Report No: ACS13221 . East Asia and Pacific Wastewater to Energy Processes: a Technical Note for Utility Managers in EAP countries . January 2015 . GWADR EAST ASIA AND PACIFIC . Document of the World Bank . . . Standard Disclaimer: This volume is a product of the staff of the International Bank for Reconstruction and Development/ The World Bank. The findings, interpretations, and conclusions expressed in this paper do not necessarily reflect the views of the Executive Directors of The World Bank or the governments they represent. The World Bank does not guarantee the accuracy of the data included in this work. The boundaries, colors, denominations, and other information shown on any map in this work do not imply any judgment on the part of The World Bank concerning the legal status of any territory or the endorsement or acceptance of such boundaries. . Copyright Statement: . The material in this publication is copyrighted. 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WA S T E WAT E R TO E N E R GY A Technical Note for Utility Managers and Decision Makers on Urban Sanitation in East Asian Countries January 2015 The International Bank for Reconstruction and Development 1818 H Street, NW Washington, DC 20433, USA February 2015 www.worldbank.org Disclaimer Rights and Permissions This report is a product of the staff of the World Bank with external con- The material in this work is subject to copyright. Because The World Bank tributions. The findings, interpretations, and conclusions expressed in this encourages dissemination of its knowledge, this work may be reproduced, report do not necessarily reflect the views of the World Bank, its Board of in whole or in part, for noncommercial purposes as long as full attribution to Executive Directors, or the governments they represent. The World Bank this work is given. Any queries on rights and licenses, including subsidiary does not guarantee the accuracy of the data included in this work. Questions rights, should be addressed to the Office of the Publisher, The World Bank, regarding figures used in this report should be directed to persons indicated 1818 H Street NW, Washington, DC 20433, USA; fax: 202-522-2422; in the source. e-mail: pubrights@worldbank.org. b WASTEWATER TO ENERGY FOREWORD iii TABLE OF CONTENTS ACKNOWLEDGEMENTS iv ACRONYMS AND ABBREVIATIONS EXECUTIVE SUMMARY vi viii SECTION I: CONTEXT AND PROBLEM STATEMENT 1 1. Background in East Asia Pacific Countries 2 2. Objective of the Technical Note 5 3. Electricity Consumption in Wastewater Treatment Operations 6 Electricity Consumption at WWTPs from a Macroeconomic Perspective 6 Electricity Costs from the Utility’s Point of View 7 Energy Requirements of Different Treatment Technologies 10 Energy Efficiency Improvement 12 4. Wastewater Treatment: From Necessary Evil to a Source of Beneficial Products 14 5. Renewable Energy Generation at WWTPs 17 Technologies for Renewable Energy Generation via Biogas from Wastewater 18 The Use of Biogas from Human Waste as a Resource 19 Sludge Digesters for Renewable Energy Generation at WWTPs 20 Quantification of Renewable Energy Generation Potential at WWTPs 20 The Specific Conditions in EAP Regarding Renewable Energy Generation 22 SECTION II: CASE STUDIES AND ASSESSMENT TOOL 27 6. Methodology 28 7. Main Findings from the Analysis of Case Studies 29 Wastewater Influent and Effluent 32 Biogas Production and Potential for Energy Generation 33 Operation Capacity Needs and Biogas Safety 36 Institutional Aspects Related to the Case Studies 36 GHG Reduction and Co-financing through Carbon Trading 38 Energy Costs and Viability of Investment in Biogas Utilization 39 8. Simple Assessment Tool 42 Development of the Tool 42 Application of the Tool to a Specific Case Study 42 SECTION III: LESSONS LEARNED AND RECOMMENDATIONS 47 9. Constraints and Enabling Factors 48 Technical Aspects 48 Knowledge Aspects 49 Institutional Aspects 52 Economic and Financial Aspects 54 10. Road Map for Decision Making 55 References 56 WASTEWATER TO ENERGY   i ii  WASTEWATER TO ENERGY The East Asia Urban Sanitation Review: A Call for Action (World Bank 2013) FOREWORD highlighted the importance of improving collection, treatment, and disposal of human waste in cost-effective ways in East Asian cities. It also recommended the systematic exploration of opportunities to use wastewater as a resource for the production of energy at treatment facilities and an increased emphasis on this approach, together with others, such as the generation of biosolids from sludge, as parts of a climate-smart sanitation strategy. This technical note explores in greater depth the production of energy in wastewater treatment plants as an option to save costs in the operation of these facilities. This is relevant for two reasons. First, in East Asia, where urban populations have been growing rapidly and becoming increasingly dense, an exclusive reliance on onsite sanitation services is not possible, which presents a clear need to invest in infrastructure to collect and treat wastewater. This infrastructure is expensive to build and run; however, identifying smart cost-saving measures can help relieve the burden of utilities that struggle to expand wastewater collection and treatment services in a financially sustainable manner. Second, research has traditionally focused on energy efficiency measures and energy generation with respect to wastewater treatment technologies that are energy intensive and work well in the cold climates usually found in developed countries. This leaves a knowledge gap that needs to be bridged to inform utility managers in developing countries about the factors that need to be in place for the adoption of options like “wastewater to energy,” particularly applied to low- cost treatment options and conditions in warm developing climates. With the urban wastewater sector in its early stages of development in many East Asian countries, the World Bank Group is committed to working with these countries to promote informed decisions and find innovative, cost-effective solutions that will contribute to improving the environmental conditions of rapidly growing cities and expanding sanitation services to increasing numbers of people, including the poor. Jennifer J. Sara Director Global Practice Water WASTEWATER TO ENERGY   iii This report has been prepared with the financial support of the Water Partnership ACKNOWLEDGMENTS Program. It includes contributions from stakeholders in China, Indonesia, the Philippines, and Vietnam, provided through workshops where preliminary findings of the study were presented. The task team leader for producing this report was Victor Vazquez, and the sector managers were Charles Feinstein and Ousmane Dione. The main author was Konrad Buchauer (consultant). Main technical inputs were provided by Daniel Nolasco and Amit Pramanik (consultants) and the following staff from the World Bank and the Water and Sanitation Program (WSP): Sudipto Sarkar, Iain Menzies, Hung Duy Le, Sing Cho, Irma Setiono, Demilour Reyes Ignacio, Carmen Yee- Batista, Alexander Danilenko, and Christopher Ancheta. Mara Baranson and Lisa Ferraro Parmelee also made important contributions. The peer reviewers for this work were Kartik Chandran (Columbia University), Tim Shea (CH2MHill), Feng Liu, Peter Johansen, Satheesh Kumar, Manuel Mariño, and the East Asia WSP team at the World Bank. Finally, the task team for this report greatly appreciates the generous technical contributions in the form of data provided by the following utilities: COPASA in Brazil, ENACAL in Nicaragua, Melbourne Water in Australia, AV Zirl u.U. from Austria, and SAGUAPAC in Bolivia. The report contains three parts, namely, the Main Report, Technical Annex and Assessment Tool. Only the Main Report is printed. The full report is available through the GP Water website at www.worldbank.org/water. iv  WASTEWATER TO ENERGY WASTEWATER TO ENERGY   v ABR anaerobic baffled reactor ACRONYMS AND ABBREVIATIONS AD anaerobic digestion AeP (mechanically) aerated pond AFR Africa (World Bank region) ANEEL Agencia Nacional de Energia Eléctrica, Brazil AP anaerobic pond ASE Alliance to Save Energy AT aeration tank BAR baffled anaerobic reactors BOD5 five-day biochemical oxygen demand CAP covered anaerobic pond CAPEX capital expenditure (=investment cost) CAS conventional activated sludge CDM Clean Development Mechanism CH4 methane CHP combined heat and power CO2e CO2 equivalent COD chemical oxygen demand COPASA Companhia de Saneamento de Minas Gerais CW constructed wetland DBO design-build-operate contract DS dry solids DWA German Association for Water, Wastewater, and Waste EA extended aeration (=activated sludge system with simultaneous aerobic sludge stabilization) EAP East Asia Pacific (World Bank region) ECA Europe and Central Asia (World Bank region) ENACAL Empresa Nicaragüense de Acueductos y Alcantarillados ESMAP Energy Sector Management Assistance Program EU ETS European Union Emissions Trading System FOG fat, oil, and grease FST final sedimentation tank FY fiscal year GHG greenhouse gas GRP glass fiber reinforced pipe IBRD International Bank for Reconstruction and Development IDB Inter-American Development Bank IWA International Water Association KfW Kreditanstalt für Wiederaufbau LAC Latin America and Caribbean (World Bank region) MBBR moving bed bioreactor MBR membrane bioreactor MDG Millennium Development Goals vi  WASTEWATER TO ENERGY MENA Middle East and North Africa (World Bank region) MGD, mgd million US gallons per day (1 MGD = 3.7853 MLD) MLD, mld million liters per day (1 MLD = 1,000 m3/d) MLSS mixed liquor suspended solids N nitrogen NH4 ammonia NO3 nitrate O&M operation and maintenance OPEX operation and maintenance expenditure (=O&M cost) P phosphorus PAC poly-aluminum-chloride PE population equivalent PE60 population equivalent, based on 1 PE60 = 60 gBOD5 per capita per day PE110 population equivalent, based on 1 PE110 = 110 gCOD/cap/d PE120 population equivalent, based on 1 PE120 = 120 gCOD/cap/d PS primary sludge PST primary sedimentation tank SAR South Asia (World Bank region) SBR sequencing batch reactor SST secondary sedimentation tank STP sewage treatment plant TF trickling filter TSS total suspended solids UASB upflow anaerobic sludge blanket USAID U.S. Agency for International Development USD ultrasound sludge disintegration VDS volatile dry solids VS volatile solids VSS volatile suspended solids WAS waste activated sludge (also called secondary sludge) WEF Water Environment Federation WERF Water Environment Research Foundation WSP waste stabilization pond WWTF wastewater treatment facility WWTP wastewater treatment plant Currency equivalents Exchange Rates used in this report AUD 1.5 (Australia) = EUR 1.0 R$ 2.5 (Brazil) = EUR 1.0 C$ 30.0 (Nicaragua) = EUR 1.0 US$ 1.35 (USA) = EUR 1.0 WASTEWATER TO ENERGY   vii EXECUTIVE SUMMARY Sanitation services in many East Asian cities struggle to keep pace with rapid urban growth. The East Asia Urban Sanitation Review (World Bank 2013) showed the enormous challenges the sanitation sector faces in most urban areas in the region, primarily excessive dependence on defective onsite sanitation in cities with high population densities and persistently low wastewater collection and treatment coverage levels (1 percent, 4 percent, and 10 percent in Indonesia, the Philippines, and Vietnam, respectively). In addition to upgrading existing onsite sanitation services, the growing population densities necessitate expanding collection networks and building sustainable treatment plants that prevent the accumulation of wastewater in the numerous waterways and canals crossing the cities’ packed neighborhoods. Plans to invest in scaled-up urban sanitation services and expanded wastewater collection and treatment infrastructure are already in place. For instance, in Vietnam alone, more than thirty new wastewater treatment plants are to be built in the coming years. Meanwhile, existing wastewater utilities in East Asia are struggling to perform. The high expense of operating modern sewerage collection networks and, more in particular, wastewater treatment plants is often an obstacle to expanding and improving services for a sector that usually has low cost recovery rates and depends on unpredictable government transfers. Utilities tend to reduce costs where they can, most notably by saving on maintenance and electricity supply. The result is deteriorating treatment efficiencies, shortened lifespans for facilities, which often fall into disuse, and wasted investments. In Indonesia, for instance, only 47 percent of the treatment capacity installed in the 1990s is being used today (World Bank 2013). viii  WASTEWATER TO ENERGY In short, cost efficiency in the operation and builds on that contribution and shows that, with a maintenance (O&M) of treatment plants is essential. series of enabling factors in place, considerable savings It can be achieved in three ways: can also be realized by adopting energy generation in • By implementing effective and realistic energy low-cost treatment technologies, which will contribute efficiency processes. to putting utilities in a better financial position to improve their service provision. • By selecting appropriate treatment technologies that are generally low-energy consumers. Also taken into consideration is a paradigm shift in the way wastewater is considered by society. Previously • By generating electricity onsite from biogas resulting seen as a costly “problem,” nowadays it is increasingly from anaerobic digestion of sludge or wastewater. treated as a resource that can raise returns on Work conducted by the Energy Sector Management investments. The potential for resource recovery from Assistance Program (ESMAP) and the Water wastewater is wide, with the following options among Environment Foundation (WEF) in 2012 focused on the most common: energy efficiency in operations. This technical note WASTEWATER TO ENERGY   ix • Treated wastewater as a water resource for • It aims to fill a knowledge gap in the topic of energy applications in agriculture, industry, aquaculture, generation in wastewater treatment plants with a urban and recreational uses, groundwater recharge, focus on low-cost treatment options suitable for or drinking water supply developing countries. • Wastewater/sludge as a nutrient resource, from • It builds on the East Asia Urban Sanitation Review, which phosphorus and nitrogen can be extracted conducted by the World Bank in 2013, which and sold provided an overall assessment of the main challenges in the urban sanitation sector in Indonesia, the • Sludge as an agricultural resource, whose fertilizing Philippines, and Vietnam. While this technical note effects and soil improvement functions also give likewise focuses mainly on these countries, many it an important role to play in the mitigation of of its conclusions and recommendations could be greenhouse gas (GHG) emissions applied to other countries with similar conditions • Wastewater/sludge as a renewable energy resource, and challenges. whose use also helps reduce GHG emissions • It provides an opportunity for the many EAP cities The focus in this technical note is on the last aspect, with low coverage of centralized sanitation services paying attention not only to lower operation and that plan to expand wastewater infrastructure to “get maintenance expenditure on wastewater treatment, it right” in the first place by learning from existing but also to a reduction in the carbon footprint of practical experience and knowledge of how to keep sludge management. A comprehensive comparison O&M cost low from the investment stage. of energy recovery options with respect to different • It provides the following in its explanation of how to treatment schemes, particularly from the perspective generate energy from wastewater: of developing countries in warm climates, is absent from the specialized literature. • Evidence on the relevance of energy costs in the operation of WWTPs Objectives of the Technical Note • Evidence on the potential savings from combining This technical note is directed to technical decision the adoption of smart treatment technologies with makers and utility managers in developing countries investment in energy recovery in East Asia Pacific (EAP). Its purpose is to facilitate learning on how to achieve significant savings in the • Examples of best practices in the sector operation of wastewater treatment plants (WWTPs) • A rapid assessment tool for conducting a through the selection of appropriate treatment preliminary evaluation of the viability of energy technologies and the utilization of financially viable recovery options wastewater-to-energy potentials and to explain the factors that need to be considered when investing in • Typical constraints and enabling factors that these processes. To these ends, the technical note does need to be considered when deciding on the following: wastewater-to-energy investments x  WASTEWATER TO ENERGY Methodology technologies that should be considered in warm The study is divided into three main sections. Section climate countries like those in the region. Among them I presents the results of a comprehensive desk review are typical technologies commonly used in developed describing the problem of utilities dealing with high countries, including examples from Europe, and operation costs in wastewater treatment plants, the technical developments appropriate for developing or link between energy consumption and the type of transition countries. The analysis of the case studies technology used for treatment, and the potential for looks into energy consumption at the WWTP, energy generation. biogas quantities and characteristics, the potential for electricity generation, operation capacity needs, Section II summarizes the findings from a series of safety concerns, institutional aspects, greenhouse case studies presenting a wide range of wastewater- gas (GHG) reduction, co-financing through carbon to-energy options that could be considered in trading mechanisms, cost-related aspects of capital developing countries, paying particular attention expenditures (CAPEX), operational expenditures to the characteristics of EAP countries (see table 1). (OPEX), and overall financial viability. The case studies cover all major biogas generation Table 1: Case Studies Analyzed in this Technical Note Biogas from Biogas from Location Case study wastewater treatment sludge treatment of case study 1. CAS + sludge digestion — X Europe 2. TF + sludge digestion — X Nicaragua 3. UASB X — Brazil 4. Covered anaerobic ponds X — Bolivia, Australia 5. Co-digestion of organic waste — X Europe 6. Ultrasound sludge disintegration — X Europe Note: CAS = conventional activated sludge; TF = trickling filter; UASB = upflow anaerobic sludge blanket. WASTEWATER TO ENERGY   xi Finally, section III draws conclusions from the that a WWTP’s OPEX structure depends mainly on previous sections to identify existing constraints the selected technology and on various parameters that need to be addressed and factors that need to influenced by local conditions. Electricity cost is an be in place when considering investments in energy important operational expenditure, contributing up generation at WWTPs. to 50 percent of the WWTP’s total OPEX. Existing cases indicate this percentage will be even higher in Key Findings from the Desk Review and EAP than in Europe or the United States. Case Studies It is important to highlight that wastewater to energy The first of the key findings discussed in sections I and does not compromise treated water quality. The II of this technical note is that the electricity produced overarching goal of all WWTPs, which is wastewater by wastewater-to-energy facilities can be sufficient to treatment that complies with locally prevailing achieve substantial cost reductions at well-functioning standards, is usually not constrained by wastewater WWTPs. Both the desk review and case studies show to energy. Only in cases where sludge digesters are xii  WASTEWATER TO ENERGY used and no nutrient emission standards exist does generate electricity. The cost-saving potential in wastewater to energy imply a slight increase in effluent absolute terms of biogas utilization is, thus, similar nutrient emissions. for all technologies. In relative terms, though, the potential is higher for technologies with low energy The case studies analyze the electricity consumption consumption, where the OPEX levels are already and potential for electricity production from biogas low. These technologies may even become energy at WWTPs. The summary in figure 2 shows that independent, which not only has financial benefits the various wastewater treatment technologies differ but improves operational safety due to reduced significantly in energy consumption, while the same dependence on public power supply.1 technologies are more similar in their potential to Figure 2: Electricity Consumption versus Production of Different Technologies Notes: kWh/capita/y x 16.67 = kWh/kg BOD5 /y. CAS = conventional activated sludge; TF = trickling filter; UASB = upflow anaerobic sludge blanket; AP = anaerobic pond. The cost of generating electricity from biogas is low A series of factors needs to be considered to assess the and usually competitive with the unit cost of electricity overall viability of investments in wastewater-to-energy from the public grid. Large biogas facilities can projects. Table 2 summarizes the commonly found generate electric power at US$0.02/kWh,2 whereas barriers and the factors that may make it possible to the cost to purchase power in EAP countries ranges overcome them. from US$0.06 to US$0.22/kWh. 1 Although the utilization of biogas can also generate considerable quantities of thermal energy, heat is in low demand in warm climate countries. This technical note focuses, therefore, on electricity, which has a higher economic value. 2 These results are based on life cycle assessments of CAPEX and OPEX of all installations typically required for this practice, including biogas treatment. WASTEWATER TO ENERGY   xiii BARRIER ENABLING FACTORS A SIZE OF THE PLANT Plant size can be a barrier to wastewater-to-energy A preliminary assessment for conditions in EAP countries projects, as investments are usually only beneficial above showed the threshold in this region may vary between 10,000 certain minimum capacity thresholds for wastewater and 100,000 PE60 (2,000–20,000 m3/d). A case-by-case treatment and, therefore, sludge generation. These thresholds analysis is required to determine the real threshold in each are around 10,000 PE60,* or 2,000 cubic meters per day (m3/ case. The tool included in this technical note can be used for day) in developed countries. that purpose. *Population equivalent, based on 1 PE60 = 60 gBOD5 /capita/day. B WASTEWATER DILUTION The most common technical barrier to wastewater-to-energy A case-specific analysis, for which the assessment tool projects is wastewater dilution, a problem particularly common provided by this technical note may prove helpful, should in many EAP cities where wastewater reaching the plants has become the standard approach. low pollution concentrations. Hence, the conditions in EAP may A key indicator worth considering is the average influent total reduce the potential for biogas and energy generation. suspended solids concentration (TSS). If TSS is < 80 milligrams per litre (mg/L), then neither sludge digesters (lacking primary sludge) nor anaerobic wastewater technologies (requiring large volumes) are attractive. Yet, even under these conditions, co-digestion of organic feedstock or fecal sludge could make wastewater to energy viable. C UNINFORMED DECISIONS Uninformed technical decisions are frequent in the countries Introducing holistic technology benchmarking to the sector considered here and can be attributed to (a) a lack of will allow operators to learn from the best performers. Both comprehensive information on all options for wastewater to average performance and benchmarks will usually improve energy; (b) a tendency to “copy and paste” technologies used in over time. other countries, thus ignoring low-cost treatment technologies better suited to warm climates; (c) a preference for “cutting- The knowledge gap can be closed through publications like edge” technologies; and (d) too much emphasis on CAPEX and this technical note, pilot plants, workshops, the regular exchange less concern about OPEX. of operational experiences among different WWTPs, and operator training. D INSUFFICIENT OPERATOR TRAINING Operators are not always well trained and informed Providing regular, good quality training will ensure that about regular operating routines and even less so about operators understand potential problems and have the means troubleshooting techniques and necessary conditions for for process control and intervention. adequate biogas system functioning. An interesting option may be involving the private sector by subcontracting out energy generation as a separate operation unit within the WWTP, thus eliminating the need for operator training for this specialized task. xiv  WASTEWATER TO ENERGY BARRIER ENABLING FACTORS E INADEQUATE O&M AND SAFETY ISSUES A utility should not invest in waste-to-energy options at its Maintenance of the WWTP should be understood as an WWTPs if it follows a practice of undermaintaining the essential expenditure that helps reduce total life cycle cost existing facilities. Failures of wastewater-to-energy options in rather than an expenditure that should be minimized. Proper existing WWTPs are often caused by insufficient maintenance, instruments for asset management should be in place. slow procurement of spare parts, or unwillingness to involve specialized third parties. Safety issues are also a common concern among practitioners Wastewater-to-energy technologies are not complicated to in the sector. Risks usually only arise, however, in cases of operate, and safety and operation risks are low if (a) projects inappropriate design, material quality issues, or ignorance of are properly designed (wastewater + sludge + biogas); (b) simple O&M precautions. Problems may also arise if power specifications in the bidding documents are tailored to needs; supply is unreliable. and (c) operational protocols developed for these technologies are followed. Design-build-operate (DBO) contracts for the complete WWTP, including the biogas component, can be an attractive option. If public power supply is needed but considered unreliable, then additional backup systems or smart biogas and power management strategies are indispensable. F REGULATORY FRAMEWORK Power companies may add barriers to the production and use Generally, it is recommended that electricity from biogas be of electricity in wastewater treatment plants. In cases where used onsite at the WWTP to cover its own operation needs. a power surplus is produced at the plant, electricity cannot be For electricity surpluses, a clear tariff policy that includes the stored inexpensively, and flaring biogas is a waste of resources. option of supplying bioelectricity to the public grid is needed to make wastewater to energy viable. A lack of a clear regulatory framework for co-digestion could The institutional tasks and responsibilities governing the be a problem, particularly if responsibilities for collection and collection and disposal of various wastes need to be clarified disposal are not clearly distributed among the waste producer, while still allowing the necessary flexibility for co-digestion of the waste collector, and the entity responsible for final disposal. sludge and waste and the subsequent disposal or reuse of the digested mixed product. It is helpful for wastewater utilities to have contracts directly with other utilities, private collection companies, and/or waste producers. The required effluent quality has implications for both the In countries where treatment levels are as low as in EAP, the energy consumption and the electricity generation potential first priority should be installing facilities that remove the of WWTPs. The stricter the effluent standards, the lower the bulk of the organic pollution. Nutrient removal may only be coverage ratio for electricity (production versus consumption) introduced at a later stage, where environmentally justified. A will be. Strict standards thus not only increase CAPEX (because sensible approach should allow for (a) more lenient standards installations are larger), but also OPEX. for small WWTPs, since their environmental impacts are small as well and (b) stricter standards for large WWTPs only where the recipient water is indeed sensitive to the discharges. WASTEWATER TO ENERGY   xv BARRIER ENABLING FACTORS G SUBSIDIZED ELECTRICITY COST Subsidies that reduce unit costs of electric power can prove a Subsidies to electricity should be minimized as much as possible. major obstacle to energy recovery from renewable resources. The decision to undertake an energy recovery project is based mostly on an assessment of its financial viability. Thus, the more subsidized the cost of electricity is, the less attractive the investment in energy recovery will be. H ECONOMIC AND FINANCIAL ANALYSIS Utilities or municipal departments responsible for wastewater Reduced OPEX could have positive effects on cash flows and operations usually have little margin for financial maneuvering, free funds for vital investments at given points in time. Decision which implies difficulty in obtaining financing for wastewater- makers should perform more comprehensive cost–benefit to-energy investments. They also may have other priorities, given analysis by calculating net present values, operational savings, and their limited capital resources. The economic analysis for this potential gains in cash flows. Considering alternative sources of type of investment is often limited to requirements for a short, funding is also advisable. predetermined payback period. The present low price level of carbon credits renders most Many facilities are nevertheless interested in quantifying wastewater-to-energy projects unattractive for Clean Development greenhouse gas (GHG) emission reductions achieved as proof of Mechanism (CDM) application. environmental stewardship. The Way Forward: A Wastewater-to-Energy Also presented is an example of the tool’s application, Preliminary Assessment Tool based on a specific WWTP in the Philippines. The Since project-specific analysis is usually indispensable, assessment considers different influent characteristics, this technical note presents in section II a simple drawing conclusions on the viability of biogas assessment tool developed in spreadsheet format. generation in each case. This tool allows a quick preliminary quantification of Finally, figure 4 summarizes the main actions OPEX-related implications of wastewater-to-energy recommended for successful wastewater-to-energy facilities, as well as preliminary design of its major projects. components. The CAPEX estimation and combined life cycle assessment remain up to the user, since they depend on a multitude of local factors that defy simple generalizations. xvi  WASTEWATER TO ENERGY Figure 4: Guidance on Decision Making and Required Actions for Wastewater-to-Energy Projects EXISTING WWTP Data collection NEW WWTP Forecast of future development Define appropriate wastewater treatment technology Preliminary assessment of W2E (e.g., with tool) Viable Not Viable Detailed analysis (considering financial, institutional, and technical factors explained in this technical note) Viable Not Viable Secure financing Detailed design, bidding Implementation Periodic review of operational results to improve input to new projects WASTEWATER TO ENERGY   xvii xviii  WASTEWATER TO ENERGY SECTION I: CONTEXT AND PROBLEM STATEMENT WASTEWATER TO ENERGY   1 1. Background in East Asia Pacific Countries services in these areas is a serious challenge. As table Wastewater collection and treatment levels in the I-1 shows for some typical cases, many of these cities, rapidly growing cities of the East Asia Pacific (EAP) where land availability is a constraint, are dealing with region are low, and providing adequate sanitation increasing urban population densities.3 Table I-1: Typical Growth Characteristics of Cities in EAP Countries Population Population density Population Country City Population 2010 increase since increase since density in 2010 2000 2000     (%) (per sq. km) (%)   Garut 1,136,926 70 24,749 26 Indonesia Jepara 515,777 70 10,783 23   Tasikmalaya 1,594,737 50 17,090 26   Angeles City 683,176 61 3,678 17 Philippines Cebu 1,527,407 50 9,461 14   Manila 16,521,948 35 12,958 9   Hanoi 5,642,882 60 6,634 10 Vietnam Hai Phong 1,221,115 49 6,144 21   Da Nang 869,178 55 9,870 10 Source: World Bank 2014. Most such cities have traditionally relied on onsite wastewater from households. As shown by figure sanitation services, characterized by large numbers I-1 and table I-2, the areas covered by centralized of septic tanks (usually poorly constructed), wastewater collection and treatment services in informal desludging services, and unsafe disposal EAP are still too small. The consequences are of waste (World Bank 2013c). While improving cities packed with people living along waterways septage management is necessary, the right strategy and open canals polluted with wastewater, with the to adopt when urban densities are so high is to resultant risk to public health. progressively extend sewerage systems to collect This is often not the case in some cities in China, where urban population densities remain stable or even decline, despite the high population growth rates 3 2  WASTEWATER TO ENERGY Figure I-1: Sewer Connection Rates of Selected Cities in Indonesia, the Philippines, and Vietnam, as Compared to Other Asian Cities Source: World Bank 2013, Siemens AG, 2011. Large Investments Will Be Required to Tackle the sized cities, and in Metro Manila, Philippines, the two Existing Sanitation Deficit. Most cities in EAP have concessionaires are or will be undertaking ambitious plans or are already implementing projects to expand wastewater collection and treatment projects to and upgrade centralized collection and treatment comply with a 2008 Supreme Court mandate to services. For instance, in Vietnam alone, where improve the water quality of Manila Bay. Table I-2 seventeen WWTPs are currently in operation, more shows that more than 90 percent of the wastewater/ than thirty are in the pipeline or under construction septage (representing 176 million out of a total of (World Bank 2013c). Indonesia is planning to 194 million urban people) is not collected or treated construct area-wide sewage systems in forty medium- in these three countries. Table I-2: Summary Status of Urban Wastewater and Septage Management in EAP Countries Indonesia Philippines Vietnam Total urban population 110 million 61 million 23 million 194 million Urban population without wastewater/ 105 million 51 million 20 million septage treatment Wastewater treated 1% 4% 10% Septage treated 4% 10% 4% 176 million 176 million Source: World Bank 2013c. Urban populations are expected to increase in these sewerage and treatment systems are estimated at countries by more than 50 percent by 2025, and US$74 billion (World Bank 2013c). sanitation investments needed to connect them to WASTEWATER TO ENERGY   3 The Existing Wastewater Utilities in the Region Often utilization of scarce funds and smart investment in Struggle to Perform. Sustainability of wastewater low OPEX technologies are essential. treatment facilities is usually a major challenge. Energy Efficiency in Water and Wastewater Utilities: Departments responsible for wastewater collection Ongoing Initiatives in EAP and Other Regions. In and treatment often have to deal with low levels of cost 2012, to help water and wastewater utilities reduce recovery and inadequate operation and maintenance their operating costs and contribute to cost efficiency (O&M) budgets resulting from low tariffs, low tariff and the overall sustainability of investments in collection rates, low household connection rates to them, the Energy Sector Management Assistance sewers, or some combination of these. Program (ESMAP), administered by the World This problem is aggravated by the high costs associated Bank, published a “Primer on Energy Efficiency with operating WWTPs, which, in many cases, use for Municipal Water and Wastewater Utilities,” inadequate and/or unnecessarily expensive technologies. providing strategies for implementing energy This problem is commonly found in many developing efficiency measures in water and wastewater utilities. countries, where decision makers tend to install “cutting- A key measure mentioned in the report was the edge technologies” used in developed countries, even production of energy from anaerobic sludge digestion when they are not necessary or affordable (Libhaber in WWTPs. A portfolio review of all World Bank– et al. 2012) or are in places where stable and reliable funded projects in fiscal years 2000–2010 pointed to sources of energy (electricity or gas) do not exist. EAP as the region with the most new construction and expansions in urban water and sanitation (see Consequently, utilities usually undermaintain the figure I-2). Energy efficiency considerations were plants and networks to cut costs, thus reducing the applied to only about 10 percent of projects in this life cycle of these structures or the efficiency of their period, leaving considerable work still to be done in operations. Under these circumstances, the optimized energy efficiency projects and improvements. Figure I-2: Regional Orientation on Rehabilitation and/or New Construction/Expansion in 178 World Bank–funded Water and Sanitation Projects during FY2000–2010 Source: ESMAP 2012. Note: ECA = Europe and Central Asia; AFR = Africa; SAR = South Asia; EAP = East Asia Pacific; MENA = Middle East and North Africa; LAC = Latin America and Caribbean. 4  WASTEWATER TO ENERGY In other regions, efforts to improve energy efficiency operational expenditures (O&M costs or OPEX) of in the water and sanitation sector are ongoing. The wastewater treatment plants and thus improve the Watergy program, conducted by the Alliance to Save long-term sustainability of the investments. Energy (ASE), is funded by the U.S. Agency for This technical note also intends to fill a gap in the International Development (USAID) and currently existing literature by providing a comprehensive operates in Brazil, India, Mexico, the Philippines, picture of energy generation applied to all available South Africa, and Sri Lanka (ESMAP 2012). In Latin wastewater treatment technologies, with special America and the Caribbean (LAC), initiatives are focus on the interests of developing countries, and being carried out by the Inter-American Development more particularly those in the East Asia Pacific Bank (IDB). The World Bank also continues to region. A review of a number of case studies will support efforts to improve energy efficiency in LAC provide experience-based data and lessons learned water utilities in collaboration with ESMAP and the from large-scale projects that can reliably be applied Water Partnership Program (WPP), as well as with in similar contexts. Most of the content and external partners, such as utility associations and recommendations made here will be valid in other nongovernmental organizations (NGOs). developing regions, as well. 2. Objective of the Technical Note With regard to energy, this technical note focuses The objective of this technical note is to inform utility on electricity generation, since it is usually more managers and technical decision makers in East Asian valuable from a financial perspective than thermal countries about appropriate technologies available for or heat energy, which can also be generated from wastewater treatment with energy recovery processes. wastewater. This analysis concentrates on centralized It aims to explain how, with consideration of specific wastewater treatment plants where investment in local conditions and a series of required enabling energy recovery technologies can be financially viable factors, wastewater-to-energy technologies can reduce and recommended. WASTEWATER TO ENERGY   5 3.Electricity Consumption in the total OPEX of most urban WWTPs. Potential Wastewater Treatment Operations electricity savings can be very relevant from the Electricity consumption at WWPTs can be analyzed utility’s perspective and, if aggregated at the national both from the utility’s perspective and from a larger level, can also contribute to a country’s hitting macroeconomic perspective at the national level. renewable energy targets. Box I-1 provides relevant data from the wastewater sector in Germany and the Electricity Consumption at WWTPs from a United States, where the sector is fully developed and Macroeconomic Perspective covers the entire urban population. The cost of electricity is a major component of BOX I-1. MACROECONOMIC ENERGY PERSPECTIVE OF WWTPS IN GERMANY AND THE UNITED STATES According to the German Association for Water, Wastewater, and as schools, hospitals, water supply, solid waste management, public Waste, the existing German WWTPs (approximately 10,000 facilities) lighting, traffic, administration, and so forth (UBA 2008). consume a total of 4.2 million MWh/y, equal to the emission of about Data from the United States indicate that “the 16,000 publicly owned 2.36 million tons of CO2e per year based on CO2 emissions from fossil U.S. [WWTPs] consume significant quantities of electrical energy, fuels consumed for electricity generation of 562 g CO2e /kWh (DWA estimated to be approximately between 1–4 percent of total energy 2013b). Assuming an average electricity cost of US$0.20/kWh for production varying regionally, or approximately 40 million megawatts WWTPs, this is a cost item of US$840 million per year. Based on the per year (MWh/year). At the average U.S. electrical price (September total national electricity consumption of over 500 million MWh/y, 2009) of US$0.0718 /kilowatt-hour (kWh), this amounts to US$2.8 WWTPs thus consume somewhat less than 1 percent of the country’s billion being spent on electrical power for wastewater treatment total electricity. Nevertheless, WWTP consumption represents about country-wide in 2009” (WERF 2010b). 20 percent of the electricity consumed by municipal utilities, such This technical note estimated the electricity the expected power production is based on very requirements for WWTPs in Indonesia, the conservative assumptions to reflect t he r educed Philippines, and Vietnam. This analysis determined power potential under country-specific conditions, the additional energy required to provide wastewater such as wastewater dilution or existence of large treatment coverage services to the urban population numbers of septic tanks. who already have access to improved latrines but The assessment found that an increase in wastewater whose wastewater is not being properly collected and treatment coverage levels to serve the population treated. Several scenarios for future development have with access to improved sanitation would produce an been created, using different treatment technologies increase in the total power consumption in Indonesia, with different energy consumption requirements: the Philippines, and Vietnam combined from 0 to activated sludge (high energy consumption), trickling 7.6 million MWh/y. This range corresponds with an filters (medium), and upflow anaerobic sludge increase of 0–2.5 percent in energy production and blankets (UASBs; low consumption). In addition, US$0–500 million/y4 in energy cost, depending on each scenario is considered with and without biogas the process technology selected and whether or not utilization. Where biogas utilization is considered, biogas utilization is considered. 4 Based on a power unit cost typically between US$0.06 and US$0.22/kWh (Indonesia US$0.12/kWh; Philippines US$0.22/kWh; Vietnam US$0.06/ kWh). The value of 0 would correspond to a hypothetical situation where all the future WWTPs were using low-cost technologies and incorporating energy generation. The cited electricity unit cost values were taken from PWC (2011) for Indonesia, private information (2013) received from Maynilad for the Philippines, and data from SCE (2013) for Vietnam. 6  WASTEWATER TO ENERGY Putting the electricity generation potential from biogas particular interest for a utility operating WWTPs at WWTPs into perspective with the production of are the main components of its overall operational electricity from renewable sources in EAP countries, cost, the structure of which is strongly influenced by this source can amount to as much as 10 percent of the treatment technology. Furthermore, the relative total electricity from renewables in Indonesia and contribution of electricity to the overall cost also about 5 percent in the Philippines and Vietnam. depends on the unit cost for personnel, the disposal/ reuse cost for sludge (biosolids), or the quantity of Electricity Costs from the Utility’s Point of View chemicals employed in treatment. A WWTP’s OPEX structure depends mainly on the selected treatment technology and on various Figure I-3 presents examples of OPEX structures for parameters influenced by the local context. Of different technologies in countries in different regions. Figure I-3: Comparison of Typical OPEX Structures at WWTPs with Different Technologies in Different Regions—Brazil, Germany and Tunisia CHEMICALS, MATERIALS SLUDGE OTHER AND OTHER 5% 7% 13% ENERGY STAFF SLUDGE 20% BRAZIL 53% 31% GERMANY UASB +TF ACTIVATED SLUDGE CHEMICALS, MATERIALS AND OTHER OTHER 3% MAINTENANCE, MAINTENANCE, THIRD PARTIES 8% THIRD PARTIES AND CHEMICALS ENERGY AND CHEMICALS 15% 15% 14% STAFF TUNISIA 37% EXTENDED ENERGY AERATION 48% MAINTENANCE, THIRD PARTIES Source: FWT 2013a (Brazil); MURL 1999 AND CHEMICALS (Germany); FWT et al. 2009 (Tunisia). 4% WASTEWATER TO ENERGY   7 Electricity cost makes up about 15–50 percent of they fluctuate within the following ranges (based on total OPEX in the examples in figure I-3. Similar 2014 costs): Germany (CAS): ≈US$5–10/PE60/y values are cited in ESMAP (2012), which found the (benchmarks ≈US$3–5/PE60/y); Brazil (UASB): electricity cost of water and wastewater utilities usually ≈US$0.5–2.0/PE60/y; and Tunisia (EA): ≈US$1–2/ varies from 5 to 30 percent and can be 40 percent or PE60/y. These figures are valid for medium and more in some countries. This share is reported to be large WWTPs. For very small WWTPs, the price generally on the higher side in developing countries. variation can even double due to the implications of economies of scale, lower efficiency of installations, In the case of Germany, the percentage of electricity less sophisticated automation, and lower staff skills. cost is relatively low because of several other expensive cost components, such as the cost of staff, Electricity cost as a percentage of total OPEX of of maintenance, which is subject to strict protocols, WWTPs in East Asia Pacific is expected to be at the and of sludge disposal/reuse, which is expensive. In upper end of these ranges. Actual operating costs Brazil, the electricity cost is low for other reasons, for large WWTPs in East Asia Pacific are difficult such as the selection of anaerobic process technology, to estimate, as cost information is only available for which requires no energy for aeration, and the low some small WWTPs with capacity barely above one unit power cost relative to Germany. In Tunisia, million liters per day (1 MLD). These plants are not electricity for aeration is clearly the most significant representative of the larger WWTPs, where biogas cost component, as staff costs are relatively low, and utilization is indeed recommendable. sludge disposal costs almost nothing. The future WWTP in Ho Chi Minh City’s District Per capita electricity costs can vary widely, depending 2 in Vietnam will be more representative of the cost on country and technology. In the above three cases, structure of future medium and large WWTPs in Figure I-4: OPEX Structure at Nhieu Loc Thi Nghe WWTP in Ho Chi Minh City, Vietnam, Based on SBR Technology, 2015 CHEMICALS STAFF 13% 7% SLUDGE 8% VIETNAM NHIEU LOC THI RENEWAL OF EQUIPMENT NGHE WWTP AND WORKS (SBR TECHNOLOGY) 25% ENERGY 47% Source: SCE 2013. 8  WASTEWATER TO ENERGY the region. It is designed for a capacity of 480 MLD cost and the choice of process technology are the to serve a projected population of 1.4 million when main factors determining the cost of electricity as a it starts operation in 2020. For the recommended percentage of total OPEX. process technology (sequencing batch reactor, or The actual electricity costs of several newly built SBR), the cost structure in 2015 was calculated in WWTPs in Metro Manila, Philippines, are the feasibility study conducted for the project (SCE presented in figure I-5. These facilities, with design 2013) and is presented in figure I-4. capacities between 0.5 and 4 MLD, are all based As the figure shows, energy cost makes up almost 50 on conventional activated sludge (CAS) or moving percent of the total OPEX of the Nhieu Loc Thi Nghe bed bioreactor (MBBR) technologies; only Tandang WWTP, which would be equivalent to an absolute Sora STP is running a different technology (STM- electricity cost of US$2.77 million/year in 2015. Aerotor). The available data refer to the actual annual This is on the upper end of the range found for other cost of electricity and annual wastewater flows for countries discussed here. The high electric power 2013. Due to wastewater dilution—caused by a cost is, in part, associated with strong wastewater combination of factors, such as sewers intercepting dilution, with wastewater pumping contributing wastewater from traditional open drainage canals, 30 percent of the total. However, as the price of high groundwater tables, and seasonally heavy electricity is low in Vietnam (US$0.06/kWh), it is tropical rains—per capita specific flow rates are expected that the share of energy cost compared with higher in Metro Manila than they are in other the total OPEX for similar plants will be higher in regions. The assessment assumes a flow range of other countries with higher electricity prices. Even 200–500 L/capita/day entering a typical WWTP in places with less wastewater dilution, power unit under these conditions. Figure I-5: Actual Capita Specific Power Cost at Selected WWTPs in Metro Manila, Philippines, 2013 Source: Data provided by MWSI, Metro Manila. WASTEWATER TO ENERGY   9 The capita-specific power cost ranges from US$5 traditional sanitation handbooks, this trend is to US$25/cap/y for activated sludge and MBBR changing, and awareness is increasing worldwide of technologies for only the electricity needed for the need to lower the operating costs of wastewater wastewater treatment. Electricity costs at these plants infrastructure, since proper operations require high were also found to comprise nearly 50 percent of the tariffs and subsidies. total OPEX of the treatment process. Consequently, more and more technical publications, mostly focused on developed countries, have been Energy Requirements of Different comparing in detail the energy needs of different Treatment Technologies technologies. Germany recently presented a A desk review was conducted for this technical note systematic comparison of the energy consumption to collect data on energy requirements at WWTPs of technologies used at about 2,500 German for different plant sizes and treatment technologies. WWTPs (DWA 2013a; DWA 2014). The results are While the topic is not covered extensively in most summarized in table I-3 and figure I-6. Table I-3: Median Electricity Consumption for Different Treatment Technologies and WWTP Design Size Categories Plant design size category Median electricity consumption in kWh/PE60/y (number of WWTPs ) (SC) CAS EA5 SBR TF WSP AeP CW SC1 — 65.2 (184) 92.8 (45) 53.2 (65) 23.8 (45) 41.5 (44) 19.1 (26) SC2 — 44.2 (476) 44.4 (46) 22.7 (119) — 35.6 (123) — SC3 37.9 (37) 39.4 (269) 50.2 (19) 24.7 (28) — — — SC4 33.8 (509) 36.2 (345) 35.2 (27) 26.5 (15) — — — SC5 31.9 (114) — — — — — — Source: DWA 2013a, DWA 2014. Notes: kWh/PE60/y x 16.67 = kWh/kg BOD5/y. SC1 = 0–999 PE60; SC2 = 1,000–5,000 PE60; SC3 = 5,001–10,000 PE60; SC4 = 10,001–100,000 PE60; SC5 = >100,000 PE60.6 CAS = conventional activated sludge; EA = extended aeration; SBR = sequencing batch reactor; TF = trickling filter; WSP = waste stabilization pond; AeP = aerated pond; CW = constructed wetland. 5 Data from German EA plants show energy consumption 5–10 percent higher than with CAS. This difference is less than what might be expected, indicating an in-depth analysis beyond the scope of this study is needed. 6 It is common practice in many European countries to define WWTP design sizes according to their incoming pollution loads (expressed as PE), while in other countries (particularly English-speaking ones), design size is often defined according to flow rate (expressed as MLD or MGD). In Germany, when BOD5 load is used, 1 population equivalent (PE) is defined as 60 g BOD5 /PE/d; when COD is used, 1 PE is defined as 120 (sometimes also 110) g COD/PE/d. To indicate the reference, PE is indexed with the number used. PExy should not be confused with actual (physical) population numbers Depending on lifestyle, use of in-sink grinders, type of wastewater collection system (combined or separate), and so forth, the actual per capita pollution load emission reaching a WWTP can vary considerably from region to region, typically within 30–80 g BOD5 /cap/d, and need not be exactly 60 g/cap/d. 10  WASTEWATER TO ENERGY Figure I-6: Germany—Specific Electricity Consumption (Statistical Distribution) for Different Treatment Technologies and WWTP Design Size Categories Source: DWA 2013a, DWA 2014. Note: kWh/PE60 /y x 16.67 = kWh/kg BOD5 /y. WASTEWATER TO ENERGY   11 Three main conclusions can be derived from for low-energy technologies in small plants, such as this analysis: constructed wetlands (CW) or waste stabilization ponds (WSP), to ≈10 kWh/PE60/y for trickling • In general, the smaller a specific WWTP design filters, and they can go up to ≈20 kWh/PE60/y for size, the higher the energy consumption per capita. high-energy technologies, such as CAS, SBR, or Medium and large WWTPs >5,000 PE60 rarely extended aeration (EA). exceed a consumption of 50 kWh/PE60/y. In the United States, analysis of the energy consumption • The different technologies differ greatly in energy of existing wastewater treatment technologies (WERF consumption. 2010b) has produced data similar to those from • Benchmarks on energy consumption per capita, set Germany, showing a wide range of energy requirements at the fifth percentile, range from ≈1 kWh/PE60/y for different treatment technologies (see figure I-7)7. Figure I-7: Specific Electricity Consumption for Different Treatment Technologies in the United States, Related to Unit Pollution Load (based on assumption of 250 mgBOD5/L) kWh/PE60/y Source: WERF 2010b. Note: kWh/PE120 /y x 16.67 = kWh/kg BOD5 /y. No overview of the energy consumption of different Energy Efficiency Improvement WWTP technologies is available for the EAP region. Since the vast majority of energy assessments relate Generally, it is expected that consumption patterns for to CAS only, reliable energy benchmark values are the same technologies will be similar to or higher than only available for this technology, while existing those observed in Germany and the United States, in information for other processes is limited. The high the case of inadequate maintenance, instrumentation, energy consumption of the CAS process has itself and control systems. become relevant only in the last ten to fifteen years. While sporadic attempts to optimize energy needs were made earlier in various places in Australia, Canada, 7 WERF reports unit energy consumption related to flow rate MGD instead of pollution load PE. To allow for direct comparison, figure 3-6 presents the reported values converted to PE. 12  WASTEWATER TO ENERGY Europe, and the United States, a more systematic • About one-third of cost saving is, on average, achieved and structured approach to energy optimization at through improved efficiency of installations and WWTPs is a recent phenomenon. operation; the rest comes from energy generation from biogas. A summary description of the strategies applied and results achieved from energy optimization at WWTPs • Energy optimization is usually financially attractive in Europe and the United States is presented in for WWTPs because annualized life cycle cost annex 1, which also contains state of the art energy (derived from OPEX and CAPEX) can be reduced. benchmarks and target values. The major findings of Of all possible approaches to reducing energy costs this assessment are as follows: in WWTPs, this technical note focuses on energy generation. • Energy cost at optimized CAS plants can be reduced by an average of 30–50 percent in developed countries. WASTEWATER TO ENERGY   13 4. Wastewater Treatment: From Necessary Evil This constant need to build new facilities and/or to a Source of Beneficial Products upgrade existing ones implied very large investments. For most of the last century, wastewater treatment CAS proved to be the main technology of choice, since was considered a necessary evil, seen exclusively as it was applicable to most effluent standards, it worked a “problem” that required considerable investment, well in cold climates, and it provided much flexibility with little thought devoted to O&M costs. Laws for well-trained operators. addressed the need to protect the environment and Nowadays, a real paradigm shift is taking place, with the public, promoting public health by mitigating wastewater increasingly seen and treated as a resource. the negative impacts of untreated wastewater. Key terms like climate change, carbon footprint, green Increasingly strict environmental regulations drove technologies, sustainability, and energy and resource the development of improved treatment processes recovery feature prominently in discussions, both and better effluent quality. Initial requirements at the specialist level and in public opinion forums. for mechanical treatment of wastewater evolved to The water, organic, nutrient, and energy content of include more efficient removal of carbon compounds, wastewater can be put to beneficial use. The former enhanced removal of nutrients, and disinfection. “waste sludge” produced from wastewater treatment, Lately, the removal of micropollutants has become a when treated to certain specified levels, now becomes hot topic in some regions. “biosolids,” whose nutrient and calorific content make them valuable as fertilizer or a source of energy. BOX I-2: CHANGES IN TERMINOLOGY Changes in terminology observed in literature, laws, and regulations association of water quality professionals in the US, for instance, began regarding wastewater are clear indicators of the paradigm shift to as the Federation of Sewage Works Associations in 1928, changed its considering and treating it as a resource. A typical example is “discharge name to the Federation of Sewage and Industrial Wastes Associations criteria for treated wastewater,” now referred to as “environmental in 1950 and to the Water Pollution Control Federation in 1960, and protection laws.” Also notable are the professional organizations finally became the Water Environment Federation (WEF) in 1991. in the wastewater sector that have changed their names. The trade The following are the main resources derived from uses, environmental and recreational uses, and wastewater and sludge: groundwater recharge are all increasingly interesting options for water recycling. • Treated wastewater as a water resource: Treating and recycling wastewater can help mitigate the impacts • Wastewater/treated sludge as a nutrient resource: The of water scarcity in the many regions of the world primary macro nutrients that can be extracted from that are becoming increasingly water stressed. This wastewater and sludge are nitrogen and phosphorus. does not necessarily mean recycling wastewater to The commercial focus of recent years has been drinking-water quality. Rather, industrial reuse, particularly on phosphorus, since it is a limited mineral irrigation reuse, aquaculture, non-irrigation urban resource that is essential in agriculture and for life on 14  WASTEWATER TO ENERGY the planet. Also critical is the world’s dependence energy-intensive industrial processes to produce on a small number of countries with phosphorus ammonia fertilizer from air. The extraction of resources, mainly China, Morocco, Russia, and nitrogen from wastewater or sludge is much more the United States. Furthermore, the financial expensive. Currently, the focus is on exploring more feasibility of developing this resource is improving energy- and cost-efficient removal of nitrogen from for larger WWTPs, with several technologies now wastewater, and not so much on the recovery of commercially available that can extract phosphorus nitrogen as a product. from wastewater sludge and help control potential • Sludge as an agricultural resource: The beneficial deposition problems in pipes, pumps, and digesters properties of treated sludge as a fertilizer—its or from ash incinerators. The phosphorus products soil amendment, moisture retention, and soil produced can then be marketed. improvement qualities—are well established. This The situation for nitrogen recovery is different. The traditional view has now been supplemented, most common method of nitrogen production uses however, by an interesting application for sludge in WASTEWATER TO ENERGY   15 agriculture not considered in previous years: it plays • The potential limitations on available land for an important role in the mitigation of greenhouse agricultural reuse in urban environments gas (GHG) emission effects. Not only does treated • The possibility that public opinion will turn against sludge offset energy-intensive production of them, which is usually due to concerns about odor chemical fertilizers; it also replenishes soil organic and food safety carbon subjected to climate change–induced wind and water erosion (WEF et al. 2013b). • Wastewater/sludge as a renewable energy resource: Many WWTPs worldwide already implement A 2012 analysis by ADB of various sludge energy recovery from wastewater and sludge, with management options in China came to the three methods being the most common: through conclusion that the combined effects of anaerobic anaerobic sludge digestion, through anaerobic digestion and land application of properly treated wastewater treatment, and through sludge sludge produced the smallest carbon footprints incineration. Of these, the least desirable is the of all sludge management options. The largest third, as from a financial perspective, the electricity carbon footprints resulted from direct landfilling generated from biogas in anaerobic sludge digestion without landfill gas management. Consequently, and anaerobic wastewater treatment is worth more the study recommended closing the nutrient cycle than the extra thermal energy generated from by applying sludge to agricultural reuse after proper incineration of undigested sludge. treatment, including anaerobic digestion with biogas utilization. Where this is not possible, the next Murray and others (2008) analyzed a wide range of best recommendation is energy recovery through sludge treatment options, including dewatering, lime digestion, followed by dewatering and incineration addition, mesophilic anaerobic digestion, heat drying, with heat recovery. incineration, and various combinations of these. A life cycle assessment led them to conclude that “anaerobic Agricultural applications for sludge may be limited digestion is generally the optimal treatment” (Murray for a number of reasons: at al. 2008). While the authors based their analysis on a • Concern about the heavy metal content in sludge if specific case study of four large WWTPs in Chengdu, pretreatment requirements for industrial dischargers China, they maintained that the outcome should be are inadequate, particularly in urban areas representative for many other WWTPs worldwide. Since the energy produced is, in any case, a renewable • The emerging challenge of organic pollutants in sludge, the uncertainties about which may be form of energy, all these energy recovery options can prompting various developed countries to phase help reduce GHG emissions. out its use in agriculture 16  WASTEWATER TO ENERGY 5. Renewable Energy Generation at WWTPs • Closing the nutrient cycle by land application of The focus on energy resource recovery via biogas digested sludge is an attractive option that allows generation from wastewater/sludge should be seen the further utilization of resource benefits from as just one among a wide range of resource recovery wastewater. options. The biogas-centered approach of this technical • A comprehensive comparison of different schemes to note is justified for various reasons: recover energy from wastewater/sludge is still absent • Reduction of OPEX of wastewater treatment from the specialized literature, particularly from provides financial relief to wastewater utilities. the perspective of developing countries with warm climates. The energy attention so far has been almost • The approach implies a reduction of the carbon exclusively on CAS systems with digesters. Closing footprint for sludge management. this knowledge gap is considered important, too. WASTEWATER TO ENERGY   17 Therefore, if the right factors are in place, it is possible biosolids, can be enhanced through various means. to recover energy in urban WWTPs by building on One increasingly popular option is co-digestion of practical experience nowadays available in energy organic waste in sludge digesters. This “add-on” can optimization and recovery in wastewater treatment, contribute to achieving a positive energy balance, a field in which significant improvements have been with the WWTP’s annual electricity production made in recent years. Twenty years ago, a typical exceeding its annual consumption. The effect on WWTP producing 30 percent of its electric energy nutrient loading also has to be considered if there are from biogas was doing well, in a specialist’s perception. nutrient effluent standards. The practice has become a Today, it is possible to achieve reductions in energy widespread standard in Central Europe and is drawing consumption of 50 percent, on average. increased attention in Japan, Singapore, South Korea, and the United States. Case study 5 in this technical At the same time, energy production from renewable note focuses on this technology. biogas, generated from a WWTP’s wastewater and BOX I-3: THE FUTURE OF WWTPS? The current enthusiasm for energy generation at WWTPs goes beyond co-digestion of organic waste from households in the WWTP’s sludge achieving energy balance. Some utilities have started considering digesters. The future WWTP/energy park is expected to produce WWTPs as energy production centers. One example is the Swiss some 10 million kWh/y—equivalent to seven times the electricity it Morgental WWTP, which currently produces some 50 percent of consumes—and will deliver 22 million kWh/y in thermal energy to be the 1.4 million kWh of electric power it consumes annually from its used for district heating. All this will come at an economically viable own biogas from sludge digestion (Strässle 2012). In 2012, the city and attractive cost and will have a positive carbon impact. While this council decided to install an energy park at the WWTP. It will feature may be an extremely ambitious scheme from a developed country that more efficient biogas utilization installations, a hydropower station for might not be easily implemented in other countries, it does indicate the wastewater, heat exchangers in the sewers to utilize its thermal energy, direction in which the sector is heading. a biomass incinerator for wood chips, a new photovoltaic plant, and Technologies for Renewable Energy Generation via Biogas from Wastewater • Other sources of energy: The various options for introducing renewable energy generation at WWTPs can be classified as follows: • Electricity from hydropower from a plant’s influent or effluent • Energy from anaerobic sludge or wastewater treatment: • Electricity and thermal energy captured from solar • Anaerobic digestion of sludge from wastewater radiation at facilities treatment • Electricity captured from wind power at facilities • Co-digestion of energy-rich organic waste • Thermal energy and/or electricity from sludge materials in sludge digesters incineration • Anaerobic wastewater treatment 18  WASTEWATER TO ENERGY • Heating or cooling energy collected from the improved sludge digesters were already constructed wastewater’s thermal energy in the 1920s, and in Southeast Asia today, household digesters are widespread at technically This technical note focuses on the first family of small scales. Box I-4 provides a brief overview of options: sludge and wastewater anaerobic digestion the historical background of the use of biogas from for biogas production. human waste. The Use of Biogas from Human Waste as a Resource Knowledge about biogas formation from anaerobic digestion of human waste is not new. The first BOX I-4: BRIEF HISTORY OF BIOGAS FROM HUMAN WASTE AS A RESOURCE That a combustible gas is generated when organic waste is allowed to and is still being applied for anaerobic sludge digestion. As improved rot in piles has been known for centuries, and that this gas is rich in reactor shapes, mixing systems, and heating systems have sprung methane became clear at the beginning of the nineteenth century. In up over time, some of the earlier technical developments have been the 1860s, the Frenchman John Louis Mouras came up with the idea phased out, while others have continued to evolve. of a large, deep sedimentation tank for wastewater to prolong the Southeast Asia and East Asia Pacific are among the regions where intervals of sludge removal. This idea of a “fosse Mouras” (Mouras pit) these processes have grown in popularity; Bangladesh, China, India, was subsequently taken up by an Englishman, Donald Cameron, who in Nepal, Pakistan, and Vietnam have been using household biogas 1895 constructed an improved version, calling it a “septic tank.” Already plants for decades (Abbasi et al. 2012). China in particular stands out in some of the first installations of that type, the generated biogas was because of the sheer number of its digesters, located mostly in rural used for heating and lighting (Abbasi et al. 2012). areas. Today, over 25 million households are using biogas in China, Just a decade later, in 1906, the German sanitary engineer Karl accounting for over 10 percent of all rural households. The number of Imhoff proposed the so-called “Imhoff tank,” with two separated large-scale digesters (over 300 m3) has also been increasing rapidly. compartments. The upper compartment is used for the sedimentation By the end of 2012, over 20,000 large anaerobic digesters were in of raw wastewater, and from it the sludge glides into a lower sludge operation in China, representing about 30 percent of the total number digestion compartment. In the Imhoff tank, biogas is usually not worldwide (Ren 2013). These large digesters predominantly feed on collected and is released to the open air (Roediger et al. 1990). waste from livestock, poultry farms, and food industries. Although the Imhoff tank is a robust and simple installation, it has During the last decade, interest in household digesters has been some disadvantages, particularly its deep foundation, the absence of growing in South American countries. Biogas produced by these sludge mixing, and no heating. Lack of mixing and heating reduces the systems is usually used for cooking, thereby replacing firewood, rate of biogas production. which preserves the environment through reduced deforestation, These problems were overcome with separate sludge digestion decreases household expenditures on fuel and/or fertilizer, and reactors, complete with mixers and heating, which were first reduces the workload of the women and children who collect the constructed in Germany and the United States in the 1920s (Roediger firewood (Ferrer et al. 2013). et al. 1990). This concept has been further improved over the years WASTEWATER TO ENERGY   19 Sludge Digesters for Renewable Energy • By enhancing energy savings at all stages of Generation at WWTPs wastewater and sludge treatment through optimized Anaerobic sludge digestion has become a standard process selection, infrastructure, instrumentation, WWTP component in developed countries, where and control anaerobic digesters are a state of the art element of many • By implementing various means of maximizing WWTPs with design capacities above about 10,000– electricity production from biogas: 20,000 PE60 (1–2 MLD). Digesters serve several purposes: the destruction of organic matter reduces • Co-digestion of waste sludge, food waste, FOG the need for expensive disposal of sludge quantities (fats, oils, and grease), and industrial organic by about 30 percent, reduces the sludge’s potential for wastes the emission of bad odors, and reduces the pathogen • Adoption of new hydrolysis technologies to release content of the biomass; and the generated biogas can cell liquor from the sludge’s micro-organisms be used to produce energy. Anaerobic sludge digestion prior to its digestion, thereby increasing biogas is still not common in developing countries, however. production further (for example, Cambi8 and To date, of the three countries on which this study ultrasound sludge treatment, among others) focuses, only one—Vietnam—has a single sludge • Building of high-efficiency and low-maintenance digester, located at Yen So WWTP (200 MLD). combined heat and power (CHP) installations for Furthermore, even though many WWTPs in Europe the conversion of biogas into electric energy (for and the United States feature sludge digesters, the example, co-generation with improved efficiencies potential to generate electricity from biogas is not and micro turbines)9 exploited fully, which leaves room for increased power • Improved infrastructure for improved mixing generation. Detailed information on the use of sludge and temperature combinations at the anaerobic digesters and the potential for renewable energy reactor level (for example, digestion at mesophilic production from biogas in Europe and the United States, [around 35°C] and thermophilic [around 50°C] as well as the expected electricity consumption and temperature levels) generation potentials at future WWTPs in Indonesia, the Philippines, and Vietnam, are provided in annex 2. Although some developing countries are paying more attention to anaerobic wastewater treatment Quantification of Renewable Energy Generation technologies, biogas utilization and low-energy Potential at WWTPs wastewater technologies are generally underdeveloped. Utilities in developed countries are pursuing energy While Europe and the United States overwhelmingly efficiency improvement to reduce OPEX and present rely on activated sludge technologies, which work well a greener image in a number of ways: in cold winter temperatures, developing countries 8 At Blue Plains WWTP in Washington, DC, the world’s largest Cambi plant is currently being installed by the local utility (DC Water). 9 There are several options to produce electricity from biogas: fuel cells, Stirling motor, direct drive engines, co-generation or microturbines. Evaluations of these options show that the combined production of electricity and heat (CHP) through co-generation or microturbines usually results as the most economical option for biogas reuse at WWTPs. This has become the common international standard approach at WWTPs, which is also applied in all case studies of this technical note. More details on these options are provided in annex 3, case study 1. 20  WASTEWATER TO ENERGY have the opportunity to select technologies that may All of these are, however, either regionally limited be better suited to their specific conditions. The or taking place in small numbers. The sharing following are the most notable signs of movement in of knowledge about the advantages, specific this direction: requirements, realistic large-scale operation results, operators’ skills, and cost features associated with • Increased numbers of anaerobic wastewater these developments would increase their appeal and treatment technologies, such as upflow anaerobic spur their wider adoption. sludge blanket (UASB) reactors, baffled anaerobic reactors (BAR), and covered anaerobic ponds One way of finding novel approaches other than CAS is to look at recent international awards won • Utilization by a few facilities of the biogas they by WWTP technologies in developing countries10. produce The awards provide important incentive for • Revitalization of other low-energy technologies, technological development, and they indicate the such as trickling filters and constructed wetlands, direction in which the future of energy efficiency among others, and various combinations of these is heading. 10 The IWA Projects Innovation Awards chose as the winner of its Global Honor Awards in 2013 a WWTP in Batumi, Georgia, that combines anaerobic ponds with trickling filters. This decision was justified by the “extremely low investment cost” and “low power consumption . . . [representing] less than 50 percent of [that of] any process technology.” (IWA 2013). In biosolids treatment, a solar sludge drying facility in Managua, Nicaragua, was nominated for the Global Water Award 2010 in the category of Environmental Contribution of the Year on the basis that “low-cost, low-energy systems such as this are going to be an important part of the solution in developing countries.” At the time of startup, this facility was the largest of its kind worldwide. Since then, a proliferation of similar and even larger plants in warm climate countries has been observed. WASTEWATER TO ENERGY   21 The Specific Conditions in EAP Regarding Renewable Energy Generation ponds (WSPs) or aerated ponds require large areas, The current trend in WWTP technologies in EAP they are usually not feasible in urban environments, points in a direction similar to that taken by other so CAS systems are usually preferred. countries (see figure I-8). Since waste stabilization Figure I-8: Distribution of Wastewater Treatment Technologies in Germany, LAC, Vietnam, and Indonesia Source: DWA 2013a (Germany); Noyola et al. 2012 (Latin America and Caribbean [LAC]); World Bank 2013f (Vietnam); World Bank 2013d (Indonesia). China, where the great majority of WWTPs use CAS Impact of wastewater dilution and large numbers of technology, is one example of this trend. CAS systems septic tanks. A rather unique feature of EAP countries are well suited for meeting required treatment levels, is their high levels of wastewater dilution—that is, the but they have high CAPEX and OPEX, which stresses low concentrations of pollutants in their wastewater. the financial situation of sanitation utilities. Although In a wastewater treatment plant, dilution increases potentially interesting alternatives for urban WWTPs pumping costs, requires larger settling tanks, and in warm climate countries, such as trickling filters and reduces treatment efficiencies. Dilution is a common UASB, do exist, their numbers are relatively modest. problem in many areas around the world, but there are not many regions where it is as severe as in EAP. 22  WASTEWATER TO ENERGY WASTEWATER TO ENERGY   23 When very low concentrations of suspended solids are is diluted. If these larger reactors are expensive to found in influent wastewater, a primary sedimentation build, the whole technology becomes less attractive. tank (PST) is not necessary11. This matters in terms Other technologies might be less affected by diluted of biogas production because the sludge coming out wastewater. For instance, CAS and trickling filters, of PSTs is richer in volatiles that produce biogas. If being designed on total biochemical oxygen demand PSTs are not needed, sludge will only be an output of (BOD) load criteria, will require the same reactor the biological treatment process. The activated sludge volumes, with or without dilution. coming out of this process has less biogas potential than Assessment of measures to address the dilution that coming from PSTs, so overall biogas production problem is beyond the scope of this technical note, but is significantly reduced. some actions to consider were suggested in the East Wastewater dilution is usually caused by a combination Asia Urban Sanitation Review (World Bank 2013): of factors frequently found in the EAP region, such as • Conduct robust analysis when designing sewerage the use of combined sewers that intercept wastewater networks, and consider separate systems for new from traditional open or poorly constructed drainage development areas.12 canals, seasonally heavy tropical rains, and high groundwater tables infiltrating the sewers. In the • Minimize the runoff and, therefore, the infiltration wet season, wastewater concentrations may be very flows in combined systems by introducing measures low, sometimes even below the required treatment that favor natural infiltration in the soil. standards, putting the need for wastewater treatment • Maximize the number of household connections, into question. In addition, septic tanks in urban areas progressively eliminating septic tanks for new are very common in the region. While these onsite construction where sewerage networks and treatment systems may be in bad physical shape and/or poorly plants are in place. maintained, they still succeed in retaining a large The consequences of the phenomenon of wastewater percentage of the solids usually present in wastewater, dilution are still not well understood, however. A thus contributing to the dilution problem. thorough analysis of actual wastewater concentrations Dilution has additional impacts on process technology and its consideration in process design are very for wastewater treatment. Technologies in which the important to producing optimal designs and correct main treatment unit is designed based on retention OPEX forecasts. Although dilution is generally time criteria (for instance, UASB or anaerobic ponds) recognized as a problem affecting wastewater-to- require reactors with larger volumes if the wastewater energy potential, project-specific conditions do 11 In a situation with no dilution problem, the TSS in a typical PST effluent would normally be ≈80 (50–150) mg TSS/L, based on TSS efficiencies of 50–75 percent, and a conventional raw wastewater influent concentration of some 200–300 mg TSS/L. Consequently, if influents already have less than about 80 mg TSS/L, a PST is usually not recommendable. 12 The Vietnam Urban Wastewater Review (World Bank 2013) shows the significant difference between influent concentrations of pollutants in separate versus combined sewerage collection networks. 24  WASTEWATER TO ENERGY matter, and a case-specific analysis based on sound • Less costly technologies become inappropriate data is always recommended. because they cannot deliver the required N quality, and more costly technologies must be used. Impact of required treatment standards. As also highlighted in the EAP Urban Sanitation Review • Larger reactor volumes are required. (World Bank 2013c), stricter effluent standards lead • Operation and maintenance of larger and more to increased cost in terms of both CAPEX and OPEX. sophisticated technologies becomes more costly. This is usually justified by the environmental capacity • The potential for electricity generation from biogas of the receiving waters, although it is not always the case. Effluent standards can be categorized at three decreases because a higher percentage of organic levels, depending on the level of environmental material is oxidized in the treatment process. protection required: 3 Requirements for even lower levels of BOD, chemical oxygen demand (COD), total suspended solids 1 Normal values for carbon parameters and (TSS), and phosphorus (P). These imply additional phosphorus. These are BOD5 <15–50 mg/L, COD and more costly treatment stages. Usually the biogas <50–150 mg/L, TSS <15–40 mg/L, P <5 mg/L, potential is just marginally affected, as long as the with no requirements on nitrogen (N). preceding main treatment stages remain unchanged. 2 Nitrogen removal requirements. These usually But, generally, additional treatment stages imply imply imposing limits on ammonia, and even on increased electricity consumption, thus reducing total nitrogen, which usually increases cost through the electricity coverage through power from biogas. various effects: Consequently, the economic and environmental advantages and disadvantages of pursuing more ambitious standards must be carefully considered. Feed-in tariffs. Regulations for power supply to the public grid already exist in many East Asian countries for various renewable energy sources, such as landfill gas or power from biomass. Energy from sludge biogas is, therefore, not expected to encounter obstacles if power surpluses are to be supplied to the grid in the future. WASTEWATER TO ENERGY   25 26  WASTEWATER TO ENERGY SECTION II: CASE STUDIES AND ASSESSMENT TOOL METHODOLOGY WASTEWATER TO ENERGY   27 6. Methodology In this section, six large-scale case studies are analyzed generation. Figure II-1 presents a summary of the in detail, covering all of the wastewater-to-energy main biological wastewater treatment systems. Those options appropriate for East Asia Pacific. used for biogas generation from municipal wastewater are highlighted in bold. Although a wide range of wastewater treatment technologies exists, just a few are suited for biogas Figure II-1: Summary Description of Main Biological Wastewater Treatment Systems and Their Use for Biogas Generation from Municipal Wastewater WASTE STABILIZATION PONDS LAND DISPOSAL CONSTRUCTED WETLANDS • Facultative pond • Slow-rate system • Surface flow • Anaerobic—facultative pond • Rapid infiltration • Subsurface flow • Facultative aerated pond • Subsurface infiltration • Aerated lagoon—sedimentation pond • Overland flow • High-rate pond • Maturation pond ANAEROBIC SYSTEMS ACTIVATED SLUDGE AEROBIC BIOFILM REACTORS • UASB (upflow anaerobic • CAS (conventional activated sludge) • Low-rate trickling filter sludge blanket) • EA (extended aeration) • High-rate trickling filter • Anaerobic filter • SBR (sequencing batch reactor) • Submerged aerated biofilter • Anaerobic reactor—post-treatment • AS (activated sludge) with biological N removal • AS with biological N + P removal Source: Sperling and Chernicharo 2005. The main biological wastewater treatment systems This technical note presents practical experiences typically used to produce biogas from wastewater/ with wastewater-to-energy options through a detailed sludge fall into four groups: waste stabilization ponds, analysis of the six case studies listed in table II-1. anaerobic systems, activated sludge, and trickling filters. 28  WASTEWATER TO ENERGY Table II-1: Biogas Production Technologies Analyzed in this Technical Note     Biogas from Location Case study wastewater treatment sludge treatment of case study 1 CAS + sludge digestion — X Europe 2 TF + sludge digestion — X Nicaragua 3 UASB X — Brazil 4 Covered anaerobic ponds X — Bolivia, Australia 5 Co-digestion of organic waste — X Europe 6 Ultrasound sludge disintegration — X Europe The analysis looks into the energy consumption of the understanding of the viability of energy generation wastewater treatment technologies, biogas quantities and the preselection of appropriate options for and characteristics, the potential for electricity wastewater treatment, specifically in urban areas of generation, operation capacity needs, safety concerns, warm climate countries. institutional aspects, GHG reduction, co-financing options through carbon trading mechanisms, and 7. Main Findings from the Analysis cost-related aspects (CAPEX, OPEX, and overall of Case Studies financial viability). The technologies assessed can be grouped into those producing biogas directly in the wastewater treatment Based on the analysis, a simple assessment tool has train and those based on installations in the sludge been developed in spreadsheet format and is presented treatment train. The wastewater and sludge treatment in section II, subsection 8 below. This tool permits trains are identified in figure II-2, which represents quick, preliminary quantification of energy efficiency. a typical conventional activated sludge (CAS) plant The user will need to insert data regarding specific with anaerobic digestion of sludge. In this case, the local conditions to obtain results that quantify such two sources of sludge to treat are removed from the aspects as energy consumption, biogas potential, bottom of the primary settling tank (primary activated electricity coverage ratio, preliminary design of sludge) and from the bottom of the secondary clarifier major wastewater-to-energy components, and overall (waste activated sludge, or WAS). impact on OPEX. This tool is expected to facilitate WASTEWATER TO ENERGY   29 Figure II-2: Wastewater and Sludge Treatment Trains of a Typical CAS Plant Source: authors In sludge treatment applications, the centerpiece is In addition, wastewater treatment itself can be used always an anaerobic digester, which is a closed reactor for biogas production when using anaerobic systems in which the temperature is usually controlled through (such as anaerobic lagoons or UASBs). This approach a heating system (in cold climate countries) and the works particularly well in warm climates, as the case sludge is partly decomposed into biogas and other studies show. subproducts. What can be expected from the digester Since O&M practices and cost data from one location depends on the conditions inside the reactor and what should not be applied to another without background is being fed into it. Since conditions are controlled analysis, this technical note takes into account the and feed sludge characteristics are similar worldwide, specific conditions existing in EAP countries when experiences with these systems can be applied to assessing the case studies. The photos presented any location. Consequently, most of the case studies in figure II-3 give some indication of the physical involving digesters (1, 5, and 6) are based on data appearance of the installations in the case studies, from Europe and the United States, where a great deal which are summarized here and documented in more of practical experience and data are available. Case detail in annex 3. study 2 shows an example of one digester from a warm climate country that is operated without heating. 30  WASTEWATER TO ENERGY Figure II-3: Wastewater and Sludge Treatment Trains of a Typical CAS Plant WASTEWATER TO ENERGY   31 Wastewater Influent and Effluent All of the case studies present normal-strength raw wastewater characteristics of case studies 1–4. Case studies wastewater. Carbon removal is always required, but 5 and 6 are not included, since wastewater characteristics nutrient removal is not. Table II-2 summarizes the are not directly relevant for these technologies. Table II-2: Average Influent and Effluent Wastewater Characteristics of Case Studies Case Study #1: Case Study #2: Case Study #3: Case Study #4: CAS+digestion TF+digestion UASB Covered Anaerobic Ponds Central Europe Nicaragua Brazil Bolivia Australia WWTPs (nr.) nr. 6,823 1 22 4 2 Pop.Equivalents avg. actual PE60 n.a. 447,000 62,417 802,000 4,569,000 max. actual PE60 n.a. 606,000 577,917 1,023,000 4,994,000 WASTEWATER QUANTITY Specific wastewater production L / PE60 /d 201 225 220 147 105 WASTEWATER QUALITY COD Influent mg/L 602 505 697 946 1,009 Effluent mg/L 35 101 194 197 32 Elimination % 94 80 72 79 97 BOD5 Influent mg/L 255 248 297 407 571 Effluent mg/L 5 28 62 60 4 Elimination % 98 89 76 85 99 Ntotal Influent mg/L 47 28 n.a. 92 73 Effluent mg/L 9 18 41 66 21 Elimination % 81 37 n.a. 28 72 NH4-N Effluent mg/L 1 n.a. 38 2 5 NO3-N Effluent mg/L 6 n.a. 1 0 15 Ptotal Influent mg/L 8 4 7 15 11 Effluent mg/L 0.7 1.7 4.5 4.4 9.0 Elimination % 91 54 33 71 14 Notes: 1 cap = 60 g BOD5 /d in Central Europe and Australia; 46.5 g BOD5 /d in Nicaragua; 54 g BOD5 /d in Brazil; and 40 g BOD5 /d in Bolivia. 1 PE60 = 1.0 cap in Central Europe and Australia; 1.29 cap in Nicaragua; 1.11 cap in Brazil; and 1.5 cap in Bolivia. L/PE60 /d = L/cap/d in Central Europe and Australia; x 1.0 (1.29; 1.11; 1.50) in Bolivia, Brazil, and Nicaragua respectively. The following points can be highlighted: • In case studies 1, 2, 5, and 6, with sludge digesters, an increased nutrient load enters wastewater • Most influent concentrations represent normal- treatment due to increased N and P concentrations strength wastewater conditions. Only case study in the filtrate from sludge dewatering after digestion. 4 includes plants with lower specific wastewater Therefore only where effluent regulations do not production and consequently higher influent require nutrient removal (case study 2) there will concentrations. be an increase in the nutrient load discharged to • Case studies 1, 5, and 6, in Europe, feature enhanced the environment. The return loads of N and P nutrient (N + P) removal. typically amount to less than 20 percent and less than 10 percent of influent loads, respectively. The • All other cases describe systems with only carbon overall increase in nutrient emissions of WWTPs removal. Only the Australian pond + CAS system of with wastewater-to-energy systems under such case study 4 is also performing enhanced N removal. 32  WASTEWATER TO ENERGY conditions is still small compared to other nutrient biogas, and that other technologies with generally emissions to the aquatic environment (for example, lower electricity consumption, such as trickling filters, diffuse entries via surface runoff and/or through UASB, and covered anaerobic ponds, can. The case groundwater fed from septic tanks and agriculture, of co-digestion demonstrates that this option is an industries, improper waste disposal, and so on). efficient instrument to further increase biogas in sludge digesters, so if all the generated biogas can be When • applying case study results to EAP put to good use, the financial benefits are substantial. conditions, diluted wastewater and nutrient removal requirements are very important factors to consider, Table II-3 summarizes both the biogas production and and a case-specific analysis is recommended. subsequent power generation potential found in case studies 1–5, as compared to the power consumption Biogas Production and Potential for of the respective technologies or installations. Results Energy Generation show that different required wastewater treatment The case studies confirm that CAS technology usually levels (that is, considering carbon and nitrogen cannot achieve full electricity coverage from digester elimination) do have an impact on energy production. Table II-3: Biogas and Power Generation Potential of Case Studies, Compared to Power Consumption   Case study 1: Case study 2: Case study 3: Case study 4: Case study 5:   CAS + digestion TF + digestion UASB Covered anaerobic ponds Co-digestion   Central Europe Nicaragua Brazil Bolivia Australia Central Europe Biogas production             - N elimination (L/PE60/d) 20–23 — — — — 17.5 (sludge) + 30 (waste) - C elimination (L/PE60/d) 24–29 16 13 25 13 — Power generation from biogas             - N elimination (kWh/PE60/year) 15–18 — — — — 11 (sludge) + 19 (waste) - C elimination (kWh/PE60/year) 18–22 11 9 15 13 — Power consumption             - N elimination (kWh/PE60/year) 37 — — — 16 **** 25 - C elimination (kWh/PE60/year) 25 9–10 6 (29)* <4 *** — — - Electricity coverage from biogas 35–80%** 115% 150% (40%)* >300%*** 50–70% 110% *Large (small) WWTPs. **Depending on electric efficiencies of all WWTP installations. ***Estimate. ****Including downstream CAS systems. Note: L/PE60 /d x 16.67 = L/kg BOD5 /d; kWh/PE60 /y x 16.67 = kWh/kg BOD5 /y. WASTEWATER TO ENERGY   33 Figure II-4, derived from the analysis of all the case case studies relate to different wastewater technologies studies, provides a broader picture of the ranges of (CAS, TF, UASB, and covered AP), and the fifth (co- electricity consumption and production within which digestion) can optionally be added to CAS and TF. the various technologies usually operate. Four of the Figure II-4: Electricity Consumption versus Production of Different Technologies Note: kWh/capita/y x 16.67 = kWh/kg BOD5 /y. CAS = conventional activated sludge; TF = trickling filter; UASB = upflow anaerobic sludge blanket; AP = anaerobic pond. The following observations can be made: • The power consumption ranges, at their respective upper ends, also include requirements for • Power consumption (blue bars in figure II-4): enhanced nutrient removal for all technologies • The case studies confirm that CAS is the except covered APs. If APs did, indeed, require frontrunner in terms of high energy consumption, enhanced nutrient removal, additional treatment with a power requirement range of 20–50 kWh/ stages would be needed, which were not included cap/y. TF requires only 8–25 kWh/cap/y, equal to in the case studies. about 35–50 percent of the energy CAS needs to • Power production from biogas (orange bars in operate. UASB requires about 2–13 kWh/cap/y, equal to 10–30 percent, and covered APs require figure II-4): 1–4 kWh/cap/y, equal to 5–10 percent of CAS’s • The CAS + digester in case study 1 produces about energy requirements. 20–40 percent more electricity from biogas than other technologies. 34  WASTEWATER TO ENERGY • While the most efficient means of increasing power • Similarly, covered APs can always achieve full production is co-digestion, using it is only possible electricity coverage if only carbon removal is with those technologies that feature separate sludge required and polishing ponds are sufficient digesters. Depending on the quantity and quality to meet the effluent criteria. If stricter carbon of the extra feedstock, doubling the biogas/power standards and/or nitrification are required, a generation from sludge alone can be feasible with combination of covered APs with TFs will still the existing sludge installations. be able to achieve full electricity coverage. Yet if additional denitrification is required as well, or if • Ultrasound sludge disintegration (USD) is a additional energy-intensive installations have to be simple way to increase biogas/power generation operated, the electric power from the biogas can further, but more than a net increase of 10–15 be insufficient to cover all these needs. percent should not be expected. This option is only applicable to CAS + digester. EAP countries may be able to enhance existing CAS systems with digesters for biogas production, with • Electricity consumption coverage through power a potential to cover 20–80 percent of total power production from biogas at the plant: requirements through power generation onsite, • The CAS + digester case study shows that enabling depending on the local circumstances. The extent of full electricity coverage is usually not possible for the coverage primarily depends on wastewater and this technology.13 installation characteristics. The remaining power gap • In the cases with TFs + digester and UASBs, full is still the largest of all analyzed technologies if co- electricity coverage can be achieved more easily if digestion is not considered. primary sedimentation tanks are included in the If figure II-4 is amended to show the effects of treatment train, wastewater treatment standards wastewater dilution, the energy consumption values are limited to carbon removal and nitrification, will be in the upper range, and the energy production sludge treatment is limited to thickening, will be in the lower range indicated. The only means digestion, and mechanical dewatering (no thermal to counter this trend are (a) elimination or reduction drying or incineration), and the sludge digesters of the underlying causes and (b) application of co- are properly mixed and operated at mesophilic digestion to the greatest extent possible, as described temperatures of about 30–35°C. in case study 5. 13 A few exceptions are characterized by very low energy consumption at benchmark level and optimum installations for biogas production and utilization. WASTEWATER TO ENERGY   35 Operation Capacity Needs and Biogas Safety Table II-4 summarizes all the factors that can cause and electricity generation systems in each of the concern in the operation of the respective biogas case studies. Table II-4: Possible Types of Concerns and Relevance for the Technologies Analyzed   Case study 1: Case study 2: Case study 3: Case study 4: Case study 5: CONCERNS CAS + digestion TF + digestion UASB Covered anaerobic ponds Co-digestion Safety concerns YES YES YES YES (no change) Digester foaming YES YES — — (no change) Deposits in the digester YES YES YES YES YES Insufficient biogas treatment YES YES YES YES (no change) Scum formation — — YES — — These concerns are discussed in depth in the annexes. because its benefits were not well understood. Only in Problems only arise if these factors are not properly recent years, with increasing electricity costs and high considered at the design stage, in the specifications OPEX, has interest emerged in options for biogas of the bidding documents, or in daily O&M. If they utilization in CHP. are properly handled, though, no sustained negative Also notable is that, although the private sector is consequences are anticipated. Addressing these factors is often involved in O&M tasks in many wastewater-to- not costly, nor does it require a great deal of knowledge. energy projects in Europe and the United States, none of the case studies from elsewhere involves the private Institutional Aspects Related to the Case Studies sector in the operation of CHP for energy generation. The wastewater-to-energy components in the case Below are summarized the institutional aspects of the studies were usually not incorporated out of a particular case studies; a more detailed analysis of each case is interest in energy production per se, but rather to provided in annex 3. find the least costly solutions to treat wastewater and sludge or, in case study 1, to stabilize and minimize Regulatory framework. As shown in case studies 1 sludge quantities, since the cost of sludge disposal in and 5, the utilization of electricity from biogas is Europe and the United States is very high. explicitly regulated in Europe; however, this is not true in the other cases. In those where power surpluses Case studies 2, 3, and 4 were selected because they are produced, transferring electricity to the public combined competitive CAPEX with low electricity grid is usually an objective (case studies 2, 3, and consumption. But in none of these cases was energy 4), since storing it is too expensive to be considered. production from biogas included right from the Alternatives, such as supplying the biogas to natural start. Biogas utilization was deemed unattractive gas pipelines or producing biofuel, are technically for financial reasons, due to operation concerns, or possible but not common practice because they are 36  WASTEWATER TO ENERGY not financially attractive. The low feed-in tariffs to withdraw the same electricity at a different site, paying the public grid in all the case studies provide little a reasonable grid transmission fee only. Large utilities incentive for wastewater utilities to transfer their that operate several WWTPs, not all of them producing surplus electricity (see table II-6, below). electricity, and even water supply facilities find this option attractive. This innovative policy was, indeed, the Case study 5, on co-digestion, shows the feedstock main enabling factor for the utilities to start considering supply is just sufficient to cover 100 percent of the investments in energy generation at their WWTPs. WWTP’s own power needs. Surpluses are intentionally avoided. In this case it was interesting to see well- Know-how. While developed countries base many of defined institutional arrangements in place, where their decisions on wastewater to energy on analysis collection and pretreatment of the organic waste is of benchmarking data, this approach is unknown in carried out by a private company that made all the other countries, where local specialists are usually quite necessary investments, whereas the wastewater utility hesitant to promote wastewater-to-energy projects receives the sludge free of charge. because they are unfamiliar with many of the technical matters involved. Apart from rare exceptions, such as A smart option found in case studies 3 and 4 (Brazil and in Brazil, the technology is incorporated mostly by Bolivia) is to supply electricity to the public grid and projects with international co-financing. WASTEWATER TO ENERGY   37 While access to financing would appear to be a GHG Reduction and Co-financing through major obstacle for wastewater to energy in developed Carbon Trading countries (WERF 2012a; ESMAP 2012), the findings All the case studies were analyzed according to their of the case studies did not confirm this. Rather, the potential for GHG reduction, taking into consideration main obstacles were low electricity unit cost and lack co-financing from CDM. Following the approach of knowledge, as shown by case studies 2, 3, and 4. It usually taken by these utilities, the potential reduction can be concluded, however, from case studies 1, 5, and in CO2e is calculated from the combined effects of (a) 6 that European utilities already opt for investing in the amount of electricity generation from fossil fuels that energy generation if the investment can be paid back is being replaced by electricity from renewable sources within the average lifespan of the required installations, and (b) the reduction of emissions of methane, a GHG which is typically about fifteen years. Utilities in these twenty-one times stronger than CO2. Not included in cases are particularly keen to present a “green image” to this assessment are the effects of nitrous oxide (N2O), the public. This trend has also been detected in other which can play an important role in nutrient removal countries, yet it is still not translated into a decisive (WERF 2012b). N2O is subject to ongoing research impact on decision making in case studies 2, 3, and 4. activities. However, quantifications of its effects for any process technology are still under discussion. Table II-5: GHG Reduction Results of Case Studies   CASE STUDY 1:  CASE STUDY 2: CASE STUDY 3: CASE STUDY 4:  GHG reduction CAS + digestion  TF + digestion UASB Covered anaerobic ponds    Germany Austria   Santa Cruz Melbourne GHG reduction             tons CO2e /y n.a. n.a. 2,350 1,100 65,392 302,019 kg CO2e /PE60 /y 7 3 5 1 82 66 kg CO2e /kgBOD5 0.3 0.1 0.2 0.04 3.7 3.0 kg CO2e /cap/y 7 3 4 1 54 66 Aspects considered             GHG reduction by electric power generation YES YES YES YES YES YES GHG reduction by methane emission reduction n.a. n.a. n.a. n.a. YES YES Source: Geyer and Lengyel 2008. Note: Data for case study 1 are based on an electricity production of 16 kWh/PE60/y, which is an average yield in case of N elimination (see annex 3). 38  WASTEWATER TO ENERGY The case study assessments show that the present CH4 generated at the plant under generally accepted low price of carbon credits renders most wastewater- carbon trading schemes. to-energy projects unattractive for carbon trading. Case study 1 shows that the price of carbon credits is as Table II-5 summarizes the GHG reduction results low as US$6.80/tCO2e in the European Union Emissions from the case studies. Trading System (EU ETS). Prices are not substantially The case studies have major differences in terms of higher at other trading places, either, which reduces the GHG reduction. Case study 4 (covered anaerobic attractiveness of this financing option. Applying these ponds) achieves most reductions by eliminating CH4 unit prices to any of the other case studies produces (methane) emissions when the anaerobic ponds are absolute prices that are lower than the cost of preparing covered. Technologies that already collect biogas as an those carbon trading projects, particularly if only the intrinsic part of the treatment process, such as CAS, electricity generation can be claimed.14 TF, or UASB, cannot claim the elimination of the Energy Costs and Viability of Investment in Biogas Utilization Table II-6 summarizes the electricity feed-in and purchase tariffs of the case studies. Table II-6: Feed-in Tariffs for Electricity Generated from Biogas at WWTPs, as Compared to Unit Power Cost for Electricity Purchases from the Public Grid Country Feed-in tariff Electricity cost from public grid   US$/kWh US$/kWh Australia (=purchase cost minus small fee) ≈0.09 Austria 0.08 ≈0.14 Bolivia (only power transmission is targeted) 0.06 Brazil (only power transmission is targeted) 0.25 Germany 0.08–0.09 ≈0.20 Nicaragua (not yet defined) 0.08 14 A change would be possible if the price of carbon credits reflected the real costs. Annex 3, case study 1 indicates the real cost by presenting companies’ “internal carbon price” per ton of CO2e - about US$40 - which they use for planning purposes. If a price around this value were to materialize, CDM co-financing could become a much more appealing funding instrument, both in general and specifically for wastewater-to-energy projects in the future. WASTEWATER TO ENERGY   39 The electricity unit cost in the countries of the case studies The cost of generating electricity from biogas is generally ranges from US$0.06 to US$0.25/kWh—a ratio of four lower than the above-cited unit cost of purchasing between the minimum and maximum electricity unit electricity from the grid. Figure II-5 presents the cost. This can have a decisive influence on overall financial cost of electricity generation from biogas, based on viability, since the investment cost of the installations in life cycle cost assessment. These results are derived question does not tend to vary that much. from CAPEX and OPEX information provided by Geyer and Lengyel (2008) for implemented projects Feed-in tariffs in many of the case studies are uncertain. of different sizes. The cost assumptions used in this In some of these cases, only a general agreement has been analysis are on the conservative side. The life cycle cost cleared with the power utility, without specific unit values calculation includes all installations typically required for kWh supplied to the grid. In these cases, the feed-in for biogas utilization, including gas treatment.16 tariff is expected to be lower than the retail price.15 Figure II-5: Total Life Cycle Cost of Electricity Generation from Biogas 15 In Austria and Germany, the feed-in tariff is regulated by law, and equals roughly 50 percent of the electricity unit purchase price. 16 Further assumptions are a twelve-year lifespan of installations with an availability of about 90 percent, discount factor of 5 percent, and conservative biogas production assumptions (production of 10 L/cap/d, 62 percent methane, 30 percent electric efficiency of CHP). Similar total cost values are also cited in other sources (U.S. EPA CHP Partnership 2011). 40  WASTEWATER TO ENERGY Comparing these findings against the electricity into account other possible cost components, such tariff in Vietnam (US$0.06/kWh) suggests biogas as improved preliminary treatment for efficient grit utilization is viable for plant sizes larger than about and screenings removal or power feed-in installations, 80,000 capita. With higher electricity unit costs, as minimum WWTP design sizes over a total range of in Indonesia (US$0.12/kWh) and the Philippines about 10,000–100,000 capita may be realistic for (US$0.22/kWh), smaller plants (less than 80,000 financially viable wastewater-to-energy projects. capita) can also be financially attractive; and, since Table II-7 summarizes the financial viability of the latter unit cost values are comparable to those wastewater-to-energy projects for the case studies in Europe, financial viability may be possible, as in presented by looking at their respective payback Europe, for plants down to a minimum size of about periods under their specific local cost conditions. 10,000 capita (see annex 3, case study 1). Taking also Table II-7: Financial Viabilities of Case Studies   Case study Payback period (y) Observation 1 CAS + sludge digestion <15 Relates to a wide set of cases with different base configurations. Generally, anaerobic sludge digesters, combined with biogas utilization in CHP, are considered financially viable in Central Europe for WWTPs with a design size larger than 10,000–20,000 PE60. The larger a WWTP, the shorter the payback period. 2 TF + sludge digestion ≈10 Relates to the introduction of a biogas utilization project with CHP (microturbines). 3 UASB ≈7 Relates to the introduction of a biogas utilization project with CHP. 4 Covered anaerobic ponds Relates to the complete cost of covers + biogas utilization project in Santa Cruz (Bolivia) ≈10 with CHP. High value mainly due to low cost of electricity in Bolivia. 5 Co-digestion of organic waste <1 Very low investment (pre-treatment of waste done by private company; at WWTP only minor adjustments are necessary, since infrastructure for sludge digestion and biogas management already exist); additional reduced OPEX. 6 Ultrasound sludge disintegration ≈5 Relates to complete cost involved. All the presented wastewater-to-energy case studies standard WWTP components—as, for example, are deemed financially viable by their respective in case studies 1, 4 (Australia), 5, and 6—they utilities. Nonetheless, while in many developed have not as yet been included in case studies 2, 3, countries these projects nowadays have become and 4 (Bolivia). WASTEWATER TO ENERGY   41 8. Simple Assessment Tool • The upper part of the sheet is where the user can insert A simple tool has been developed to provide a quick the necessary input data, reflecting conditions of a and preliminary assessment of wastewater-to-energy specific project. The sheet also contains information projects. It is conceived as a first step, to be followed on standard values, which can be utilized if project- by more in-depth analysis. The tool can be used for specific input data are not known. the following: • The lower part summarizes output results, • Estimation of the potential for biogas production facilitating the modification of input data and with various wastewater-to-energy technologies directly checking the impact on results without the need to switch between sheets. • Estimation of the electricity generation potential from that biogas • Sheet 2 (“Details”). Sheet 2 includes the detailed calculations automatically made by the tool. • Preliminary assessment of the electricity coverage that can be achieved with various WWTP treatment The following wastewater-to-energy technologies can and wastewater-to-energy technologies be analyzed with this tool: • Preliminary design of major components of a • CAS + digestion (+ optional co-digestion) wastewater-to-energy project, such as required digester • Trickling filter + digestion (+ optional co-digestion) volume, required gas holder volume, and total CHP power requirements • UASB • Estimation of the overall impact on OPEX of • Covered anaerobic ponds investing in energy generation technology Since this tool is intended for preliminary assessments The tool does not provide a detailed cost–benefit only, it should not be used as a substitute for a analysis considering life cycle costs, as many factors feasibility study, pre-designs, or final designs. influencing CAPEX depend on the particular situation in each plant. This type of analysis would Application of the Tool to a Specific Case Study be the natural next step after using the tool to deem The assessment tool has been applied to the specific wastewater to energy potentially viable. case of the Valenzuela Sewage Treatment Plant located in Metro Manila, Philippines, comparing results for Development of the Tool actual influent characteristics with a range of realistic The tool is based on a simple Excel spreadsheet modifications. Results show the significant impact calculation, containing two sheets:17 of project-specific wastewater characteristics on the viability of biogas generation at a WWTP. • Sheet 1 (“Input and Results”). Sheet 1 consists of two parts: Both sheets of the tool are open, so components or modifications can be added to it. A code provided as a footnote in both sheets can be applied by users to 17 unlock cells that are initially protected to avoid unintentional changes. 42  WASTEWATER TO ENERGY The concessionaire responsible for this project is • Influent VSS = 0.3 x BOD5 = 24 (17) mg/L in dry Maynilad Water Services, Inc. As of this writing, the (rainy) season design and construction of the WWTP were open to • Influent TSS = VSS / 0.7 = 34 (24) mg/L in dry bids. Preliminary versions of the assessment tool were (rainy) season used in the preparation of the bidding documents to assess the feasibility of a wastewater-to-energy project. • SCENARIO B: Diluted wastewater + many The results indicated the project would be feasible septic tanks. CAS + digester, with the following only if additional feedstock were co-digested, due to (theoretical) changes: the effects of the heavy dilution and lack of solids in • Increased influent BOD5 = 180 (155) mg/L in dry the raw wastewater. Consequently, the decision of (rainy) season including a wastewater-to-energy component was left • Influent VSS = 0.3 x BOD5 = 54 (47) mg/L in dry open to bidders. (rainy) season For the purposes of this report, the tool was applied to • Influent TSS = VSS / 0.7 = 77 (66) mg/L in dry investigate the following scenarios for Valenzuela STP: (rainy) season • SCENARIO A: Very diluted wastewater + many • Introduction of primary sedimentation tank septic tanks. CAS + digester, based on actual (PST) influent data as analyzed in 2013: • Co-digestion of 5 m3/d of fat, oil, and grease • Influent BOD5 = 80 (55) mg/L in dry (rainy) (FOG) season WASTEWATER TO ENERGY   43 • Installation of ultrasound sludge disintegration year) and 60 MLD in the rainy season (seven months (USD) a year), so all scenarios relate to a 60 MLD plant, but with different influent concentrations and technology • SCENARIO C: Diluted wastewater. CAS + components. digester, similar to scenario B but with additional changes of influent concentrations: The focus of this example is exclusively on CAS + digester, since CAS and its variations are the selected • BOD5, PST, co-digestion, USD: same as technology in this case. The assessment tool is also scenario B providing results for trickling filter + digestion, UASB, • Influent VSS = 0.7 x BOD5 = 126 (109) mg/L in and covered anaerobic ponds. While these results are dry (rainy) season not discussed in this example, the discussion may be • Influent TSS = BOD5 = 180 (155) mg/L in dry relevant to other projects. (rainy) season Table II-8 summarizes the electricity generation and All three scenarios are assessed with the same flow rate, coverage of the plant’s total electricity consumption, which is 40 MLD in the dry season (five months a as well as total OPEX savings for the three scenarios. Table II-8: Key Results Taken from Exemplary Application of Assessment Tool to 60 MLD WWTP with CAS + Digestion Technology, for Three Scenarios Scenario A Scenario B Scenario C Electricity generation from biogas 264,981 1,222,604 2,239,332 kWh/year Electricity coverage from biogas 12% 22% 40% % of total consumption Total OPEX saving –25,083 –472,657 –729,645 US$/year The results reveal how dependent biogas production Using the preliminary assessment generated by the is on specific project conditions. For the same plant tool, additional information was introduced to capacity of 60 MLD, supposedly minor changes estimate CAPEX and assess financial viability. Table of influent characteristics—the introduction of co- II-9 presents a basic CAPEX estimate for scenario C. digestion of small quantities of FOG and the application CAPEX was also calculated for the two other scenarios: of ultrasound sludge disintegration technology—can in scenario B, it was US$3.4 million, and in scenario increase biogas production almost tenfold. A, US$0.7 million18. 18 These financial assessments are somewhat simplified: (a) for scenarios C and B, the CAPEX reduction caused by the reduced aeration tank volume has not yet been considered, so the financial appeal of these scenarios is actually higher; and (b) financing cost has not been taken into account. 44  WASTEWATER TO ENERGY Table II-9: CAPEX Estimate for Scenario C, Based on Results from Exemplary Application of Assessment Tool to 60 MLD WWTP with CAS + Digestion Technology   Required Unit cost (US$) Cost (US$) Primary sedimentation tank 2,000 m3 300 600,000 Aeration tank volume saving –40%   300 Not considered Reception and dosing station for FOG 1 sum 50.000 50,000 Ultrasound sludge disintegration 1 sum 370,000 370,000 Anaerobic sludge digester incl. piping 3,231 m3 600 1,938,631 Biogas holder 517 m3 800 413,250 CHP 339 kW 1,500 508,204 Flare, gas piping 1 sum 100,000 100,000 Sludge holding tank after digester 40 m3 400 16,000 Subtotal       3,996,085 Contingencies and engineering 20%     799,217 Total additional CAPEX       4,795,302 Conclusions: including financing cost, the payback period of this • In scenario C, an investment of US$4.8 million investment is 28 years. This is financially not viable. leads to annual OPEX savings of US$0.73 million. The conclusion of this preliminary assessment is Not including financing cost, the payback period that scenarios C and B deserve in-depth analysis of of this investment is 6.6 years. Most likely, this is a a wastewater-to-energy component, while scenario A financially viable investment. should probably be ruled out. • In scenario B, an investment of US$3.4 million This example also confirms the finding that once leads to annual OPEX savings of US$0.47 million. the wastewater is so diluted that a PST is not Not including financing cost, the payback period necessary, which is typically the case with TSS less of this investment is 7.2 years. Most likely, this is a than about 80 mg/L, sludge digestion (without co- financially viable investment. digestion of extra feedstock) is not viable. But as soon as a PST is recommendable, the chances for • In scenario A, an investment of US$0.7 million leads a financially viable wastewater-to-energy project to annual OPEX savings of US$0.025 million. Not greatly increase. WASTEWATER TO ENERGY   45 46  WASTEWATER TO ENERGY SECTION III: LESSONS LEARNED AND RECOMMENDATIONS WASTEWATER TO ENERGY   47 9. Constraints and Enabling Factors neither sludge digesters (lacking primary sludge) nor From the experience with the implementation of anaerobic wastewater technologies (requiring large wastewater-to-energy processes captured in both the volumes) is attractive because of the consequent desk review and the case studies, it is possible to derive negative implications for the generation of biogas. a series of lessons learned and recommendations, Yet even under these conditions, co-digestion of summarized below, in the form of typical constraints organic feedstock could make wastewater to energy and enabling factors that need to be taken into account viable. In EAP, investigating the potential of fecal when considering these types of investments in EAP sludge or other organic material such as food waste for countries. Some of these recommendations are already co-digestion may also prove promising. described to by WERF (2012a) and Willis and Stone (2012). Effluent quality requirements. At present, effluent requirements are quite different from country to Technical Aspects country in EAP. Whereas nutrient criteria are already The main technical aspects to consider when assessing in place in Vietnam, in the Philippines a discussion wastewater-to-energy investments are the following: is ongoing about the introduction of such standards. Indonesia also does not apply nutrient standards Size. Not any plant size is suitable for waste-to-energy at present. As explained in the previous section, the investments. A preliminary assessment for conditions required effluent quality has implications for both the in EAP countries showed that the threshold in this energy consumption and the electricity generation region may vary between 10,000 and 100,000 PE60 potential of WWTPs, as the stricter the effluent (2,000–20,000 m3/d). A case-by-case analysis is standards, the higher the consumption of electricity required to determine the real threshold in each case. and the lower the electricity generation potential. The tool included in this technical note can be used for that purpose. In countries where treatment levels are as low as in Wastewater dilution. Wastewater dilution is EAP, the first priority should be installing facilities perhaps the most important technical barrier to that remove the bulk of the organic pollution. investment in wastewater to energy because it Nutrient removal should only be introduced later, may lead to reduced biogas production and energy where environmentally justified; effluent standards generation potential. For this reason, it is crucial have been similarly approached stage-wise in other to have a reliable set of data, with a time series countries. A sensible approach should allow for (a) long enough to capture seasonal variability in the less strict standards for small WWTPs, since their concentration of relevant wastewater parameters, environmental impacts are small as well, and (b) such as BOD5, COD, and suspended solids. The stricter standards for large WWTPs only where the tool presented in this technical note can provide recipient water is indeed sensitive to the discharges. useful information on the potential viability of Co-digestion. Alternative feedstock (organic waste) energy generation options at a plant, to be followed can be used in addition to sludge to increase biogas by a case-specific analysis. In general terms, if TSS is production. When evaluating co-digestion, apart less than about 80 milligrams per litre (mg/L), then from other organic wastes (FOG, organic municipal 48  WASTEWATER TO ENERGY waste, food waste, industrial waste, and so on), it is Knowledge Aspects also important to consider fecal sludge as a potential The main knowledge constraints and enabling factors extra feedstock. Experience from Vietnam points to are related to the following aspects: the possibility that fecal sludge may also be a suitable co-substrate if it is collected from appropriate sources. Informed decisions. Holistic technology benchmarking is missing from the wastewater sector in EAP countries, Consolidation of solids handling. Consolidation so decisions are frequently made without evidence of the solids handling of small plants at a larger, from real operations, using data or experiences from centralized facility is usually financially viable for small contexts different from the local ones—a practice that WWTPs that produce sludge after thickening. The leads to suboptimal solutions. Added to the lack of extra sludge is delivered to a nearby medium-sized or comprehensive information on all possible options large facility, where it is “co-digested” with the larger for wastewater to energy is the sparseness of research facility’s own sludge. applied to and published on low-cost options. The tendency is to “copy and paste” solutions from other countries that do not always consider the low-cost WASTEWATER TO ENERGY   49 50  WASTEWATER TO ENERGY technologies best suited to warm climates. Project so operators can compare themselves to and learn owners sometimes prefer technologies that are from the best performers. This practice usually implies “cutting edge” and place more emphasis on CAPEX motivation to do better, and both average performance than on OPEX. and benchmarks will improve over time. Particularly While the resulting designs are not wrong per se, important is conducting research on how these this knowledge gap can lead to projects that perform processes can be applied in developing countries, and less than optimally, which may negatively affect their on how operational results from large-scale plants with lifespans and even result in project failures. energy generation compare to technologies without it. The following are some of the most typical Training of operators. Operators are not always misconceptions and bad practices from a technical well trained and informed, not only about regular standpoint: operating routines, but also about troubleshooting techniques and necessary conditions for adequate • Underestimation of the impacts of inefficient biogas system functioning. Operators often do not grit chambers, which result in undesired sand understand potential problems, or they lack the accumulation, particularly in anaerobic lagoons means for process control and intervention. Training and digesters needs should be well identified and addressed, and • Underestimation of the negative impacts of inefficient training programs should target the understanding of screening on scum formation in UASB systems potential problems and provide the means for process • Lack of FOG removal prior to UASB, which control and intervention. Involving the private sector contributes to scum formation in UASB, resulting by subcontracting energy generation as a separate in reduced performance operation unit within the WWTP is an interesting option to consider, eliminating the need for operator • Unrealistic biogas yield assumptions training for this specialized task. Most manufacturers • Lack of efficient and affordable biogas treatment of CHP offer this service at competitive cost. • Unrealistic O&M cost assumptions Operation and maintenance. Undermaintaining • Suboptimal design of biogas-related installations has a negative impact on the efficiency of treatment systems and increases life cycle costs. A relatively • Exaggerated safety concerns minor financial savings on maintenance can result in • Lack of adequate mixing considerably larger financial losses. This link between O&M and the lifespan of facilities is not always well For all these reasons, gradually introducing holistic understood at the time of making the investment and technology benchmarking to the sector is important. planning the operational arrangements. Increased efforts to collect data should be the starting point for identifying and quantifying savings potentials Insufficient maintenance is often not so much a matter in more efficient operations. Initiatives like the ibNet of negligence on the operator’s side as it is hampered should be further promoted in the wastewater sector by a procurement system that is devised with WASTEWATER TO ENERGY   51 little understanding of urgent maintenance needs. documents are tailored to the real needs, and (c) Procurement is often conducted with an eye toward operational protocols developed for these technologies saving money by bargaining with operators about the are properly followed. necessity of specific maintenance requirements. Reliability of power supply. In situations where Poor O&M can also be a consequence of inexperience. power supply from the public grid is not reliable, Some of the few existing sludge digesters in East Asia additional backup systems or smart biogas and power are suffering from problems associated with foaming management strategies are indispensable. and deposits in the digester. Presumably this is a typical consequence of inadequate preliminary treatment Institutional Aspects (screening and grit removal). To avoid such problems The main institutional aspects to consider are the in the future, it may be worthwhile to consider following: DBO (design-build-operate) contracts for WWTPs with sludge digesters. With their use, experienced Regulatory framework to utilize electricity from private companies in charge of the complete WWTP biogas. WERF (2012a) and Willis and Stone (2012) design and operation are expected to install proper report that many water and wastewater utilities run components at all stages. As demonstrated by case into problems with power utilities when they decide study 2, this approach can work well. to start a biogas project. Sometimes power companies do not want the utilities to produce power onsite and In any case, a utility that follows a culture of threaten “that the plant [will] lose their eligibility for undermaintaining the existing facilities should reverse lower power rates and rebate programs.” this tendency before considering investment in energy generation solutions. Maintenance of the WWTP In addition, while the priority for utilization of the should be understood as an essential expenditure electricity generated from biogas should always be that helps reduce total life cycle cost rather than one onsite at the WWTP, in some cases a power surplus that should be minimized. Asset management and/or is produced. Energy generation at facilities with low maintenance plans need to be already in place at the electric power consumption, such as UASB plants or planning stage. Again, considering the private sector covered anaerobic ponds, can produce more electricity for tasks related to O&M is an interesting option. than the plant requires. If good financial use cannot be made of this surplus, simply flaring the biogas off may Safety. While safety issues are a common concern seem more attractive than investing in infrastructure among practitioners in the sector, risks usually only to utilize it. arise in cases of inappropriate design, questionable material quality, or ignorance of simple O&M Subsidies that reduce the unit cost of electric power precautions. Wastewater-to-energy technologies are can prove a major obstacle to energy recovery from not complicated to operate, and safety and operation renewable resources. The decision to undertake an risks are low if (a) designs are done properly (wastewater energy recovery project is mostly based on a financial + sludge + biogas), (b) specifications in the bidding assessment of its viability. The more subsidized the 52  WASTEWATER TO ENERGY cost of electricity is, the less attractive the investment Co-digestion. Since co-digestion is a relatively new in energy recovery will be. After all, investments practice, the rules and institutional arrangements that in energy generation from biogas are usually not govern the use of organic solid waste at WWTPs may subsidized and still have to compete with subsidized not be developed yet. Co-digestion implies collection unit cost per kWh. Such a distortion of electricity of different types of organic waste, so responsibilities prices through subsidies has a negative implication, could fall under different utilities. Disagreements on regardless of whether the electricity from biogas is who “owns” the waste and how it should be collected used at the WWTP or sold to the public grid. and transported could arise between the waste collector and the WWTP, so this must be clarified. Similarly, Therefore, a clear tariff policy that includes the the rules that govern the disposal of the digested option for supplying bioelectricity to the public product from co-digestion need to be clear. Having grid utilities will raise interest in investment in contracts with other utilities or service providers wastewater-to-energy technologies. High feed-in (municipal departments or private companies) will tariffs can facilitate the implementation of biogas be necessary to determine responsibilities and define projects, but the rules for this practice should be implementation arrangements for co-digestion of well defined. organic waste at WWTPs. WASTEWATER TO ENERGY   53 Economic and Financial Aspects extending coverage, reducing losses, connecting According to a survey carried out by WERF (2012a) more households, and meeting effluent standards in Australia, Canada, and the United States, the most (World Bank 2013; ESMAP 2012). All these factors significant barriers to biogas use are economic. The translate into little margin for financial maneuvering following were the main findings of the survey: and, therefore, impose an important constraint on investing in energy generation. • Utilities may have other priorities for limited capital resources than investing in biogas use. In particular, For these reasons, potential gains from reduced OPEX the ongoing challenges to rehabilitate and maintain can be interesting for financially weak utilities. Sound existing infrastructure do not leave much room for economic and financial analysis should be carried new investments. out to determine the impacts of investing in energy generation on reduced OPEX and overall performance • The economic analysis conducted to determine the of the utility. Only then will it be possible to place viability of a wastewater-to-energy project is often this option on the long list of priorities the utility limited to a requirement for a predetermined, short may have. payback period for the investment, neglecting such other factors as impact on cash flow, annual reduction Economic analysis should therefore be more in OPEX, or improved present worth. comprehensive by considering net present value, net revenue, and operational savings. In particular, cash • Paradoxically, small WWTPs with capacities flow potential, especially over the long term, should of 2–10 MGD (≈20,000–100,000 PE60) were be highlighted for decision makers, tying maximum found to overcome barriers with more creative acceptable payback periods to the average service life approaches (for example, grants or carbon of the equipment, not to predefined periods. credits), while those between 10 and 25 MGD (≈100,000–300,000 PE60), despite being more In addition, it is important to consider all possible viable, were often ruled out for biogas utilization sources of funding, such as grants, low-interest loans, due to the larger investments needed and the or state-supported financing. difficulty of finding financing options. Finally, the present low price level of carbon Some of these situations are also found in EAP, where credits renders most wastewater-to-energy projects autonomous utilities are rare and usually constrained unattractive for Clean Development Mechanism by low revenues from low tariffs in the sector due to (CDM) application. Nevertheless, many facilities little willingness to pay or to charge. Also, wastewater are interested in quantifying greenhouse gas (GHG) and water supply businesses are often not merged emission reductions they have achieved as proof of under a single utility, so no opportunity exists to environmental stewardship. cross-subsidize wastewater operations. Utilities also have a long list of challenges to deal with, such as 54  WASTEWATER TO ENERGY 10. Road Map for Decision Making the potential of various treatment alternatives for Following the steps in the road map below may be energy consumption and generation. helpful to managers of utilities in charge of running b Pursue a detailed financial analysis, including different WWTPs as they decide whether to invest in both CAPEX and OPEX projections in project wastewater-to-energy solutions: evaluations. Insist on detailed OPEX structuring, 1 Collect data on flows and concentration of pollutants with solid justification of underlying assumptions. (BOD, COD, TSS, VSS, P, N). 5 If viability is confirmed, proceed to financing, 2 Forecast future development in terms of extension detailed design, bidding, and implementation. of the collection network and new connections. 6 Periodically review operational results to reassess and 3 Conduct a preliminary assessment of wastewater to improve design parameters in future investments at energy by, for example, using the tool developed in other plants owned by the utility. this technical note. Taking an unbiased look at all The same decision flow outlined above can be applied possible biogas options and not defining technologies to new WWTPs, with the additional need to select the prematurely is important for this purpose. right technology for wastewater treatment. Among 4 If viability looks promising, proceed to a more in- the different criteria to be assessed, the importance depth analysis, considering all institutional, technical, of low OPEX should be highlighted. Alternative and financial factors explained in this technical note. technologies combined with biogas utilization offer a The following are particularly important: potential for strongly reduced electricity cost. These savings can make the decisive difference between a Compare electricity consumption values of operating a treatment plant in a sustainable manner or the project being evaluated with the reference doing so suboptimally with negative implications on numbers presented in this study. Check energy the lifespan of the investment. designs (consumption and production) using the assessment tool, which can be used to quantify WASTEWATER TO ENERGY   55 References Cao,Y.S. 2011. “Mass flow and energy efficiency of municipal wastewater treatment plants.” IWA Publishing. 111. 2011. Abbasi, T. et al. 2012. “A Brief History of Anaerobic digestion and Biogas. 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