From Waste to Resource Shifting paradigms for smarter wastewater interventions in Latin America and the Caribbean Background Paper I: Efficient and Effective Management of Water Resource Recovery Facilities © 2019 International Bank for Reconstruction and Development / The World Bank 1818 H Street NW, Washington, DC 20433 Telephone: 202-473-1000; Internet: www.worldbank.org This work is a product of the staff of The World Bank with external contributions. The findings, interpretations, and conclusions expressed in this work do not necessarily reflect the views of The World Bank, its Board of Executive Directors, 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. 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From Waste to Resource Background Paper I: Efficient and Effective Management of Water Resource Recovery Facilities The World Bank is working with partners around Shifting Paradigms for Smarter Wastewater the world to ensure that wastewater’s inherent Interventions in Latin America and the Caribbean”, value is recognized. Energy, clean water, fertilizers, a product of the “Wastewater: from waste to and nutrients can be extracted from wastewater resource”, an Initiative of the World Bank Water and can contribute to the achievement of the Global Practice. Sustainable Development Goals. Wastewater There is extensive literature on the effective man- can be treated up to different qualities to agement of wastewater treatment plants (WWTPs) satisfy demand from different sectors, including (WEF 2016). This paper seeks neither to replace nor industry and agriculture. It can be processed to summarize the existing literature but rather to in ways that support the environment, and can outline a list of aspects to consider when managing even be reused as drinking water. Wastewater water resource recovery facilities (WRRFs),1 from treatment for reuse is one solution to the world’s cradle to grave. In addition, examples of best prac- water scarcity problem, freeing scarce freshwater tices are presented. resources for other uses, or for preservation. In addition, by-products of wastewater treatment Clear policies, adequate intersectoral legislation, can become valuable for agriculture and energy efficient regulation, and continuous training of hu- generation, making wastewater treatment man resources are required as a first step toward plants more environmentally and financially resource recovery. Assuming these aspects have sustainable. Therefore, improved wastewater been adequately covered, the following consider- management offers a double value proposition ations will contribute to an effective management if, in addition to the environmental and health of WRRFs. This list is not exhaustive and is mostly benefits of wastewater treatment, financial geared toward avoiding common obstacles and returns can cover operation and maintenance challenges usually found in Latin America and the costs partially or fully. Resource recovery from Caribbean (LAC).2 wastewater facilities in the form of energy, reusable Effective management of WRRFs starts with ad- water, biosolids, and other resources, such as equate planning and design. Adequate process nutrients, represent an economic and financial selection and design offer the most “bang for the benefit that contributes to the sustainability of buck.” When treatment facilities are well planned, water supply and sanitation systems and the water with resource recovery and sustainability in mind, utilities operating them. One of the key advantages the road to efficient management is paved. With of adopting circular economy principles in the this concept in mind, planners would do well to processing of wastewater is that resource recovery take several initial steps: and reuse could transform sanitation from a costly service to one that is self-sustaining and adds value • Identify and forecast key wastewater influent to the economy. characteristics. • Set reasonable targets for effluent quality, This background paper is part of the supporting based on the characteristics of the receiving material for the report “From Waste to Resource: water body and on water quality objectives. 1 WRRFs is the term currently used by the Water Environment Federation to refer to WWTPs that aim at recovering resources in some fashion. 2 The same may apply to low- and middle-income countries in other regions of the world. 3 From Waste to Resource When possible, plan for the gradual application increasing the size of treatment facilities. The of such targets. textbook approach, though quick and easy, • Select an adequate treatment process, using generally results in treatment processes that are data from wastewater characterization and not adequately selected or sized, with CAPEX and projections and effluent quality objectives, OPEX values higher than necessary and resulting and considering resource recovery goals plus financial and environmental burdens. capital expenditure (CAPEX) and operating expenditure (OPEX) through a life-cycle analysis. In some cases, the textbook approach is used for lack of knowledge and understanding of the • Design a realistically sized process. dynamics of municipal sewage systems. In other • Plan for reduce energy consumption (i.e., cases, the application of standard values is done generating “negawatts”) and set potential to save time and costs in the initial stages of energy cogeneration strategies. planning and design. Nothing could be more • Evaluate, optimize, and determine the actual counterproductive. The total costs of adequate treatment capacity of existing infrastructure, engineering and planning are minuscule (less so as to maximize the use of it – existing than 0.10 percent) in comparison with the life- infrastructure is also a resource! cycle costs (CAPEX and OPEX) of future facilities. Therefore, savings in the initial stages generate problems during the life of a utility, representing Identifying the characteristics of one of the main challenges to the sustainability of wastewater influents these facilities (particularly in Latin American and the Caribbean, but arguably in other parts of the Every municipality is unique, resulting in different world as well). wastewater characteristics (e.g., flow rate, concentration of contaminants, temperature, For greenfield projects (i.e., new treatment seasonal variations). Most of these characteristics facilities), influent characterization must be tend to differ considerably from city to city. In planned in advance. This activity will involve the use spite of these differences, it is very common to of, for example (i) sampling techniques (which may see treatment plant designs based on textbook require automatic samplers); (ii) multiple points influent parameters. Examples include the use of sampling (if the main sewer line to the future of flow rate per capita values (e.g., 350 liters per WWTP is nonexistent); (iii) experienced personnel capita per day) or biochemical oxygen demand to operate samplers and carry samples to the loadings (e.g., 60 grams of a five-day biochemical laboratories with appropriate techniques and a oxygen demand [BOD5] per capita per day) in lieu well-documented chain of custody documents; of adequate wastewater characterization using and (iv) certified laboratories. Depending on the sampling techniques and laboratory analysis. importance of the future facility, the sampling work In Latin America and the Caribbean, textbook may last from a few days or weeks to a few months. parameters are generally used with current In many cases, the goal is to not only determine the population growth projections without considering concentration of various contaminants but also to the possibility that some neighborhoods may record flow rates. not be served by secondary collection systems (sewers). Even if all neighborhoods were served, When recording influent wastewater flow rates is not all households may be connected to the sewer not possible during the initial sampling process, lines running along their streets. In most cases, flow rates must be projected based on realistic these textbook approaches result in wastewater population growth rates, service areas (i.e., flow rate projections and contaminant loadings those areas covered with secondary sewer lines), that far exceed reality, thereby unnecessarily connectivity to sewers, and future expansion work 4 From Waste to Resource planned in sewer networks in the plant’s area of adjust targets based on knowledge they gather influence. Simply multiplying future population over time on influent wastewater characteristics projections by consumption per capita tends and the effect of final effluent on the receiving to yield unrealistically high flow projections. water quality (river modeling calibration). In Unfortunately, this last approach is quite common, addition, the gradual application of effluent resulting in plants being larger than necessary. requirements will permit extending the coverage Remember: a larger-than-necessary facility is a of treatment, as opposed to having high levels waste of resources, i.e., exactly the opposite of of treatment in a few plants, leaving larger areas what circular economy for sustainability stands for. without treatment. When expanding existing facilities (brownfield projects), adequate records of influent wastewater There are no international effluent quality characteristics should be available from the standards. The reason is that effluent standards existing facility. If so, these records must be must consider multiple factors influenced by local audited for accuracy and complemented, when conditions, such as: needed, with additional sampling and monitoring efforts. Sampling and monitoring should take place • The existing state of the receiving water body at the existing plant, immediately downstream • Desired uses and related quality requirements of of preliminary treatment. These efforts can last the receiving water body one to four weeks, depending on the importance • State of wastewater treatment in the area (e.g., of the project. The existence of predetermined coverage) sampling points makes the process simpler than in the case of greenfield projects, which in most • Financial implications of treatment levels cases require multiple sampling points. If the (CAPEX and OPEX) and funding available plant to be expanded or retrofitted is medium to (including existing tariff structures and large (100 liters per second and above), effluent willingness to pay) characterization can be used to calibrate a dynamic • Climate conditions (e.g., ambient temperatures, model of the plant for design purposes. Other seasonal precipitation patterns) aspects to consider when assessing future influent • Other physical conditions (e.g., altitude) wastewater characteristics include (i) future industries operating in the area of service, and (ii) When possible, total maximum daily limits (TM- water consumption reduction measures (e.g., tariff DLs) for effluent should be defined and applied structure changes, introduction of water saving to facilities as part of the cleanup plan for the devices, expansion of micrometering coverage). receiving water body. As opposed to blanket ef- fluent concentrations (expressed in milligrams per Setting reasonable targets for liter, mg/L), TMDLs allocate maximum loadings of effluent quality contaminants, expressed in a mass of a specific contaminant per day (e.g., 4 tons of total nitrogen Water quality objectives can be defined based per day), to each discharging facility. This approach on the receiving water body characteristics and is much more sensible since, with the exception of desired uses (e.g., recreational, irrigation, etc.). certain compounds that could be toxic to fish at Using river water quality modeling techniques, high concentrations (e.g., ammonia), the contami- reasonable targets for effluent quality can nation/cleanup of a receiving water body depends be set and used to plan WRRFs. The gradual on the mass of contaminants discharged (e.g., tons implementation of such targets in phases (when nitrogen per day), and not their concentration (mil- applicable) will likely enhance the sustainability ligrams nitrogen per day). Copying standards from of the treatment system by allowing planners to other countries (e.g., EU directives for effluent 5 From Waste to Resource quality, EPA 503c3 for biosolids management, etc.) Such a daily limit is approximately equivalent to may seem easy and cost-effective, but to ignore imposing a limit of 10 mg/L of BOD5 based on the specificities of the local context has negative a monthly average of daily samples, which will environmental and financial implications. require tertiary treatment (e.g., sand filtration), increasing in many cases the CAPEX and OPEX of Extremely stringent effluent quality standards the facility unnecessarily. Both numerical values of imposed on areas with low levels of treatment the limit may be the same (25 mg/L of BOD5), but coverage prevent, in many cases, the utility from the one applied as a threshold not be exceeded is reaching adequate treatment coverage. In this much more stringent and expensive to attain. case, the cost of building a new plant or upgrading an existing plant may exceed existing funding. In these situations, the expansion, upgrade, and Selecting an adequate treatment creation of greenfield WRRF projects elsewhere process in the catchment are postponed since all funding Appropriate treatment processes are key to goes to one or two plants, resulting in lower recovering resources in a sustainable fashion. coverage, with detrimental implication for Selecting such processes depends on realistic population health, receiving water body quality, wastewater characterization and projections and and environmental conditions. reasonable effluent quality objectives. In addition, the CAPEX and OPEX of treatment processes vary When developing effluent quality requirements widely and must be considered. based on concentrations of contaminants, it is of upmost importance to determine the period In Latin America and the Caribbean, there is over which the requirements must be applied. For a strong tendency to prefer activated sludge example, meeting 25 mg/L of BOD5 on a monthly systems to other type of treatment processes average of daily samples is reasonably achievable (World Bank 2016). Even though activated sludge with secondary treatment. On the other hand, a is a well-proven technology that results in over requirement not to exceed 25 mg/L of BOD5 on any 90 percent BOD removal (figures 1 and 2), the daily sample is very stringent, given the natural OPEX of this type of technology cannot always be variability in influent quality and operational modes. supported by tariffs. Figure 1 Treatment plant with activated sludge system Primary Clarifier Biological reactor Secondary settler Receiving Primary BOD5 removal: ~ 90 — 95% water body Sludge Secondary sludge Biosolids disposal Thickening Stabilization Dewatering Source: Adapted from Pacheco Jordao (2013). Note: BOD5 = five-day biochemical oxygen demand. 3 U.S. Environmental Protection Agency’s Part 503 Biosolids Rule. 6 From Waste to Resource Figure 2 Removing organic matter in aerobic in extended aeration activated sludge systems (no biological systems primary clarifiers, longer retention times in the aerobic reactors, aerobic digesters), the energy O2 devoted to aeration is on average 75 percent of BIOMASS a plant’s total energy consumption (WEF 2010). (SLUDGE) This share increases if the plant operates at high % altitude. For example, at 3,500 meters above sea 50 Y= level, a plant will consume approximately twice as Organic Aerobic EFFLUENT much air (and energy to pump it) than the same 2-5% Matter Process plant operating at sea level. This is especially relevant for the Latin American and Caribbean 50% CO2 region, since several cities are located at altitudes + higher than 2,000 meters above sea level. H2O Figure 4 Energy consumption in a conventional Source: Adapted from Pacheco Jordao (2013). activated sludge plant Note: CO2 = carbon dioxide; H2O = water; O2 = oxygen. 4% Chemical 14% Activated sludge processes have aerobic reactors, addition Pumping which require air supplied by mechanical surface 13% aerators or by submerged diffusers supplied by air Others blowers (see figure 3). 11% Centrifuge Figure 3 Ceramic and membrane fine pore diffusers 9% Anaerobic 49% digestion Aeration Aeration is Energy is Extended the largest the major aeration (i.e., contribution operational long SRT) is to treatment component in much worse: processs energy the present value Aeration energy calculation of ~75% Source: Pacheco Jordao 2013. (Reardon, 1995; Rosso and Stenstrom, 2005; treatment costs MOP32, 2009) (Reardon, 1995; Rosso et al., 2005; WEF, 2009) Aeration represents the most significant use of energy in an activated sludge plant (WEF 2009; Source: Adapted from WEF (2010), adopted drom MOP32, 2009. Note: Process involves primary clarifiers and anaerobic Reardon 1995; Rosso and Stenstrom 2005). If the digesters. activated sludge is “conventional” (i.e., primary clarification, followed by relatively small aeration Selecting an adequate process while considering tanks operating with short solids retention times, energy consumption is paramount in the design of with anaerobic digestion of primary and secondary sustainable WRRFs. Figure 5 shows the electricity sludge), the energy consumption for aeration may consumed by different processes. vary from 45 to 65 percent (see figure 4). However, 7 From Waste to Resource Figure 5 Electricity consumed (per population activated sludge plants, such as the one in figure equivalent) by various treatment processes 4, to other less energy consuming processes is expensive and not always easy to do once a plant is already operational. Adequate process The impact of OPEX on the sustainability of selection reduces WWTPs must be considered when selecting energy costs the optimal treatment process. In general, for activated sludge systems (commonly used in Latin America and the Caribbean), the influence of 160 CAPEX and OPEX can be graphically represented (based on assumption as an iceberg (figure 6), in which CAPEX is the tip 140 of 500 mfCOD/L) of the iceberg, and OPEX extends along the life kWh / PE210 / y 120 100 of the investment (brought to net present value), 80 60 representing the bottom of the iceberg. 40 20 Figure 6 Capital and operating costs of activated 0 sludge systems Lagoon TF CAS EA MBR Source: Graph: WEF 2010; photograph: Nolasco 2017; overall figure: Nolasco 2019. Note: CAS = conventional activated sludge; EA = extended aeration activated sludge; kWh = kilowatt-hour; MBR = CAPEX membrane bioreactor; mg COD/L = milligrams of chemical oxygen demand per liter; PE120 = population equivalent discharging 120 grams of COD per day, i.e., per person discharging to the plant; TF = trickling filter. In figure 4, a photo of an extended aeration activated sludge plant is shown. This plant is located in Peru, at 2,400 meters above sea level. OPEX This altitude increases the energy consumption from 75 kilowatt-hours/PE1204/year (shown in figure 4 and calculated at sea level) to more than 120 kilowatt-hours/PE120/year (i.e., three times the energy needed by a conventional activated sludge Source: Adapted from Brischke (2017). process, CAS, at sea level). Processes with such Note: The figure represents relative net present values along high electricity consumption are hard to sustain the life cycle of capital costs (CAPEX) and operation and at normal tariff rates and should be avoided (at maintenance costs (OPEX) for a conventional activated least for medium-sized and large plants) in areas sludge system. located at 2,000 meters above sea level or higher. Other processes that produce a similar effluent Realistic sizing of unit processes quality but consume considerably less electricity are available and should be evaluated as options Traditional WWTP design guidelines developed during the planning stage of these projects. in the 1970s and based on experience from the Unfortunately, retrofitting extended aeration 1960s are still cited in current literature (Metcalf 4 Population equivalent discharging 120 grams of COD per day, i.e., per person discharging to the plant. 8 From Waste to Resource & Eddy Inc. et al. 2013; WEF 2016; WEF, ASCE, Reducing energy consumption and and EWRI 2018).5 These guidelines are steady- setting energy cogeneration strategies state (i.e., assume all influent parameters and operational conditions to be constant, which is far The first step toward achieving the sustainability from reality) and very conservative, resulting in of existing treatment plants (tied with the the volumes of reactors being considerably larger circular economy) is to reduce the consumption than necessary. These guidelines are of little to no of electricity (i.e., to produce “negawatts”6). use when designing systems for biological nutrient Illustrated in figure 7, a reduction of the relative removal or when trying to predict effluent quality. weight of the energy consumed by a plant (the For these reasons, the use of steady-state design left side of the balance) is needed to permit the guidelines has been discontinued in most middle- reasonable coverage of this consumption with the and upper-middle-income countries. In countries energy to be generated from biogas (the right side with adequate wastewater treatment practice, of the balance). A reduction in consumption can process specialists use dynamic simulators with be planned at the design stages, when processes complex and realistic mathematical models for are selected and sized, or in existing facilities by sizing reactors and other unit process treatment implementing energy saving measures. systems. The use of such simulators makes a design considerably more realistic, resulting in smaller Figure 7 Energy balance in an activated sludge and more efficient plants that can save and even system produce energy. Unfortunately, the use of steady-state design Primary clarifiers guidelines from the 1970s is still common in Latin America and the Caribbean. We could argue Secondary Primary clarifiers clarifiers Energy that these systems are still used for the sake of recovery Aeration Other with simplicity, and for the apparent savings in time and equipment biogas cost at the initial stages of planning (steady-state design guidelines can be easily implemented in an Excel spreadsheet, requiring little mathematical skill and data on influent data characteristics). A reduction in energy However, such savings at the initial stages of consumption is needed planning and design result in the gross oversizing to reduce OpEx of utilities, which impacts the sustainability of systems and the capacity of WWTPs to become Source: Rosso et al. 2018. WRRFs. Note: OPEX = operating expenditure. 5 In 1969, the Cuyanoga River (Cleveland, Ohio) caught fire and burned for several days due to the quantity of pollutants floating on its surface. Arguably, this event, combined with the polluted state of numerous water bodies in the United States, triggered the development and approval of the USA Federal Water Pollution Control Act (Clean Water Act 1972). Almost concurrently, in 1970, the Canada Water Act was approved. These laws started an unprecedented investment in the infrastructure of wastewater treatment facilities to control water pollution. To get financial support from the federal government for these new facilities, design guidelines were needed (at the time, municipal and state officials did not have the information available today on what constituted a well-designed WWTP). This led to the development of a series of guidelines, based mainly on the experience gained in the 1950s and 1960s. One of the most well-known guidelines is the “Recommended Standards for Wastewater Facilities,” prepared by the Great Lakes–Upper Mississippi River Board of State and Provincial Health and Environmental Managers, generally referred to as the “10-States Design Guidelines,” since it is undersigned by 10 American states and the Province of Ontario, Canada. These guidelines were based on experience from the 1950s and 1960s, when the knowledge of the biology involved in wastewater treatment was limited by the availability of instrumentation, adequate laboratory equipment, advances in biochemistry and genetics, etc. Therefore, the guidelines used for design were quite basic and meant to be on the “safe side” (i.e., conservative), which in turn resulted in oversized tanks, reactors, and treatment processes in general. 6 Taken from a conversation between Nolasco and José Luis Inglese, president of Aguas y Saneamientos Argentinos (AySA), a “negawatt” is a fictitious unit of power not spent, thanks to the adequate design of future facilities or by the savings realized in existing facilities. 9 From Waste to Resource In existing activated sludge plants, the aeration Not all plants can generate biogas. Only those systems offer the most opportunity for energy with anaerobic processes of adequate size and savings, since they consume somewhere in the design can attain biogas generation and capture range of 50 to 75 percent of the total energy used sufficient volume and quality to be used for energy by the facility. Potentially effective energy saving cogeneration. measures in these types of plants include the following (Baquero-Rodriguez et al. 2018; Rosso Obviously, those plants that treat wastewater in and Stenstrom 2005): anaerobic systems (e.g., upflow anaerobic sludge blankets, covered anaerobic lagoons, etc.) are likely • Implementing automatic dissolved oxygen to have much less energy demand on the left- control systems, which prevent unnecessary hand side of the balance and more potential for over-aeration of the biomass in the reactors cogeneration with biogas on the right-hand side. • Cleaning fine pore diffusers Therefore, they have more potential to become energy-neutral plants (i.e., not requiring external • Replacing broken/old fine pore diffusers sources of electricity to operate) or energy- • Replacing inefficient air blowers positive plants (i.e., being able to produce surplus • Dosage of coagulants in primary clarifiers: to to sell to the network or for transport and use remove part of the organic loading going to the elsewhere).8 aeration tanks (which demands aeration) and redirect it to the anaerobic digesters, where it Plants with anaerobic digestion of sludge can also can generate more biogas, which in turn can be cogenerate energy. If these are activated sludge used to cogenerate energy plants, in most cases, the energy produced will be able to cover the heat demand of the digester and • Introducing unaerated zones in the front part about one-third of the electricity demanded by of the aeration tanks of activated sludge plants the plant (and thus the plants will not be energy that nitrify, so as to reduce oxygen demand neutral).9 A quick rule-of-thumb applicable to most by denitrification (i.e., the reduction of nitrate conventional activated sludge plants is that the to nitrogen gas), while improving aeration energy cogenerated from biogas can be converted efficiency by reducing fouling of diffusers and into heat (about one-third) and electricity (about increasing the alpha factor – key to improve one-third), and the remaining one-third will be lost oxygen transfer efficiency) in heat with the exhaust gases. Depending on the • Reducing nitrogen loading to aeration basins cost of electricity and equipment for cogeneration, by the nitrification and denitrification of recycle systems for cogeneration with biogas may start streams from the sludge treatment train (e.g., becoming viable at 500 megawatts of installed Sharon-Annamox processes) generating capacity. The complexity and cost of application of these energy-saving strategies vary between plants, but Tools to analyze the feasibility of converting in most cases, the first three measures are quite wastewater to energy have been prepared by the cost-effective energy management strategies. World Bank and constitute a good starting point when deciding whether such a system is viable The second step is to try to implement (World Bank 2015). Additional information can be cogeneration of energy from biogas (the right- extracted from the relevant literature (EPA 2011; hand side of the balance shown in figure 6).7 EPA and WERF 2010; WEF 2010). 7 Cogeneration indicates generation of both heat and electricity. 8 See the case of SAGUAPAC in Santa Cruz de la Sierra, Bolivia. 9 There is a growing number of activated sludge plants in the European Union and North America that are becoming energy neutral. However, the investment in technology and infrastructure and the technological sophistication of such systems are considerable. 10 From Waste to Resource Evaluation, optimization, and adequate many cases (pretreatment, primary treatment, use of existing infrastructure and aeration tank volume), the real capacity exceeds the nominal and meets or exceeds the Any infrastructure already in place (i.e., existing new requirements, thereby not calling for any WWTPs) constitutes a valuable resource whose expansion. Other unit processes, while meeting actual treatment capacity may be evaluated early the nominal capacity, do not have enough capacity in the planning process. Specifically, what is the to meet the new requirements. In the generic maximum flow rate the facility can treat while example of figure 7, these processes involve the meeting effluent criteria? This step of the planning diffusers and blowers (i.e., the aeration capacity) process is often overlooked or the existing and the secondary clarifiers. These two units capacity is miscalculated, leading to unnecessary are the actual bottlenecks to meet the new expansions—and thus a waste of valuable resources requirements. and an increase in CAPEX, OPEX, and the system’s carbon footprint, inter alia. Figure 7 The circular economy approach: Wise use of existing infrastructure as a resource During the 1990s in the United States and Canada, Capacity plants built during the 1970s were starting to reach of unit maturity and there was a need to expand their processes Waste of CaEx & m3/s OpEx + C, H2O & capacity or impose more stringent effluent limits. Energy footprints Instead of presuming that their “nominal” (design) treatment capacity was correct, Environment Canada and the U.S. Environmental Protection Agency decided to evaluate the actual capacity of New requirement these facilities using field testing. This led to the Capacity development of protocols and methodologies for real "Nominal" Capacity plant evaluation (also referred to as process audits) (Environment Canada 2006). Prim. Aeration Diffusers & Sec. Etc. Pretreat Treat Tanks Clar. Blowers The application of these capacity evaluation tools demonstrated that existing plants, designed using Source: Nolasco 2014. traditional guidelines, have considerable excess Note: C = carbon; CAPEX = capital expenditure; H2O = capacity in several of their unit treatment processes. water; m3/s = cubic meters per second; OPEX = operating Thereby, to expand the capacity of these plants expenditure. to meet future higher flows, only those processes that present a bottleneck to meeting new demand Field tests performed as part of a plant audit need to be expanded, while the rest can be left approach, combined with modern design methods untouched. This realization has led to considerable (e.g., dynamic simulation), maximize the life of savings in CAPEX and OPEX.10 The success of existing infrastructure, thereby enhancing the several applications of these methodologies sustainability of overall systems. The evaluation led Environment Canada to impose their use in techniques involved are not necessarily complex expansions that required federal funding. or expensive. In a recent project carried out by AySA, the water and wastewater utility in Buenos Figure 7 shows the nominal (design) capacity Aires, Argentina, the application of some of these of a typical plant, combined with the real process audit techniques resulted in savings of capacity of several of its unit processes. In CAPEX valued at about $150 million. 10 In 1994, the Metro Toronto Ashbridges Bay Treatment Plant, using the Environment Canada process audit methodology, cancelled a plant expansion estimated at $200 million (approximately $400 million at current value). 11 From Waste to Resource References Baquero-Rodriguez, G. A., J. A. Lara-Borrero, D. Nolasco, and D. Rosso. 2018. “A Critical Review of the Factors Affecting Modeling Oxygen Transfer by Fine-Pore Diffusers in Activated Sludge.” Water Environment Research 90 (5): 431–41. Brischke, K. 2017. Personal communication. Environment Canada, Environmental Protection Branch. 2006. Guidance Manual for Sewage Treatment Plant Process Audits. Ottawa, Ontario: Environment Canada. http://www.publications.gc.ca/site/ eng/290345/publication.html. EPA (Environmental Protection Agency). 1998. Optimizing Water Treatment Plant Performance Using the Composite Correction Program. EPA/625/6-91/027. Washington, DC: EPA. https://cfpub.epa.gov/si/ si_public_record_report.cfm?Lab=NRMRL&dirEntryId=23902. EPA and WERF (Water Environment Research Foundation). 2010. “Evaluation of Combined Heat and Power Technologies for Wastewater Treatment Facilities.” EPA 832-R-10-006, EPA, Washington, DC. https:// www.cwwga.org/documentlibrary/121_EvaluationCHPTechnologiespreliminary[1].pdf. Metcalf and Eddy, Inc., G. Tchobanoglous, H. D. Stensel, R. Tsuchihashi, and F. Burton. 2013. Wastewater Engineering: Treatment and Resource Recovery, 5th Edition. New York: McGraw-Hill. Nolasco, D. 2014. “Water-Energy-Carbon Nexus in Water Reclamation, Reuse, and Wastewater Treatment.” Keynote speech at the Plenary Session of the International Water Association’s (IWA’s) ECO STP Technical, Environmental, & Economic Challenges Seminar, organized by the IWA, the University of Verona (Universita degli studi di Verona), and Polytechnic of Milan (Politecnico Milano), Verona, Italy, June 23–25, 2014. Pacheco Jordao, E. 2013. “Wastewater Treatment Course, Montego Bay, Jamaica.” Rosso, D., and M. K. Stenstrom. 2005. “Comparative Economic Analysis of the Impacts of Mean Cell Retention Time and Denitrification on Aeration Systems.” Water Research 39 (16): 3773–80. Rosso, D., M. Garrido-Baserba, F. Pasini, L. M. Jiang, and D. Nolasco. 2018. “Aeration Testing as a Tool to Improve Oxygen Transfer and Process Optimization in WRRFs: The North American Experience.” Proceedings of the International Water Association Water Congress and Exhibition, Tokyo, Japan, September 16–21. WEF (Water Environment Federation). 2010. Energy Conservation in Water and Wastewater Facilities, MOP-32. Alexandria, VA: WEF Press. WEF (Water Environment Federation) 2016. Operation of Water Resource Recovery Facilities, 7th edition, MOP-11. Alexandria, VA: WEF Press. 12 From Waste to Resource WEF (Water Environment Federation), 2009. Manual of Practice No. 32 (MOP32). Energy Conservation In Water And Wastewater Treatment Facilities. WEF (Water Environment Federation) WEF, ASCE (American Society of Civil Engineering), and EWRI (Environmental and Water Resources Institute). 2018. Design of Water Resource Recovery Facilities. Alexandria, VA: WEF Press. World Bank. 2015. East Asia and Pacific Wastewater to Energy Processes: a Technical Note for Utility Managers in EAP Countries. Report ACS1322. Washington, DC: World Bank. http://documents. worldbank.org/curated/pt/489941468188683153/pdf/ACS13221-v1-Revised-Box393171B-PUBLIC- Wastewater-to-Energy-Report-Main-Report.pdf. 13