percent of liquid depth Water line 2 -X E *: _ ~~~....., : :................ '.. ' -''"-'- . .......... 40 'per:::e.-; :::...: -:-::':t 2 ' ' ' - ' - ' | 20 percent Scum 40 p - - of liquid depthoflqidet (bO mm, minimum) Scum clear space2 (75 mm, minimum) .4 o ': Clear space {Sludoe clear space . (300 mm, minimum) _ Sludge Q ~~~~~. . : , ..'.': . --.: : i-, . . :. : : - : . z , :,, ~~. . . -. :. :. -. . . .,, . . . . . . . . .,:.: , .. ..,, .:::,-:: .--:::- : :: :::::::: .:- o pc a w. .on f E 13-2 , -3. an -4:, c tk ms . p. . L , : : : , : - :: - -~~~~~~~.:-:--.- :. .................... First compartment 2/3 length |Seconcd compartment 1./3 length Total length equals two to three times width Note: If vent is not placed as shown on figure 13-2, -3, and -4, septic tank must be provided with a vent. effluent-soil interface results from slaking (hvdra- sewage solids (which form an interface between the tion) and swelling of the soil particles, from physical soil and the drainage trench). This rate of infiltration movement of fine solids in the effluent into the in- has been shown to be within the range of 10 to 30 terface, from chemical deflocculation of clay parti- liters per square meter of sidewall area per day for cles when the effluent water has more sodium than a wide range of soil types. The bottom of the trench the original interstitial groundwater, and from the is not considered to have any infiltrative capacity formation of an organic mat made up of bacterial because it quickly becomes completely covered and slimes feeding upon nutrients in the effluent. This clogged with sewage solids. The trench length re- means that the life of a drainfield is limited. Provision quired is calculated from the equation: must therefore be made to set aside land for use as a future replacement drainfield. Soil percolation tests L = NQ should be used to determine whether the soil is suf- 2DI' ficientlv permeable. The infiltration should not be estimated solely from percolation test results, how- where L = trench length in meters ever, because these merely indicate the infiltration N= number of users rate of clean water into virgin soil. The infiltration Q = wastewater flow in liters per capita daily rate that should be used in drainfield design is the D = effective depth of trench in meters rate at which septic tank effluent can infiltrate the I = design infiltration rate in liters per square soil surface that has become partially clogged with meter daily. SEPTIC TANKS. SOAKAWAYS. AND DRAINFIELDS 103 Figure 14-2. Alternative Septic Tank Designs (millimeters) Inlet Compartment Outlet baffle Outlet "T" | 17 \/ '; ' - \' / E, '--/" \ -S/lOutlet Inlet fI A - 40 percent liquid depth .o . |Clear space . clear space _ * . - Sludge . Sludge . \ Scum clear space 43 length 1/3 length ~~~~~~~~~~~~~T Conventional two-compartment Conventional two-compartment septic tank septic tank with inlet with baffle walls connector and outlet "T" Effluent weir Sludge channel - /* drainfield * ~~~~~Filter |TTililwstst onlte Sullage Toilet wastes 1- ~ ~ ~~ M ~~ Sullage and settled wastes Two-compartment septic tank with upflow filter Three-compartment septic tank Animal excreta Sullage inlet Slurrv 600-mm diameter and animal excreta removal access manhole a a Human Human | excreta b excreta. Equal Equal Equal Section a-a Section b-b Three-compartment septic tank for resource recovery 104 SANITATION TECHNOLOGY OPTIONS Figure 14-3. Schematic of Soakaway (whose growing roots may damage them). Table 14- (millimeters) I gives general guidelines for location in the form of minimum distances from various features. Evapotranspiration mounds Variable soil cover . o 4 ° In areas where the water table is near the surface Tight joints or the soil percolation capacity is insufficient, an evapotranspiration mound may be substituted for a drainfield. Design criteria for these mounds depend :: . t _ _g; .on climate, soil type, and native grasses. Pilot studies - ; _ _g .-. .are therefore required to confirm or modifv the sug- : : ; _ _ .: -.gested dimensions in figure 14-5. In addition, gravity- fed systems require adequate slope between the sep- tic tank outlet and the mound. Open R cfl -_ . I Technical Appropriateness Rock fil (in5m mm') Q _ _ i i,Septic tanks of the conventional design described above are indicated only for houses that have both an in-house water supply and sufficient land for ef- : 4 _ $ ? - - fluent disposal. These two constraints effectivelv * ; _r r .Llimit the responsible use of septic tanks to low-den- sity urban areas. In such areas they are a very ac- . . . 9 . 9 . :.ceptable form of sanitation. It is all too common, however, to see septic tanks provided in medium- density areas where the effluent, unable to infiltrate Source: Adapted after Wagner and Lanoix (1958). into the soil, emerges onto the ground surface, where it ponds, or is discharged into street gutters or storm The factor 2 is introduced because the trench has drains; in these cases it causes odor nuisance, en- two sides. The design infiltration rate for soakaways or drainfields should be taken as 10 liters per square meter daily, unless a more accurate figure is known Table 14-1. Minimum Required Distances from local experience. from Variouis Physical Features for Septic Tanks and Soakaways Located Soil percolation tests in Common Well-developed Soils (meters) The soil must have a sufficient percolative capac- Physical feature Septic tank Soakaway ity, which can be determined by appropriate tests. A satisfactory field procedure is to drill at least three Buildings 1.5 3.0 Property boundaries 1.5 1.5 150-millimeter-diameter test holes 0 to 5 meters deep Wells 10.0 10.0, across the proposed drainfield. These are filled with Streams 7.5 30.0 water and left overnight so that the soil becomes Cuts or embankments 7.5 30.0 saturated; on the following day, they are filled to a Water pipes 3.0 3.0 depth of 300 millimeters. After thirty and ninety Paths 1.5 1.5 minutes the water levels are measured; the soil is Large trees 3.0 3.0 considered to have sufficient percolative capacity if Source: Adapted from Cotteral and Norris (1969). the level in each hole has dropped 15 millimeters per a. Up to 30 meters for sands and gravels and greater distances hour. for jointed or fissured rocks. As noted in the text, drainfields clog up and must be taken out of service periodically to permit their recovery. This is ordinarily done by adding a second drainfield. Location of septic tanks and drainfields operating it to the point of refusal, and diverting the flow back to the first one. Alternatively, intermittent discharge of the septic Septic tanks and drainfields should not be located tank effluent will tend to keep the drainfield aerobic and thus too close to buildings, sources of water, or trees increase its operating life, SEPTIC TANKS, SOAKAWAYS. AND DRAINFIELDS 105 Figure 14-4. Drainfield for Septic Tank Effluent (millimeters) Future diversion box L J 9 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~0- a Drainfield trenches Tight lines Overflows in a I [ g undisturbed earth %_r----__-}-_____-- - Future replacement drainfield trenches Plan Trench spacing , ?< ~~~~~~Overflow NatuTal earth t,~~~~ln backfill Silt barrier (untreated paper) Q JC Undisturbed --f Open drain tile (75- to 125-mm diameter) , Rcfl '' Effective , , * §sidewall area Trench Rock-soil or' width liquid-soil interface Bottom area Section a-a Source: Adapted from Cotteral and Norris (1969: 9 American Society of Civil Engineers: original used by permission). courages mosquito breeding, and is a general health are discharged into the first compartment and sullage hazard. directly into the third; the second compartment pro- It is possible to alter the design of the septic tank vides additional and more quiescent settling for fecal to make it more suitable for use in medium-density solids. This arrangement avoids excessive dilution of areas (up to approximately 200 persons per hectare). the toilet wastes with sullage. This increases reten- One design modification is the provision of three tion time and reduces the hydraulic disturbance in compartments (see figure 14-2), only toilet wastes the first and second compartments, minimizing the 106 SANITATION TECHNOLOGY OPTIONS Figure 14-5. Evapotranspiration Mounds (millimeters) 100 mm of straw-Sandy loam soil Grass coVerPerforated lateralf Sand fll 2150 mm of topsoil S = 3:1. maximuim- ; ~ Topsoi oil Plo.ved0or di sf I I rfac) Clean rock (20 to 61 mm) Cross section a-a -Pipe from septic tank X ~~~Dike, ? Perforated laSteral I I r X (75 to 125 mm in I I - cliameter) I , IM. Bed area (220 to II _ _60 mm of clean rock) 0g t , |-- | I | I I Bed length l ~~~~~500 1 11,000 II ,000 500 = L llofjo 1_ Dike mm maxike -Total width S Slope Plan/top view Note: An acceptable alternative to a mound is an evapotranspiration bed, which has the same construction but is built in a natural or manmade depressi'on not subject to floodinig and has a more or less level surface. SEPTIC TANKS. SOAKAWAYS, AND DRAINFIELDS 107 resuspension of settled excreta and carryover of sol- through sandy, gravelly, or fissured overburden. ids into the second compartment. The third com- Therefore, if the drainfield is properly designed and partment acts as a sullage settlement chamber before located, no health hazard should result. the effluent is discharged into the drainfield. The first compartment should be designed on the basis Costs of 0.15 cubic meter per user, so that desludging is required approximately every two years. The second Septic tanks and leaching fields are among the and third compartments should be sized to provide most expensive forms of household waste disposal. one day of retention time in each. Since the effluent Capital operation and maintenance costs have been from the third compartment contains very few fecal found to exceed costs of conventional sewers and solids (which are the principal cause of the clogging sewage treatment by 50 percent in the United States of drainage trenches receiving conventionally de- and to be about equal to the costs of sewerage, in- signed septic tank effluents), the infiltration rate of cluding conventional activated sludge with effluent the effluent is much higher, approximately 30 to 60 chlorination and sludge incineration, in Japan.' It liters per square meter daily. The trench length is must be noted, however, that these costs are derived correspondingly smaller, and thus septic tanks with from installations where high water consumption soakaways become technically feasible, and the need prevails and none of the improvements recom- for sewerage obviated, at higher housing densities mended herein had been applied. than is possible with conventionally designed septic tanks. If low-volume cistern-flush (or PF) toilets and other water-saving fixtures are installed, it is possible Potential for upgrading and resource recovery to use septic tanks and soakaways at even greater PF or cistern-flush toilets with septic tank systems housing densities, perhaps as high as 300 persons per are readily connected to small-bore or conventional hectare. sewerage systems. The conversion is often required when water use and/or population density exceed Factors Affecting Suitability limiting characteristics of the soils in which the drain- fields are placed. The main physical factors that affect the suitability The three-compartment septic tank was specifi- of septic tanks are low soil permeability. restricted cally designed and operated for recovery of fertilizer space for drainage fields. high water service levels, from human and animal excreta and is particularly and proximity of wells that supply drinking water. popular in rural areas of China. Excreta and the required flushwater are discharged via a PF bowl (or, alternativelv, via a straight or curved chute as in a Maintenance requirements ROEC) into the first compartment of the septic tank. To provide the minimum twenty-four-hour deten- The retention time in this chamber is ten to twenty tion time in the first compartment required for days. The contents of the first compartment overflow proper operation, septic tanks should be inspected into the second, to which may also be added animal periodically to ensure that neither scum particles nor excreta (usually of pigs) from an adjacent animal suspended solids are being carried out with the ef- pen. The retention time in the second compartment fluent. In any case, tanks must be desludged at reg- is also ten to twenty days; allowance has to be made ular intervals. For example, the accumulation rate for the additional daily volume of animal wastes. The of 0.04 cubic meter per capita yearly used for de- third compartment, which receives the effluent from signing a septic tank with capacity for ten people and the second, is a storage tank for treated excreta with with a working volume of 1 meter wide, 3 meters a holding capacity of twenty to thirty days. The con- long, 2 meters deep, and one-third of the volume to tents of the third compartment are removed for use provide for sludge and scum accumulation will ne- as liquid fertilizer on agricultural crops; alternatively, cessitate a pumping interval of five years. they could be used to fertilize fishponds. Experience in rural China has shown that the Health aspects three-stage septic tank system reduces fecal coliform counts to below 1,000 per 100 millimeters and In general, enteric bacteria do not survive more achieves an efficiency in removing Ascaris ova ap- than 10 meters of travel through soil. Greater travel proaching 100 percent (with at most 5 percent via- distances have been observed, but these have been bility of the few remaining ova). The contents of the 108 SANITATION TECHNOLOGY OPTIONS third tank are reported to be relatively odorless, light increase in vault volumes. The three-stage septic tank brown to yellow in color, and with only finely divided design shown in figure 14-2, which provides for in- suspended solids. creased retention and destruction and for introduc- During the forty- to sixty-day retention time in the tion of sullage to the third chamber., is a modification septic tank a high degree of excreted pathogen re- of the proven Chinese design. moval occurs; nonetheless, the final product prob- ably will contain pathogenic bacteria, viruses, and helminths. There is no doubt that the agricultural Advantages and disadvantages reuse of excreta treated in the three-stage septic tank The main advantage of septic tank systems is their is superior to the direct use of untreated excreta. It flexibility and adaptability to a wide variety of in- is, however, questionable whether in many parts of dividual household waste disposal requirements. the world such treatment and reuse would be socially Their major disadvantages include large space re- acceptable or advisable from the viewpoint of health. quirements, a reasonably high degree of user atten- The three-stage septic tank system, however, is ap- tion, and high costs. plicable to rural areas where there is a tradition of using liquid excreta for crop or fishpond fertilization. In such areas its pathogen removal efficiency can be Note to Chapter 14 considerably increased by providing thirty days' re- tention in each compartment, with a corresponding 1. See Kalbermatten. Julius, and Gunnerson (1982). 15 Conventional Sewerage THIS CHAPTER represents a brief overview of con- sewer systems that carry both sewage and storm- ventional sewerage. It is neither an authoritative nor water. At present, however, it is customary to build comprehensive treatment, nor is it intended to pro- separate sewer systems rather than to provide large vide guidance to the designer of conventional sew- combined sewers, the capacity of which is only fully erage systems. Those interested and requiring fur- utilized during periods of intense rain and which are ther information will find a wealth of publications likely to have dry weather flows with insufficient ve- readily available. The discussion here is intended locities to transport excreta. merely to point out some of the reasons why con- Sanitary sewer pipes are normally made of con- ventional sewerage is only one of the sanitation al- crete, asbestos cement, vitrified clay, or polyvinyl ternatives that should be considered in communities chloride (Pvc). They are generally designed for grav- of developing countries. ity transport of maximum (peak) flows of two and one-half to four times the mean daily flow at veloc- ities of 0.6 to 1.0 meters per second at mean daily Excreta Disposal flow. This velocity is required to resuspend and trans- port solid material that may have settled during pe- The conventional cistern-flush toilet is basically a riods of lower flows and lower velocities. In areas water-seal squatting plate or pedestal unit in which where bulky anal cleansing materials are used or excreta are deposited and then flushed away by 10 where sand is used for scouring kitchen utensils, ve- to 20 liters of clean, potable water that have been locities of not less than 1 meter per second are nec- stored in an adjacent cistern; the cistern is connected essary to prevent blockage of sewers. Achieving to the household water supply and is provided with scouring velocities in flat areas may require relatively a float valve so that it automatically refills to the steep pipe grades and expensive pumping stations to correct volume in readiness for the next flush. The lift sewage to higher elevations. excreta and flushwater are discharged, together with Conventional sanitary sewer systems have many all the other household wastewater (sullage). into an merits: they provide the greatest user convenience underground network of sewers for transport to a of all the waste disposal systems, for they permit the sewage treatment works or marine discharge station. discharge of large amounts of water: they do not Alternatively, in low-density areas discharge may be pose any risks to health when functioning properly; into a septic tank (see chapter 14). their maintenance is assumed by the municipality, and they generally operate with few service inter- ruptions or emergencies. Yet sewer systems also have disadvantages: they are, first of all, very expensive Sewage Collection to construct; they require skilled contractors for the construction, a municipal organization for operation Conventional sewerage is designed to transport a and maintenance, and a substantial amount of flush- mixture of excreta and water from the house to the ing water, which adds to the operating costs. They central treatment plant through a network of pipes. are not suitable if water supply is limited because This is done in a separate sanitary sewer system that they are prone to malfunction (blockage) where total transports domestic, commercial, and institutional water use is less than about 75 liters per capita daily, wastewater, although some cities have combined and in hot climates concrete and asbestos-cement 109 110 SANITATION TECHNOLOGY OPTIONS pipes are subject to rapid deterioration from corro- * Extremely poor pathogen removal efficiencies sion due to hydrogen sulfide formed in the sewer. (see below) Given the high convenience level of sanitary sew- * Very high capital and operating costs (usually erage, this system of excreta disposal has been the with the need to import all or much of the me- one of choice almost to the exclusion of other alter- chanical equipment, with a correspondingly natives. Unfortunately. the usually high costs asso- high foreign exchange cost) ciated with the construction of such systems have * A requirement for a very high level of operation virtually prevented large segments of society from and maintenance skills. obtaining benefits from this solution. Thus, a search has been underway to find ways and means to reduce There are many conventional sewage treatment the cost of sanitary sewerage and to make the system works in developing countries, but few of them op- affordable for a much greater number of people. erate satisfactorily. Most plants are not maintained Attempts have been made to find new pipe materials, properly, a problem that is often exacerbated by long such as Pvc, which have reduced the cost somewhat. delays in importing spare parts and disinfectants So far, however, no substitute has been found for needed to destroy pathogens not removed by the the expensive large pipes that are needed for main treatment process. and interceptor sewers. Other advances made are Effluents from conventional treatment works (pri- the introduction of plastic pipes for house plumbing mary sedimentation, trickling filters, and secondary and connections from the house to the street main. sedimentation) contain significant concentrations of Nevertheless, overall costs have remained high and viruses, bacteria, protozoa, and helminth ova and conventional sewerage, therefore, still is beyond the are thus unsuitable for unrestricted direct reuse in financial capacity of vast numbers of poor people in agriculture. Effluents may often be unsuitable for developing countries. discharge to freshwater bodies where those water bodies are used for domestic water supplies by down- Conventional sewage treatment stream populations. The minimum hydraulic reten- tion time in the total plant may be only five hours, The purpose of sewage treatment is the elimination which largely explains why the effluent will be of from wastes, prior to discharge to receiving waters poor microbiological quality even if it meets quality and land, of pathogens, chemicals, organics, and standards of no more than 20 milligrams per liter of other material that could have detrimental effects on 5-day biochemical oxygen demand (BOD,) and no human health and the environment. more than 30 milligrams per liter of suspended solids. A variety of unit processes are combined to form Effluent quality may be improved by using double a conventional sewage treatment works. These typ- filtration or recirculation, but the final effluent will ically consist of: still be highly pathogenic. The only way to produce an effluent of reasonably good quality from a health * Preliminary treatment (screening or comminu- viewpoint is by certain tertiary treatment processes. tion, flotation, and grit removal) Activated sludge effluent will be of marginally bet- * Primary sedimentation ter quality than that from trickling filters but will still * Biological treatment by biofilters (trickling fil- be heavily contaminated, regardless of its chemical ters) or activated sludge process quality. The minimum hydraulic retention time in * Secondary sedimentation the plant may be less than twelve hours, and the final * Treatment of the sludge from the sedimentation effluent will contain significant numbers of all path- tank (commonly anaerobic digestion and drying ogens found in the raw sewage. Tertiary treatment beds). is needed before reuse and may also be necessary before discharge into a river that downstream pop- Tertiary treatment (microstraining, sand filters, ulations use. chemical precipitation, and the like) is rarely incor- The quality of the sludge depends on what treat- porated in developing countries. Alternative pro- ment it receives. Fresh sludges from primary and cesses for sludge dewatering (such as pressure filtra- secondary sedimentation tanks will contain patho- tion and centrifuging) are also rarely used in developing gens of all kinds. Batch digestion at 50°C for thirteen countries. days will kill all pathogens, at 32°C for twenty-eight Conventional sewage treatment has three major days will remove protozoa and enteroviruses, and disadvantages in developing countries: for 120 days unheated will remove all pathogens ex- CONVENTIONAL SEWERAGE 1II cept helminths. Sludge drying on open beds for at "rotors." placed across the ditch. The effluent from least three months will be very effective against all the oxidation ditch sedimentation tank has a path- pathogens except helminth ova. Other unheated de- ogen content similar to that produced by the con- watering techniques will have little effect on the path- ventional activated sludge process, although, as a ogenic properties of sludge. result of the increased retention time, slightly lower Continuous digestion at 40 to 50°C may produce survivals are achieved. a sludge containing helminth ova, or containing en- teric bacteria and ova if sludge drying beds are not Tertiarv treatment used. All other alternatives will produce a sludge containing helminth ova, and some (such as digestion Tertiary treatment methods are increasingly used at 35 to 40°C followed by vacuum filtration) will pro- in Europe and North America to improve the quality duce a sludge containing enteric viruses and bacteria of effluent produced by conventional secondary as well. Thus, no sludge digestion and drying process treatment works. These processes were not primarily in common use offers any safeguard against patho- designed for pathogen removal, but some of them gens. do have good characteristics of pathogen removal. The importance of temperature and time for path- ogen destruction is shown in figure 15-1. From the RAPID SAND FILTRATION. This is perhaps the most viewpoint of health, the object of a sewage treatment common tertiary treatment method found in larger works should be to retain all solids and liquids for treatment works. High loading rates (200 cubic me- the maximum time, to heat them to the maximum ters per square meter daily) and frequent backwash- temperature feasible, or both. Batch processes are ing (one to two days) prevent the buildup of biolog- far more reliable in achieving this than continuous ical activity in the filter. Some viruses will be processes, particularlv when the sludge is to be absorbed and some bacteria retained; cysts and ova reused in agriculture. Batch digestion of municipal may be retained because of their size. In short, the sludges, however, will require both seeding and from pathogen content of the effluent may be improved, thirty to ninety days' start-up time to reach effective but not substantially, and probably not enough to operating temperatures. justify the investment on health grounds. Numerous modifications of the activated sludge process exist. Two are mentioned below because SLOW SAND FILTRATION. Slow sand filters may be their simplicity makes them especially attractive for used on smaller treatment works where their low application in developing countries. Aerated lagoons loading rates (2 to 4 cubic meters per square meter resemble small waste stabilization ponds (see chapter daily) cause them to occupy a large land area. Sub- 21) with floating mechanical aerators, but they are stantial biological activity builds up in the upper lay- more correctly considered as a simple modification ers of the filter, and pathogen removal may be very of the activated sludge process. high. Removals of viruses and bacteria of four orders of magnitude may be expected from a well-run unit, AERATED LAGOONS. These will, as a result of with viral removal a little higher than bacterial re- their longer retention times, achieve better pathogen moval. Complete retention of cysts and ova has been removal than that obtained in the conventional ac- recorded. Although slow sand filters are therefore tivated sludge process. In the settling pond there will highly effective in removing pathogens from a con- be complete removal of excreted protozoa and hel- ventional effluent, their land requirement makes minth ova, although hookworm larvae may appear them suitable only for small treatment works. in the effluent. which will also contain bacterial path- ogens and viruses. Schistosome larvae will be elim- LAND APPLICATION. This is another appropriate inated if the snail host is prevented from infesting tertiarv treatment method for small communities. the lagoon. The effluent can be treated in one or Effluent is distributed over grassland. ideally at a more maturation ponds to achieve any desired level slope of about 1 in 60, and is collected in channels of pathogen survival. at the bottom of the plot. Loadings are in the range 0.05 to 0.3 cubic meter per square meter daily. There OXIDATION DITCHES. These are another modifi- is little or no information about this process applied cation of the activated sludge process: screened sew- in the tropics or in developing countries. If well man- age is aerated in and circulated around a continuous aged, it should provide a high level of pathogen re- oval ditch by one or more special aerators, called moval similar to slow sand filters. If poorly managed, 112 SANITATION TECHNOLOGY OPTIONS Figure 15-1. Influence of Time and Temperature on Selected Pathogens in Night Soil and Sludge 70 - 70 Enteric viruses 65 _ - 65 ,~11 Shigella 60 Safety zone -60 55 \55 50 50 Vibrio cholerae \ N 4 E 45 4 E~~~~~~~ 40 \ Ascariis 40 Salmonella 35 _ 5. 35 30 _: 30 25 -'Entamoeba \ 25 ,h is to lytica 20 1 1 20 I. I 30. 10 to O 30000 I day I week 1 month I year Time (hours) Note: The lines represent conservative upper boundaries for pathogen death-that is. estimates of the time-temperature combinations required for pathogen inactivation. A treatment process with time-temperature effects fatling within the "safety zone" should be lethal to all excreted pathogens (with the possible exception of hepatitis A virus-not included in the enteric viruses in the figure-at short retention times). Indicated time-temperature requirements are at least: I hour at 2620C, I day at 250'C, and I week at -'460C. Source: Richard G. Feachem and others, Sanitation and Disease: Health Aspects of Excreta and Wastewater Management, World Bank Studies in Water Supply and Sanitation, no. 3 (Baltimore: Johns Hopkins University Press, forthcoming). CONVENTIONAL SEWERAGE 113 it will probably lead to the creation of a foul and coliform concentrations of less than 100 per 100 unsanitary bog. millimeters * Because viruses have been found to be more MATURATION LAGOONS. Conventional effluents resistant to chlorination than bacteria, doses of can be upgraded in maturation lagoons. The prin- 30 milligrams per liter and above have been rec- ciples involved are exactly as described for waste ommended; even at these doses, complete viral stabilization pond systems. If two or more matura- removal may not be achieved tion ponds are used, with five to ten days' retention * It is most unlikely that chlorination of effluents in each, total removal of cysts and ova will result. will be effective in eliminating protozoan cysts Very high levels of viral and bacterial removal are because these are more resistant than both bac- also achieved, and by adding sufficient ponds a path- teria and viruses ogen-free effluent may be produced. * Most helminth ova will be totally unharmed by effluent chlorination. EFFLUENT CHLORINATION. The chlorination of sewage effluents is practiced in only a few countries Thus, effluent chlorination-which is not only ex- (notably the United States, Canada, and Israel). Its I purpose is to reduce the high pathogen content of pensive but also exceedingly difficult to operate uni- formly and efficiently-may not be particularly ef- conventional effluents, but it has a number of serious fetvinrmigpahesfomcvninl limitations. fectve removg pathogens from conventional effluents. In addition, it may have deleterious en- * Chlorine has to be applied in heavy doses (10 vironmental consequences, including creation of car- to 30 milligrams per liter) to achieve effluent cinogenic chlorinated hydrocarbons. 16 Small-bore Sewers IN THIS CHAPTER. conventional sewerage is dis- water has increased to the extent that on-site disposal cussed and reference is made to the various sources is no longer possible. In such situations small-bore of information on sewer design. Small-bore sewers sewers can provide relief at a lower cost than con- are described to point out the possibility of using ventional sewers while providing the same level of them as an alternative in the sanitation sequence to service. They can represent, in such a case, the last conventional sewerage and to describe the aspects stage of a planned sanitation sequence. Small-bore of their design and operation that are different from sewers should also be considered in the initial plan- those of conventional sewerage. ning of a sanitation system in areas where anticipated water consumption or soil conditions make on-site Technical Appropriateness disposal of sullage water infeasible. The small-bore sewer system, which carries settled Design Criteria effluent only, is one promising possibilitv in the search for less expensive sewerage. The reduction in Design and maintenance parameters based on the cost is possible because such a system requires fewer few small-bore systems that exist today are sum- manholes (access to the underground pipes is pri- marized here for the guidance of sanitation planners. ma'lv to remove blockages in systems that carry These guidelines are neither comprehensive nor final solids): pipe slopes can be flatter because scouring and will be modified and updated as more experience velocities to resuspend settled solids (or keep them is gained. Design of a two-stage septic tank suitable from settling) are not necessary in a system that does for small-bore systems is described in chapter 12. not carry these solids: and pipes are laid at shallower Miniimum velocitv and pipe size depths because grades are flatter and because ef- fluent is discharged from settling tanks close to A minimum velocity of 0.3 meter per second at ground surface. peak daily flow is recommended. Some flushing of For proper functioning. small-bore sewer systems mains may be required until sufficient connections require facilities to settle solids. usually at each are made. household or for groups of households. Settling tanks A minimum diameter of 75 millimeters is recom- mav be septic tanks. soakage pits, vaults, or similar mended for connecting mains and septic tanks, aqua- units. Where sullage water is discharged separately privies, or other settling tanks. Minimum main di- to sewers, a sand and grease trap should be provided. ameter should be 100 millimeters. Where sand is used for cleaning kitchen utensils, a n Minimum grades for laying pipe sand trap should be provided. even if sullage water is discharged to a common settling tank, because a The recommended minimum grades, by diameter sand trap can be more easily cleaned than a tank of pipe, are: containing a mixture of sludge and sand. Grade Small-bore sewers are particularly suitable where 75 and 100 millimeters I In 150 on-site disposal has been practiced but cannot be i50 millimeters I in 250) continued without modification because infiltration 200 millimeters I in 30)0. beds are no longer adequate. clogged soakage pits The above grades should not be used as a standard cannot be rehabilitated, or the amount of sullage but as the minimum allowable, and greater slopes 114 SMALL-BORE SEWERS 115 Table 16-1. Slopes and Capacities of Circular Pipes Flowing Full Diameter of pipe (millimeters) Item 50 100 150 200 250 300 Velocity N = 0.3 meter per second Slope (meters per 100 meters) 0.373 0.148 0.086 0.(59 0.044 0.034 Flow (liters per second) 0.589 2.356 5.301 9.424 14.726 21.205 Velocity N = 0.6 meter per second Slope (meters per 100 meters) 1.493 0.592 0.345 0.235 0.174 0.136 Flow (liters per second) 1.178 4.72 1(0.602 18.849 29.452 42.411 Velocitv = I meter per second Slope (meters per 100 meters) 4.148 1.646 0.958 0.653 0.485 0.380 Flow (liters per second) 1.963 7.854 17.67 31.41 49.08 70.68 Velocitv = 1.5 meters per second S!-Vpe (meters per 100 meters) 9.333 3.7(3 2.157 1.470 1.092 0.856 Flowv (liters per second) 2.945 11.78 26.50 47.12 73.63 106.03 Note: Calculations are based on Manning equation with roughness coefficient of 0.011. should be used wherever possible. In general. grades initially and install additional manholes as necessary should be maintained fairly accuratelv. Nevertheless, if a main has to be excavated to remove a blockage. and in contrast to conventional sewers, slight devia- tions are permissible because there are no solids that Minimum cover on pipes would settle out in a pipe partiallv filled with standing effluent. The minimum cover on all pipes in roadways or areas subject to wheel loads should be 1 meter above Roughness coefficient the collar of the pipes unless special arrangements are made to protect the pipe from damage. In other The adoption of an n-factor of 0.013 for vitrified situations a general minimum of 0.5 meter. subject clay pipe and 0.011 for PVc pipe is recommended. to the nature of the terrain and the possibility of Table 16-1 lists capacities of sewers flowing full at mechanical damage, is recommended. various slopes; figures are based on the Manning equation using a roughness factor of 0.011. The table Venting is provided for easy reference for the most suitable and easily handled PVc pipe. For other pipe mate- Various methods of venting are applied to sew- rials, consult appropriate and easily obtainable hy- erage systems, but the most general method in small draulic charts and tables. installations is to use the head vents on the house to provide venting conditions for the reticulation sew- ers. In the case of a septic tank or aquaprivy system, ventilation is provided between the vent at the outlet Manholes or flushing points should be provided of the septic tank. through the air space in the tank. at the heads of all drains, at major branch connec- and through the drains to the vent on the house. If tions, and at pipe size changes. Because small-bore a PF privy or toilet is connected directly to the small- sewers are usually laid at shallow depth, it is probably bore sewer svstem, a vent should be provided on the least expensive to construct even fewer manholes sewer side of the water trap. 17 Bucket Latrines THE TRADITIONAL bucket latrine (figure 17-1) con- local depression. Only rarely are the buckets and sists of a squatting plate and a metal bucket located handcarts washed after use; spillage of night soil in a small compartment immediately below the squat- is frequent and health hazards are alarmingly ob- ting plate. Excreta are deposited into the bucket, vious. The bucket lavatories are rarely disin- which is periodically emptied by a night-soil laborer fected. They are almost always unhygienic. offen- or "scavenger" into a larger collection bucket that sive and usually surrounded by insects, many of when full is carried to a night-soil collection depot; which help spread human diseases; sometimes a from there the night soil is usually taken by tanker degree of cleanliness is unintentionally achieved to either a trenching ground for burial or to a night- by keeping poultry which devour these insects. soil treatment works. (Canter and Englande 1970; cited in Mara 1976, Improved bucket systems provide satisfactory p. 137.) service in parts of Australia and Singapore. There full creosoted household buckets are replaced by It is common to see a scavenger moving with a clean ones, removed, covered, carried by truck to heavy load of night soil on his/her head in a bam- central stations, emptied, washed, creosoted as nec- boo basket or leaky drum, the contents trickling essaTy, and returned to service. Other bucket latrine over the carrier. (Clare and others 1961; cited in systems are widely used in Africa, the Indian sub- Mara 1976, p. 138.) continent, and the Far East; in these locations buck- ets are generallv onlv emptied. This traditional sys- Although It iS possible to make several improve- ments to the traditional bucket latrine system (for tem is, however, an extremely poor form of sanitation, onlv slightlv better than no sanitation at all. The example, by providing facilities for washing and dis- African infecting the buckets, and covering collection buck- following two descriptions (the first about Ana the second about Indi illustrate the usual ets with tightly fitting lids to reduce spillage), it is unhygienic nature of the system: still in practice difficult, if not impossible, to ensure that the system is operated satisfactorily, especially The collection and disposal of night soil from so that spillage of night soil is avoided. The bucket bucket lavatories is usually nauseating. Although latrine system, even if it is an improved bucket latrine in some cases the buckets are manually carried system, is not a form of sanitation that can be rec- long distances to the disposal ground, the usual ommended for new communities. Existing bucket practice is to empty the buckets into handcarts, latrines should be improved as a short-term measure each comprising an empty drum supported hori- only; in the long term they should be replaced by zontally across two wheels; when full, the hand- some other sanitation facility. Often the most ap- carts are dragged away and [the contents] either propriate replacement facility, especially in high- buried or emptied into a sewer, septic tank or density areas, is the vault toilet (see chapter 18). 116 BUCKET LATRINES 117 Figure 17-1. Bucket Latrine and Cartage (millimeters) Squatting plate Fypofdo Soakage pit forr bucket washwero Bucket oatrine N - collection c collection ucket vault ~ ~ ~ ~ b iperad uce avedsurfaceanddre a au _ . ~25 mm _ _K t . v v t;22 ~maximum e*o !_C,...+ ..M 'ioakage pit for bucket washwaterATl Bucket latrine N'ight-soil collection bv dipper and bucket (here a vault rather than a bucket is located in house) Night-soil bucket and scraper Cartage wheelbarrow for three or six buckets Note: Fly-proof doors and paved surfaces and drains are commonly missing in most existing bucket latrines. Sources: Top left, adapted from Wagner and Lanoix (1958): top right, from a photograph courtesy of Michael G. McGarrv'; bottom. Department of Social Welfare, Ahmadabad, India. 18 Vault and Cartage Systems IN VALULT TOILETS, which are extensivelv used in the struction and emptying costs are known, it is there- Far East, the excreta are discharged into a sealed fore possible to minimize the total cost by optimizing vault that is emptied at regular intervals (figure 18- the combination of vault size and emptying fre- 1). It is preferable that the vault be emptied by vac- quencv. The vault need not be very large. For ex- uum tanker ("vacuum truck" refers to a tank truck ample, for a family of six using 10 liters per capita equipped with a suction pump), although in areas daily with a PF system that is emptied every two where access is difficult it may be necessary to use weeks, and with K taken as 0.5. the required vault alternative methods (see below). volume is only 1.68 cubic meters. and 0.84 cubic meter of night soil must be removed each time the vault is emptied. Design Criteria The tankers transport the vault contents to a trenching field, a sewer. a night-soil treatment works eitherlwith'the vault t imtmediaty beinstalowd te a(see chapter 21), or a marine discharge point. tf small cetsquatting tankers or other collection vehicles (see below) are plate or with a completely offset vault (figure 18-1). used, the night soil can be transferred to larger ve- In the latter case the vault may be shared by adjacent hides for conveyance to the treatment works or dis- houses. with some savings in construction costs. charge point. The vault volume may be calculated from the fol- lowing equation: Collection vehicles V= NQDIK. To minimize collection costs, the night-soil collec- where V = vault working volume in liters tion vehicles generally should be as large as possible. N = average household size Vacuum tankers usuallv have capacities of 1,500 to Q = excreta and PF water flow in liters per 5,000 liters, and the length of vacuum tubing that capita dailyv D t days y between successive emptying of the can be attached to them can be as much as 100 me- vault ters. In areas where access is difficult even this length K = vault volume underutilization factor. is insufficient, and smaller collection vehicles must be used. These may be hand- or animal-drawn carts From 0.8 to 1.8 liters per capita daily of night soil with capacities of only a few hundred liters equipped are collected from vault latrines. The maximum with manually operated diaphragm pumps, or small probable amount of excreta plus PF water for vault mechanically or electrically operated vehicles (even latrines may be estimated as 10 liters per capita daily. three-wheeled vehicles) fitted with mechanically op- The vault volume underutilization factor. K, is in- erated pumps. Since vault toilet systems are so much troduced since the vault will normally be emptied cheaper than sewerage (see Kalbermatten, Julius, before it is completely full. In areas where mainte- and Gunnerson 1981), it is extremely important that nance of tanker vehicles is excellent. K may be taken design engineers should consider all possible collec- to be 0.85: in other areas K may need to be as low tion methods, with some site-specific improvisation as 0.5. as required. Access may be extremely difficult, but It is evident from the above equation that V and only very rarely will it be impossible for any sort of D are proportional to each other. Once vault con- vehicle to be used to empty the vaults. For those 118 VAULT AND CARTAGE SYSTEMS 119 Figure 18-1. Alternative Designs for Vault Toilets (millimeters) 75-mm vent pipe Vacuum tanker Toilet-_ ~Manhole t House Vault belowv squatting plate Hose to tanker House /H Offset vault households where vehicle access is impossible, man- ual emptying of the vault by the dipper and bucket Matriala l e method may have to he used, although this is only The vault may be constructed from concrete. a marginal improvement over bucket latrines, since brick, or concrete blockwork suitablv rendered with some night-soil spillage is inevitable. A pipe con- a stiff mortar to make it watertight; alternatively, for nection to an accessible communal vault would be small vaults, prefabricated plastic tanks may be used a preferable solution in such cases. if these are locally made and economically compet- 120 SANITATION TECHNOLOGY OPTIONS itive. Note that loss of water from a vault latrine adequate tanker washwater should be available at (figure 18-1) may cause pumping problems. Vault the treatment site or at the treatment works or ma- contents that are more than 12 percent solids may rine disposal point. have to be scooped or ladled. Another approach is to loosen and dilute the contents with a small amount of water (or previously diluted night soil) carried on Factors Affecting Suitabilitv the truck and jetted into the vault. The number of tankers (or other collection vehicles) ma' be esti- The vault toilet, emptied by mechanically. elec- mated from the following equation: trically, or manually operated tankers, is a flexible form of sanitation in which capacitv can be closelv N, = 7(N^,/nD), matched to changes in urban land use. where N, = number of tankers required Vaults are also suitable for medium-rise buildings Nv = number of vaults to qe serviced because excreta can be readily flushed down a ver- N, =numer f vult tobe serviced v = average number of vaults that 1 tanker tical pipe into a communal vault at or below ground can service daily level. n = average number of days that the tankers In most developing countries, foreign exchange is can be expected to be operational each required to pay for the collection tankers or pumps. week All other materials are likely to be locally available. D = the number of days between successive emptyings of each vault. HTealth aspects The average number of vaults that a tanker can service each day depends on the ratio of tanker size From the users' point of view, there is little dif- to vault size, the average time taken to empty one ference between vault and vacuum-tanker systems vault, the average time to empty and clean the tanker and PF toilets connected to septic tanks or sewers: at the disposal point, and the collection and round- the only area of increased risk is the very small trip travel times. The average number of days that amount of night-soil spillage that may occur when each tanker is operational each week depends on the vault is emptied. how many days per week vaults are emptied (usually five or six) and how many days per week on average Cost are required for tanker maintenance (at least one, especially if adequate stocks of spare parts are not Since the vault is usually located inside or imme- maintained locally); thus. in practice, n mav be as diately adjacent to the house, superstructure costs low as 3 to 4 or as high as 5. If transfer stations are may be minimal The vault itself is relatively small. used, fewer collection tankers will be required. The although skilled labor usually is required to ensure number of transfer vehicles depends on the ratio of that it is properly sealed. The total cost of a vault their size to that of the primary collection vehicles with PF squatting plate. vent pipe, and superstructure and the numnber of round trips they can make each is in the range of $75 to $200. depending mostly on day to the discharge station. superstructure costs. Labor requirements for vehicle operation are one The collection and treatment costs associated with driver and one laborer per tanker. In addition vault toilets vary widely depending on the type of tanker maintenance mechanics are required. collection vehicle used and the type of treatment selected. Because of these factors, it is not possible to give a meaningful range of cost estimates. Oper- Complementary investments ating and maintenance costs of existing systems are and water requirements given in Kalbermatten, Julius, and Gunnerson (1982). Facilities for the treatment and disposal of the vault contents and for sullage disposal are required Potential for upgrading and resource recovery (see chapters 20 and 21). In addition, adequate fa- Vault toilets may be converted to sewered PF toi- cilities for tanker (or other collection vehicle) main- lets (see chapter 12) if at some stage in the future it tenance must be provided. is desired to improve facilities for sullage disposal or Water is required (approximately 3 to 6 liters per if sewer lines are laid in the vicinity. capita daily) for vaults with PF toilets. In addition, Vault toilets have high potential for resource re- VAULT AND CARTAGE SYSTEMS 121 covery: the night soil may be composted (often with * Possible location within the house domestic refuse), used for fishpond fertilization, or * High degree of planning flexibility for biogas production (see chapter 22). * Suitability for high-density areas * High potential for resource recovery * Minimal space requirements. Advantages and disadvantages Their main disadvantages are that separate facil- ities for sullage disposal are required, foreign ex- The principal advantages of vault toilets are: change is required for the collection vehicles,.and a * Low initial costs, with system capacity closely high degree of municipal involvement is required to matched to demand (trucks can easily be added ensure equitable service and proper vehicle main- as housing density increases) tenance. Alternatively, it may be possible to contract * Moderate labor requirements, with consequent servicing of the vaults to private firms that have a employment generation profit incentive to operate the system satisfactorily, * Low risks to health especially if the rights to (and profits from) resource * Minimal water requirements recovery are given to the same firm. 19 Communal Sanitation Facilities COMMUNAL SANITATION FACILITIES provide a min- its own cubicle and keep it clean, but that mainte- imum service level ranging from sanitation only to nance of the communal parts (for example, the pas- a combination of latrine. shower, and laundry units sageways and particularly the effluent disposal sys- such as that illustrated in figure 19-1. tem) can cause organizational problems. This system is undoubtedly superior to the truly public system, but it is also more expensive, since a greater number Effluent Disposal (depending on the average household size) of toilet compartments is needed. The advantage to the mu- Low-cost sewerage systems, soakage pits for PF nicipality is that it is relativelv easy to levv rental fees toilets, and sullage water disposal to storm drains and collect payment from each household using the have been used successfully. If the toilets are of the facility. cistern-flush type, a septic tank should be provided A third approach to the design of communal fa- so that the sewers can be of small diameter and laid cilities is to provide a sanitation block of the first at flat gradients. The septic tank should follow the type but reserved for the exclusive use of a large design described for sewered PF toilets in chapter 12. kinship group. This has been successful in the densely If the toilets are aquaprivies, the equivalent of a populated old city of Ibadan, Nigeria. Individual septic tank is already included, and provision needs households that belong to a patrilineal kinship group to be made for only a tank to settle sullage. If the or extended family of between 100 and 1,000 mem- terrain is such that velocities of 1 meter per second bers are located on the same piece of land, which is can be obtained in the sewer without the need for held in communal ownership by the kinship group. excessive excavation or pumping, the sewerage sys- Each kinship group is (or is planned to be) provided tem can be of the conventional kind, and the septic with a "comfort station," essentially a communal tank would no longer be necessary. In areas where sanitation block with toilets, showers, and laundry communal sanitation blocks can be installed near a facilities. Part of the construction cost is borne by trunk sewer serving other parts of the town, they the extended family and part by the government: the should of course be connected to it. family is responsible for maintenance and also for paying the water and electricity charges. Clearly, this approach to the provision of communal sanitation Design Criteria facilities can only work under suitable social condi- tions. The success of the Ibadan comfort stations probably owes more to their social setting than to of communal sanitation blocks. The first is to have their technical design. a truly public system in which a user can enter any toilet compartment not in use at the time. The second approach is to provide within the communal block N cubicles for the exclusive use of one household. This second system. essentially a compromise between In the truly public communal sanitation block, the public and private facilities, has been tried with con- best available evidence suggests that one toilet com- siderable success in some parts of India; experience partment can serve twenty-five to fifty people. Al- has shown that each household will zealously guard though it seems prudent to take a design figure of 122 COMMUNAL SANITATION FACILITIES 123 Figure 19-1. Schematic of a Communal Sanitation Facility Sewer Wall urinal Night-soil (night use) | deposit vault r~~~~~~~~~r- r - X tH |~~- C Rof I 11111ants I I Wash basins rosWash basins l E | Srtngtable Sorting table l l I Laundry' tubs Laundry tubsI twenty-five users per compartment, it must be of urinals and compartments in the men's block stressed that there are hardly any good field data should be the same as the number of compartments available to support such a figure. For example, the in the women's. OXFAM disaster sanitation unit in the "bustee" areas of urban Bangladesh, which is designed for a pop- Location ulation of 500 and is provided with twenty squatting° plates, is able to serve a population of 1,000 to 1,500 In high-density areas (over 1.000 persons per hect- (that is. fifty to seventy-five users per squatting plate are), the number of people that can be served by or two to three times the design figure). How well one communal sanitation block (usually 20)0 to 500), it serves that number of people-in the sense of the rather than the distance people can be expected to time spent in queuing, especially at "peak'' periods- walk to the block will usually determine the required has not been reported. number and location of communal facilities. For ex- The toilet compartments should be arranged in ample, if the population density is such that only one separate blocks for men and women. Urinals should communal block is required per hectare. then the be provided in the men's block, and the total number maximum distance that people would be required to 124 SANITATION TECHNOLOGY OPTIONS walk is around 100 meters, which is a 1.2-minute mitment by individual users to keep it clean and op- walk at a speed of 5 kilometers per hour. erating properly. Once a toilet compartment is fouled, the next user may have no choice but to foul it further. As a result, many communal toilet blocks are in a very unhygienic state. To avoid this it is The ideal toilet for installation in a communal san- essential to provide one or more well-paid attendants itation facility is a PF or low-volume cistern-flush toi- to keep the facilities in good operational order; light- let. Water use may amount to 15 to 20 liters per ing and a water supply must also be provided. It is capita daily. Other toilets have been used: for ex- also essential that the employers of the attendants ample. aquaprivies in the Ibadan comfort stations, (often the municipality) should regularly inspect the where communal facilities serving individual house- facilities to make sure that they are being properly hold compartments or large kinship groups have maintained. been successful. There are four technical disadvantages of com- munal sanitation facilities. First, there is the difficult question of privacy. A community's requirements for Shower and laundry facilities privacy must be clearly understood and respected. If shower and cohCultural attitudes toward defecation varv, but gen- If shower and clothes-washing facilities are not erlyiisegddasapvt,pronlc.Th, available in individual households, these should be erally It IS regarded as a private personal act Thus provided at the communal sanitation blocks; the at the least, each toilet within the communal block provdedat te cmmual snittio bloks;the should he designed as a separate compartment and water requirement for showering is 15 to 25 liters per capita daily. Additionally, hand basins should be provided with a door that can be bolted; this may provided at the rate of one for ten people; water use appear obvious, but there are many public toilet provide at th rat of on blocks that merely contain a row of holes with no may be estimated as 5 to 15 liters per capita daily. nte Water use for both showers and hand basins may be mternal partitioning whatsoever. In some societies. considerably reduced by the provision of water-sav- however, privacy is not so highly regarded. It is clear ing plumbing fixtures In warmclimatesitisusual that questions of privacy must be discussed with the ing plumbing fixtures. In warm climates it is usually community by the program's behavioral scientist (see not necessary to provide hot water, since the water chapte 3 c the the pro blemtof dee storage tank will normally contain water warm chapter 3). Second, there iS the problem of defeca- storh gr tankowil nal c a tr. tion at night and during illness and wet or cold enough fsor personaleswashing. to provide laundfaci weather. If the communal block is not lit, it mav not It may also be necessary to provide laundry facil- busdanih. In an.aeissreyuraoal ities. The exact style of these facilities should con- be used at night. In any case it is surely unreasonable form to local preference. Approximatelv one wash- to expect even fit adults-let alone the young, the ing tub should be provided for fifty people old, or the infirm-to walk 100 meters or more in Clotheslines may be required. the middle of the night or in torrential rain, often In communal facilities with comprartments re- along a dark or muddy street or alleyway. There served for the exclusive use of one household. each must be some general provision (including guidance compartment may contain a shower and hand basin to the comrnunity) for the disposal of what accu- comadtment may cont. ahower andchand mulates during the night or inclement weather. provide t te toilet. the is necessar to If it is accepted that the provision of individual providenalprivate laundry .tu as well, rat tan household facilities (of whatever type) is the ultimate after discussion with the communitv. objective of sanitation program planning, then the third disadvantage of communal facilities is that they cannot be upgraded. This means that they should be designed with eventual replacement by individual household iacilities in mind. In this connection it is The principal advantage of communal facilities is sensible to tie the provision of sanitation facilities to their low cost. Because they serve many people, they residential upgrading programs; this is especially ad- are substantially cheaper on a per capita basis than visable in the case of slum improvement schemes. individual household facilities. They have many dis- The fourth disadvantage of communal facilities is advantages, however, and the decision to install com- their space requirement. Depending upon the type munal facilities is one that should never be taken of excreta disposal and the service level provided. lightly. The basic problem is that the facility appears this space may vary from 5 to 10 percent of the total to belong to no one, so that there is very little com- area occupied by the community. 20 Disposal and Treatment of Sullage THE ADOPTION of on-site excreta disposal technol- mately 60 percent of the water consumption (ex- ogies such as improved pit latrines, composting toi- cluding garden watering). In other (less affluent) lets, and PF latrines with soakage pits or vaults (but urban communities in developing countries, the pre- excluding septic tanks) requires that separate pro- diction of sullage volumes is more difficult. Tentative vision be made for sullage disposal. Sullage is defined estimates, however, are: here as all domestic wastewater other than toilet wastes: the wastewater from showers and sinks, in- * In households with a hand-carried water supply cluding laundry and kitchen wastes as well as water (obtained from public standpipes or vendors) used for personal washing. It contains some excreted and pit latrines or composting toilets, sullage pathogens; per capita contributions of enteric indi- generation may be conservatively estimated as cator bacteria in sullage are generally 104 to 105 lower the water consumption; that is, normally around than those in sewage. Sullage also contains a variety 20 to 30 liters per capita daily less any amount of organic compounds, most of which are readily used for PF toilets. biodegradable (with the notable exception of "hard" * In households with an on-site, single-tap water detergents if these are present in locally manufac- supply and PF toilets or vaults, the sullage vol- tured washing powders). Approximately half of the ume can be taken as the water consumption total household production of waste organics (ex- (excluding that used for garden watering and cluding garbage) is associated with sullage-that is. the 3 to 6 liters per capita daily of flushwater); with some 20 to 30 grams of biochemical oxygen that is, normally about 50 to 100 liters per capita demand (BOD) per capita daily. This figure, how- daily. ever, depends on water consumption; a family with Local figures of water use should of course be used suitable facilities and abundant water for personal wherever possible. They are seldom difficult to ob- dish and clothes washing will obviously generate tain even bv actual measurement in the field. In more sullage BOD than one that obtains only small ' . . v . c contrast, It IS very time consuming to obtain good quantities of water for drinking and cooking purposes estimates of the daily per capita BOD contribution in from a public standpipe and uses stream water for sullage. Reliable data on this are not available for washing clothes or sand to clean cooking utensils. urban areas in developing countries, but it is prob- ably reasonable to estimate that the BOD, of sullage Sullage Volume and BOD is of the order of 100 to 350 milligrams per liter. In developing countries sullage may have a waste- The volume of sullage generated is clearly related water with as much BOD5 as raw sewage in North to water consumption. In many industrialized coun- America. Indeed, there are many canals and streams tries sullage accounts for 50 to 70 percent of total in urban areas of developing countries that are domestic water use, the balance being used to flush grossly polluted (BOD5 of up to 250 milligrams per cistern-flush toilets. A similar situation exists in the liter) by sullage and garbage. Indiscriminate sullage more affluent communities of developing countries. disposal may not only damage the environment but In communities that have a water consumption of also may have serious public health consequences. 200 to 300 liters per capita daily and cistern-flush There are four basic kinds of sullage disposal sys- toilets, the volume of sullage generated is approxi- tems: 125 126 SANITATION TECHNOLOGY OPTIONS * Disposal by tipping of containers in the street. of garbage and are well designed, they will flow freely house yard, or garden and provide few sites for mosquitoes to breed. The * On-site disposal in soakaways presence or absence of sullage will therefore make * Disposal in open drains (commonly stormwater no difference. In areas of seasonal rainfall, however, drains) especially where the drains may become blocked with * Disposal in covered drains or sewers. garbage or trash during months of low rainfall, the Each system has different health risks, and these are addition of sullage will create year-round water and reviewed before design considerations are discussed. thus year-round mosquito breeding where previously only seasonal breeding may have occurred. Here it is not the quality of the sullage that is important, Health Aspects since ponded stormwater would also be sufficiently polluted to allow Culex pipiens to breed, but it is Tipping sullage on the ground in backyards or gar- rather the continuous production of sullage that may dens may create breeding sites for either anopheline have the effect of converting wet season breeding or culicine mosquitoes, including Culex pipiens, into year-round breeding in areas where the storm- which is a cosmopolitan nuisance, a potential vector water drains may pond. The change from wet-season of bancroftian filariasis in some areas of the world, breeding to year-round breeding may lead to an in- and a species reported to prefer polluted water. Tip- crease in the transmission, prevalence, and intensity ping may also create muddy and unsanitary condi- of filariasis, although there are no field data to con- tions that could help to promote the development of firm this hypothesis. helminth ova, which require a fairly moist environ- Sullage disposal in closed drains or sewers is ex- ment. In a clean dry yard, ova from children's feces pensive but causes no special health problems unless are unlikely to develop. A wet muddy yard, however, sullage is eventually discharged without treatment will conceal any feces deposited and will promote into a sluggish or intermittent stream where it may development of worm eggs and larvae. There is evi- promote Culex breeding. The disposal of sullage, dence that families whose yards are clean and dry along with excreta, into sanitary sewers also presents (because of hygienic practices, soil type, or both) no additional health risks, but this in itself is no jus- have lower intensities of Ascaris infection than do tification for the provision of conventional sanitary other families. Sullage containing pathogens from sewers. bathwater may infect children playing in the yard. In permeable soils or where evaporation is high, and where sullage production and housing densitv are low, tipping of sullage onto the ground is unlikely Design Criteria to give rise to a significant health haza-d. Where the soil is less permeable, evaporation is low, and land This section outlines design features for seepage slopes permit ponding, a separate system for sullage pits, storm drains, and sullage treatment facilities. disposal becomes necessary. Similarly, where either water use or housing density is high, an alternative method of sullage disposal becomes essential. Sullage disposal in properly designed and con- Seepage pDtS structed ground seepage pits causes only a low risk A suitable design for a seepage pit for use in of groundwater contamination. The risk of micro- permeable soils is shown in figure 14-3. The pit may biological and nitrate pollution of groundwater from be circular, square, rectangular, or even irregular in sullage is very much lower than it is from sewage, plan to suit the space available. The side walls may since sullage contains far fewer pathogens. It also be lined with open brickwork or unlined and filled contains much less nitrogen, which can pose a sep- with rock (50- to 100-millimeter grading) or broken arate problem in areas where infant formulas are bricks. The rate of infiltration of sullage is approx- used. imately three times higher than that of conventional Sullage disposal in open drains, such as stormwater septic tank effluent; that is. up to 90 liters per square drains, provides the most readily identifiable poten- meter of sidewall area daily. For the purposes of tial health risk-namely, promotion of mosquito design, a rate of 30 liters per square meter should breeding. In areas of year-round rainfall, these drains be used, unless a higher rate is known to be more will contain water continuously; if they are kept free appropriate. DISPOSAL AND TREATMENT OF SULLAGE 127 Stormwater drains Figure 20-1. Improved Stormwater Channels for Drainage of Sullage If stormwater drains are used for sullage disposal, they must be designed so that they can handle low sullage flows, as well as flood peaks, without nui- sance. Storm drains are normally designed with an approximately trapezoidal cross-section with a fairly wide base. This means that the depth and velocity of flow of the relatively small amounts of sullage (relative, that is, to the drain's stormwater capacity) will be low, and the risk of blockage and ponding high. If the storm drains are already in existence and lined, it is advisable (but somewhat costly) to modify the channel section by placing a small trapezoidal or semicircular channel along the invert where the sul- lage can flow with a higher velocity in the central section only. If the drains are not already lined, it would be advisable to pave the invert to provide a Existing channel section similar channel. If surface drainageis to be provided at the same time as the improvements in excreta and \ sullage disposal, it may be advisable to consider al- Proposed improvement ternative channel sections (see figure 20-1). Whatever channel section is adopted. it is neces- Existing channel section sary to maintain the drains routinely. This includes removal of blockages and perhaps flushing with sur- face water. The maintenance can be done by mu- nicipal workers, by contractors from the private sec- tor, or by community effort motivated and organized on a neighborhood basis. The material removed from the drains should be disposed of in a landfill. Sullage treatment As noted above, sullage may have a high BOD, and P large volumes of sullage may require treatment prior Proposed improvement to discharge into local streams or rivers, unless the reticulation or the flow of these watercourses is such porating a simple stormwater overflow weir at the that the sullage would cause little additional pollu- pond inlet structure. For a detailed discussion of tion.' If stormwater drains are used for sullage col- pond design criteria, see chapter 21. lection, these should discharge into a single facul- tative waste stabilization pond, which is normally the most convenient method of treatment wherever land Note to Chapter 20 is available. Maturation ponds are not necessary be- I See Kalbermatten. Julius. and Gunnerson (1982). chapter cause the concentration of excreted pathogens in sul- 2arison of a conveftional sewerage system with a vault lage is small. The pond should be protected from and vacuum truck system with sullage disposal to surface drains high stormwater flows in the wet season by incor- and channels. 21 Off-site Treatment THE DEGREE tO which excreta and sewage are systems can treat raw sewage, the effluent from sew- treated is largely influenced by what is to be done ered PF toilets, diluted night soil, or sullage. with the resulting solid and liquid products. Minimal Waste stabilization ponds are the most economical treatment is required for small flows discharged to method of sewage treatment wherever land is avail- the sea; maximal treatment is needed for effluents able at relatively low cost. Their principal advantages used for irrigation of food crops. in developing countries are that they remove ex- In general the treatment of human wastes in de- creted pathogens at a much lower cost than any other veloping countries has two principal objectives: the form of treatment and that they have minimum op- removal or destruction of excreted pathogens and erating and maintenance requirements. In fact, a the oxidation of organic matter. The first objective pond system can achieve the total removal from the is required to protect public health and the second effluent of all excreted pathogens. This is not nor- to prevent pollution in the watercourse receiving the mally done because the possible additional benefits effluent. In communities where the incidence and resulting from achieving zero survival, rather than prevalence of excreta-related infections are high and very low survival, commonly are less than the as- where the density of excreted pathogens in human sociated incremental costs. wastes is therefore also high, the first objective is the There are three types of ponds in common use: more important. It is usually achieved by providing * Anaerobic pretreatment ponds, which function a suitable combination of time and temperature in much as open septic tanks. They have retention the treatment works (see figure 15-1). It is fortuitous times of one to five days and depths of 2 to 4 that the commonly selected combinations of time and meters. Anaerobic ponds require periodic de- temperature for pathogen removal enable simulta- sludging and, if not properly designed and op- neous achievement of the second objective. erated, will have strong odors. In this chapter emphasis is placed on the effec- * Facultative ponds, in which the oxvgen neces- tiveness of simple, low-cost processes in achieving sary for biooxidation of the organic material is low rates of pathogen survival. A brief discussion of supplied principally by photosynthetic algae that conventional sewage treatment processes, which are grow in them naturally and with great profusion. not only more expensive but, without disinfection of Thev have retention times of five to thirtv days the effluent, not very effective in pathogen removal, (sometimes more) and depths of I to 1.5 meters. is given in chapter 15. Design examples of treatment The lower layers of these ponds are usually an- processes discussed below are shown in the appendix aerobic. to this chapter. Layout and design details are shown * Aerobic maturation ponds, which receive fa- in figures 21-1 through 21-4. cultative pond effluent and are responsible for the quality of the final effluent. They have re- Waste Stabilization Ponds tention times of five to ten days and depths of about 1 to 1.5 meters. Each pond in a series of Waste stabilization ponds are large. shallow ponds ponds will generally reduce the fecal coliform in which organic wastes are decomposed by micro- concentration by about an order of magnitude. organisms in a combination of natural processes in- Anaerobic and facultative ponds are designed for volving both bacteria and algae. Stabilization pond BOD removal, whereas the function of maturation 128 OFF-SITE TREATMENT 129 Figure 21-1. Stabilization Pond Layout and Details (millimeters) Aerobic pond a~~ l l a 2 Aerobic pond Inlet Facultative pond * - (for details,* see fig. 21-2) Interpond connection (for details, see fig. 21-3) Outlet u | 2 , ll(for details. l l l t Aerobic pond see fig. 21-4) Anaerobic | X pond - Plan lavout (not to scale) 5,400 4.000 Varies s °° t -Water line - . W XPrecast concrete slabs Precast concrete slabs 1 for protection . Ee !._;-: .l -.-:. .; 3 against wave erosion 300 Water line 100 mm of selected fill Section a-a Detail of a typical embankment Figure 21-2. Inlet Structures for Stabilization Ponds (millimeters) Top of bank Overflow weir ,, C _> t/ ~~~~~~~~~~~~Water line 2 Concrete slabs Inlet arrangement for a deep anaerobic lagoon (the pipe should discharge well away from the embankment to avoid the development of sludge banks) Top of bank Overflow weir >/ ~~~~~~~~~~~~~~~~Water line Optional design Concrete slabs 1,000 2,500 Varies a a Plan Water line !150 1,100 Section a-a Inlet chute for a facultative or maturation lagoon Source: Mara (1976). $ John Wiley and Sons Ltd.; used by permission. 130 OFF-SITE TREATMENT 131 Figure 21-3. Alternative Interpond Connections (millimeters) a ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~a L _ -- L _ | - 1 1 - | ----- ,-=- -==--~~~iii -- --= Plan Emergency concrete Top of bank overflow weir Water line _ er.w./ zNTAY 200-mm pipe with00mm pip Section a-a 200-mm pipe Interpond connection with concrete overflow weir Scum board Top of Bank mm, Concrete slabs Simple interpond connection suitable for small lagoons Note: Interpond connection, comprising a concrete overflow weir and a downstream junction chamber, would be connected to an inlet chute similar to that shown in figure 21-2. Source: Mara (1976). ©John Wiley and Sons Ltd.; used by permission. 132 SANITATION TECHNOLOGY OPTIONS Figure 21-4. Outlet Structures for Stabilization Ponds (millimeters) Poured cement Top of bank AScum guard 250 mma stndrdpe sti Water line g minimum f i ~ ~~ ~ _ I H Ede of ea150-mmn pipe with I in 75 falC oConcrete footing Top of bank Sctuua ,me guarHd 52 Poured cement w Wat er line ci esee d ,i ;Bb t /I 150-mm pipe with I in 75 fall Concrete footinig Alternative interpond connections made from standard pipe rittings Brass auge V" notched bolted Brass gauge to face of concrete Plan Section a-a Flow-measuring chamber for hinal effluent Metal strip Oknwnt Upstream water l H \ fH Crest F i ) j > ~~~~~~Edge of weir (secition a-a) ' a _ .\ 90° triangular weir (Q, m3/ec = 1.38H 52Rectangular weir (Q, ml/see = 1.84BH3'2 Note: Q, quantity; m3'/sec, cubic meters per second; H, heights; B, breadth. Sources: For flow-mleasuring chamber, Mara (1976: (DJohn Wiley and sons Ltd.: used by permission). For weirs, Okun and Ponghis (1975). OFF-SITE TREATMENT 133 ponds is the destruction or removal of excreted path- than the contents of bucket latrines. In areas where ogens. Thus, these three types of ponds should nor- PF latrines are used, the vaults will contain 3 to 6 mally be used in conjunction to form a series of liters per capita daily of PF water. Assume that the ponds. A single facultative pond treating domestic average adult daily produces 250 grams (wet weight) wastes is unsatisfactory; good designs incorporate a of excreta, with a moisture content of 80 percent, facultative pond and two or more maturation ponds. and 1.2 liter of urine, with a total BOD5 of 21 grams. For strong wastes (BOD5 > 400 milligrams per liter), The vault contents will thus have a solid concentra- the use of anaerobic ponds as pretreatment units tion of 0.7 to 1.1 percent and BOD5 of 2,800 to 4,800 ahead of facultative ponds is often advantageous milligrams per liter, depending on the amount of PF since the anaerobic ponds minimize the land require- water. If additional water is used for anal cleansing, ments of the whole pond system. these figures will decrease slightly, and if paper is Well-designed pond systems, incorporating a min- used they will be higher. Thus night soil from vault imum of three ponds in series and having a minimum toilets is a dilute slurry with a reasonably high BOD. overall retention time of twenty days, produce an It is often thought to be similar to primary sewage effluent that will either be completely pathogen free sludge, except that it has a higher pH (usually >8), or will contain only small numbers of enteric bacteria and about 60 percent of its solids are present in true and viruses. Pathogenic helminths and protozoa will solution. be completely eliminated. Any bacterial or viral pol- lution can be reduced or eliminated by adding more Thermophilic Composting ponds to the system. The effluent is suitable for direct reuse or discharge into r.eceiving waters. Another suitable treatment method is thermo- Snail and mosquito breeding in properly main- philic composting. Before vault night soil, septic tank tained waste stabilization ponds does not occur. It sludge, or raw or digested sludge can be composted, is associated only with poor maintenance, which al- however, its moisture content must be reduced to lows vegetation to emerge from the pond bottom or between 40 and 60 percent. Mechanical dewatering, to grow down the embankment into the pond, although simple enough in theory, is not considered thereby providing shaded breeding sites. This can be appropriate because it is in practice a complex pro- prevented by providing pond depths of at least 1 cess with many snags. Experience with conventional meter and concrete slabs or stone riprap at top water sludge dewatering in Europe and North America, level. The latter strategy also prevents erosion of the especially at smaller works, has not been encour- embankment by wave action. aging, and there is no reason to suppose that night- Proper and regular maintenance of ponds is simple soil dewatering is likely to be more successful in de- but nonetheless essential. It consists merely of cut- veloping countries. Mechanical dewatering of any ting the grass on the embankments and removing type requires a reliable and continuous supply of floating scum mats from the pond surfaces. chemicals and energy. In addition, the liquor re- moved from the dewatered sludge contains high con- centrations of both BOD and excreted pathogens and Night-Soil Treatment Ponds requires treatment in aerobic waste stabilization ponds. There is little experience with pond systems that In contrast, moisture control of vault night soil is treat night soil, but there is no basis for suggesting more simply achieved, and at lower cost, by mixing that the design and operation of night-soil ponds is it with moisture-absorbing, biodegradable waste ma- different from that of ponds treating strong agricul- terials such as sawdust, wood chips, rice husks, cot- tural wastes or, indeed, domestic sewage. Since ton gin trash, straw, leaves, or previously composted night-soil ponds are not discussed in standard sani- night soil. Sufficient materials should be added to tary engineering texts, a typical design example is reduce the moisture to below 60 percent; the precise presented in the appendix to this chapter. The design quantities required must be determined by experi- criteria adopted are conservative, and it is antici- ment. The same materials will raise the carbon-ni- pated that, as more field data on night-soil ponds trogen ratio in the night soil from about 10 to 1 to become available, the criteria may be considerably the 20 or 30 to 1 needed for preventing loss of am- refined. monia and for optimum composting. Note that pre- Night soil is taken here to mean the material re- viously composted material can be recycled and used moved from vault toilets. This may be more dilute as the moisture-absorbing material. Figure 21-5. Behtsville Agricultural Research Center (BARO) System for ffigh-rate Thermophilic Composting (millimeters) Acration pipc is perfor.ited for even air distrihtitionb hb j a a' b~. As neededi Plan / ~~~~~~~~~~ 5 3~~~~~~~~~~~~00 2,500 to 3,500 3,000 j2 Weight4 - ---- Y Finished compost bed 7 500 Section a-a Section b-b Note: BARC (Beltsville, Marylind) is a facility of the U. S. Department of Agriculture, OFF-SITE TREATMENT 135 Night soil with moisture levels below 60 percent which air is forced through the composting wastes, may be composted in windrows in the open air for as in the Dano BIOREACTOR system: and closed sys- a period of two to three months. Windrows are long tems that can recycle a portion of the product for mounds of the composting material, usually approx- bulking and moisture control. imatelv a trapezoidal cross-section. Typical dimen- Some proprietary composting systems include sions are: base width, 1.5 to 2.0 meters; top width, "seeding" with expensive special cultures of micro- 0.75 to 1.0 meter; height, 1.5 to 2.5 meters. Aerobic organisms; these have been marketed from time to conditions within the windrow may be maintained time for many years on the basis of promotional by turning over the windrow contents daily at first, promises. They do neither harm nor good; the bac- decreasing to three- to five-day intervals by the end teria and other microflora needed for composting are of a three- to five-week composting period; this es- already present in raw wastes in more than sufficient sentiallv entails building a second windrow from the number to provide the seeding. contents of the first. This procedure also ensures that Information on composting presented in this chap- all the material is exposed to the high temperatures ter has been limited to the BARC process because this of 55°C or more generated within the windrow by system is simpler, less expensive, and less compli- thermophilic bacterial activity. cated than other aerobic systems and because it High-rate composting can be achieved in the wind- works. The alternative system, designed for limited row by forced draft ventilation with air blowers. space and based on similar principles, is the BIO- Alternative applications of this process, known as REACTOR. The most complete single source of in- the BARC' aerated pile composting system, are shown formation on the science and technology of com- diagrammaticaliy in figure 21-5; further details of the posting is published serially by Kumpf, Maas, and process are given in the appendix to this chapter. Straub (1964-80). A current summary in which The process essentially consists of the maintenance health aspects are stressed can be found in Shuval, of highly aerobic conditions in the windrow by draw- Gunnerson, and Julius (1980). A detailed description ing air in through the windrow surface and exhaust- of the BARC system and its operation is contained in ing it from the bottom through a series of perforated the appendix to this chapter. pipes and a 1/3-horsepower blower. Very high tem- peratures (>80°C) have been achieved using this process, even during wet weather and when the am- Appendix. Examples of Waste bient temperature was below 0°C. Pathogen destruc- Treatment Calculations tion is complete within a few days, but the process is continued for up to thirty days to produce a more stable compost. Odors are eliminated by passing the Waste stablization ponds exhaust air through a filtering pile of finished com- post. The BARC process is inexpensive: estimated ANAEROBIC PONDS. The kinetics of BOD removal total annual per capita costs, based on U.S. expe- in anaerobic ponds is similar to that in conventional rience. are $0.64 to $0.85 (1977 prices for a plant anaerobic digesters. In practice, lack of reliable field treating 10 tons of dry night-soil solids per day). data has led to inherently conservative empirical de- These costs can be reduced further if the compost signs based on the daily quantity of BOD, applied per is marketed. If there is no local use for the compost, unit volume:2 the process should be stopped after ten days and the L,Q pathogen-free product disposed of on land. (21.1) V There are many other technologies for aerobic composting of various combinations of night soil, where X,, = volumetric BOD, loading in g/m3/d sewage sludge, livestock manures, and refuse with L, = influent BOD- concentration in mg/I high organic contents. Among these is the Dutch Q = influent flow rate in m3/d VAM system, in which unsorted municipal refuse is V = volume of pond in m3. mechanically placed in large windrows into which air Provided that the volumetric BOD5 loading is below may be forced from pipes lying underneath the pile 400 g/m3/d and stable alkaline fermentation with (the opposite of the BARC system). Other systems methane evolution is established, minimal odor re- include: rotating inclined cylinders, which tumble lease occurs. If the wastewater is acidic. the pH and aerate solid wastes for six to eight days; closed should be adjusted with lime soda ash to a pH be- bins or towers, built where space is restricted and in tween 7 and 8. 136 SANITATION TECHNOLOGY OPTIONS Anaerobic ponds should be desludged when they MATURATION PONDS. Maturation ponds are usu- become half full of sludge. A sludge accumulation ally designed on the basis of fecal coliform removal rate of 0.04 m3 per person yearly is generally ob- rather than BOD removal. The model most com- served at temperatures above 15°C. monly used in design for the removal of fecal coli- forms in waste stablization ponds is first-order ki- FACULTATIVE PONDS. There are a number of de- netics in a completely mixed reactor. The kinetic sign procedures for facultative ponds, which gener- equation is: ally have a depth of between 1 and 2 m. The one N. described here is based on the areal BOD5 loading, (21.6) "V = + XA; this parameter is the daily quantity of BOD, ap- (1 + T plied to the pond per unit surface area: where N, = number of fecal coliforms per 100 ml Q of effluent (21.2) XS = 10Li, N, = number of fecal coliforms per 100 ml of influent where XA = areal BOD5 loading in kg/ha/d, A = pond K,,T) = first-order rate constant for fecal coli- area in m2, and Li and Q are as defined above. form removal at T °C. day-1, The maximum value of X, that can be used for t* = mean hydraulic retention time in days. design is a function of temperature from an analysis The rate constant varies with temperature according of performance data of facultative ponds obtained to the equation: worldwide. It is recommended that design be based on the relationship: (21.7) K,'7' = 2.6 (1.19)72". (21.3) AS = 20T - 120, In a series of anaerobic, facultative, and maturation ponds, equation (21.6) is written as: where T = mean temperature of the coldest month, N in degrees Celsius. (This formula works well in areas (2 .) e 1 ± KbT,t*an) (1 + Kb?. t*>J (1 + Kb(Tt1*,a_d having a temperature range of 15'C and up.) Thus, the pond area is given by: where t* t*f,a, and t*mat are the retention times in LiQ the anaerobic, facultative, and maturation ponds., (21.4) A = i respectively, and n is the number of maturation 2(T - 6) ponds (which have the same retention time and BOD, removal in facultative ponds is a function of which ideally are all the same size); AV and NA, refer the loading. McGarry and Pescod (1970) found the to the fecal coliform concentrations in the raw sew- following relationship in equation (21.5). where X age and the final effluent, respectively. is the f ow 5 removed in kg/ha/d: r Retention times in maturation ponds are usually in the range of five to ten days, and the number of (21.5) X, = 0.725X, + 10.75. maturation ponds required depends on the desired values of N,. A representative design value of N is Percentage BOD- removal is generally from 70 to 85 1 x 103 per 100 ml. Note the two maturation ponds, percent. An effluent BODs over 100 mg/l indicates a each with five to ten davs' retention, will normallv predominantly anaerobic pond; 40 to 80 mg/1 indi- reduce the BOD5 of facultative pond effluent from cates a predominantly aerobic one. Additional re- about 60 to 100 mg/l to below 30 mg/I. movals are achieved in maturation ponds. In facultative ponds that treat raw or screened sew- PHYSICAL DESIGN OF PONDS. In general, rectan- age, a sludge layer forms on the pond bottom. Fa- gular ponds with leiigth to breadth ratios of 2 or 3 cultative ponds should be desludged when they are to 1 and embankment slopes of 1 in 3 are used wher- a quarter full of sludge; as with anaerobic ponds, a ever possible. The embankment is protected from sludge accumulation rate of 0.04 m3 per person yearly erosion by wave action by placing precast concrete may be predicted (assuming that suitable traps are slabs or stone riprap at surface water level. provided to remove grit, sand, or ash residues that The pond base should be impermeable. In coarse may be in the incoming sewage). Facultative ponds permeable soils, the pond base should be sealed with that receive the effluent from anaerobic ponds (or plastic sheeting or clay. sewered PF toilets) do not normally require desludg- The inlet and outlet structures should be as simple ing. as possible; a wide variety of low-cost designs is avail- OFF-SITE TREATMENT 137 able. For all ponds, V-notch weirs, rectangular weirs, conservative BOD removal of 70 percent, the effluent or, if necessary, Parshall flumes may be installed to BOD5 would be 60 mg/I. measure influent and effluent flows as required for 3. Maturation ponds: performance evaluation. For Ne approximating 100 per 100 ml, try Typical layouts and details are shown in figures three maturation ponds, each with a retention 21-1 through 4. Sample design calculations are given time of five days: in the following paragraphs. Assume a population (P) of 100,000, a BOD5 con- N, - K (+ tribution of 40 gcd, and a wastewater flow of 80 lcd. e + K,T,t*,,) (I + K,,,('f,d (1 + K6,T)('_d3 The design temperature is 20°C. The design concen- = i0 tration of fecal coliforms in the final effluent is to be [1 + (2,6 x 2)][1 4- [2.6 x II)] [1 + (2.6 x 5)]3 100 per 100 ml. The sewage is to be treated by an- - 200. aerobic, facultative, and maturation ponds operating This value is too high. Repeating the calculation, in series. assuming three ponds with six and one-half days of 1. Anaerobic ponds: retention each, gives a value for Ne of 95, which is satisfactory. The area (A) of each pond, assuming Flow. Q = 80 3 10-3 x 100,000 a depth of 1.5 m, is given by: = 8,000 m3/d. A = Qt*/D Influent BOD5, L, = (40 x 103)/80 = 500 mg/I. = 8,000 x 6.5/1.5 = 35,000 i2. Taking &, as 250 g/m3/d, the volume (V) Thus, the total working area of the pond system is is given by: approximately 17 ha. The total retention time is V = LQIX, thirty-two and one-half days; since this is greater than -00 x 8,000/250 = 16,000 m3. twenty days, the effluent will be completely free of - 500 x 8,000/250 = 16,000 in. helminth eggs, larvae, and protozoan cysts. If the If the depth is 3 m, the area would be 0.53 ha. The anaerobic pond were not included in the design, the hydraulic retention time (= V/Q) is two days, so that required area would be 25 ha (for one facultative the BOD5 removal would be around 60 percent. De- pond of twenty-seven days' retention and four ma- sludging would be required every n years, where n turation ponds each of five days' retention). is given by: V/2 P x 0.04 Night-soil treatment ponds 16,000/2 Assume a population of 100,000, a night-soil pro- 100,000 x 0.04 2 duction of 8 lcd (including PF water), a night-soil BOD, of 5.000 mg/l and a temperature of 200C. This assumes a sludge accumulation rate of 0.04 m3 Equations (21.1) through (21.3) are used for the per person yearly and that the pond is desludged design of anaerobic and facultative ponds. Design when it is half full of sludge. computations are as follows. 1. Anaerobic ponds: 2. Facultative ponds: Flow, Q = (8 x 10-3 m3/c/d) x 100,000 people From equation (21.4) the area (A) is given = 800 m3/d. by: BOD,, Li = 5.000 mg/I. LiQ Assume X, = 250 g/m3/d as in previous example. A = L Q From equation (21.1): 2T - 12 V = Li Q/A,. = (5,000 x 800)/250 = 16,000 m3. (500 x 0.4) x 8,000 For a depth, d, of 3 m, A = 0.53 ha. (2 x 20) - 12 57,000 m2 or 5.7 ha. Detention time = 20 days (assuming evapora- tion = precipitation). If the depth is 1.5 m, the volume would be 86.000 Assuming 75 percent removal, the effluent BOD5 m3 and the retention time eleven days. Assuming a = 1,250 mg/I. Figure 21-6. Alternative Flow Diagrams for Composting Night Soil by BARC System Volatiles Night soil ' r\ ~ ~~ ~~~~~~~~ S.S.~ Rapd/ Storage Mixing pile c and Utilization aeration \ curing New bulking material No recycling of bulking material Night soil Voatiles | /~~~~~~~~~a Storage\ New Bulking Mixing Rapile / and '_ _Utiization material aeration curing Partial recycling of unscreened compost Night soil Volatiles 4 > Rapid 0 / Storage N New bulking Mixing p Screeing ard I Utilization material aeaincuring/ Recycled hulking material Recycling of bulking material Volatiles Rapi / Storage \ merblia Mxi pileS and Utilization material ~~~~~~eratin ecuring/ Recycled bulking mateial Recycling of bulking material and unscreened compsot M Biogas Volatiles ANaertobiclRai / vStorage\ I Dilution n e n pile and cu-0n' Utilization I Vegetable L matter Composting of digested night soil 138 OFF-SITE TREATMENT 139 2. Facultative ponds: would be in the range of 40 to 100 mg/I. Further treatment in a small maturation pond with a reten- From equation (21.3). maximum BODs loading, tion time of ten to twenty days might therefore be Xs = 20T - 120 = (20 x 20) - 120 required if the effluent is to be discharged into a = 280 kg/ha/d. small watercourse. Since the facultative pond ef- From equation (21.2), area (A) of pond: fluent would be completely free of excreted patho- A 10 x (0.25 x 5.000 mg/l) x 800 ml/d = 35.714 m2 gens, however, further treatment would not be re- 280 kg/ha/d = 3.57 ha. quired if the effluent is to be reused in aquaculture For d = 001.5 m, V = 53.6 m3, or agriculture. Some caution is needed in the agri- and detention time = 67 days. cultural reuse of night-soil pond effluent because it Note that if daily evaporation equals or exceeds may contain too high a concentration of dissolved 800 m3/d . 3.57 ha = 22.4 mm/d, there will be salts, especially sodium. The available evidence is no outflow. that chloride and sodium concentrations in night-soil Assuming 80 percent removal, the effluent BOD, pond effluents are in the range of 200 to 300 mg/l = 250 mg/I. and 140 to 330 mg/l respectively, which compares The minimum area of a second facultative pond well with concentrations of 100 to 660 mg/l and 60 is: to 360 mg/l respectively in effluents from ponds treat- 10 x 250 mg/l x 800 m-3/d = 7,143 m2 ing domestic sewage. In areas where evaporation A = greatly exceeds precipitation, however, make-up 280 kg/ha/d = 0.7 ha. water may be necessary to prevent build-up of salts to concentrations that inhibit algae growth. Night-soil treatment ponds have two additional Assuming as above that evaporation = precip- requirements over ponds treating sewage. First. itation. the retentiontime 7,143m2/800 m-d there must be an adequate source of water locally = 9 days. available to replace evaporation losses. River water 3. Maturation ponds: is normallv suitable. Second, there must be unload- ing facilities for the night-soil tankers. The design A maturation pond with 5 days' detention should include a manually raked medium screen (for would have a volume of 800 m3/d x 5d = 4,000 example, tO-mm bars with 20-mm spacings), a night- m. For a depth of 1 m. the area equals 0.4 ha. soil pond with a capacitv twice that of the largest A total pond area of about 5 ha would thus night-soil tanker used. and a maccrating pump that he needed to treat the excreta produced by a ngtsi akrue.adamcrtn upta population of treat the excretional pro d is avail- should discharge below the pond surface water level population of 100.000. If additional land is avail- and approximately 10 to 20 m away from the em- able, it is often more convenient not to have an bankment. Provision should be made for the night anaerobic pond so that the need to desludge it soil to flow by gravity directly into the pond when every 2 years can be avoided. In this case the the pump is under repair. facultative pond area (A) is given by equation (21.3) as: A = 10 L,Q/X,~ Beltsville aerated pile composting system Flow diagrams presented in figure 21-6 are based = 10 X 5,000) x 80/280 on mixing each volume of night soil or sludge with = 14,285 m2 = 14.3 ha. two volumes of woodchips, straw, rice hulls. ground- nut hulls, leaves, or other carbonaceous bulking The retention time, assuming a depth of 2 m (to material that has a low moisture content of, say. 30 allow for additional sludge storage capacity). is 358 percent.3 Finished composts can also be used. During days-nearlv a year. Make-up water would be re- mixing. temporary odors are usually produced. Mix- quired to maintain the depth when the daily evap- ing can be done by turning with a Fresno scraper, oration exceeds 5.6 mm. roadgrader. front-end loader, or other machine. The The kinetics of BOD removal in night-soil ponds final mix should be similar to the consistency of stiff have not been studied, and so it is difficult to estimate concrete. with any precision the BOD, of the effluent. A con- The purpose of the bulking material is to: (1) re- servative estimate, based on BOD removal in ponds duce the moisture content of the mixture to 40 to 60 treating domestic sewage, is that the effluent BOD, percent; (2) provide structure or porosity for air 140 SANITATION TECHNOLOGY OPTIONS movement through the mixture; and (3) provide car- plastic pipe that extends beyond the pile base. bon to raise the carbon-to-nitrogen (C:N) ratio to The solid pipe is connected through a moisture approximately 20 to 30 to 1. This C:N ratio of sewage trap and thence to a ½/3-horsepower blower con- sludge is in the range of 9 to 15 to 1. Raising the C:N trolled by a timer. Condensate draining from ratio reduces the loss of nitrogen as ammonia. The the moisture trap should be discharged to a addition of carbon as a bulking material ensures the sewer or a soakaway. Aerobic composting con- conversion of nitrogen into organic constituents of ditions are maintained bv drawing air through the biomass. the pile intermittently. The exact aeration schedule will depend on pile geometry and the THE AERATED PILE. A three-dimensional sche- amount of sludge to be composted. For a pile matic diagram of the Beltsville4 aerated pile method containing up to 80 tons of sludge (20 m x 5 for composting night soil in sewage sludge is shown m x 2.5 m), the timing sequence for the blower in figure 21-6. In their simplest form the individual, is five minutes on and fifteen minutes off. stationarv, aerated piles are constructed as follows: a The effluent air stream from the compost pile *A loop of 4-inch (10-cm) diameter perforated is conducted into a small cone-shaped pile of plastic pipe is placed on the composting pad, cured, screened compost approximately 1.2 m and oriented lengthwise, directly under what high and 2.5 m in diameter, where malodorous will become the ridge of the pile. Perforated gases are effectively absorbed. These are com- steel pipe can also be used and later removed monly referred to as odor filter piles. The mois- for reuse. The perforated pipe-should not extend ture content of compost used for this purpose under the end slopes of the pile because exces- will increase slowly. A 10-cm base layer of sive amounts of air may be pulled through the woodchips or other bulking material under the sides, causing localized zones that do not reach odor filter pile will minimize back pressures that the thermophilic range (that is, "cold spots"). could cause leakage of malodorous gases around The pipe should be placed at least 2.5 to 3 m the blower shaft and will absorb excess mois- from the ends of the pile. ture. Research has shown that the odor filter * Woodchips (or other bulking material) are pile should contain about 0.75 cubic meter of placed over the area to be covered by the pile screened compost for each 10 wet tons (4 dry in a layer that will cover the pipes by a depth tons) of sludge being composted. In the case of of at least 3 to 5 cm. This layer forms the pile new operations, where screened compost is not base and facilitates the movement and distri- yet available, some bulking materials or soil (or bution of air during composting. The base ma- a mixture thereof) could be used in the filter terial also absorbs excess moisture that may con- piles. dense and leach from the pile. Variations in pile shape and size can adapt the * The mixture of sludge and woodchips is then process to differences in the rate of sludge production placed loosely upon the prepared base (with a by most treatment plants. The individual pile method front-end loader or conveyor system) to form described here has been used for operations of from a pile, with a triangular cross-section, 5-m to 5 to over 100 tons per week of raw or digested sludge 7.5-m wide and 2.5-m high (see figure 21-5). with 20 percent solids. * The pile is completely covered with a 30-cm layer (often referred to as the "blanket") of THE EXTENDED AERATED PILE. Another version cured, screened compost. The blanket layer pro- of the aerated pile is the aerated extended pile. Each vides insulation and prevents the escape of mal- day's sludge production is mixed with a bulking ma- odorous gases during composting. If finished terial, and a pile is constructed that utilizes the slope compost is not available, as would be the case (lengthwise dimension) of the previous day's pile, for the first piles of a new operation, the bulking thus forming a continuous or extended pile. The ex- material itself can be used for this purpose. The tended pile offers certain advantages for larger mu- blanket thickness may have to be increased, nicipalities. For example, the area of the composting however, to achieve the same degree of insu- pad can be reduced by about 50 percent compared lation and odor control as obtained with cured with that required to accommodate an equal amount compost. of material in individual piles. Moreover, the amount * During construction of the pile base, the per- of blanket material (that is, screened compost) forated pipe is connected to a section of solid needed for insulation and odor control and the OFF-SITE TREATMENT 141 amount of bulking material for the pile base are both in the pile between 5 and 15 percent for rapid de- decreased by half. composition of the sludge and extended thermophilic In constructing an extended pile, the first day's activity. This level has been achieved at Beltsville sludge production is placed in an individual pile with with an aeration rate of about 14 ml per hour per triangular cross-section as described earlier. The ex- dry ton of sludge obtained by intermittent operation ception is that only one side and the ends are blan- of the blower. Continuous aeration results in rather keted. The remaining side is dusted with about 2.5 large temperature gradients and cooling within the cm of screened compost for overnight odor control. pile. On the next day, an additional aeration pipe is placed Four-inch (10-cm) flexible perforated plastic on the pad surface parallel to the dusted side, the drainpipe has been used to collect the air under the pile base is extended, and the sludge-woodchip mix- piles and to deliver it to the odor filter piles. The ture is placed in such a manner as to form an ex- pipe is damaged beyond reuse when the piles are tended pile. On the second day, the flat top and ends taken down, but since it is relatively inexpensive it are blanketed with screened compost and the re- is regarded as an expendable item. Rigid steel pipe maining side receives a thin layer of compost as be- has also been used and can be pulled lengthwise out fore. The pile is extended each day for twenty-eight of the pile without damage and can be reused. The days. After twenty-one days, however, the first day's pipe spacing for the extended piles should not exceed section is removed for either drying and screening the pile height. The pipe should be large enough so or placing in a curing pile. After the removal of seven that friction losses will not cause a pressure differ- sections in chronological sequence, there is sufficient ential of more than 15 percent along the length of space for operating the equipment so that a new the perforated section. Manifolding the outer ends extended pile can be started where the old one has of the pipe will equalize pressure in the event of been. Thereafter, a section is removed each day from accidental damage to the pipe. the old pile and a section is added to the new one. CONDENSATE AND LEACHATE CONTROL. As air TEMPERATURES ATTAINED DURING COMPOST- moves down through the composting sludge, it is ING. The conversion of sludge into compost is es- warmed and picks up moisture. Temperatures near sentially complete after three weeks in the aerated the base of the pile are slightly cooler as a result of pile. Microbial decomposition of the volatile organic heat loss to the ground. As the air reaches this area, fraction of the sludge in an aerobic atmosphere soon it is cooled slightly. causing moisture to condense. raises the temperature throughout the pile to from When enough condensate collects, it will drain from 60° to 800C, which effectively destroys pathogenic the pile and leach material from the sludge. Con- organisms that might cause diseases in human beings. densation will also collect in the aeration pipes and. Temperatures begin to decrease after about two and if not vented, can accumulate and block the air flow. one-half weeks, and this indicates that the more de- The combined leachates and condensate mav amount composable organic constituents have been utilized to as much as 20 liters daily per ton of drv sludge. by the microflora. stabilized, and transformed into If the bulking material is sufficiently dry to begin compost. Studies in Maine and New Hampshire in with, there will be no leachate drainage from the the United States, and Ontario in Canada, have pile. The leachate can be a source of odor if it is shown that neither cold weather nor snow affects allowed to accumulate in puddles. so it should be composting. collected and handled in the same manner as runoff water from the site. AERATION AND OXYGEN SUPPLY. Centrifugal fans The physical and chemical characteristics of the with axial blades are usually the most efficient final product can affect the agronomic or utilization machines for developing the necessary vacuum to value of the compost. Particle size can affect appli- move air through the compost piles and into the odor cation systems. Fine particles of material can be ap- filter piles. A pressure differential of about 125 mm plied with standard fertilizer spreaders. whereas (water gauge) across the fan has been adequate when coarse particles may require special equipment. The woodchips are used as the bulking material. When chemical characteristics will affect the quantitv and finer-textured materials such as sawdust are used, the wav the material can be used. The C:N ratio of however, an increase in pressure differential will be the compost used as fertilizer should not exceed 30 required. to 1, since this will require additional supplemental The aeration rate should maintain the oxygen level nitrogen. Woodchips and other material of high C:N 142 SANITATION TECHNOLOGY OPTIONS ratio therefore need to be screened out if the product week. Once temperatures peak at the desired level, is to be used as a low-analysis fertilizer. If refuse is only periodic spot checks are needed. Bimetallic used as a bulking material, screening is needed to probe thermometers are appropriate for such checks. remove undesirable material. CURING; AND STORAGE. Comipost should be cured ODORS. Although night-soil sludge can emit a for about thirty days (screened or unscreened). This strong, unpleasant odor initially, odor disappears maybe done in the original pile with aeration turned quickly as the sludge is aerated. Each of the unit off, or in a support pile. After airing, the compost operations can be a potential source of odors. Some may be used immediately or stored until demand for of the odors emitted are intermittent, whereas others compost develops. Curing further stabilizes the com- are continuous. Odor potential increases consider- post. Use of the compost is ordinarily seasonal. with ably during and immediately following periods of the bulk of it applied either at planting or harvest excessive precipitation. times. Thus. a curiny aLnd storage area is needed to To minimize the odor potential throughout the accommodate three to six months' production. composting process, it is essential to manage each During storage, the compost will continue to de- operation as follows: compose at a slow rate. Even though compost is well * The mixing operation: Prompt mixing of sludge stabilized, if it is stored in lar_e piles at a moisture and hulking material and placement of the mix- content above 40 percent. temperatures mav increase ture in the aerated pile reduces the time for odor to the thermophilic .ange. and additional composting generation. will occur. This is no cause for concern; it may. in * Aerated pile surface: This will not be a source fact. actually improve the quality of the compost for of strong odors if the blanket of compost is ad- some uses. equate for insulation. Thin spots or holes in the The compost can be stored without cover and may blanket will be a potential source of odors. The be piled as high as is convenient with the equipment effectiveness of the blanket for odor control available. Care should be taken to round the tops of decreases when its moisture content exceeds 60 the storage piles so that rain will run off and wet percent. pockets will not develop. * Air leakage between the blower and odor filter pile: Since air leakage can occur at this point. MONITORING AND MANAGEMENT. Monitoring is all joints should be sealed. Back pressure from essential to ensure proper operating conditions, high the odor filter pile should be minimized to pre- temperatures for pathogen reduction, and odor con- vent loss of gases around the blower shaft. Back trol. Operational monitoring can be kept at a mini- pressure can be reduced by placing a 4- to 6- mum with low-cost, unsophisticated equipment. inch layer of bulking material under the filter Temperatures will reveal more about the process pile; it will increase as the moisture content of than any other single parameter. Most of the pile the pile increases. should reach 55°C within two to four days. a tem- * Odor filter piles: As mentioned earlier, the odor perature that indicates satisfactory conditions with filter piles are a potential source of odors. They respect to moisture content, bulking material ratio, should be cone shaped, symmetrical, and con- mixing. aeration, and pH. tain about 0.75 m" of dry (40 percent moisture Low average temperatures (below 60C) can result or less) screened compost per 10 wet tons of from excessive aeration or too high a moisture con- sludge being composted. tent. The former can be corrected by reducing the * Condensate and leachate: These are potential blower cycle or placing a baffle in the pipe just in sources of odors. As these liquids drain from front of the blower. If the moisture content is too the compost pile, they should be collected into high. it indicates an improper sludge-to-bulking ma- a sump and piped to a soakaway or stabilization terial ratio in the mix. The pile can then be torn pond. down and rebuilt with additional bulking material * Removal of compost from the aerated pile to and future piles built with the correct ratio. Cold the curing pile: If the sludge has not been ad- spots in the pile may also result from improper pipe equately stabilized before this operation. odors spacing or an inadequate insulation cover. Temper- will be released. Excessive odor during this op- ature monitoring should be done daily for the first eration can probably be attributed to too high OFF-SITE TREATMENT 143 a moisture content in the composting mixture and soil conditions. In areas where precipitation is and can he avoided bv lowering the moisture high or distributed over the entire vear. some cover content of the mix with additional bulking ma- may be needted for the various operations. These terial. areas may also require a stable site underlain by con- * Curing pile: This can be a source of odors when crete or asphalt. Separate surface drainage systems the material removed from the aerated pile has may be needed. not been completely stabilized. The use of drier In drv or subhumid climates cover is not essential. materials in the initial mixing operation will pre- Operations have been composting in the open with- vent this problem. Blanketing the curing pile out any problems. A stable base is recommended. with drv cured compost will also help to contain however, where muddy conditions make it difficult any odors. Where night soils or sludges are in- to operate equipment and provide a potential for completelv composted after twentv-one davs odors. because of excess moisture. low temperatures, A sludge-composting facilitv should comprise the or improperlv constructed piles, the odor po- following areas: (1) receiving and mixing; (2) com- tential will be high. In these cases, the sludge posting pad; (3) drying and screening; (4) compost should not be put on a regular curing pile but curing and storage; (5) storage of bulking material; should be mixed with additional bulking mate- (6) administrative and maintenance: and (7) runoff rial and composted another twenty-one davs (or collection and disposal. put into a separate isolated pile. heavily blan- As indicated earlier, several of these areas mav keted with screened compost, and allowed to not be needed. The administrative, parking, and compost for several months). maintenance area may alreadv bc part of an existinig = Storage piles: Odors would arise only if the piles facility. A runoff collection system mav not be were constructed with excessivelv wet compost. needed if the runoff can be channeled into a sewer. * Aggregates or clumps of night soil or sludge: The areas that need to have a stable base are those When aggregates of night soil or sludge, even for mixing, the composting pad. and screening. Ma- though small in size. are allowed to remain on terials that can be used for the base are gravel, the compost pad after mixing and processing, crushed rock, asphalt, concrete. or flv ash. Concrete thev can soon emit unpleasant odors. Workers is the preferred material. should be made aware of this possibilitv so that In arid areas with high winds, precautions need to all aggregates of night soil or sludge are carefully be taken to avoid excessive dust. A shelter belt can removed from the mixing area as soon as pos- sible. Table 21-1. Equipment Needed * Ponding of rainwater: When rainwater is al- for Night-Soil Composting lowed to pond on the site, anaerobic decom- Type of equipment Specifications or model position can occur and cause unpleasant odors. Therefore, the site must be graded and compost Front-end loader Rubber wheeled, with bucket and piles located so that ponding will not occur. operation Options for mixing SITE DESIGN. The compost site should be located Tractor and rototiller Standard farm equipment as close as possible to existing wastewater treatment Easy-over compost or other waste disposal facilities. The advantages are: turner and tractor Mounted on tractor (1) low sludge hauling and transport costs; (2) use Pug mill Mixing material needs to be fed of existing institutions and infrastructure: and (3) into millbyconvevers,hoppers -and the like as required combined composting of night soil. sewage. treait- Screens, trommel. or shaker Specifications depend on capacitv ment sludgue, and septic tank sludge. needed: 7- to 9-mm opening The site should be located awav from residential Blowers, fans V-horsepowet: 9-inch (22-cm) areas. with easv access for transport and removal of centrifugal blower with nominal the product. This mav be adjacent to a rail line or ratingoft)cubic feet per mm- - . ~~~~~~~~~~~~~~~~~utc at 5 inches (4.5 m' per nun- river barge facilitv if the product is to be transported ute at 12.7 cm) static pressure to remote agricultural areas. Thermometers Bimetallic dial thermometers, or The design of facilities should take into consid- similar, with 3(0- and 60-cm eration climate (especiallv precipitation and wind) probes 144 SANITATION TECHNOLOGY OPTIONS greatlv reduce the wind velocitv within the site. Un- paved areas may require watering to reduce dust. Notes to Chapter 21 Land area requirements are estimated at I ha for 1. The Beltsville Agricultural Research Center (BARC). located each 12 dry tons daily (total solids) of night soil or in Beltsville, Maryland. is a facility of the U.S. Department of sludge. This will provide for mixing, piles, screening, Agriculture. drying, curing, and storage. If extended piles are 2. Abbreviations for units of measure used in this appendix. used, the figure is about 1 ha for each 15 dry tons in addition to the standard ones for metric units, are: gcd, gram(s) daily. per capita daily; g/m3!d. gram(s) per cubic meter daily: kg/ha/d. kilogram(s) per hectare daily; 1. liter(s); lcd, Iiter(s) per capita COMPOSTING EQUIPMENT. Equipment needed for daily; m3icid, cubic meter(s) per capita dailv; mgil. milligram(s) a composting operation include: (1) front-end loader, pelir;md,ilmtr()al. 3 This material is taken largelv from the appendix bv E. Ep- (2) mixing equipment, (3) screening equipment, (4) stein in Shuval. Gunnerson. and Julius (1980). blowers, and (5) thermometers. Brief descriptions 4. Beltsville Agricultural Research Center (BARC). U.S. De- are given in table 21-1. partment of Agriculture. Beltsville. Maryland. 22 Resource Recovery HUMAN EXCRETA, in whatever form, are a resource that may be conserved and reused rather than dis- Agricultural Reuse carded. Excreta and sewage contain many essential nutrients for the growth of terrestrial and aquatic Agricultural use is the most common form of ex- plants; often sewage is also a valuable source of ir- creta reuse, and in many ways the simplest. There rigation water. The anaerobic digestion of excreta mav be risks of infection, however, to those who yields biogas, which can be used as a source of energy work in the fields and to those who consume the for cooking and lighting. Some form of treatment, crops. The latter group includes both man and ani- however, is always required to reduce the health risks mals. There may also be problems associated with caused by excreted pathogens to an acceptable min- the chemical quality of the compost, sludge, or sew- imum. The only exception to this is biogas produc- age effluent coming partly from industrial areas, for tion, but if the digested sludge from the biogas gen- example, crops may concentrate heavy metals. and erator is to be reused on the land, additional high sodium concentrations can damage the soil treatment or storage is necessary unless digestion structure. occurred within the thermophilic temperature range. Excreted pathogens present in the wastes mav There are three principal ways in which excreta reach the field. Different treatment technologies will and sewage can be reused: agricultural reuse, aqua- remove different pathogens to differing degrees. cultural reuse, and biogas production. There are, Where sewage effluent is reused, the onll treatment however, cultural, institutional, and occasional eco- processes that will produce an effluent essentially nomic constraints to the reuse of excreta in many free from pathogens include maturation ponds, waste areas of the world. Cultural constraints are appar- stabilization ponds followed by maturation ponds. ently based on religious custom (rather than religious land application. or sand filtration, or conventional law) and on aesthetics and convenience. Institutional sewage treatment with effluent chlorination. Where constraints are found in various kinds of restrictive sludge or night soil are reused, processes that will legislation and in the teaching and practice of con- produce a pathogen-frec material are storage or ventional sanitation technologies based on systems drying for a minimum of twelve months or thermo- in the industrial countries. Economic constraints to philic composting. reuse have included availability of low-cost or sub- If pathogens are not removed by these processes. sidized chemical fertilizers; economic development they will be carried to the field. The survival times in farming areas now makes the convenience of in soil of excreted pathogens can be generalized as chemical fertilizers affordable to the farmer. In any follows: event, the greatest concerns are usually those relating to infection by pathogens and parasites present in the wastes. Accordinglv, much of this chapter is Survival time in soil taken from Feachem and others (forthcoming), who Birueria Up to 6 month but generll less than 3 months Bacteria Up to 3 years. hiut gener-allv less than 2 mionths. have reviewed aspects of excreta-related infections. Protozoa Up to 10 davs, but generallv less than 2 davs A schematic diagram of a number of possible reuse Helminths Up to 7 years. but generally less than 2 years. options is shown in figure 22-1. with few viable alter 12 months. 145 146 SANITATION TECHNOLOGY OPTIONS Figure 22-1. Reuse Potential of Wastes Refuse HoshXlo Comp<)st _ X municipal . X Farm * Produce compostingI | ~~~~~~Farm wastes Three-st ace I septic tank Excreta - Additponao Gas soaeMake-up water Make-up water fcot co dpn unhm o f - n cmaredization Ducks Sewage Depraio -0; Fish Freshwater Whethcr the pathog4ens become attached to the sur- Once on the crop. pathogen survival is not verv face of the crops depends upon the method of ap- long compared with survival in soil. Survival of ex- plication and the crop. Crops grown on. near. or creted pathogens on crop surfaces may be summa- below the ground are most likely to become contain- rized as foltows: inated. Where wastes are sprayed or flooded on fields of growing crops. contamination is also certain. Survival time on crops Viruses tip to 2 months, but generally less than I month Crops may be protected by subsurface irrigation. by Bacteria Up to 6 months, but 2enerallv less than I mnonth drip or trickle irrigation where crops are not on the Protozoa Up to 5 davs. hut generally less than 2 days ground. bv irrigation through furrows not immedi- Helminths Up to 5 months. but generally less than I month. atelv adjacent to the crops. or by similar techniques. Alternatively. wastes may be applied only before The factors most lethal to pathogens are desiccation planting. or application may be discontinued one and direct sunlight. Survival may be expected to be month before harvesting begins. in view of the prob- considerably shorter in dry. sunny climates than in ability that the pathogens will die before the crops humid, cloudy climates. are harvested (see on-crop survival times. below). Survival times are thus quite sufficient for at least These methods are effective in preventing crop con- some viable pathogens (except, perhaps, protozoa) tamination when the applied waste has been properly to be transported into markets, factories, and homes, treated. When a waste rich in pathogens is reused. and subsequently to infect those who handle, pro- however. pathogens are likely to reach the crops in cess, prepare, or eat the crop. A distinction is some- significant numbers despite these protective meas- times made between crops that are eaten raw (to- ures. matoes. for instance) and those that are normally RESOURCE RECOVERY 147 cooked (such as cabbage). Conservative public health at some time of the year, and so all may be exposed policy, however, is to regard these similarly because, to the risk (although not equally so). The only sure even if a cabbage, say, is eventually cooked, those way to protect the health of the agricultural workers who handle and prepare it are still at risk, and path- is to use only wastes that have been properly treated. ogens may be transferred to crops that are eaten raw. Aerosols from sewage treatment plant operations There is much evidence to suggest that, where an and from spray irrigation with treatment plant ef- excreted infection is highly endemic in a communitv fluents have been regarded as potential hazards to and where poverty and squalor are found, the intro- treatment plant and agricultural workers, respec- duction of the particular pathogen into the home on tively. Careful studies, however, have shown no dif- contaminated vegetables or other crops has a neg- ferences in morbidity between these workers and the ligible effect on transmission. Where excreted infec- general population (Pabren and Jakubowski 1980). tions are not widespread in a community and where An additional health problem is that associated there are improved standards of hygiene and hous- with cattle that graze on sewage-irrigated pastures ing, however. the introduction of contaminated crops or that are fed fodder crops grown in excreta-fertil- into the home may be the major transmission route ized or sewage-irrigated fields. Although the path- for some excreted pathogens. This can be illustrated ogens of a variety of animal diseases have been de- in the following way. tected in sewage, they occur in very small numbers, Imagine a town of moderately wealthv people who and transmission of these diseases by sewage is of live in houses with water connections and flush toi- negligible veterinary import. The one principal ex- lets. Outside this town there is a village where people ception to this is beef tapeworm (Taeuiit saginata). are extremelv poor, houses have earth floors, water This helminth circulates between man and cattle and is drawn from an open well, and there is no adequate infection only continues when cattle eat Taenia eggs excreta disposal svstem. The main source of income that humans have excreted. Therefore, any excreta for these villagers is the cultivation of vegetables for disposal or reuse technology that brings cattle into sale in the town. The villagers also use the vegetables direct contact with human excreta may promote the themselves as a subsistence crop. These vegetables transmission of the disease unless adequate treat- are fertilized by untreated excreta collected in the ment is provided. Taenia ova are very hardy and are village and by sewage sludge obtained free of charge surpassed only by Ascaris ova in their ability to sur- from the treatment works on the outskirts of the vive outside the host. They may survive in soil or on town. Let us consider infection with Ascaris llmlbri- pasture for over six months. Their removal from sew- coides. The prevalence of ascariasis in the town is age will require either the use of waste stabilization onlv 8 percent, and the principal means of entrv of ponds or tertiary treatment in the form of sand fil- viable Ascairis ova into the home is on the vegetables tration or lagooning. Removal from sludge requires bought from the villagers. Transmission among the either a thermophilic process or retention for ap- wealthv townsfolk is not taking place because their proximatelv one year. The prevention of cattle's ex- excreta are flushed away, and high standards of hv- posure to untreated human excreta is crucial because giene prevail in the town. The prevalence of ascar- beef tapeworm is an important health problem in iasis in the village is 68 percent. Transmission occurs both man and cattle in areas in which the parasite intensively in the village and particularlv in the is highly endemic. home. The house tloor and yard are contaminated To reduce health risks associated with the agri- with viable ova from the feces of infected children. cultural reuse of excreta and sewage, the wastes Most transmission is unconnected to the contami- should be treated to the following standards for path- nated vegetables, which the villagers also eat. If the ogens in sewage effluents: supply of contaminated vegetables suddenlv ended. the transmission of ascariasis in the town viould beStandard the transmission of ascariasis in the townvri would be Fecal coliform bacteria Less than 100 per 100 milliliters reduced sulbstantially. whereas the village would be Fecal streptococci Less than 100 per 10() milliliters unaffected. Protozoa Not applicable There are also potential health risks to those who Helminth ova and larvae Not applicable work in excreta-fertilized or sewage-irriaated fields. Limited epidemiological evidence indicates that those and in sludges and composts: who work on sewage farms are at greater risk than Standard others. Also, in manv agricultural communities, Ascaris ova 200 per 100 grams and less than 5 practicallv the whole population works in the fields percent viability 148 SANITATION TECHNOLOGY OPTIONS The standards for fecal coliform and streptococci on the design of fishponds. Training of local person- may be relaxed to less than 1.000 per 100 milliliters nel in the proper management of fishponds is also if only fodder or industrial crops are irrigated. No essential. figures are given for protozoa and helminths in ef- There are three distinct health problems associated fluents since 100 percent elimination can be confi- with fish farming in excreta- or sewage-fertilized dently obtained if waste stabilization ponds with a ponds: total retention of twentv days or more are used, The passive transference of excreted pathogens which is usually necessary to ensure the required WmCI IS sualy neessay toensue th req1redbv the fish, which become contaminated in the removal of fecal bacteria. In areas where ascariasis b is absent (such areas are rare in developing coun- polluted water tries), theIova of either Taenia sa.inata or Tichuris . * The transmission of certain helmimths whose life tries),-the. ovaofeitherT a . o T cycles include fish as an intermediate host trichiura or other appropriate helminth indicator or- C I * The transmission of other helminths with life ganisms should be used. cce cvcles Involving other pond fauna, such as the snail hosts of schistosomes. Aquacultural Reuse The first of these problems is a cause for concern throughout the world, whereas the second and third Human excreta can be used to promote the growth applv onlv in areas where particular eating habits are of aquatic plants and animals, This practice is termed found and wfrere the helminths concerned are en- aquaculture. Four main types of aquaculture are demic. practiced: Fish may passively carry human pathogens in their * Freshwater fish farming intestines or on their body surfaces. and these path- . Mariculture (the culture of marine animals such ogens may subsequently infect people who handle. as fish, shellfish, and shrimp) prepare. or eat the fish. There is little risk to fish * Algal production eaters, except in areas where fish are eaten raw or * Aquatic plant (macrophyte) production. partially cooked. Thorough cooking will destroy all excreted pathogens. Of these, freshwater fish farming is the most common The second health problem associated with fish (especially in Asia) and also the easiest. Mariculture farming is the transmission of worms parasitic to man is by its nafure restricted to coastal communities; it that have an intermediate fish host. The most im- is not as widely practiced as freshwater fish farming. portant of these are Clonorchis sin ensis (Oriental The production of microalgae and aquatic macro- liver fluke) and the related species Opistorchis viv- phytes has received considerable research effort, but errini and 0. felineus, which are the only species current knowledge is still very limited. Algal har- associated with excreta-fertilized fishponds. Thev are vesting involves complex and expensive processes intensively transmitted where fish is eaten raw or that have yet to be demonstrated as technically and only partially cooked. Cooking of fish must be thor- economically feasible in large operational ponds. ough to kill the encysted larvae, and most fish pres- Although practiced traditionally in a few parts of the ervation and pickling techniques have little effect. world, the fertilization of aquatic macrophytes with Where fish are grown in pretreated or presettled sew- excreta and sewage (and its converse, the treatment age, Clonorchis eggs will have been removed by sedi- of excreta and sewage by aquatic macrophytes) are mentation. Clonorchis eggs are fragile and die if processes that have not yet been fully economically stored for a few days in night soil. Seven days' storage or technically evaluated. prior to pond enrichment is a sound strategy for the Freshwater fish farming is the only aquacultural control of this infection. It must be noted. however. reuse process about which enough is known to con- that there are other important definitive hosts apart sider it for widespread replication. Cultured fish are from man (such as dogs and cats), so that the control the major source of animal protein for many low- of human excreta may only partially reduce trans- income communities in countries in the Far East, mission. where the most common method of fishpond fertil- To summarize, fish farming using excreta or sew- ization is the use of human and animal excreta. En- age carries with it the hazard of passive carriage of gineers and others involved in sanitation program a range of pathogens and., in some parts of the world, planning are strongly advised to consult with local of Clonorchis transmission as well. Control measures fish farmers and other specialists before embarking are as follows: RESOURCE RECOVERY 149 * Enrich ponds only with settled sewage or stored ograms per hectare yearly can be achieved, especially night soil or sludge. if supplemental feeding with grass, other vegetation, * Allow the fish to reside and depurate in clean rice bran, groundnut cake, and the like is practiced. water for several weeks prior to harvesting. Basically the construction and physical mainte- * Clear vegetation from pond banks to discourage nance of fishponds is the same as that required for snails, which are the first intermediate host of waste stabilization ponds. Depths are usuallv greater Clonorchis. This also eliminates other helmin- than 1 meter to prevent vegetation from emerging thiases involving snails, such as schistosomiasis. from the pond bottom; deep ponds (greater than 2 * Promote good hygiene in all stages of fish han- meters) are disadvantageous because there is little dling and processing. oxygen, and hence few fish, in the lower layers. * Discourage the consumption of undercooked There is. however, little information available on fish. the range of retention times that should be provided The adoption of all these control measures will elim- in fishponds fertilized with sewage effluent. Too inate, or reduce to an acceptable level, the health short a retention time may waste nutrients, and with hazards associated with the aquacultural reuse of long retention times the nutrient supply may be in- human wastes and so permit the production of val- sufficient for optimal yields of fish. The retention uable, pathogen-free protein at low cost. time depends on the mean doubling time of the algal Although the number of fish species that have species present and the grazing rate of the fish. In been successfully grown in excreta- and sewage-fer- general, one to five days may be required. but this tilized ponds is large, two groups are the most im- needs to be determined by experiment. portant: carp and tilapia. There are several species For ponds that are fertilized with stored excreta of carp and tilapia, the most useful being those that or with the effluent from a low-flow night-soil treat- feed directly off the microalgae that grow profuselv ment pond, the retention time is unimportant. What in fertilized ponds; these include the silver car' matters is the correct rate of supply of nutrients: (Hypophthalamichtys mnolitrix), the bigear (Aristi- regular batch feeding on an empirically determined chthys novilis), and the two tilapia, Sarotheroden basis is recommended. mossambicus and S. niloticus (formerly called Tilapia It is possible to grow carp and tilapia in maturation mossambica and T. nilotica). In India different spe- ponds. Yields are in the range 200 to over 1,000 cies of carp are used for fish farming; the four most kilograms per hectare yearly, depending on man- important are Catla catla, Cirrhinus mrigala, Labeo agement (stocking density, frequency of harvesting). rohita, and L. calbasu. Facultative ponds should not be used for fish culture Yields of carp in fertilized ponds vary from 200 since the concentration of dissolved oxygen often kilograms per hectare yearly in rural subsistence falls, especially at night. to too low a level. Air- ponds to above 1,000 kilograms per hectare vearlv breathing fish such as catfish and snakeheads, how- in carefully managed commercial ponds; yields of ever, can be grown in facultative ponds: considerable tilapia are even higher, 2,000 to 3,000 kilograms per success has been obtained in India and southeast hectare yearly in well-maintained ponds. Tilapia are Asia with several species that are highly prized for prolific breeders; to eliminate breeding in fishponds. their nutritional and supposedly therapeutic value. which reduces yields, the ponds should be stocked The pacu, a species of freshwater fish found in the with fish of only a single sex. This can be readily Amazon basin, is showing great promise in aqua- achieved by using hybrids of male S. mnossarnbiculs culture systems. The pacu is both a filter feeder and and female S. niloticus, a cross that produces only a herbivore, can gulp air during periods of low dis- male fish. Fish vields can be increased bv several solved oxygen, grows rapidly, and has a higher ratio techniques. Ducks can be reared on the ponds, and of edible flesh to total body weight than other tra- their feces provide additional nutrients for the pond ditional species (50 percent versus 35 percent for algae. This increases fish yields by as much as 50 to carp). Use of this fish is still in the experimental 100 percent. Other species of fish that occupy dif- stage. but all results look promising. ferent ecological niches in the pond can be intro- Health risks can be reduced to acceptable levels duced; for example, the common carp (C'vprinus car- if the fish are transferred to clean water depuration pio) and the grass carp (Ctenopharvngodoni idella) ponds for several weeks prior to marketing. feed primarily on benthic zooplankton and aquatic weeds, respectively. This process is known as "poly- culture," and fish yields of up to 5,000 to 7,000 kil- Figure 22-2. Schematic of Typical Biogas Digesters (millimcters) 2,00)( I.X( ~~~~2UO ~- I: 111 Gas CI C slinder m hadc tl L~~~w d eldd iron sheet PolN s in I _ cl loride pipe ililet Used sump oil Liquor ouLtIlet pipe Dii estinL Settling ' Istlc tanic C(oncretc or brCick Concrete slab Floating metal gasholder Slurry Gas drasw-off pipe Displaced liquid Connected scttlement \ storage arca opening area Ground a D \ Gas storage area : -_er D etLi4d inletcL qi level c r . 0 . . _ Sturrv otitlct Excicna inlet ::__. chambcr Digcesting Groove for drop board Chinese design 150 RESOURCE RECOVERY 151 pected to be around a third to a half of the digester Biogas Production volume per day if the digester is operated semicon- tinuously (that is, fed daily or twice daily). Semi- When organic wastes are digested anaerobically, continuous operation is preferable to batch feeding a mixture of methane, carbon dioxide, and other because the rate of gas production is fairly constant. gases is given off. This gas has become known as The material added to the biogas plant should have "biogas" and can be produced on various scales by a C:N ratio in the range 10 to 30, and preferably 20 different technologies. In conventional sewage treat- to 25. Night soil has a C:N ratio of 6 to 10 and so, ment works, anaerobic sludge digestion produces for efficient operation of the unit, requires the ad- biogas that is sometimes used to heat the digesters dition of material with a high C:N ratio (such as or for some of the other energy needs of the works. leaves, grass, straw, or bagasse). Biogas units in rural The term "biogas production," however, is usually areas are commonly designed for cow dung (which used to describe the production of methane on a has a C:N ratio of 18 to 25), and the relatively small small scale by individual farmers, communes, or rural quantities of human excreta from a few households institutions in developing countries. can be added without adverse effect. The feed ma- Biogas plants are found in large numbers in China terial should have a solid concentration of about 10 and India, and it is probably in these countries that percent. and thus some dilution is usually needed; the technology has become most developed. Signif- one volume of animal dung is commonly diluted with icant numbers are also in operation in Korea and on one volume of water. the island of Taiwan. The units are fed with diluted animal feces, with or without human excreta and with or without vegetable refuse. The effluent slurry Social, Institutional, and Economic mriay be reused in agriculture, aquaculture. and as Aspects of Reuse animal fodder. The gas is used primarily for domestic cooking and lighting. The dung from one medium- The health and technical requirements for a safe size cow, or similar animal, can produce around 500 and productive resource recovery process have been liters of gas per day; it contains 50 to 70 percent described above. Much less is known about the methane, and its calorific value is around 4 to 5 kil- equally important social and institutional require- ocalories per liter. In contrast. human excreta yields ments, and few good economic evaluations have only 30 liters of gas per person daily. The process is been made for reuse schemes. The real test of any very sensitive to temperature. In the mesophilic reuse product is whether it is demanded by. and can range. optimal gas production occurs at around 35°C. be delivered to. an ultimate consumer at a price he In rural areas digesters are not heated, although they is willing to pay. The social and cultural factors that may be buried to conserve their heat, because gas influence people's attitudes toward recycled waste production falls off at lower temperatures. Ther- products vary widely around the world and are not mophilic digestion of feed-lot manures is under de- readily changed. Therefore it is imperative that a velopment in Israel and the United States. careful market study be carried out by behavioral There are several designs for rural biogas plants. scientists and economists before the development of Construction and operation requirements for some schemes for resource recovery. of the designs are presented by the U.S. National Reuse processes require careful planning and im- Academy of Sciences (1977). Two designs are shown plementation to reduce the health risks to acceptable in figure 22-2. The Chinese design is advantageous levels, to organize the delivery and retailing aspects in that it contains no moving parts, avoids the need as well as traditional collection and treatment tasks, for a metallic gasholder (which has corrosion prob- and to provide for integrated systems in which mul- lems), and permits the gas to be stored at a relatively tiple sources of wastes (such as animal dung and constant pressure. human night soil) can be managed to provide opti- The design of biogas plants is empirical. Loading mum multiple outputs (such as biogas, protein, and rates vary between 0.5 and 3 kilograms of volatile fiber). Demonstration projects may be needed to solids per cubic meter of digester volume per day,' show farmers and officials alike that the known ag- and retention times of five to thirty days are com- ricultural benefits of irrigation with raw sewage will mon. At the present time it seems prudent to adopt be essentially retained by upgradeable treatment and a retention time of thirty davs as the controlling pro- irrigation systems which provide health benefits. cess design parameter. Gas production may be ex- Although well-run municipalities may be cost con- 152 SANITATION TECHNOLOGY OPTIONS scious and may attempt to minimize expenditure, or without reuse products. If the private sector is to they frequently lack the incentive and entrepreneu- be involved in the operation of the reuse scheme, rial skill to manage a revenue-producing operation this may mean that the municipality will have to pay successfully. Often it will be more advantageous for the private firm a commission (based on the lowest a municipality to contract excreta and sewage reuse competitive bid) rather than expect to sell a fran- processes to the private sector where these skills are chise. more likely to exist. It should be remembered, however, that the eco- nomically appropriate test of a reuse process is not Note to Chapter 22 that it make a positive profit, but only that its net 1. Equivalent to approximately 6 to 40 kilograms of cow dung cost be lower (in discounted cash flow) than that of (wet weight) or 14 to 66 kilograms of night soil (wet weight) per other waste treatment and disposal alternatives with cubic meter per day. Bibliography American Society of Civil Engineers. 1977. Wastewater of Rural and Urban Fringe Areas in Latin America. Treatment Plant Design. ASCE Manual of Practice no. Washington, D.C.: World Bank. 36. New York. Elmendorf, Mary, and Patricia. K. Buckles. 1980. Appro- Appleton, B. 1976. 'Acid Test for Middle East Brain priate Technology for Water Supplv and Sanitation. vol. Drains." New Civil Engineer (February 19), pp. 23-29. 5. Sociocultural Aspects of Water Supply and Excreta Appropriate Technology. 1979. Vol. 6. no. 3 (November). Disposal. Washington, D.C.: World Bank. Arlosoroff, Saul. 1979. "Tradition and Innovation in Feachem, Richard G. 1976. "Appropriate Sanitation," Water Use and Reclamation." In Charles G. Gunner- New Scientist. vol. 69, pp. 69-80. son, and John M. Kalbermatten. eds., Appropriate Feachem, Richard G., Michael G. McGarry. and David Technology in Water Supply and Waste Disposal. New Duncan Mara. 1977. Water, Wastes, and Healtlh in Hot York: American Society of Civil Engineers, pp. 61-84. Climates. New York: Wiley. Assar, M. 1971. Guide to Sanitation in Natural Disasters. Feachem. Richard G., and Sandy Cairncross. 1978a. Small Geneva: World Health Organization. Excreta Disposal Systems. Ross Bulletin no. 8. London: Bardach, J. E., J. H. Rvther, and W. 0. McLarney. 1972. Ross Institute Information and Advisory Service. Aquaculture: The Farming and Husbandry of Freshwater 1978b. Small Water Supplies. Ross Bulletin no. 10. and Marine Organisms. New York: Wiley. London: Ross Institute Information and Advisorv Serv- Barnet, A., L. Pyle, and S. K. Subramanian. 1978. Biogas ice. Technology in the Third World. Ottawa: International Feachem, Richard G., D. Duncan Mara, and Kenneth 0. Development Research Centre (IDRC). Iwugo. 1980. Appropriate Technology for Water Supply Blackmore, M., R. Boydell, N. Mbere, and P. Moselele. and Sanitation, vol. 7, Alternative Sanitationi Teclhnolo- 1976-78. Low-cost Sanitation Research Project: Interim gies for Urban Areas iTn Africa. Washington. D.C.: Reports 1-3 and Final Report. Gaborone, Botswana: World Bank. Ministry of Local Governments and Lands. Feachem, Richard G., David J. Bradley, Hemda Garelick, Canter, L. W., and A. J. Englande. 1970. Journal of the and D. Duncan Mara. 1980. Appropriate Tcchnologv for Water Pollution Control Federation, vol. 42. Cited in Water Supply and Sanitation, vol. 3, Healtlh Aspects of Mara (1976, p. 137). Excreta and Sullage Management: A State-of-the-Art Clare, H. 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"Sanitation and Low-cost Hous- American Society of Civil Engineers. vol. 95, pp. 715-46. ing." In Water Quality: Management and Pollutioni Con- Elmendorf, Mary, ed. 1980. Appropriate Technology for trol Problems. Oxford: Pergamon Press. pp. 115-25. Water Supply and Sanitation, vol. 8, Seven Case Studies Kalbermatten, John M. . DeAnne S. Julius. and Charles 153 154 BIBLIOGRAPHY G. Gunnerson. 1982. Appropriate Sanitation Alterna- Aerosols and Disease: Proceedings of a Symposium, tives:A Technical and Economic Appraisal. World Bank Sept. 19-21, 1979. U.S. Environmental Protection Studies in Water Supply and Sanitation no. 1. Baltimore, Agency, EPA-600/9-80-028. Springfield. Va.: National Md.: Johns Hopkins University Press. Technical Information Service. Appropriate Technology for Water Supply and Pradt, L. A. 1971. 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Appropriate Technology for Water Supply pp. 119-93. and Sanitation, vol. 10, Night-soil Composting. Wash- McGarry, Michael G. 1975. Developing Country Sanita- ington, D.C.: World Bank. tion. Ottawa: IDRC. South Australia Department of Public Health. 1968. Septic McGarry, Michael G., and M. B. Pescod. 1970. Proceed- Tank Effluent Drainage Schemes. Public Health Inspec- ings of the Second International Conference on Waste tion Guide no. 6. Norwood, South Australia. Treatment Lagoons, Kansas City. Squire, Lyn, and Herman G. van der Tak. 1975. Economic McGarry, Michael G., and J. Stainforth. 1978. Compost, Analysis of Projects. Baltimore, Md.: Johns Hopkins Fertilizer, and Biogas Production from Human and Farm University Press. Wastes in the People's Republic of China. Ottawa: IDRC. U.S. Environmental Protection Agency. 1973. Water Metcalf and Eddy, Inc. 1975. Wastewater Engineering: Quality Criteria. Washington, D.C.: U.S. Government Collection, Treatment, and Disposal. New York: McGraw- Printing Office. Hill. . 1977. Health Effects of Nitrates in Water. EPA Mohanrao. G. J. 1973. "Waste Collection, Treatment, and Report no. EPA-600/1-77-30. Washington. D.C.: U.S. Disposal in India," Indian Journal of Environmental Government Printing Office. Health (CPHERI, Nagpur), vol. 15, no. 3, pp. 222-35, U.S. Public Health Service. 1957. Manual of Septic Tank National Academy of Sciences (U.S.). 1976. Making Practice. Public Health Service Publication no. 526. Aquatic Weeds Useful: Some Perspectives for Developing Washington, D.C.: U.S. Government Printing Office. Countries. Washington. D.C. Wagner, E. G., and J. N. Lanoix. 1958. Excreta Disposal - 1977. Methane Generation from Human. Animal, for Rural Areas and Small Communities. World Health and Agricultural Wastes. Washington, D.C. Organization Monograph Series no. 39. Geneva. National Environmental Engineering Research Institute White, Ann E.,- and Gilbert F. White. 1978. "Behavioral (NEERI). 1972. Night-soil Wheelbarrows. Technical Di- Factors in the Selection of Technologies." In Charles G. gest no. 32. Nagpur, India. Gunnerson and John M. Kalbermatten, eds.. Appro- Okun, Daniel H., and G. Ponghis. 1975. Community priate Technology in Water Supply and Waste Disposal. Wastewater Collection and Disposal. Geneva: World New York: American Society of Civil Engineers. pp. Health Organization. 31-51. Pacey, A., ed. 1978. Sanitation in Developing Countries. Winblad, U., W. Kilama, and K. Tortensson. 1978. San- London: Wiley. itation without Water. Stockholm: Swedish International Pahren. H., and W. Jakubowski, eds. 1980. Wastewater Development Authority. BIBLIOGRAPHY 155 Winneberger, J. H. 1974. Manual of Graywater Treatmenit World Bank. 1980. Water Supply and Waste Disposal. Pov- Practice. Ann Arbor, Michigan: Ann Arbor Science erty and Basic Needs Series. Washington, D. C. Publishers. I Index Page numbers in italics indicate tables or illustrations Aerated composting pile, 138, 139. 140 posting toilets and, 83, 87; night soil Community organization: community fa- Aerated lagoons, 111 and, 133 cilities and, 122; cost of, 32 Aerosols from sewerage treatment plant, Biogas, 150; from anaerobic digestion of Community participation and prefer- 147 excreta, 145; carbon-nitrogen ratio of ences, 44; characteristics of. 23-25; in Africa. See North Africa raw materials for, 151; from dung, 151. design of latrines and toilet superstruc- Agricultural re-use of wastes, 145-48 152nl; production of, 151; sludge from tures, 61. 64: importance of, 23, 81; Algal production, 148, 149 generators of, 145; temperature and, sanitation program planning and. 42. Amebiasis control measures, 19. See also 45, 151; from vault toilet wastes. 52 See also Cultural attitudes and design Protozoa Biological oxygen demand (BOD): sullage of sanitation facilities Anal cleansing: aquaprivy and materials and, 125, 127; treatment ponds and, 128, Community support activities, costing of. used for, 99; choice of fixtures and, 61; 135. 139 32-35 disposal of materials used for, 45, 64; BIOREACTOR system, 135 Community workers. 25. See also Self- PF toilets and materials used for, 99 Birds and tapeworm transmission, 20 help Ancylostoma duodenale, 13, 14. See also Bore-hole latrine, 80, 81 Complementary investments, 44 Hookworm Bucket latrines, 116, 117 Compost. 43; aeration and oxygen supply Appropriate technology: defined, 5; eco- Bulking materials. 139. 141 and. 141; ashes in, 84, 87; carbon-ni- nomic and financial aspects of choos- trogen ratio in. 87; condensate and ing, 27-35; planning and, 23. See also Carbon-nitrogen ratio, 134, 140, 151 leachate control, 141-42; curing and Technology Carcinogenic chlorinated hydrocarbons, storage of. 142; equipment for. 143. 144: Aquacultural re-use of wastes, 148-50 113 moisture level of, 84: monitoring and Aquaprivies: advantages and disadvan- Carp, 149 management of, 142; odors and, 142: tages of, 100; anal cleansing materials Cartage systems. See Vault and cartage site design for. 143; systems for treat- for, 44; for communal sanitation facil- systems ment of. 133, 134, 135, 138. 139-40; ities, 124; per capita effluent flow, 94; Cattle, 20; beef tapeworm and, 147. See temperature in, 83. 141, 142. See also requirements for. 99, 100; self-topping, also Cow dung for biogas Composting toilets: Night soil 41, 99; sewered, 94, 97, 99; tank for, Children: control of stools of. 21: ex- Composting toilets, 83-84, 85, 86, 87-88. 94. 99; types of, 94, 95, 96, 97, 98 creted infections and, 21; hygiene ed- See also Batch and cartage systems; Aridity indexes, 45 ucation for, 21; latrines and safety of, Compost: DVC toilets Ascaris lumnbricoides, 13, 14; epidemiol- 64, 66: as main source of infections. 17; Control measures for excreted infections. ogy of infection with. 147: ova in com- methemoglobinemia in, 22: schisto- 18 post, 83, 87; ova in pits. 42. 82; in sew- somiasis and, 15; toilet use by, 21 Conventional sewerage systems: advan- erage and sludge, 147: sullage disposal Chlorination of sewerage effluent, 113 tages of sewered PF svstem over, 57: and, 126; three-stage septic tank and, Choice of technology, 24: algorithm for, cistern-flush toilets and, 109; disadvan- 107 46, 48, 49, 50; checking the tentative, tages of, 109, 110: economic costing of Asia. See Southeast Asia 51; critical information for. 50; eco- (example). 33-35; high costs of, 110: Attitudes toward sanitation facilities. See nomic and financial aspects of, 31, 41. pipes for. 109-10: sewerage collection Cultural attitudes toward sanitation fa- 43-44; environmental factors in, 45: in- and, 109-13. cilities stitutional constraints and, 45; popu- Cost-benefit analysis, 27 Average incremental cost (AIC). See Costs, lation density and, 81; soil conditions Costs. 30, 43. 82. 122; average incremen- average incremental (AIC) and, 41, 42, 81: water supply service to tal (AIC), 30, 34, 35; of sanitation serv- houses and, 46: water table and. 81. See ices, 3. See also Economic costing; Fi- Bacteria: chlorination and, 113; patho- also Sanitation technologies nancial costing genic (inexcreta), 12: survival on crops. Cholera. 12. 15-16; control measures and. Cow dung for biogas. 151. 152nl 146; survival in soil, 145. See also Path- 19 Crops, pathogens on, 146 ogens; name of specific bacteria or dis- Cistern-flush toilets: anal cleansing ma- Culex: pipiens, 12, 22n2, 126: quinque- ease terials and, 44; for communal sanitation fasciatus, 20; species, 22n2. See also Balantidium coli, control measures and, facilities, 124; low-volume, 55 Mosquitoes 19 Clonorchis sinensis, 12, 13. 148 Cultural attitudes and design of sanitation Beef tapeworm, 13, 14, 19-20. 147, 148. Collection vehicles: importance of access facilities, 23, 47. 51. 61, 77, 122, 124. See also Tapeworm for, 118; labor requirements, 120: night See also CommunitY participation and Beltsville (BARC) aerated pile composting soil and. 118, 119 preferences: Personal choice svstems, 134, 135, 139 Comfort stations, 122. 124 Benefits received in future, value of, 30 Communal sanitation facilities, 122, 123; Defecation: cultural aspects, 14, 23-24. Biochemical reaction rates, temperature advantages and disadvantages of. 124: 39, 124: position for (and choice of toi- and, 45 design criteria for, 122-24. See also name let fixtures), 61: terms for, 23 Biodegradable household waste: com- of specific type of facility Diarrhea. 11, 12. See also nane ofspecific 157 158 INDEX Diarrhea (continued) Flotation (sewerage treatment), 110 72; for PF toilets, 69, 72; for ROECS, 66, diarrheal infection or of causative or- Flush toilets, 29; costs of (with septic 69; for vault toilets, 69. 72; for vip la- ganism tanks), 43; water requirements for, 89. trines, 64, 66, 69 Digesters, winter temperatures and, 45 See also Cistern flush toilets; PF toilets; Latrine and toilet superstructures. 61, 62, Double vault composting (DVC) toilets, 39, Toilets 63 41, 84; costs of, 43; PF toilet as replace- Funding: financial costing and, 31-32; by Laundry facilities, 45, 124 ment for, 52; population density and, government, 32 Least-cost choice, 27, 44 88; VIDP latrine as replacement for, 52; Lending agencies, general policy of in- water for anal cleansing and, 45 Giardia, control measures and, 19. See ternational, 31 Drainfields, 101-02, 104, 105 also Protozoa Lighting for latrines and toilets, 61 Drains for sullage disposal, 126 Groundwater: choice of sanitation tech- Liver flukes, 148. See also Clonorchis si- Ducks raised in ponds, 149 nology and level of, 42; danger of pol- nensis lution of, 82; nitrate pollution of, 22; Loans from banks (securing), 32 Economic costing, 27-28; AIC and, 30; di- on-site excreta disposal and pollution rect inputs and, 29-31; as earlv screen- of, 21-22; sullage disposal and contam- Maintenance: attendants and, 124: of ing of sanitation technoLogies, 31: ex- ination of, 124. See also Water; Water community facilities, 124; of drains, 127; amples of, 32-35; of foreign exchange, table; Well water expenses of, 45, 100; of water seal, 39, 28-29, opportunity cost of capital and, 94 29; of unskilled labor, 28. See also Fi- Helminths: with aquatic hosts, 20; chlo- Mara, D. Duncan, 116 nancial costing rination and, 113; indicator organisms, Mariculture, 148 Education: exchange visits and, 25; pref- 148; pathogenic (in feces), 13; sewerage Maturation lagoons, 113, 145 erence differences and, 24; sanitation treatment and, 110-11; soil transmit- Methane, 52, 151. See also Biogas program planning and, 45: for use of ted, 19; sullage disposal and, 126; on Methemoglobinemia in children, nitrate DVC toilets, 87. See also Training of crops, 146; in soil, 145. See also Tre- levels in drinking water and, 22 community workers matodes; name of specific helminth or Mosquitoes: breeding inhibitors for, 81; Elephantiasis, 12, 14. See also Filariasis disease disposal pits and breeding of, 42; in Emergencies, provision for, 25 Hepatitis, 12, 15. See also Pathogens; Vi- ROEC'S, 82; septic tank overflow and, Entrobius vermiculans, 19 ruses 105: sullage disposal and, 126: in vIP Escherichia coli, control measures and en- Hookworm, 14, 111 latrines, 82. See also Culex teropathogenic, 19 Hosts, nonhuman, 17. See also name of Multrum, 83, 84 Excreta: anaerobic digestion of, 74; chute specific host Municipal revenues, 31 cleaning and, 77: community attitudes Household-based facilities, 122 and, 45; deposition in dry climates, 14; Household wastes. See Biodegradable Nioht soil deposition in wet climates, 11, 12; household wastes , 1'16.9 cbont foro t, flushing of. 74. helminth pathogens in, Housing density: choice of sanitation of, 15 defied, 133; ponds for treat- 13; insect-free, 20; pathogens in, 12; technology and, 42-43; sullage disposal mnt of, 133 trmpic mosting percolation of liquid fraction in soils, and, 126. See also Population densitv and. 133, 135: treatment works for, 118: 74;re-use of. 44, 50 82, 145-52, sewers Humus production, DVc toilets and, 3 See also Compost; Resource recovery 74 re-use of, 44. 50, 82, 145-52; 83, Nitrate pollution of groundwater, 22, 126 not required for, 57 88 North Africa. example of sanitarv con- Excreted infections, 15-17; children and, Hymenolepsis, control measures for, 19 dont in, 13-15 21; control of, 18, 20-21; environmen- tal classification of, 17-20. See also Ibadan comfort stations, 122, 124 Pathogens Infections: disease and, 15; latency and Odors, 69, 73. 97, 100; compost and, 142- Excreted load, 15-16 16; reservoirs of, 12, 15. See also Ex- 43; septic tank effluent and, 104; vent creted infections; Pathogens; name of pipes to control, 77 Fasciolopsis buski, 13; infestation from specific infection or causative agent Off-site treatment of wastes, 129, 130, 131, aquatic vegetables. 12 In-house connections, 39, 42 132; aerated pile for, 140, calculations Feasability study, 26, 43. See also Sani- Insects: poultrv in control of, 116; trans- for, 134, 136; night-soil treatment ponds tation program planning mission of pathogens by, 15, 20. See for, 133-37, 140; objectives of, 128; Fecal coliform and streptococci stand- also name of specific insect thermophilic composting for, 133-34; ards, 148 Institution-communitv linkage, 25. See also waste stabilization ponds for, 128. 135 Feces, excreted load of pathogens in, 15- Communitv participation and prefer- Opistorchis, 148 16. See also Excreta ences Oxfam disaster sanitation unit, 123 Fertilizers: septic tanks and, 55; from vault International Drinking Water Supply and Oxidation ditches, 111 toilet wastes, 52; See also Compost Sanitation Decade, 3, 4, 7 Filariasis: bancroftian, 12, 126; Culex Pacu (fish) in aquaculture, 150 quinquefasciatus and, 20, 22; See also Kinship group-based facilities, 122 Pastures, sewerage irrigated. 147 Elephantiasis Pathogens: aerated lagoons and, lll; Filtration methods, 110, 111 Labor (self-help), 44 chlorination and, 113; in compost, 83, Financial costing, 27, 31-32. See also Eco- Latency, 15, 16 87, 135, 147; control of intrafamilial nomic costing Latrine programs, reasons for failure of, transmission of, 21; destruction of, 112, Fish: control hazards associated with, 149; 20-21 133; excreted load of, 15-16; in fish disease and, 148 Latrines: anal cleansing materials and me- ponds, 148; host response to, 17; in- Fish ponds, 148-49 chanical seals for, 44; distance from wells fective dose of, 16-17; land application Fixtures. See Latrine and toilet fixtures of, 22; land areas required for sewered, of effluents and, 111, 113; lethal factors Flies: aquaprivies and, 97, 100; covers on 45; nature of soil and, 22; requiring no for, 146; maturation lagoons and, 145; toilets to exclude, 69; ROEC'S and, 77, water, 39; in schools, 21. See also Toi- multiplication after excretion, 16; oxi- 82; in unimproved pit latrines, 73; vent lets; name of specific kind of latrine dation ditches and, l11; sand filtration pipes and, 77; vip latrines and, 82. See Latrine and toilet fixtures, 65, 66, 67, 68, methods and, 111; in septic tank ef- also Insects 69, 70, 71; for composting toilets, 69, fluents, 101, 107; in sewerage effluents INDEX 159 (standards for), 147; in sludges and Public facilities. See Communal sanitation Self-help, 32. 44. 87 composts (standards for), 147; sullage facilities Septic tanks. 41, 43, 101, 104-08; bio- and, 126; survival in environments, 16, chemical oxygen demand and, 93; de- 145. 146; temperature and time in de- Reed odorless earth closets (ROEC'S), 39, signs for, 103; effluent disposal from. struction of. 112; time required for de- 41, 55, 78, 79; advantages and disad- 101-02, 104; for PF toilets, 89. 92, 93; struction of (in pits), 42, 43. 82; waste vantages of. 77. 82; compared to aqua- sludge and, 56, 94. 101; slurrv and, 52. stabilization ponds and, 148; in waste- privv, 97; costs of, 43, 82; lifetime of, 55; soil pollution and, 101, 107; sullage treatment ponds. 139 43; requirements for, 81; maintenance and, 52. 105; three-compartment. 41, Pedestal seats, 67, 71; "Colombian," 89; of, 81; offset pits for, 77; population 52; two-compartment, 55. 101. 102 preventingchildrenfromfallingthrough, density and, 81. See also VIDP latrines; Sewerage. 109-11, 113; costs and, 3, 4. 66. See also Latrine and toilet fixtures vtp latrines 43, 57; disposal and soil conditions. 42; Personal choice. 52, 61. See also Com- Resource recovery: agricultural. 145-48; resource recovery and use, 111-13. 145- munity participation and preferences aquacultural, 148-50; biogas and. 145. 52; sullage and. 57; tertiarv treatment Pigs. 20 150, 151; social, institutional, and eco- of, 110, 111. See also Conventional Pinworm, 19 nomic aspects of, 151, 152 sewerage system; Small-bore sewers Pit latrines, 74; basic components of. 73; Roundworm. 13, 14. See also Ascaris lum- Sewerage systems: cost of additional water costs of, 43; disadvantages of unim- bricoides for, 28; pathogenic effluents and. 110; proved, 73; double pits for, 73, 76; im- per capita average incremental cost of. proved, 73, 75: as initial improvement, Salmonella: control measures and, 19; in 30; for PF toilets, 91, 92.93; sullage and, 55 raw sewerage in England. 16 30, 55, 57, 90, 109, 126; volumetric cal- Pits, 75, 80; alternating, 43, 57n1; anal Sand filtration methods. 110. 111 culation of costs for. 30. See also Con- cleansing material in, 74. 77; design of. Sanitation: in high-rainfall areas, 11; pro- ventional sewerage systems; Sewerage; 77-78; double, 74, 76; high water table portion of cash income devoted to, 43; Sludge; Small-bore sewers and, 74; infiltration capacitv of, 55; life Southeast Asian family example. 11, 12 Sewered aquaprivies. See Pour-flush (PF) of, 42, 43, 74; offset, 77. 89; pathogens Sanitation facilities: based on kinship toilets in, 82; seepage in, 126: soil conditions group, 122; communal, 122-24; low-cost. Sewered pour-flush toilets. See Pour-flush and, 42; for specific types of latrines, 4, 124; most common, 73; operation and (PF) toilets 55, 73, 76, 77. 89 maintenance of, 25; primary con- Sewers: small bore. 56. 93. 99. 107. 114- Planning. See Sanitation program plan- straints on, 4; unsatisfactory operation 15; for sullage, 55, 57, 90. 93, 109. 126. ning due to lack of maintenance of, 45; up- See also Sewerage systems; Storm water Plumbing fixtures. See Latrine and toilet grading sequences for, 52-57. See also Shadow pricing. See Economic costing fixtures Cultural attitudes toward sanitation fa- Shigellosis, control measures and, 19 Ponds for waste treatment: aerobic. 128; cilities; name of specific kind of facility Shower facilities, 45. 124 anaerobic, 135. 137; anaerobic pre- Sanitation improvements: alternative se- Sludge: activated effluent. 110; biogas treatment, 128, 133; design of, 136; fac- quences for, 56; of community facili- from. 145, 151; collection of.56; path- ultative, 128, 133, 136, 137, 150; fish ties, 124; costsof samplesequencesfor. ogens in, 110-11. 113; qualitv of. 110; grown in maturation in, 150; land re- 56; economic costs of. 56; incremental. rate of accumulation of. 101; removal quirements for. 133; maintenance of, 4-5, 7, 45, 52; priority for, 55; staged. of, 94, 101; treatment and disposal of. 133; maturation of. 136. 137, 139-45; 55-57; of VIP and VIDP latrines and 110-13 night-soil treatment and, 133. 137. 139; ROEC'S, 82 Slurry: as fertilizer. 55; septic tanks and. sullage and, 127; waste stabilization and. Sanitation program planning. 5, 7, 81; 52, 55 128, 133. 135; winter temperatures and, community participation in. 23-26, 42, Snails, 16. 148 45 44; data collection for, 5; education and Soakawavs, 101-02, 104, 105 Population density: choice of sanitation institutional development programs and. Soil pollution, 42; children and, 21; from technology and. 42-43, 81; DVC toilets 45 septic tanks, 101. 107 and. 88. See also Housing density Sanitation services, cost of, 3 Soils. 45; latrine-to-well distance and na- Pork tapeworm, 13, 14, 19-20 Sanitation technologies: alternative, 4. 40; ture of, 22; low absorptive capacity and Poultry to control insects, 116 complementary investments in, 44; sewered PF systems, 9; percolation tests Pour-flush (PF) toilets, 39. 41. 55; anal comparing, 39, 44-45; deriving costs for of, 102. 104; sanitation technology and cleansing materials and. 44, 99; for different. 30; description of. 41; eco- nature of. 42; survival time of patho- communal sanitation facilities, 124; nomiccostingforearlyscreeningof,31; gens in. 145 compared with aquaprivy, 97. 99; con- household financial contribution and Southeast Asia, sanitary conditions in version of ROEC'S to, 55; costs of, 43, choice of, 44; housing density and choice (example), 11-12 93; design of, 89, 90, 91; for flat areas, of, 42-43; land-use and, 45; nonsew- Spray irrigation hazards. 147 93nl; maintenance of. 91; material and ered options. 7; rural-urban suitabili- Squatting plates, 68, 69. 70, 71; commu- labor requirements for, 89; septic tanks ties of, 41; selections of, 24; training nity preferences and. 64; composting for, 93; sewered, 41, 55. 91, 92. 93; and, 25; variety of, 39, 40, 41; water toilets and, 84, 87; placement of (VIP suitability of, 91, 93nl; sullage and, 55, requirements of, 41. See also Appro- latrines), 72; preventing children from 89, 91, 93; as vault toilets, 118; water priate technology; Selection of sanita- falling through. 64; preventing soiling requirements for, 89 tion technology; Technology; name of of, 64; replacement by waterseal unit, Precipitation (weather), choice of sani- specific technology 55. See also Latrine and toilet fixtures tation technology and level of. 45 Schistosoma species, 20; aerated lagoons Storm water, 30, 127 Privacy and design of latrines and toilets. and, 111 Subsidies, 44 61, 123, 124. See also Cultural attitudes Schistosomiasis, 12. 13. 14; transmission Sullage, 125-27; aquaprivies and, 97, 99; and design of sanitation facilities of (by children), 15; urine as fertilizer costsof sanitary technology and. 30, 57; Protozoa: pathogenic (in excreta). 12; and. 84 disposal of large volumes of, 56; PF tOi- sewerage treatment and, 110-11. 113; Screening (sewerage treatment), 110 lets and disposal of. 89, 91; ROEC's and survival time on crops, 146; survival time Sedimentation (sewerage treatment), 110 disposal of, 82; sewers and drains for, in soil. 145. See also Pathogens; name Seepage pits for sullage, 126. See also 55, 57, 90, 93, 109, 126; stormwater and, of specific protozoa and disease Pits 30; three-stage septic tank and, 52; two- 160 INDEX Sullage (continued) United Nations Water Conference (1977), Waste: biodegradable, 83, 87, 133: reuse stage septic tank and, 55; VIP and VIDP 3 of, 82, 133. See also Compost, Night latrines and disposal of, 82; vault and Upgrading. See Sanitation improvements soil; Sewerage cartage systems and, 120, 121 Urinals, 123 Waste stabilization ponds for elimination Swine. See Pigs Urine: in composting toilets, 83-84; of pathogens, 148. See also Ponds for drainage channel for, 69, 84; Schisto- waste treatment Taboos. See Cultural attitudes and design soma haematobium and disposal of, 20, Waste treatment ponds. See Ponds for of sanitation facilities 83 waste treatment Taenia: saginata, 13, 14, 19-20, 147. 148; User charges, 31 Water: cost of, 28, 29; domestic, 7; hand- solium, 13, 14, 19-20 User participation. See Community par- carried supplies of, 39, 42; hot, 124; Tankers. See Vacuum tankers ticipation and preferences patterns of use, 7; reducing nonessen- Tank trucks, 118 tial use of, 57; toilets and, 39, 41, 124; Tapeworm, 13, 14. 147; transmission by Vacuum tankers, 118, 120 volume of use of (sullage and), 125, birds, 20. See also Beef tapeworm; Pork Vacuum truck, 118 126; taps and connections for, 42. See tapeworm VAM system, 135 also Well water Technology: loans and affordable, 32; op- Vault and cartage systems, 118-21. See Waterborne sewerage, 4 tions for not-affordable, 32; real re- also Composting toilets; PF toilets Water consumption: achieving savings in, source cost of, 29. See also Appropriate Vault latrines and groundwater, 22 7ae consumphon tchnolog and, technology; Choice of technology; San- Vault toilets, 39, 41, 43, 52, 54, 55, 118. 7; choice of santation technology and, itation technologies; name of specific 119; to replace bucket latrines, 116; See 39,41;reductionof,57;volumeof(and technology also Composting toilets; DVC toilets; PF sullage), 126 Temperature: for methane production, 45, toilets Water-saving plumbing fixtures, 7, 124 151; sanitation technology choice and, Ventilated improved double-pit (VIDP) la- Water seals: anal cleansing materials and, 45 trines. 39, 76; advantages and disad- 44; aquaprivies and, 94, 97; mainte- Three-stage septic tanks. 41, 52, 55 vantages of, 82; costs of, 82; pit design nance difficulties with, 39; manufacture Tilapia, 149 for, 77; population densitv and, 81. See of, 89; PF toilets and, 82, 89, 97 Toilet fixtures. See Latrine and toilet fix- also ROEC'S; viP latrines Water storage vessel in house for PF toi- tures Ventilated improved pit (viP) latrines, 41, lets, 55 Toilets, 39; community preferences and, 55, 56, 73-74, 75, 77; advantages and Water supply sewerage levels, 39, 42; in- 50-51; inside, 42, 61; requiring no water, disadvantages of, 82; compared to cremental improvements in, 52 39; water consumption and flush, 29; aquaprivy, 94, 97; cost of, 56, 82; eco- Water table: high, 74, 87; selection of water tap location and, 39, 41, 42. See nomic costing of (examples), 32-33; technology and, 42, 81. See also Ground also Latrines; name of specific kind of lifetime of, 43; maintenance of, 73, 81; water toilet population density and, 81. See also Water taps, 39, 42 Toilet superstructures. See Latrine and ROEC'S; VIDP latrines Well water, soils and contamination of, toilet superstructures Ventilation for latrines and toilets, 61, 69, 22 Training of community workers, 23. See 73, 75 Whipworm 13 14 also Education Vent pipes, 73. 75, 77 Wipwo, 13, Transmission of excreted infections, 19 Viruses: control measures and, 19; path- Widrows, 135 Trematodes and snails, 16 ogenic in excreta, 12; sewage treatment Trichuris, 148 and, 110-11, 113; survival time on crops, Typhoid, 12, 15; control measures and, 146; survival time in soil, 145. See also Yard taps, 39, 42 19 name of specific virus or disease Yersinia, control measures and, 19 The full range of World Bank publications, both free and for sale, is described in the Catalog of World Bank Publications; the continuing research program is outlined in World Bank Research Program: Ab- stracts of Current Studies. Both booklets are updated annually; the most recent edition of each is available without charge from the Pub- lications Unit, World Bank, 1818 H Street, N.W., Washington, D.C. 20433, U.S.A. John M. Kalbermatten is senior adviser for water and wastes and Charles G. Gunnerson is senior project officer in the Transportation and Water Department of the World Bank. DeAnne S. Julius is acting economic adviser for the Energy Department of the World Bank. D. Duncan Mara is professor of civil engineering at the University of Leeds, England. A World Bank Publication The United Nations has designated the 1980s as the International Drinking Water Supply and Sanitation Decade. Its goal is to provide two of the most fundamental human needs-safe water and sanitary disposal of human wastes-to all people. To help usher in this important period of international research and coopera- tion, the World Bank is publishing two volumes on appropriate technology for water supply and waste disposal systems in developing countries. Since 1976, Bank staff and researchers from various countries have been analyzing the economic, environmental, health, and sociological effects of various technologies to identify the most appropriate systems for the needs and resources of different areas. The research has included field investigations in nineteen countries. Since the technology for supplying water is better understood, the emphasis in these volumes is on sanitation and waste reclamation technologies, their contributions to better health, and how they are affected by water service levels and the ability and willingness of communities to pay for the systems. This manual presents the latest field results of the research, summarizes selected portions of other publications on sanitation program planning, and describes the engineering details of alternative sanitation technologies and how they can be upgraded. The guidelines, procedures, and technologies are based on the World Bank's own research in nineteen countries. The twenty- two chapters are divided into three parts: socioeconomic aspects of sanitation program planning, sanitation program planning, and sanitation technology options. The manual is extensively illustrated with technical diagrams of the recommended sanitation systems and their components. The material is intended both for professionally trained project engineers and scientists and for technicians and field workers who are familiar with the particular geographic and cultural conditions in their project areas. The Johns Hopkins University Press Baltimore and London ISBN 0-8018-2584-9