26069 Water Resources and Environment Technical Note D.2 Water Quality: Wastewater Treatment Series Editors Richard Davis Rafik Hirji WATER RESOURCES AND ENVIRONMENT TECHNICAL NOTE D.2 Water Quality: Wastewater Treatment SERIES EDITORS RICHARD DAVIS, RAFIK HIRJI The World Bank Washington, D.C. Water Resources and Environment Technical Notes A. Environmental Issues and Lessons Note A.1 Environmental Aspects of Water Resources Management Note A.2 Water Resources Management Policy Implementation: Early Lessons B. Institutional and Regulatory Issues Note B.1 Strategic Environmental Assessment: A Watershed Approach Note B.2 Water Resources Management: Regulatory Dimensions Note B.3 Regulations for Private Sector Utilities C. Environmental Flow Assessment Note C.1 Environmental Flows: Concepts and Methods Note C.2 Environmental Flows: Case Studies Note C.3 Environmental Flows: Flood Flows Note C.4 Environmental Flows: Social Issues D. Water Quality Management Note D.1 Water Quality: Assessment and Protection Note D.2 Water Quality: Wastewater Treatment Note D.3 Water Quality: Nonpoint-Source Pollution E. Irrigation and Drainage Note E.1 Irrigation and Drainage: Development Note E.2 Irrigation and Drainage: Rehabilitation F. Water Conservation and Demand Management Note F.1 Water Conservation: Urban Utilities Note F.2 Water Conservation: Irrigation Note F.3 Wastewater Reuse G. Waterbody Management Note G.1 Groundwater Management Note G.2 Lake Management Note G.3 Wetlands Management Note G.4 Management of Aquatic Plants H. Selected topics Note H.1 Interbasin Transfers Note H.2 Desalination Note H.3 Climate Variability and Climate Change Copyright © 2003 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 First printing March 2003 2 CONTENTS Foreword 5 Acknowledgments 7 Introduction 8 The Need For Watewater Treatment 9 Wastewater treatment provides environmental benefits for downstream water users reliant on rivers and lakes. It can also provide health benefits, particularly if the waste stream is disinfected. Establishing Water Quality Objectives 15 Ambient water quality objectives are intended to pro- tect users by establishing acceptable levels of con- Author taminants after the effluent stream mixes with the Gary Wolff receiving waters. Technical Adviser Wastewater Treatment Technology 21 Stephen Lintner Effluent treatment is conventionally divided into five Editor levels: pretreatment, minimal treatment, basic (primary) Robert Livernash treatment, full (secondary) treatment, and advanced (tertiary) treatment. Research into wastewater treat- Production Staff ment, alternative sewer systems, and on-site waste Cover Design: Cathe Fadel management techniques is resulting in the emergence of promising new technologies and techniques. Design and Production: The Word Express, Inc. Financial Issues 29 Sanitation and wastewater treatment costs depend on Notes the type and level of service provided and local con- Unless otherwise stated, ditions. Utility services of all types have been, and all dollars = U.S. dollars. continue to be, subsidized in many parts of the world, All tons are metric tons. leading to overuse of water resources, discharge of contaminated wastewater, and subsequent environ- Cover photo by mental problems. Fees that recover the operating cost Curt Carnemark, World Bank of delivering services, and the involvement of the us- Wastewater treatment ers in setting these fees, is an essential part of the so- plant, Latvia lution. This series also is available on the World Bank website Further Information 31 (www.worldbank.org). 3 WATER RESOURCESANDENVIRONMENT · TECHNICAL NOTE D.2 Boxes 1. Key principles for municipal wastewater management 11 2. Improving Mexican wastewater management with regional, multisector planning 12 3. Successful, demand-oriented wastewater projects 14 4. Preventing pollution in Lake Nakuru, Kenya 15 5. Cost-benefit analysis in the Nitra Basin, Slovak Republic 18 6. Cost-effectiveness analysis 19 7. The Adaptive Environmental Assessment and Management (AEAM) process 20 8. Treatment in constructed natural systems in rural settings 23 9. Advanced treatment for phosphorus removal in Hungary 24 10. Capturing cross-sectoral benefits 27 11. The emerging techniques of vertical or horizontal unbundling 28 Tables 1. Examples of reasonably quantifiable benefits of wastewater treatment. 10 2. U.S. secondary treatment and European Community urban effluent standards 18 3. Cost ranges for on-site and sewered (conventional treatment) options 29 4 WATER QUALITY: WASTEWATER TREATMENT FOREWORD The environmentally sustainable development and priority in Bank lending. Many lessons have been management of water resources is a critical and learned, and these have contributed to changing complex issue for both rich and poor countries. It attitudes and practices in World Bank operations. is technically challenging and often entails difficult trade-offs among social, economic, and political con- Water resources management is also a critical de- siderations. Typically, the environment is treated velopment issue because of its many links to pov- as a marginal issue when it is actually key to sus- erty reduction, including health, agricultural tainable water management. productivity, industrial and energy development, and sustainable growth in downstream communi- According to the World Bank's recently approved ties. But strategies to reduce poverty should not lead Water Resources Sector Strategy, "the environment to further degradation of water resources or eco- is a special `water-using sector' in that most envi- logical services. Finding a balance between these ronmental concerns are a central part of overall objectives is an important aspect of the Bank's in- water resources management, and not just a part terest in sustainable development. The 2001 Envi- of a distinct water-using sector" (World Bank 2003: ronment Strategy underscores the linkages among 28). Being integral to overall water resources man- water resources management, environmental agement, the environment is "voiceless" when other sustainability, and poverty, and shows how the 2003 water using sectors have distinct voices. As a con- Water Resources Sector Strategy's call for using sequence, representatives of these other water us- water as a vehicle for increasing growth and re- ing sectors need to be fully aware of the importance ducing poverty can be carried out in a socially and of environmental aspects of water resources man- environmentally responsible manner. agement for the development of their sectoral in- terests. Over the past few decades, many nations have been subjected to the ravages of either droughts or floods. For us in the World Bank, water resources man- Unsustainable land and water use practices have agement--including the development of surface and contributed to the degradation of the water resources groundwater resources for urban, rural, agriculture, base and are undermining the primary investments energy, mining, and industrial uses, as well as the in water supply, energy and irrigation infrastruc- protection of surface and groundwater sources, pol- ture, often also contributing to loss of biodiversity. lution control, watershed management, control of In response, new policy and institutional reforms water weeds, and restoration of degraded ecosys- are being developed to ensure responsible and sus- tems such as lakes and wetlands--is an important tainable practices are put in place, and new predic- element of our lending, supporting one of the es- tive and forecasting techniques are being developed sential building blocks for sustaining livelihoods and that can help to reduce the impacts and manage for social and economic development in general. the consequences of such events. The Environment Prior to 1993, environmental considerations of such and Water Resources Sector Strategies make it clear investments were addressed reactively and prima- that water must be treated as a resource that spans rily through the Bank's safeguard policies. The 1993 multiple uses in a river basin, particularly to main- Water Resources Management Policy Paper broad- tain sufficient flows of sufficient quality at the ap- ened the development focus to include the protec- propriate times to offset upstream abstraction and tion and management of water resources in an pollution and sustain the downstream social, eco- environmentally sustainable, socially acceptable, logical, and hydrological functions of watersheds and economically efficient manner as an emerging and wetlands. 5 WATER RESOURCES ANDENVIRONMENT · TECHNICAL NOTE D.2 With the support of the Government of the Nether- The Notes are in eight categories: environmental lands, the Environment Department has prepared issues and lessons; institutional and regulatory is- an initial series of Water Resources and Environ- sues; environmental flow assessment; water qual- ment Technical Notes to improve the knowledge ity management; irrigation and drainage; water base about applying environmental management conservation (demand management); waterbody principles to water resources management. The management; and selected topics. The series may Technical Note series supports the implementation be expanded in the future to include other relevant of the World Bank 1993 Water Resources Manage- categories or topics. Not all topics will be of inter- ment Policy, 2001 Environment Strategy, and 2003 est to all specialists. Some will find the review of Water Resources Sector Strategy, as well as the past environmental practices in the water sector implementation of the Bank's safeguard policies. useful for learning and improving their perfor- The Notes are also consistent with the Millennium mance; others may find their suggestions for fur- Development Goal objectives related to environmen- ther, more detailed information to be valuable; while tal sustainability of water resources. still others will find them useful as a reference on emerging topics such as environmental flow assess- The Notes are intended for use by those without ment, environmental regulations for private water specific training in water resources management utilities, inter-basin water transfers and climate such as technical specialists, policymakers and variability and climate change. The latter topics are managers working on water sector related invest- likely to be of increasing importance as the World ments within the Bank; practitioners from bilateral, Bank implements its environment and water re- multilateral, and nongovernmental organizations; sources sector strategies and supports the next gen- and public and private sector specialists interested eration of water resources and environmental policy in environmentally sustainable water resources and institutional reforms. management. These people may have been trained as environmental, municipal, water resources, ir- rigation, power, or mining engineers; or as econo- mists, lawyers, sociologists, natural resources Kristalina Georgieva specialists, urban planners, environmental planners, Director or ecologists. Environment Department 6 WATER QUALITY: WASTEWATER TREATMENT ACKNOWLEDGMENTS The Bank is deeply grateful to the Government of version by Random Dubois of the United Nation's the Netherlands for financing the production of this Food and Agriculture Organization. Technical Note. This Technical Note was reviewed by David Technical Note D.2 was drafted by Gary Wolff of Hanrahan, Peter Kolsky, and Sumter Lee Travers of the Pacific Institute for Studies in Development, the World Bank. Environment, and Security, building on an earlier 7 WATER RESOURCES AND ENVIRONMENT · TECHNICAL NOTE D.2 INTRODUCTION Urban water services can include any or all of the and consequently can degrade water quality if not following: (a) provision of water for domestic and properly designed and managed. industrial uses; (b) sanitation to remove human wastes from possible contact with humans; and (c) The importance of clean water supplies and sani- treatment of wastes to remove contaminants. tation led the international community to designate Whereas the removal of wastes--sanitation--confers the 1980s as the "International Drinking Water Sup- well-established and obvious health benefits on ur- ply and Sanitation Decade." The percentage of glo- ban residents, the treatment of the wastes provides bal population with access to sanitation services rose benefits for downstream communities. These ben- from 20 to 31 percent during the decade. However, efits emerge primarily as environmental improve- there are no figures available on the extent to which ments, which support the environmental services wastewater treatment accompanied these improve- that these communities rely on, although there can ments in sanitation services. be health benefits too, particularly if disinfection is included in the treatment to remove pathogens. Pollutants can be stabilized, diluted, degraded, or removed through natural processes within the re- Sanitation sources can be provided either using ceiving waters. Microbial action can covert differ- water as a carrier (e.g., sewerage systems) or not ent forms of nitrogen to nitrogen gas, which then (e.g., pit latrines). Whether waterborne sanitation escapes to the atmosphere. Many waterbodies re- technologies are used or not, it is important to make spond to increases in pollutant loads by increasing sure that the wastes are treated before they get to these assimilation processes, and so can manage a waterbodies in order to protect downstream com- certain level of increased pollution. The ability of munities. Thus, poorly sited or maintained latrines the receiving waters to manage these pollutants is can contaminate waterbodies because the usual soil termed its assimilative capacity. However, if the processes are not able to remove nutrients and dis- pollution load increases too much, then these natu- able pathogens before the wastes emerge into the ral processes either become overwhelmed or are environment. compromised because toxicants in the pollution poison vital microbial processes. This Note does not deal with water supply or sani- tation services.1 Its focus is on the treatment of In its most recent strategy--Water and Sanitation Ser- wastes, principally waterborne effluent streams, vices for the Poor: Innovating through Field Experi- because they discharge directly into waterbodies ence--the World Bank Water and Sanitation Program states that the strategy will address the end use of wastewater, including "water conservation, waste- water treatment and re-use, and the protection of water sources." More broadly, the 1993 Water Re- sources Management Policy of the Bank supports Bank the collection and treatment of wastewater in or- orld W, der to protect aquatic environments and public health. Some Bank documents examining the ef- Mertaugh fects of wastewater discharges on receiving waters are cited at the end of this Note. Michael by 1Information on water supply and sanitation can be found Photo Naretwa River at Mostar, Bosnia-Herzegovina at http://www.worldbank.org/html/fpd/water/urban.html. 8 WATER QUALITY: WASTEWATER TREATMENT This Note on wastewater treatment is one of three and the financial issues arising from provision of that focus on water quality issues. Note D.1 dis- different levels of wastewater treatment. It does not cusses issues related to assessment and protection deal with environmental issues that can arise from of water quality. This Note covers issues of estab- disposal of solid wastes or on-site disposal of efflu- lishing water quality objectives for point source dis- ent in pit latrines, etc. Note D.3 discusses nonpoint- charges into receiving waters from wastewater source water pollution. treatment plants, different treatment technologies, THE NEED FOR WASTEWATER TREATMENT BENEFITS AND COSTS Cost-benefit analysis does not distinguish between recipients of costs and benefits. If health impacts Wastewater treatment is almost always funded as and financial costs are the only concerns, sewer part of a larger project involving sanitation services, projects often have net benefits for those living in and sometimes water supply. Consequently, many the service area, and net costs for those living down- aspects of wastewater planning and management stream. Total benefits to all affected parties may have to be discussed in the context of water supply exceed total costs, justifying the project on economic and sanitation improvements. grounds, but there are clearly distributional effects. Those who lose a fishery due to an upstream sewer Expansion of water supplies without simultaneous project are, in effect, subsidizing those receiving the wastewater facilities can lead to wastewater- new service. In recognition of the wider impacts of related environmental and public health problems. water and sanitation provision, there is now an ac- In both Manila and Jakarta, for example, the ceptance of the need to include upstream and down- provision of reticulated water without the stream water users in decisionmaking. construction of sewers in large parts of these metropolitan areas has led to the installation of Identifying the parties affected by wastewater dis- septic tanks by home owners. In essence, people charges is not simple, since the benefits and costs have personally invested in a minimal treatment can be distributed over long time periods and large of their wastewater that is poorly suited to dense geographical areas. Even after the affected parties urban areas. are defined, it is difficult to know if total benefits exceed total costs because many benefits and costs Nearly 3 billion people worldwide do not have sani- are intangible. For example, the cost of lost tation services at present. Sanitation services cre- biodiversity downstream is difficult to quantify be- ate healthier homes and streets, a direct use value cause future income from ecotourism or new phar- for those who live in newly served neighborhoods. maceuticals is highly uncertain. But waterborne sanitation systems may also create a loss of welfare for downstream users of river wa- Nonetheless, all benefits and costs should at least ter. The principal downstream impacts are environ- be identified in an economic assessment (Table 1). mental; potential health impacts can arise when the A discussion of intangible costs and benefits will effluent stream is insufficiently mixed in the receiv- allow these effects to be included in the decisions ing waters or where the water is used for drinking at least qualitatively. Omitting intangible costs and immediately below the discharge point. Both up- benefits from the initial evaluation often leads to stream and downstream impacts are significant, costly investments at a later time to correct prob- and both should be accounted for in assessing new lems that could have been avoided by thoughtful investments. and comprehensive analysis of the initial project. 9 WATER RESOURCES AND ENVIRONMENT · TECHNICAL NOTE D.2 TABLE 1. EXAMPLES OF REASONABLY QUANTIFIABLE BENEFITS OF WASTEWATER TREATMENT PROJECTS Benefit (or cost if wastewater service is not provided) Examples Avoided water supply Relocation of the water supply intake for Shanghai, protection or replacement expenses China at a cost of $300 million Avoided water supply costs Cyprus and San Jose, California (see Box 10) when reuse is implemented Protection of income from fisheries Prawn and shellfish harvests in the coastal waters of China Protection of income from agriculture Cholera in Peru in 1991 cost $1 billion in lost agricultural exports Protection of income from tourism Lake Tata, Hungary (see Box 9) LESSONS FROM BANK EXPERIENCE tures. A treatment facility and ocean outfall had to be constructed in 1989 for the previously untreated The lessons from Bank experience with wastewa- sewage at considerable cost. ter treatment plants are consistent with the key prin- ciples in a draft municipal wastewater guidance In some cases, environmental assessments can re- document prepared by the United Nations Environ- duce the immediate costs of a project by determin- ment Program (Box 1). ing that some facilities are unneeded or won't lead to the expected environmental benefits. For example, These lessons can be synthesized into six broad the EA for the Bombay sewage disposal project ana- topics: (1) assessing environmental issues from the lyzed not just the direct environmental impacts of beginning; (2) using regional and multisectoral the project, but also whether the project would at- planning; (3) creating extensive stakeholder involve- tain environmental goals for the receiving waters. ment; (4) using a demand-oriented approach; (5) Using hydrodynamic and water quality modeling, engaging the private sector; and (6) providing suf- the EA demonstrated that the impact of the project ficient funds for operation and maintenance (O&M). would be highly dependent on pollution control in upstream areas outside the legal boundaries of Assessing environmental issues from the beginning. Bombay. Consequently, it recommended that a sys- Concentrated discharges of untreated or poorly tem of aerated lagoons be dropped from the design, treated wastewater into rivers or coastal zones, or since the water quality objective in the receiving uncontrolled spreading of sewage sludge on agri- waterbody could not be achieved without address- cultural land, can create environmental, health, and ing upstream pollution that was reaching the economic problems as severe as those that are be- waterbody directly. ing solved by the sewage scheme. For example, a Bank-funded sewer project in 1974 in Abidjan, Cote Nevertheless, EAs are not fully effective in mitigat- d'Ivoire, constructed an outfall for untreated sew- ing environmental impacts. A review2 of EAs for age into the shallow Ebrie lagoon (mean depth of 3 Bank-funded projects found that EAs had been meters). EAs were not required in 1974. In this re- gion between Cote d'Ivoire and eastern Nigeria, 2 coastal lagoons are highly productive components Green, K.M., and A. Raphael. 2002. Third Environmen- of marine and freshwater fisheries, and this lagoon tal Assessment Review (FY96-00).Washington: World Bank was one of the country's most attractive coastal fea- Environment Department. 10 WATER QUALITY: WASTEWATER TREATMENT BOX 1. KEY PRINCIPLES FOR MUNICIPAL WASTEWATER MANAGEMENT 1. Political will and financial affordability are prerequisites for adequate wastewater management. Success without these two prerequisites is difficult if not impossible. First, political will is fundamental for assigning a high priority to wastewater management among other pressing public investment needs. Second, the chosen wastewa- ter management approach must be financially affordable. 2. Environment, health, and economy are important indicators for action. All three indicators are driving forces for adequate wastewater management. The non-action alternative imposes great costs on current and future genera- tions. 3. Stepwise implementation of measures is essential to reach long-term management goals. Wastewater management is not an isolated problem, but integrated with water supply, urban and rural planning, and other development sectors. 4. Demand-driven analyses and prognoses ensure effective investments. Demand-driven approaches give greater "value for money" than do supply-driven investments. Demand-driven approaches need proper analysis of the societal demands now and in the near future. 5. National and local governments are responsible for creating an enabling environment for sustainable solutions. All branches of government have a responsibility in creating solutions. A country's central government, for example, plays a significant role as facilitator and initiator even when primary governance of wastewater manage- ment issues is at the local government level. 6. Commitment and involvement of all stakeholders are assured from the start. Investment in awareness cre- ation, demonstration of win-win situations, and development of commitment and catchment solidarity are essential for success in wastewater management. 7. "Water User Pays" and "Polluter Pays" are basic principles to consider. These principles are essential and can be applied in a way that sustains equitable sharing of costs by the rich and poor. 8. Public- private partnerships and other new financial mechanisms should be explored. New partnerships are important options and potentially useful tools, if the governing regulatory system is strong enough or can be strengthened enough to avoid the negative consequences that can result from private participation in manage- ment of public goods. 9. Linking municipal wastewater management systems to other sectors, for example water supply or tourism, ensures better opportunities for adequate cost recovery. Sustainable wastewater management may involve high initial investments and long-term contracts to cover financial risks and to recover costs. As profits­or "net benefits"­are likely to be higher in other sectors, linking these to wastewater management can reduce the risks involved and enhance the feasibility of new partnerships. 10. Sustainable solutions for wastewater management build upon pollution prevention at the source, efficient water use and best available technologies, and address economic aspects and low-cost alternatives when appropriate. Wastewater management need not always involve high initial investments. A very careful search for low-cost­and thus more sustainable­technologies and approaches that target waste prevention, pretreatment, water conservation, efficient use of water, and natural systems for wastewater treatment is essential. 11. Innovative alternatives and integrated solutions are to be fully explored before final decisions on action are taken. Because innovative and integrated solutions are challenging to develop, they tend to be neglected unless full exploration of them is required as part of every wastewater management decision process. Source: UNEP. 2001. "Guidance on Municipal Wastewater: Practical Guidance for Implementing the Global Programme of Action for the Protection of the Marine Environment from Land-Based Activities (GPA) on Sewage." Working Document Version 2.0, 21 October 2001. The Hague: UNEP/GPA Coordination Office. 11 WATER RESOURCES AND ENVIRONMENT · TECHNICAL NOTE D.2 "highly effective" during the project implementa- Unfortunately, sector-specific projects often precede tion phase in only 25 percent of Category A regional multisector plans because administrative (significant adverse impact) projects and "partially authority cuts across the water cycle. When this oc- effective" in a further 60 percent. There is a need to curs, the possibilities for joint control of different move the EA process further upstream before the water pollution sources are often not recognized; project becomes too far advanced. and, if recognized, such trade-offs are outside the task assigned to project staff and consultants. This Using regional and multisectoral planning. Waste- can lead to less environmental protection at greater water treatment and water quality planning need cost, as illustrated in Box 2. However, the impor- to be approached from a regional, multisectoral per- tance of undertaking strategic plans before com- spective. Regulations, treatment requirements, mencing individual projects is more widely and pollution prevention policies or interventions recognized both within the Bank and in borrowing should compare estimated benefits with estimated countries. The increasing use of Country Environ- costs across the region and across sectors. Other- mental Analyses and Sector Environmental Strate- wise, a saving in one sector (e.g. limited wastewa- gies move in this direction. ter treatment) may result in an even larger loss in another sector (e.g. downstream water users). Note Creating extensive stakeholder involvement. A waste- F.3 provides examples where cross-sectoral ap- water management project affects numerous proaches led to re-use of wastewater at consider- people. It creates construction, operation, mainte- able savings to both the municipality generating the nance, and system administration jobs; improves wastewater and water-scarce agricultural users. water quality or habitat for downstream water us- ers; potentially affects neighboring communities Wastewater reuse is also an example of an innova- through disposal of sewage sludge; and can poten- tive solution to wastewater management (UNEP tially supply a source of water for other activities Principle 11). Similarly, demand management of (see Note F.3). Early and comprehensive involve- water supply (Note F.1) can lead to lower volumes ment of these stakeholders, along with the of effluent (although the loads of pollutants will be decisionmakers, ensures that everyone understands unchanged), thereby extending the life of wastewa- the project's costs and benefits. Neglect of one af- ter treatment plants, lowering treatment costs and, fected group or one issue can generate sufficient to some extent, reducing the occurrence of treat- opposition to delay the project and, in extreme ment plant bypass during high-flow events. cases, lead to failure. BOX 2. IMPROVING MEXICAN WASTEWATER MANAGEMENT WITH REGIONAL MULTISECTOR PLANNING Water resources management in Mexico is the responsibility of the federal National Water Commission (CNA). However, wastewater management is normally managed at the municipal level. Lack of resources and other local priorities have resulted in treatment of only 20 percent of municipal discharges and 10-15 percent of industrial discharges. Unaffordable operation and maintenance costs have also plagued many treatment plants. Less than 10 percent of the existing plants in Mexico are now estimated to be operating satisfactorily. To address this problem and the growing demand for improved water quality, a River Basin Council was established in the Lerma-Chapala river basin in 1989. The results to date suggest that the integrated water pollution approach has improved financial sustainability, increased state and local involvement in the planning and implementation of pollution control problems, and improved compliance with industrial effluent standards. CNA is currently extending the Lerma- Chapala approach to other river basins and is developing a simplified procedure for adapting effluent standards and pollution charges to the specific pollution levels of each river basin. Source: Marino, M., and J. Boland (1999). An integrated approach to wastewater management. Washington: The World Bank. 12 WATER QUALITY: WASTEWATER TREATMENT Even when stakeholder participation does not The groups benefiting from sanitation services are change the choice of facilities, stakeholder involve- not usually the ones bearing the greatest costs from ment helps ensure their commitment to the deci- wastewater discharges. Consequently, users of a sion. Knowing what is planned reduces the sewer project may be relatively unconcerned about likelihood that there will be opposition because of wastewater treatment. To include the voices of those a sense of exclusion. It is essential that governments facing the costs from effluent discharges requires are included in these stakeholder groups so that that a wider constituency be formed in sanitation high-level political support is maintained because planning and implementation. The downstream of their role in financing and regulating wastewa- benefits will occur, at least partly, as costs avoided ter discharges. The French system of river basin if the wastewater treatment plant is planned as part agencies is a successful, historical example of this of a sanitation project, and this may be difficult for approach. Seven river basin agencies were created downstream communities to accept. That is, they in 1964. In each basin, all aspects of water policy may feel that there is no benefit to them if the in- and planning are referred to a basin committee, vestment in a wastewater treatment plant merely which represents all stakeholders­including na- maintains the quality of the receiving water at its tional, regional, and local governments; industrial present level. and agricultural interests; and citizens. The com- mittee guides the activities of the technical staff of There is no simple solution to obtaining meaning- the basin agency (see Note B.2). ful stakeholder involvement in projects that include municipal wastewater discharges. It will take per- Identifying the stakeholders and quantifying the sistence, considerable time, and money in many costs and benefits to them is more difficult with cases. However, the benefits of more trouble-free wastewater treatment facilities than it is with, say, project implementation and better long-term water supply or sanitation investments. Downstream sustainability usually make this up-front investment beneficiaries are likely to be dispersed, poor, and worthwhile. often lack the political influence of urban commu- nities. In addition, it may take a scientific study to Using a demand-oriented approach. Water demand quantify the links between pollution removal, en- studies conducted by the World Bank in the 1980s vironmental benefit, and the dependence of com- concluded that sustainable provision of water and munities on these environmental services. sanitation service depended on the extent to which consumers' preferences and willingness to pay were incorporated in the investment plan- ning and implementation process. Box 3 de- scribes a successful application of this approach to both sanitation and wastewater projects, although those making the decisions about the level of investment in Indonesia did not include the downstream communities de- pendent on the receiving waters. Bank orld W, The demand-oriented approach should in- clude the needs of all those affected by sani- tation services, including those bearing Carnemark downstream costs such as effluent dis- Curt charges and sludge disposal. This lesson is by consistent with a multi-sectoral approach Photoand the early involvement of all stakehold- Delivering water, Indonesia 13 WATER RESOURCES AND ENVIRONMENT · TECHNICAL NOTE D.2 BOX 3. SUCCESSFUL, DEMAND ORIENTED WASTEWATER PROJECTS - The demand-oriented approach allows community members to take responsibility for their sanitation and wastewater treatment needs. Wastewater professionals provide technical assistance, but community members decide on the level of treatment to be constructed (within a budget) and may participate in construction, operation, and maintenance. Trunk sewers and treatment facilities in urban areas are usually still constructed and operated by a central authority. However, treatment facilities have also been constructed and operated by organizations of service users in rural areas in the Lao PDR and in Indonesia. For example, residents of five communities on the Malang Penninsula, Indonesia, have constructed community sewer systems with treatment in communal septic tanks preceded by simple screening and grit removal facilities. More than half the influent organic materials are removed by this treatment. Effluent still does not meet Indonesian standards for discharge into waters that support fisheries and livestock watering in most communities. However, these standards were met in one community, and better construction techniques and more knowledgeable operation at the other facilities would probably allow them to meet the standard. Source: Wright, Albert M. 1997. Toward a strategic sanitation approach. Washington: UNDP-World Bank Water and Sanitation Program ers in a forum where these needs can be explored. tal pollution unless there are adequate regulatory Under this approach, public agencies become fa- controls and the political and financial backing cilitators and organizers, taking on tasks only when to enforce them. The development of private sec- they have a clear comparative advantage. They be- tor involvement in sanitation and wastewater treat- come "lead agencies" in a broad search for solu- ment should be part of a package that involves tions, rather than physical suppliers of solutions. clarification of institutional roles, strengthening This approach expands participation opportunities regulatory and enforcement procedures, and op- for the private sector, nongovernmental organiza- eration of reliable monitoring programs (see tions, and individuals. Note B.3). Engaging the private sector. Government-funded Providing sufficient funds for O&M. There are agencies have traditionally built and operated wa- numerous examples where wastewater treatment ter, sanitation, and wastewater systems and the pos- plants are operating at below their design capacity sibility of using local, private sector expertise has or have failed completely because of inadequate often been neglected. Not only does the latter ap- O&M funding. The benefits from proper treatment proach relieve the government of debt burden, but are not as apparent as, say, the benefits from it can create local employment and provide a profit the treatment of drinking water and the beneficia- motive for success. ries of proper wastewater treatment are usually not a powerful lobby. Consequently, governments For example, the Government of Lesotho trained are often reluctant to enforce the collection of fees bricklayers to build improved pit latrines. Govern- for wastewater treatment. When these plants fail, ment banks provided unsubsidized credit to finance the resulting pollution can threaten the ecological the latrines. The program has been very successful, health of receiving waterbodies and the livelihoods in large part due to the marketing efforts of the brick- of those dependent on the waterbodies. Box 4 pro- layers. The latrines operate more effectively, reduc- vides an example where inadequate capital fund- ing the potencial for off-site contamination. ing is possibly threatening an internationally renowned lake. However, transferring responsibility to the private sector can lead to increased environmen- 14 WATER QUALITY: WASTEWATER TREATMENT BOX 4. PREVENTING POLLUTION IN AKEL NAKURU, KENYA Lake Nakuru in Kenya is famous for the diversity of its wildlife, including two species of pink flamingo. The lake is on the Ramsar list of internationally important wetlands and is the basis of a valuable tourism industry. However, there were serious concerns about pollution of the lake from the discharge of minimally treated sewage from the rapidly growing town of Nakuru. In 1987, the Japanese Bank for International Cooperation agreed to rehabilitate and expand the town's two sewage treatment plants­the Town plant and the Njoro plant. The upgrades were completed in 1997. A recent review has found that, while the Town plant is generally operating to design standards, the Njoro plant is receiv- ing so little influent that it does not discharge through its drainage channel to the lake. This is because the plant was not fully connected to the parts of Nakuru town that it was designed to serve. This includes the town's industrial operations. The plant's effluent either evaporates or leaches into groundwater. There is no evidence that either plant is adding nutrients, industrial pollutants, chemicals, or pathogens to the lake, and the plants appear to be fulfilling their role. However, the lack of funding to connect large parts of the town to the Njoro plant means that effluent and industrial wastes are almost certainly being transferred through stormwater runoff to the lake instead of being treated. Source: Special Assistance for Project Sustainability Team. 2002. Special assistance for project sustainability for Greater Nakuru water supply project in the Republic of Kenya. Final Report. SAPS team for Japan Bank for International Cooperation. ESTABLISHING WATER QUALITY OBJECTIVES AMBIENT AND EFFLUENT WATER Biological oxygen demand (BOD). BOD is a mea- QUALITY INDICATORS sure of the oxygen consumed by microorganisms over time as they degrade organic matter in a wa- ter body. When the BOD of an effluent depletes the Some of the more important ambient water quality dissolved oxygen in the receiving water below the indicators (see Note D.1) for wastewater discharges minimum level required to support the most sensi- are: tive aquatic species, it has the potential to cause I Dissolved oxygen and biological and harm to aquatic life. Given the typically high or- chemical oxygen demands ganic content of discharged effluent, BOD is the most I Fecal coliform as an indicator of pathogens commonly used measure of effluent quality. Because I Suspended solids wastes discharged to surface waters mostly biode- I Nutrients such as nitrogen and phosphorus grade within five days, BOD is the parameter usu- I Chlorophyll 5 ally used. I Potentially toxic substances, such as metals or organochlorine pesticides. Chemical oxygen demand (COD). COD is a mea- sure of the oxygen required to chemically degrade Dissolved oxygen (DO). Fish and other aquatic life organic materials in a water sample. COD includes require oxygen to survive. The necessary concen- BOD, because materials that can be biologically tration depends on the species, although most fish degraded can be chemically degraded. COD should species require at least 4 ppm. Consequently, a mini- be measured when industrial sewage is discharged mum concentration of dissolved oxygen is a com- because, in these circumstances, COD can be much mon ambient water quality objective. The maximum higher than BOD. In addition, physical or chemi- dissolved oxygen in water decreases as tempera- cal treatment processes are often required when ture increases. For this reason, warm ambient wa- COD greatly exceeds BOD, because biological treat- ters, all other factors equal, are more susceptible to ment cannot remove materials that microbes don't oxygen depletion than cold ambient waters. degrade. 15 WATER RESOURCES AND ENVIRONMENT · TECHNICAL NOTE D.2 Fecal coliforms. Fecal coliforms are an indicator is, on average, 1.5 percent of the dry weight of algal of contamination with human wastes and, conse- cells. Consequently, chlorophyll a is a good proxy quently, the potential for pathogens to be present. for the amount of algal biomass present in a sample. However, fecal coliforms can also arise from Chlorophyll has the property of fluorescing in re- livestock wastes. In either case, water from sources sponse to a flash of bright light, so the chlorophyll with elevated fecal coliform is a potential source concentration can be easily measured with a fluo- of pathogens and should be handled with care. rometer. Fecal coliforms should be monitored in waste streams from sewage treatment plants, but often are Secchi disks are an even simpler way to estimate not. It is essential that they are monitored when the eutrophication. A specially marked disk is attached waste stream is being reused (Note F.3). to a pole and lowered into the water from a boat. The depth at which the markings can no longer be Suspended solids. Suspended solids are a measure seen, the Secchi depth, is a measure of the water's of the small particles that remain in suspension in turbidity. The euphotic zone (the depth beyond a water sample. Suspended solids are a common which only 1 percent of the incident light penetrates) measure of effluent water quality because they can is 5 times this depth. However, turbidity can also affect water clarity, which can be detrimental to fish- be caused by suspended soil particles (the Yellow eries, recreational uses of water, and other benefi- River is a classic example), and so Secchi disks only cial uses. indicate eutrophication when algal growth is the dominant cause of the turbidity. Nutrients. Nutrients such as nitrogen and phospho- rus can cause eutrophication, which usually mani- Toxicants. Potentially toxic substances in wastewa- fests itself as an increase in phytoplankton ter discharges include heavy metals, synthetic or- concentrations to nuisance levels (see Note G.4). ganic compounds, and some inorganic compounds Both nitrogen and phosphorus are found in high such as cyanides and sulfides. In the United States, concentrations in discharges of wastewater. The ni- the following metals are listed as "priority pollut- trogen originates from human waste, breakdown ants," and monitored in municipal wastewater dis- of organic matter, and industrial sources, while the charges: antimony, arsenic, beryllium, cadmium, phosphorus comes from organic matter, detergents, chromium, copper, lead, mercury, nickel, selenium, and human wastes. In fresh waters, phytoplankton silver, thallium, and zinc. Analysis for these metals are often limited in their growth by access to phos- can be expensive, and is most critical when indus- phorus, so measurements of these nutrients, par- trial effluents are included in the waste stream. ticularly phosphorus, provide an indication of the potential eutrophication of the waterbody. Note D.3 There are numerous synthetic organic compounds provides more details of that are potentially toxic. the different measures of Bio-accumulative sub- nitrogen and phosphorus. stances such as DDT, PCBs, and organochlo- Chlorophyll a and secchi . rine pesticides are an disks. Eutrophication can Bank important group. Many of be measured more di- orld W, these compounds accu- rectly than through the mulate in the fatty tissues nutrient loads being dis- Marino of living organisms, and charged. Algae are the tend to increase in con- primary form of phyto- Manuel centration within those by plankton in most in- tissues as one moves up stances and chlorophyll a Photothe food chain. This im- Sewage treatment plant, Podgorica, Serbia and Montenegro 16 WATER QUALITY: WASTEWATER TREATMENT plies that discharges of bio-accumulative substances EFFLUENT QUALITY OBJECTIVES at very low levels can later show up at much higher levels in humans or top level predators. Because If the objectives are expressed as concentrations, these material accumulate, there is often no safe effluent needs to be treated to be below the ambi- level of discharge. Two other environmentally sen- ent water quality objectives after dilution in a small sitive groups of synthetic organics are phenols and zone around the point of discharge. If ambient qual- polyaromatic hydrocarbons (PAHs). Phenols are ity objectives are stated in terms of total mass (loads) present in many wastewaters, and PAHs are often of pollutants, then different design issues may be present in combined wastewater and storm water important. discharges. For example, discharges of some heavy metals in AMBIENT WATER QUALITY OBJECTIVES the San Francisco Bay in California are believed to be toxic to aquatic life. Concentrations of some of Wastewater discharges can harm those who use the these heavy metals in the effluent stream are not of receiving water. Ambient water quality objectives much concern (except very high concentrations), are intended to protect these users by establishing but the total loading of each metal to the Bay and acceptable levels of contaminants after the effluent the ability of natural processes to assimilate these stream mixes with the receiving waters. Ambient loads is a concern. For this reason, discharge per- water quality objectives need to be established be- mits for petroleum refineries in the San Francisco fore a wastewater treatment facility is designed. It Bay region usually restrict the total mass of dis- is not possible to design the necessary wastewater charged selenium, but have no restrictions on the treatment processes rationally unless these objec- concentration of selenium in effluent. tives are well-established. In part because past regional efforts to determine There are many beneficial uses of waterways, and effluent discharge objectives proved uneven, uni- so ambient water quality objectives differ from place form effluent discharge objectives have now been to place (see Note D.1). For example, waters from established in the United States, the European which shellfish are harvested are very sensitive to Union, and other developed countries. U.S. and bacteriological and toxic pollutants because many European Community requirements for wastewa- shellfish are filter feeders, leading to accumulation ter that has been treated to secondary level are sum- of contaminants in their flesh. Because these fish marized in Table 2. According to Marino and Boland are often consumed raw by humans, the potential (1999), the improvements in water quality achieved for transmission of disease is very high. Conse- by these national approaches have come at the ex- quently, the water quality objectives for such a pense of increased costs, reduced regional owner- waterbody would need to include fecal coliform con- ship of effluent treatment programs, and reduced centrations. innovation. Civil society should be included in the setting of ambient water quality objectives because of the fi- THE INTERACTION OF AMBIENT nancial implications. Stringent objectives will in- AND EFFLUENT OBJECTIVES evitably lead to significant wastewater treatment costs. There is a tendency in some developing coun- Ambient water quality objectives are best established tries to adopt water quality objectives that have been with the regional, multi-sector approach discussed established in the developed world when, in fact, previously using cost-benefit analysis. An example there is a limited technical capability to meet those of (partial) cost-benefit analysis for the Nitra River standards and little desire or ability on the part of Basin in the Slovak Republic illustrates how this citizens to pay for the treatment. 17 WATER RESOURCES AND ENVIRONMENT · TECHNICAL NOTE D.2 TABLE 2. U.S. SECONDARY TREATMENT AND EUROPEAN COMMUNITY URBAN EFFLUENT STANDARDS Parameter U.S. Secondary European Community Treatment Standard Directive BOD 30 mg/l (30 day average) 25 mg/l 5 45 mg/l (7 day average) COD None 125 mg/l TSS 30 mg/l (30 day average) 35 mg/l (optional) 45 mg/l (45 day average) pH (Acidity) 6-9 None approach can be used to help choose ambient wa- As this example illustrates, there is an interaction ter quality objectives (Box 5). between ambient and effluent objectives--and between cost-benefit and cost-effectiveness analy- The ambient water quality objectives can usually sis--such that these objectives may have to be set be achieved with different combinations of effluent iteratively. objectives for various pollution sources, because the most cost-effective wastewater investments in each WATER QUALITY MODELING city or area often depend on investments made in other cities or areas within the watershed. The role Uniform effluent objectives make the planning pro- of cost-effectiveness analysis in assessing the vari- cess relatively simple for individual treatment plants. ous combinations of effluent objectives, and an ex- However, when there are multiple treatment plants ample from Eastern Europe, is described in Box 6. and other effluent discharges within a region, the BOX 5. COST-BENEFIT ANALYSIS IN THE NITRA BASIN, SLOVAK REPUBLIC The Nitra is a tributary of the Vah River, which eventually enters the Danube. Its length is about 171 kilometers, and there are about 600,000 inhabitants in the Nitra River Basin. About 70 percent of BOD pollutant load comes from municipal 5 discharge sources. Some of the time, dissolved oxygen (DO) is depleted in the downstream reaches of the river. Satisfy- ing the European Community objectives listed in Table 2 would require capital costs of about $65 million and would achieve a minimum DO of 7 mg/l. Achieving a minimum year-round DO objective of 6 mg/l would require capital investments of only $26 million; and achieving a year-round minimum DO objective of 4 mg/l would require capital investment of only $13 million. Only capital costs were included in this analysis. Completing the cost-benefit analysis would require that operation and maintenance costs be summed with amortized capital costs for each of the three alternatives, and that the benefits to inhabitants of the basin of minimum DO of 4, 6, and 7 mg/l be included. In addition, it is important to ask if the costs of achieving these three DO levels represent the most cost effective investments possible. Nonetheless, the Nitra Basin example demonstrates how simple cost-benefit analysis can be used to select ambient water quality objectives. Note, however, that cost-benefit analysis simply aggregates the benefits and the costs without considering the distribu- tional impacts. For example, the 4 mg/l minimum DO level may lead to the discharge of wastewater that leads to downstream communities bearing the majority of the costs. Source: Somlyody, L. and P. Shanahan. 1998. Municipal Wastewater Treatment in Central and Eastern Europe. Washington: The World Bank. 18 WATER QUALITY: WASTEWATER TREATMENT BOX 6. COST-EFFECTIVENESS ANALYSIS Cost-effectiveness analysis is not the same as cost/ benefit analysis. The former identifies the lowest cost way to achieve a specified objective, while the latter identifies the project alternative objective that maximizes net benefits (total benefits less total costs). For example, meeting ambient water quality requirements might require reducing BOD 5 discharge by 100 kilograms per day, based on cost/benefit analysis. If only one pollution source exists, cost-effective- ness analysis would be limited to picking the treatment technology that meets this ambient water quality objective. If multiple pollution sources exist, the lowest cost of treatment for each source should be compared. If the lowest cost of treatment is the same at each source, uniform effluent objectives would be the most cost-effective solution. But if BOD can be removed at lower cost from one source than another, the effluent objective at the lower-cost source should be lower than at a higher-cost source. Cost-effectiveness analysis for pollution reduction in the Vistula River, Poland, found that the cost of reducing loads on the Baltic Sea varied by a factor of 2.5 between the most and the least cost-effective treatment plants. If Baltic Sea loads were the only ambient water quality objective guiding the selection of treatment facilities along the Vistula River, additional treatment at the lowest-cost facilities and less or no treatment at higher-cost facilities would significantly reduce the total cost of achieving the desired load reduction. Cost-effectiveness analysis, however, is usually performed for more than one water quality parameter. In the Vistula River example, ambient water quality concerns also existed in parts of the River near each city. Consequently, some high-cost treatment plants might need to be upgraded to meet a local ambient water quality objective. The local objective acts as a constraint on the cost-effectiveness analysis for the region. Consequently, cost-effectiveness analysis should be performed at various scales­starting at local water quality or health objectives (for which pollution prevention may be less costly than collection and treatment), then at various watershed scales (for example, the Baltic Sea watershed, and perhaps subwatersheds within it). Source: Somlyody, L. and P. Shanahan. 1998. Municipal Wastewater Treatment in Central and Eastern Europe. Washington: The World Bank. planning process to determine the most cost-effec- Without the modeling of dissolved oxygen concen- tive choice of treatment facilities may be much more trations in the Nitra River Basin example (Box 5), complicated. Water quality modeling is essential to the planning team could not have known what level managing this complexity successfully. of treatment would achieve the minimum DO level that would support aquatic life, and therefore could As with the Bombay sewage disposal project men- not calculate the additional cost of higher DO lev- tioned previously, water quality modeling may un- els. A variation of the same modeling tool, used in cover some unexpected results. In Gunabara Bay, the highly polluted Huangpo River at Shanghai, Rio de Janeiro, a modeling study found that high found that oxygen depletion in the tidal reaches of levels of wastewater treatment could, at least in the the river would still be a problem even after high short term, cause deterioration in ambient water levels of treatment of wastewater discharges. This quality. Cleaner water might lead to algal blooms was because incoming tides would cause treated that would be worse than the before-treatment water to be present in the tidal reaches for very long ambient water conditions. This is because removal periods, resulting in much more oxygen depletion of organic wastes (but not nutrients) would initially from discharged wastewater than in a free-flowing increase dissolved oxygen in the receiving water; river. but the nutrient availability and increased water clarity would promote algal growth, which eventu- Similarly, ocean outfalls for effluent are usually ally depletes dissolved oxygen even more severely designed so that wastewater or fecal solids do not than before treatment. As a result of the modeling wash onto shore under most weather and ocean effort, the recommended approach assigned a higher conditions. These designs rely on relatively simple priority to nutrient reduction than had originally water quality modeling that accounts for the quan- been proposed. tity of discharge, the level of treatment prior to dis- 19 WATER RESOURCES AND ENVIRONMENT · TECHNICAL NOTE D.2 charge of wastewater, the depth of the discharge, in all settings. Where these data values are miss- the location of the discharge relative to prevailing ing, they can often be estimated and uncertainty ocean currents, and so forth.3 In Barbados, an limits can be placed on the model predictions to ocean outfall was designed that takes advantage account for these estimates. of strong, unidirectional currents that sweep the coast. Modeling was used to determine that an Computer-based models are not a substitute outfall located 1 kilometer offshore would keep for hand calculations by experts, logical thinking, the wastewater-mixing zone (a small zone around and extensive stakeholder involvement. In fact, the discharge point) at least 30 meters below the economic and water quality models can be devel- ocean surface, and would satisfy ambient water oped with extensive review and input from quality objectives for bathing waters and shellfish stakeholders using, for example, the Adaptive harvesting. Environmental Assessment and Management (AEAM) process (Box 7). In this way, the model it- The Pollution Prevention and Abatement Handbook self becomes part of the consultation process, lead- and a recent World Bank publication4 describe some ing to the stakeholders having increased trust in common water quality models and, in the case of the outputs of the model. the latter publication, the experience of applying them in India, China, and the Philippines. These models include ones that are designed for predict- ing the water quality impacts of catchment runoff, 3 urban runoff, and discharges from point sources Further information can be found in the Environmen- into rivers, lakes, and marine waters. However, some tal Assessment Sourcebook Update 13. data required by these models may not be available 4Palmer, M. D. (2001). BOX 7. THE ADAPTIVE ENVIRONMENTAL ASSESSMENT AND MANAGEMENT (AEAM) PROCESS Originally developed by the ecologist C.S. Holling, AEAM is a workshop-based process for the exploration and evalua- tion of management options for complex systems. It is particularly applicable to environmental management issues, where there are complex interactions of social, economic, physical, and ecological systems. Key phases of the methodology are to (a) identify stakeholders; (b) use a workshop environment (incorporating key players) to develop and define the stakeholders' understanding of the system; (c) identify key components of the system with ongoing stakeholder input; (d) develop algorithms for the representation of the key components and combine the algorithms into an interactive model, which should have the capacity to incorporate key geographic, economic, policy, and management components for the system; (e) use gaming workshops to test the model, obtain feedback from stakeholders, and develop initial management scenarios; (f) finalize model development and present the model through a workshop with stakeholders; and (g) report the project results to the wider community. The interactive model produced by the AEAM methodology is formulated by the stakeholders and incorporates their expertise and understanding of the system. The model relies on available data and is made as simple or as complex as these data allow. The role of facilitators in the workshops is to provide skills that draw out and clarify the expertise and knowledge of the stakeholders. Source: Holling, C. S. 1978. Adaptive Environmental Assessment and Management. London: John Wiley & Sons. 20 WATER QUALITY: WASTEWATER TREATMENT WASTEWATER TREATMENT TECHNOLOGY LEVELS OF TREATMENT combined with an industrial pretreatment program was recommended. This section discusses the levels of treatment re- quired to meet the effluent objectives established Minimal treatment. Raw wastewater typically con- during planning for ambient water quality in more tains materials that clog or impair pumps or other detail, and some of the more common technology equipment needed to discharge wastewater reliably choices within each level of treatment. There is an and causes unsightly conditions in the receiving wa- enormous body of literature on wastewater treat- ter. Solid waste inappropriately dumped in sewers ment technologies (see Further Information). is another common problem. Minimal treatment re- moves these materials and is used as a first step in Effluent treatment is conventionally divided into five nearly all wastewater treatment facilities. levels: (1) pretreatment, (2) minimal treatment, (3) basic (primary) treatment, (4) full (secondary) treat- Larger objects are usually removed by either me- ment, and (5) advanced (tertiary) treatment. Pro- chanically cleaned screens or communitors that cut cesses to kill pathogens (disinfection) may be used up larger objects. The quantity of screenings usu- following most levels of treatment. ally varies from 0.0035 to 0.0375 m3 per m3 of waste- water. Pretreatment. Industrial facilities or agricultural processing may create pollutants that can be most Septic tanks are a form of minimal treatment be- effectively treated at the point of generation, such cause they also remove grit and floatable objects from as a factory or canning plant. Such treatment prior wastewater. If the tank is not overloaded, much of to discharge into a sanitary sewer is called pretreat- the organic content in grit and floatables will anaero- ment. In many countries, licenses for industrial dis- bically degrade. Tank cleaning will be required ev- charges to sewers require that the influent meet ery two to three years as inorganic grit (silt, sand, certain water quality standards. When an influent etc.) and refractory organic matter accumulates. concentration of some particular pollutant is un- Unfortunately, most septic tanks are overloaded in usually high, pretreatment is usually necessary and practice and require much more frequent cleaning. cost-effective. Often this is not done, and the tanks clog up and untreated sewage overflows onto the surface. For example, the wastewater treatment plant at Nove Zamky, in the Slovak Republic, is greatly overloaded. Disposal of screenings, grit, skimmings, and septage The capacity of the plant is about 3,500 kg of BOD (septic tank sludge) are environmental and public removal per day, but the actual load is about twice health issues that should be addressed early in as large. Sixty percent of influent is from industrial project development. Septage is usually collected sources with high concentration of BOD, TSS, TN, by private contractors who often discharge it ille- and TP. Treatment plant upgrades are required, with gally to surface waters or storm drains. Also, sub- capital costs in the range of $4 to$6 million or $11 surface discharges of seepage from the disposal to$14 million depending on the approach. Although fields of septic tanks often re-emerge in the storm- the more expensive approach would reduce nitro- water and drainage channels. These practices can gen levels in the influent more than the less expen- create ambient public health problems that are sive one, neither approach is capable of meeting sometimes more severe than if on-site, waterless ambient water quality objectives for nitrogen dis- disposal such as pit latrines had been used for sani- charges. Consequently, the less expensive approach tary wastes. 21 WATER RESOURCES AND ENVIRONMENT · TECHNICAL NOTE D.2 Basic (primary) treatment. Primary treatment typi- ally include an aeration basin in which the biodeg- cally removes organic materials by physical settling, radation occurs and a sedimentation tank in which often assisted by the addition of flocculants (chemi- the microbe-laden solids settle. Activated sludge is cals that cause particles to settle more rapidly). Well- sometimes referred to as a "suspended growth pro- operated primary treatment plants can reliably cess" because bacteria are suspended in the water reduce both BOD and SS below 50 mg/l. Primary column within the aeration basin. sedimentation tanks typically remove 50 to 70 per- cent of the suspended solids and from 25 to 40 per- Pond or lagoon systems are also capable of provid- cent of BOD5. Effluent from pond systems may have ing secondary level treatment, although the waste- higher levels of BOD and SS than this, due to the water needs to be retained much longer than in 5 algae that grow in these nutrient-enriched ponds, activated sludge basins, necessitating more land unless the algal biomass is removed by processes area for the treatment facility. Hydraulic retention such as filtration or dissolved air flotation prior to times in pond systems vary from 4 to 40 days, with discharge. secondary effluent quality achievable at longer re- tention times and primary effluent quality achieved Basic treatment is appropriate when the receiving at shorter retention times. By comparison, waste- water has a high capacity to assimilate organic water is retained in activated sludge aeration and matter. For example, ocean waters that are high in settling tanks for only 4 to 8 hours, and within the dissolved oxygen may be able to degrade organic entire treatment plant for much less than 1 day. matter without causing dissolved oxygen levels to Pond/lagoon systems have the advantage of remov- drop significantly. Increased algal biomass, due to ing bacteria more effectively than conventional sew- nutrients in the wastewater, may be eaten by aquatic age treatment and are simple and cheap to operate. species so rapidly that algal blooms and eutrophi- cation do not occur. Similarly, a small discharge into Both aerobic and anaerobic bacteria may be present a large river may be sufficiently diluted that few in pond systems. Aerobic bacteria require oxygen adverse effects occur if only basic treatment is pro- to degrade wastes, whereas anaerobic bacteria de- vided. For example, the city of Manaus5 discharges grade wastes in the absence of oxygen though a primary treated wastewater into the Rio Negro just different chemical pathway. Anaerobic treatment upstream of the Amazon. It is difficult to see the can be useful when wastewater has a high solids benefit of higher levels of treatment in these cir- content, since establishing uniform aerobic condi- cumstances. tions is difficult in this case. Anaerobic degrada- tion also takes place in septic tanks, leach fields, Full (secondary) treatment. This level of treatment other subsurface systems, and the bottoms of some removes more BOD and SS and (usually) nutri- treatment ponds. 5 ents than does basic treatment. Regulatory standards for this level are provided in Table 2 for the United There are many other systems that are capable of States and Europe. treating wastewater to the full (secondary) level. These include overland flow systems, slow and rapid The most common form of secondary treatment is infiltration land treatment systems, aquaculture (in- referred to as "activated sludge." In this process, cluding floating aquatic plants such as duckweed), bacteria are used to biodegrade organic materials and wetlands (see Note G.3). into gases (for example, carbon dioxide), water, and bacterial biomass. Activated sludge facilities usu- From an environmental perspective, constructed natural systems are often superior to conventional engineering treatments. They often use less energy, have fewer solid byproducts such as sludge, pro- 5Margulis, S., et al. 2002. Brazil: Managing Water Qual- ity. Tech Paper No. 532: Washington, World Bank. duce potentially useful biomass products, and usu- 22 WATER QUALITY: WASTEWATER TREATMENT ally have lower operation and maintenance costs. are low. Denitrification can occur in constructed Like ponds and lagoons, however, these systems natural systems used to provide secondary and ad- require more land than is usually available in ur- vanced treatment, or as a separate step after con- ban areas. Even so, these systems might prove more ventional secondary treatment ("effluent polishing"). cost-effective than conventional facilities in some urban settings if the intangible benefits (Table 1) Phosphorus is usually removed by the addition of could be quantified. Certainly, these systems are chemicals that form a precipitate that can then be often found to be cost-effective in rural settings removed by gravity settling. Aluminum sulfate where land is inexpensive. Box 8 discusses one con- (alum), lime, and ferric chloride are commonly used structed natural system that will be used in rural for this purpose. Box 9 presents an example of Hungary and the Slovak Republic. phosphorus removal by precipitation in Hungary. It demonstrates that delay in implementation of ad- Advanced (tertiary) treatment. Advanced treatment vanced wastewater treatment, if required, can be is typically used to remove nutrients, particularly very costly. nitrogen and phosphorus, or to protect waters­for example, mountain lakes­with limited natural abil- Phosphorus can also be removed by some con- ity to degrade organics. The ambient water quality structed natural systems. Soil-based land treatment objectives for the receiving waters drive the need systems are very effective at phosphorus removal for advanced treatment. Protection of ambient wa- if soil has a significant clay content or if iron or alu- ter quality in the Black Sea, for example, may re- minum are present. These elements bind strongly quire advanced treatment in some Bulgarian to the phosphorus, thus removing it from the efflu- treatment plants. ent. Aquatic systems such as ponds and permanently flooded wetlands, however, are much less effective Nitrogen removal is often accomplished by a pro- due to limited contact opportunities between waste- cess referred to as "denitrification." The nitrogen is water and soil. Shallow wetland systems that in- mostly in the nitrate form (NO ) following second- corporate soil filtration of wastewater usually 3 ary treatment. This is then reduced by bacteria to provide more phosphorus removal than ponds, but nitrogen gas (N ) if dissolved oxygen concentrations less than land treatment. 2 BOX 8. TREATMENT IN CONSTRUCTED NATURAL SYSTEMS IN RURAL SETTINGS The village of Szugy, Hungary, with a population of 1,200 and residential area of 74 hectares, is typical of rural villages in many parts of the world. There is currently no piped water or sanitary sewers. Shallow groundwater is highly contami- nated, with nitrates from improper on-site sewage disposal and fertilizer application. Shallow wells continue to be used for some purposes, but bottled water and usage of deep wells has become necessary to maintain public health. Bids received for construction of a conventional wastewater treatment facility ranged from $180,000 to $280,000 depend- ing on whether a steel or concrete tank was specified for biological treatment. In contrast, the estimated construction cost of a 4-hectare root zone treatment system is $140,000. This type of system involves a bed of reeds planted over a 15-cm compacted clay layer. Wastewater moves through the system horizontally, and is simultaneously filtered by soil and biologically degraded. The design effluent quality is 10 to 30 mg/l for BOD and 4 to 50 mg/l for SS. Effluent will be 5 disinfected prior to discharge into a creek. The feasibility of root zone treatment was also analyzed for six villages in a lowland region of the Slovak Republic. Village populations range from 400 to 2200. Four alternatives were studied: 1) individual conventional biological treatment plants for each village; 2) two conventional, regional, biological treatment plants; 3) one conventional, regional, biological treatment plant; and 4) root zone facilities for each village. Capital costs for the first three options ranged from $1.4 million to $2 million, while the six natural systems would require only $1.2 million. Source: Somlyody, L. and P. Shanahan. 1998. Municipal Wastewater Treatment in Central and Eastern Europe. Washington: The World Bank. 23 WATER RESOURCES AND ENVIRONMENT · TECHNICAL NOTE D.2 Pathogen removal. Pathogen removal is an extremely toxicity (long-term effects such as cancer, reduced important aspect of wastewater treatment. Bacte- reproductive success, lower growth rates, etc.) of- ria, viruses, protozoa, and helminths may be present ten results from long-term exposure to these chlo- in treated wastewater. Pathogens can be destroyed rinated compounds. While the presence of these by natural processes, such as the high pH levels that toxic byproducts is a concern in developed coun- occur in the anaerobic parts of some pond treat- tries where other health effects from wastewater ment systems. Many pathogens are killed by pro- discharges are now under control, the benefits from longed contact with seawater. Pathogens also die pathogen removal with chlorination in the devel- off naturally, or are killed by predation. Longer re- oping world usually outweigh the possible health tention times and higher temperatures in pond sys- effects from such byproducts. tems and other aquatic systems promote these processes. Dechlorination with sulfur dioxide is commonly used to remove residual chlorine and chlorinated Disinfection with chemicals­for example, chlorina- compounds. Dechlorination is a very reliable pro- tion­is used in most conventional treatment sys- cess provided that the residual chlorine is moni- tems. Chlorination can be used following basic, full, tored reliably. If not, toxic compounds will be or advanced treatment. Effectiveness at any given released into the receiving water or the measured dose level depends on factors such as the length of BOD and COD of the wastewater will be increased time that wastewater is held in the chlorine con- due to oxidation of excess sulfur dioxide. For this tact chamber; the concentration of pathogens; and reason, alternatives to chlorination or chlorination/ temperature. Since disinfection is hindered by dechlorination should be carefully considered dur- higher levels of BOD and SS, equivalent levels of ing project development. Although ozone or other pathogen removal require higher disinfectant doses disinfection processes such as ultraviolet light may in more highly polluted wastewaters. be significantly more expensive than chlorination or chlorination/ dechlorination, the beneficial uses Reactions between the introduced chlorine and of the receiving water might be protected more re- organic compounds in the wastewater produce liably by these other processes. trihalomethane compounds, many of which are toxic to humans and aquatic life. Even when acute The potential for environmental or public health toxicity (immediate death) does not occur, chronic damage from chlorine and chlorinated compounds BOX 9. ADVANCED TREATMENT FOR PHOSPHORUS REMOVAL IN HUNGARY Lake Tata, Hungary, is an artificial lake created by impounding the Alteler River, a tributary of the Danube. The lake and its watershed was a popular recreational area, but deteriorating water quality has reduced tourism income by half in the last decade. The lake is severely eutrophic and is no longer suitable for swimming. More than 90 percent of nitrogen and phosphorus loads in the lake originate from municipal discharges of two towns (Oroszlany and Tatabanya). Phosphorus precipitation was added to the wastewater treatment plants at both towns in the early 1990s, removing about 90 percent of the phosphorus in the effluent. The lake, however, failed to show any improvement in water quality. Subsequent analysis has shown that due to historical nutrient loads, a significant amount of phosphorus has accumu- lated in lake sediment. This provides an internal phosphorus source that more than offsets phosphorus removed from wastewater. The lake's sediment must be treated for a successful rehabilitation, at a prohibitive cost of $10 million. This example shows that prompt action to control nutrient discharges may be advisable once a problem is apparent or expected. Source: Somlyody, L. and P. Shanahan. 1998. Municipal Wastewater Treatment in Central and Eastern Europe. Washington: The World Bank. 24 WATER QUALITY: WASTEWATER TREATMENT is an example of why it is important to consider Activated sludge can be biologically digested after environmental issues early in the project develop- removal from the settling tanks, or left in a raw con- ment process. If the receiving water is sensitive to dition. Digestion reduces the volume of sludge re- chlorine residuals for its intended beneficial uses, quiring disposal, reduces its organic and pathogen then using chlorination for pathogen removal is content, and creates a sludge that is less odorous. unlikely to be the favored technology during the Anaerobic digestion can be used to convert organ- design process. ics into biogas, which in turn can be used in gas- driven pumps within the treatment plant or to MANAGEMENT OF SLUDGE produce electricity that may be used within or out- side the treatment plant. Although electricity pro- AND RESIDUALS duction from biogas at treatment plants has received much attention in recent years, biogas-driven in- Wastewater treatment creates solid residuals that fluent pumps are an older energy recovery technique need to managed in an environmentally sound that has been used successfully for many years. manner. By far, the largest such residual streams are sludge from primary and secondary treatment, Both raw and digested sludge are typically dewa- although residuals of grit, skimmings, and harvested tered prior to disposal in order to save on transport aquatic vegetation from the pretreatment can be costs. Sludge from septic tanks and pit latrines can significant too. The environmental implications of be disposed of jointly with sewage sludge. Dewa- managing these materials are rarely considered tering increases the solids content from 3-5 percent during project development. to 20-30 percent. Alternatively, digested sludge can be dried in shallow solar drying beds. Raw sludge Sludge management facilities may account for as is too odorous in most situations to be dried in open much as one-third of both the capital and operating beds, and attracts flies, rodents, and other creatures costs of conventional, secondary, activated sludge that can transmit disease. An underdrain system is wastewater treatment plants. In addition, disposal typically provided to assist the dewatering process, of sludges will result in significant releases of meth- with the drained water being returned to the treat- ane and the costs of this greenhouse gas need to be ment plant. If an underdrain is not provided, the factored into the decisions. Incremental process need to protect groundwater from wastewater in- improvements that reduce the quantity of sludge by filtration should be evaluated and addressed. Sol- 10 percent or more would create significant savings. ids content rises to 40 percent after the sludge has Treatment processes that produce little sludge (for been in drying beds. example, some anaerobic ponds) would compete more effectively with conventional treatment if the Digested sludge can be applied to land, composted avoided costs of sludge management are included. to make a soil amendment, disposed of in a sani- tary landfill, disposed of in the deep ocean, or Disposal in a sanitary landfill or incineration are incinerated. The first two techniques are environ- the most common options for disposing of screen- mentally preferable because they recycle organic ings, skimmings, and grit. If planned and managed materials and nutrients. However, they may also correctly, either of these options can be environ- cause environmental and production problems in mentally appropriate. However, if disposal is not particular situations, for example when heavy met- addressed explicitly during project development, it als are present in the sludge. is likely that inappropriate disposal will occur, be- cause operating and maintenance budgets are of- SLUDGE DISPOSAL ten inadequate in the first place. Additional demands, such as residuals disposal that were not explicitly budgeted from the beginning, will usually be Land application. Sludges from domestic wastewa- handled in the simplest and lowest cost manner. ter are often suitable for application to agricultural 25 WATER RESOURCES AND ENVIRONMENT · TECHNICAL NOTE D.2 land, but have also been used to restore degraded Liquid accumulation at the base of fill can also ren- lands, such as exposed surfaces at open pit mining der fill slopes unstable, especially during earthquake sites. Sludges that include residuals from industrial events, threatening sudden release of liquids or wastewater may be unsuitable due to the presence damage to neighboring facilities. A slide at a land- of metals, pathogens, or other potentially harmful fill located over saturated, marshy terrain in North- substances. Trace metals can be absorbed into food ern California in the 1970s caused an adjacent crops or into vegetation consumed by grazing ani- underground, 60-inch diameter, treatment plant out- mals. Local standards should be more stringent fall pipe to be displaced horizontally about 40 feet. when particularly sensitive waters adjoin or under- Fortunately, the outfall was of the gravity type (not lay the land application site. pressurized), and did not rupture. Ocean disposal. Ocean disposal typically involves SOME EMERGING TECHNOLOGIES barging the sludge to a deepwater location. The AND TECHNIQUES environmental impact may be difficult to assess because it requires an understanding of ocean cur- The previous section has described the most widely rents and biological processes, which may not be used wastewater treatment processes and tech- available at the proposed disposal location. At a niques available. Research into wastewater treat- minimum, potential impacts on ocean fisheries ment, alternative sewer systems, and on-site waste should be thoroughly investigated. Because of these management techniques is resulting in the emer- uncertainties, it is not a preferred option. gence of promising new technologies and tech- Incineration. Incineration is suitable when supple- niques. Some references are given in the Further mental energy sources are inexpensive and emis- Information section. Here, we discuss two emerg- sions from the incinerator can satisfy local air quality ing technologies and two emerging management objectives. However, local operation and mainte- techniques that may lead to environmentally sound, nance capacity should be considered carefully be- relatively low-cost, sanitation services. fore incineration is selected. A poorly operated sludge incinerator will not combust the sludge com- Demand management. Demand management of pletely, and may emit harmful or corrosive organic water supplies can potentially achieve very signifi- substances or ammonia. Even with complete com- cant savings by reducing inflows to treatment plants bustion, the possibility exists that harmful sub- and thereby reduce the need for sewer and stances, such as dioxins and metals such as mercury, treatment plant infrastructure. Techniques to will be emitted. Like ocean disposal, it is not a pre- achieve reduced water use are discussed in detail ferred option. in Note F.1. Landfill. Disposal to a sanitary landfill is appropri- So-called "effluent sewage" systems that collect ei- ate when leachate can be contained at the landfill. ther septic tank discharges or only greywater (urine Compacted clay or synthetic liners are best, but a and fecal matter are managed separately) can re- landfill situated over relatively impermeable soils duce sewer construction costs by 20 percent and or rock is also acceptable. Sludge should always be treatment costs significantly. Low flow plumbing dewatered prior to disposal in a sanitary landfill, fixtures save water and reduce hydraulic loads on unless the landfill is equipped with a leachate col- sewers and treatment plants, again reducing capi- lection system (an underdrain). Over long periods tal costs. of time, significant liquid accumulation at the base of fill can create enough hydraulic pressure to force Systems that reuse graywater on-site can reduce the leakage through even relatively impermeable soils environmental pressures on water resources in ar- or rock. eas that are short of water. These systems need to 26 WATER QUALITY: WASTEWATER TREATMENT be built and operated in a manner that satisfies strict 27 to 35 grams per kilogram of total solids; and pH public health codes. Thus, the public health code was between 6.6 and 7.1. The type of sludge­pri- in Santa Barbara County, California, now permits mary or secondary­does not seem to affect the sta- graywater systems that are designed in accordance bilized sludge quality very much. with county guidelines. Pathogen removal by vermi-composting is not yet Vermi-composting (worm composting). Some spe- fully understood although, in one test, the Texas cies of earthworms are well-suited for biological sta- Department of Health found no Salmonella in ei- bilization of wastewater sludges. Earthworms both ther the castings or the earthworms at a raw sludge aggregate loose materials into discrete, relatively facility. Earthworms may accumulate significant dry, and odorless fecal pellets (castings), and cre- concentrations of cadmium, copper, and zinc, and ate more surface area on which aerobic bacteria therefore should not be used as a major food source can feed. Anaerobic conditions are toxic to earth- for animals or fish. Testing for metals concentra- worms, so vermi-composting is not technically fea- tions in castings and earthworm bodies, however, sible for anaerobically digested sludge, unless it is should be performed in a pilot project before har- thoroughly aerated prior to introduction of worms. vesting is included in a facilities plan. Because earthworms both aerate and mix the com- post pile, mechanical equipment costs are much Capturing cross-sectoral benefits. Regional, multi- lower for vermi-composting than conventional piles. sector planning of wastewater management is one of the lessons from Bank experience. Economists Vermi-composting can be applied to sludge either describe these cross-sectoral benefits as "economies prior to or after dewatering. Investigations have of scope," because a project that delivers two or more shown that, for sludge treated with worms prior to separate services­for example, wastewater treat- de-watering, total solids vary from 14 to 24 percent; ment and irrigation water supply (see Note F.3)­is COD ranged from 606 to 730 grams per kilogram less expensive per recipient than supplying these of total solids; organic nitrogen was in the range of services separately (Box 10). Thus, many U.S. cit- BOX 10. CAPTURING CROSS SECTORAL BENEFITS - A 1984 Bank-sponsored study in Cyprus concluded that a wastewater treatment plant and ocean outfall was the least- cost solution to the groundwater and sea water pollution resulting from the on-site systems that serviced residents and high influxes of summer tourists. These facilities were not built, however, because hoteliers resisted the rate increases that were a condition of international Bank funding. After extensive stakeholder involvement, an update of the feasibility study was commissioned in 1990. The update concluded that a sea outfall was not necessary and recommended reuse of treated effluent for landscape irrigation. The San Jose/ Santa Clara, California, regional water pollution control plant discharges tertiary treated effluent to near- shore waters of the south San Francisco Bay. In the mid-1990s, the permitting agency required the treatment plant to restrict dry season discharge to no more than 120 million gallons per day in order to protect a saltwater marsh from being converted to a freshwater marsh, a loss of habitat for the endangered clapper rail and salt marsh harvest mouse. All prior analysis of alternatives to near-shore discharge had identified a deep, offshore outfall as the least-cost solution. When water supply and wastewater system needs were considered simultaneously, however, the lowest cost option was wastewater re-use for landscape irrigation. Subsequently, a 15 million gallon-per-day reuse system was put into operation, and plans are underway for up to 100 million gallons per day of reuse. The water district contributes around $100 per acre-foot to the cost of the reuse system, because it can avoid over $300 per acre-foot of expense for construction of new water supply reservoirs. With this contribution, reuse is a lower cost option for the treatment plant than construction of a deep ocean outfall. Both parties benefit financially, and the environment benefits as well. Source: World Bank.1999. Environmental Assessment Sourcebook Update No 13. Washington: World Bank. 27 WATER RESOURCES AND ENVIRONMENT · TECHNICAL NOTE D.2 ies maintain their own sanitary sewers, but a re- sibility for different stages of wastewater manage- gional plant treats the sewage. Sewer, water pipe, ment is termed vertical unbundling; the transfer of and street maintenance have an improved economy responsibility to smaller geographic entities is of scope by having one agency (typically the city) termed horizontal unbundling (Box 11). These tech- responsible for all three. niques avoid diseconomies of scope and scale, thus reducing costs per service recipient and allowing Identifying and capturing cross-sectoral economic more environmental protection at a lower cost. and environmental benefits of wastewater invest- ments is an emerging management approach that In itself, unbundling is not a solution. The impor- needs to be included in the early stages of project tant point arising from successes in vertical and hori- development. For example, the high organic and zontal unbundling arises from the recognition of moisture content of municipal solid waste in less- the possible economies and diseconomies of scale developed countries is conducive to biogas produc- and scope when all costs, including environmental tion in specially designed landfill cells. Disposal of costs, are included. For example, horizontal unbun- treatment plant sludge in such cells would be envi- dling was not environmentally or economically ronmentally sound, provide a source of energy at desirable in Chongquing, China, because there was the treatment plant site, and have lower cost than sufficient slope throughout the city to gravity drain construction and operation of anerobic digesters. standard-depth sewers to a single treatment plant location. In addition, a horizontally unbundled ap- Vertical and horizontal unbundling. Diseconomies proach involving numerous treatment plants would of scope can also occur. One agency that provides have discharged treated wastewater upstream from all wastewater services may be more costly than water intakes, necessitating treatment to the full multiple service providers, each specializing in one (secondary) level. Discharge at a single, downstream type of service. Similarly, facilities can be too large, plant requires treatment only to the basic (primary) creating diseconomies of scale. Transferring respon- level. BOX 11. THE EMERGING TECHNIQUES OF VERTICAL OR HORIZONTAL UNBUNDLING Brazil was successful at lowering the cost of sewer service to the urban poor by changing the authority and responsibil- ity for lateral sewers. As in other major cities, in-house plumbing and toilets had been traditionally owned by each household, and lateral sewers, trunk sewers, and treatment facilities had been traditionally owned and operated by a central agency. The transfer of responsibility for lateral sewers to community groups (vertical unbundling) allowed them to innovate and succeed where centralized agencies had failed. Horizontal unbundling is the practice of breaking cities into districts with separate sewers and treatment facilities. For example, sewer systems in flat areas can become prohibitively expensive as they are enlarged, because pipes either need to become larger and deeper to carry wastewater by gravity flow or pumping stations are required. Bangkok has divided its collection and treatment services into separate districts for this reason. Sewer systems are also horizontally unbundled in many parts of the United States, including Los Angeles County and Alameda County in California. Many of these horizontally unbundled sewer systems are also unbundled from the treatment plants that serve them. In other instances, separate facilities are based on history and political boundaries. In those cases, "bundling" existing districts and functions might improve cost-effectiveness. Source: Serageldin, I. 1994. Water supply, sanitation and environmental sustainability: The financing challenge. Washington: The World Bank. 28 WATER QUALITY: WASTEWATER TREATMENT FINANCIAL ISSUES COSTS FOR WASTEWATER TREATMENT Water users should be charged for at least the op- eration and maintenance cost of the water and sani- Wastewater treatment costs depend on the type and tation system plus the costs that result from level of service provided and local conditions. Table disposing of wastewater­such as downstream im- 3 provides ranges of costs for conventional treat- pacts of sewage discharges. As a practical matter, ment options. The wide range of costs arises from the cost of wastewater treatment is often included differences in the level of service, local conditions, in water rates or tariffs since water use is easier to quality of data, and methods of calculation. None observe or meter than is wastewater discharge. of the costs include environmental costs such as impacts on downstream users of water or water- Cross-subsidies between user groups may be used based resources (e.g., fisheries). to reduce the burden on poorer users of water or sanitation services. If designed properly and re- Cost recovery. Utility services of all types have been, viewed periodically, cross-subsidies can be consis- and continue to be, subsidized in many parts of the tent with full cost recovery and with price signals world. Extensive experience shows that widespread to users that lead to socially desirable results. For subsidies lead to overuse of water resources, dis- example, the capital recovery portion of the finan- charge of contaminated wastewater, and subsequent cial cost of a wastewater treatment system may be environmental problems. User fees that recover the allocated exclusively to wealthier and middle-in- cost of delivering services, such as wastewater treat- come customers without distorting the volumetric ment, are an essential part of the solution to this water-price signal. This is because capital recov- problem. ery charges are often a separate part of the water/ wastewater bill. TABLE 3. COST RANGES FOR ON SITE AND SEWERED CONVENTIONAL TREATMENT OPTIONS - ( ) Capital Plus Operation and Capital Cost1 Maintenance Cost Economy Option ($ / capita) ($ / capita/ year) Low-Income Treatment plant2 20­80 5­15 Economies Sewer + treatment2 200­400 10­403 Middle-Income and Treatment plant2 30­502 Not provided Transitional Economies Sewer + treatment2 300­5002 30­603 Industrialized Countries Treatment plant2 150­3001 Not provided Sewer + treatment2 100­2002 100­1503 Notes: 1 For primary plus secondary treatment, including land purchase and simple sludge treatment, for a capacity of 30,000 to 40,000 persons. Lower values pertain to low-cost options such as waste stabilization ponds; higher values pertain to mechanized treatment such as oxidation ditches and activated sludge plants. 2 For plant capacity of 100,000 to 250,000 persons. 3 For industrialized countries, this includes tertiary treatment and full sludge treatment; for other countries, this includes secondary treatment. Source: UNEP, 2001 29 WATER RESOURCESAND ENVIRONMENT · TECHNICAL NOTE D.2 Historically, user fees are set (after technical analy- Participation in setting charge rates can increase ses) without the involvement of those affected. How- willingness to pay, because of an improved under- ever, willingness to pay is not a fixed item that standing of the benefits of wastewater treatment or experts can extract from historical data, but a com- an increased confidence that services will actually plicated set of preferences and concerns that are be delivered. only fully sorted out during a participatory process. 30 WATER QUALITY: WASTEWATER TREATMENT FURTHER INFORMATION Good references to wastewater management are Natural wastewater disposal systems (constructed available in: wetlands, etc) are described in: Marino, Manuel and John Boland. 1999. An integrated Reed, Sherwood, E. Joe Middlebrooks, and Ronald W. approach to wastewater management. Washing- Crites. 1988. Natural Systems for Waste Manage- ton: The World Bank. ment and Treatment. New York: McGraw Hill. The World Bank. 1992. World Development Report 1992: Water Pollution Control Federation. 1990. Natural systems Development and the Environment. New York: for wastewater treatment. Manual of Practice FD- Oxford University Press. 16. Alexandria, VA: The Water Pollution Control Federation. (Note: the Water Pollution Control UNEP 2001. "Guidance on Municipal Wastewater: Prac- Federation is now called the Water Environment tical Guidance for Implementing the Global Federation.) Programme of Action for the Protection of the Marine Environment from Land-Based Activi- The following reference provides more information ties (GPA) on Sewage." Working Document Ver- on effluent disposal to agricultural lands: sion 2.0, 21 October 2001. The Hague: UNEP/ GPA Coordination Office. Khouri, Kalbermatten, and Carl Bartone. 1994. Reuse of wastewater in agriculture: a guide for plan- Two World Bank publications discuss the provision ners. Water and Sanitation Report No. 6. Wash- of wastewater services by user groups: ington: UNDP-World Bank Water and Sanitation Program. Subramanian, Ashok, N.Vijay Jagannathan, and Ruth Meinzen-Dick. 1997. "User organizations for sus- Models for predicting the water quality impacts of tainable water services." World Bank Technical wastewater treatment discharges are described in: Paper No. 354. Washington: The World Bank. World Bank, 1998. Pollution Prevention and Abatement Wright, Albert M. 1997. Toward a strategic sanitation ap- Handbook 1998. Washington: The World Bank. proach. Washington: UNDP-World Bank Water and Sanitation Program. Palmer M.D. 2001. Water Quality Modeling: A Guide to Effective Practice. Washington: The World Bank. The following reference provides overviews of the wide range of technologies available for wastewa- The following website provides access to numer- ter management: ous documents on water supply and sanitation is- sues in the developing world, including municipal Tchobanoglous, George. 1991. Wastewater Engineering: wastewater treatment: Treatment, Disposal, Reuse, 3rd edition. New York: McGraw-Hill. http://www.irc.nl/products/documentation/reference.html 31