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Renewable and Sustainable Energy Reviews 45 (2015) 52–68 Contents lists available at ScienceDirect Renewable and Sustainable Energy Reviews journal homepage: www.elsevier.com/locate/rser Energy and water autarky of wa
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  Energy and water autarky of wastewater treatment and powergeneration systems Veera Gnaneswar Gude Department of Civil and Environmental Engineering, Mississippi State University, Mississippi State, MS 39762, USA a r t i c l e i n f o  Article history: Received 1 August 2014Received in revised form5 January 2015Accepted 12 January 2015 Keywords: WastewaterPower plantDesalinationEnergy-water nexusSelf-suf  󿬁 ciencyCooling water a b s t r a c t The energy-water nexus of the water supply, wastewater treatment and power generation systems hasbeen well discussed. It is very clear that one source cannot be produced or supplied without involvingthe other source. Since the two systems are intertwined with mutual needs, it is dif  󿬁 cult to resolve theissues associated with them in isolation. However, combined solutions through integrated approachesmay not be feasible in all situations. Therefore, it is important to consider the energy or water autarky(self-suf  󿬁 ciency) of these systems. If these systems can achieve autarky for the energy and water needsindependently, such con 󿬁 gurations can be considered sustainable. This review paper presents theenergy and water needs for water supply, wastewater treatment, and power generation systems andcritically examines the potential opportunities for achieving energy and water autarky in these systems.A detailed view of the water supply and wastewater treatment systems ’  energy footprint was presentedand similarly the water footprint of various power plants. Different approaches for achieving energyautarky in the wastewater treatment systems as well as approaches for water autarky in the powergeneration systems were discussed. It is imperative that future developments should consider anintegrated design approach to improve the overall system autarky by communicating between the twoindividual systems, by considering synergistic energy-water production, by collaborating resourcesplanning and energy-water infrastructure synergies supported by science and system-based naturalresource policies and regulations. &  2015 Elsevier Ltd. All rights reserved. Contents 1. Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 532. Energy for water supply and wastewater facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 532.1. Energy for clean water production (conventional water treatment). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 542.2. Energy for desalination (thermal and membrane desalination) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 542.3. Energy for bottled water production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 542.4. Energy for wastewater treatment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 543. Paradigm shift (wastewater treatment) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 574. Opportunities for energy recovery and savings in wastewater treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 584.1. Energy conservation in water treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 584.2. Hydraulic energy recovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 584.3. Heat recovery. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 584.4. Combined heat and power (CHP) systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 584.5. Biogas generation (anaerobic digestion, AD) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 594.6. Algae growth for biofuels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 604.7. Anammox process (novel con 󿬁 gurations) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 604.8. Microbial fuel cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 604.9. Microbial desalination cells (MDCs) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 614.10. Energy ef  󿬁 ciency programs in USA and around the world . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 Contents lists available at ScienceDirect  journal homepage: www.elsevier.com/locate/rser Renewable and Sustainable Energy Reviews http://dx.doi.org/10.1016/j.rser.2015.01.0551364-0321/ &  2015 Elsevier Ltd. All rights reserved. E-mail addresses:  gude@cee.msstate.edu, gudevg@gmail.comRenewable and Sustainable Energy Reviews 45 (2015) 52 – 68  5. Water for energy production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 615.1. Water consumption in thermoelectric power plants. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 625.1.1. Boiler feed-water. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 625.1.2. Cooling water. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 635.1.3. Water consumption for ash and residue removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 635.1.4. Cooling water for auxiliary equipment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 635.1.5. Water for desulfurization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 635.2. Water consumption for renewable energy sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 636. Opportunities for water conservation and savings in power plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 646.1. Dry cooling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 646.2. Hybrid cooling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 656.3. Use of wastewater as cooling water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 656.4. Seawater for cooling and then water production (co-location with desalination plants) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 656.5. Energy from renewable energy sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 667. What can be done for the future projects? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66Acknowledgements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 1. Introduction Providing affordable drinking water sources and reliable waste-water treatment have become major challenges in many parts of the world [1]. Escalating energy demands for wastewater treat-ment due to population growth and high living standards and thewater demands for power generation combined with environ-mental degradation present complex and intertwined concerns formany local governments [2,3]. On the other hand, water with-drawals for various uses have increased by 2 – 3 times that of population growth mainly linked with high living standards andurbanization [4]. It is important now to examine the autarky of theindividual systems in terms of energy and water resources. Theautarky of the system de 󿬁 nes the use of external sources requiredto sustain the processes intended for certain bene 󿬁 ts. For example,wastewater treatment requires between 0.3 and 0.6 kW h/m 3 while the same contains an energy content equivalent to 10 timesthat required for treatment [5 – 7]. Therefore, it is logical andrational to develop process con 󿬁 gurations that would allow forextraction of this hidden energy to improve the self-suf  󿬁 ciency of the processes. Similar approaches can be implemented for powergeneration systems as well. In this review article, the potential forself-suf  󿬁 ciency of water-energy systems to provide a sustainablesolution is discussed. The self-suf  󿬁 ciency of these systems canbe de 󿬁 ned as the ability to support each other with minimaldependence on new resources. Utilizing renewable energy sourceswould further advance their independence from fossil-derivedelectricity. This paper will  󿬁 rst describe the energy usage pat-terns in water and wastewater treatment systems and the waterrequirements for power generation systems followed by an ana-lysis and discussion of potential pathways for achieving autarkyamong the systems for both water and energy production. 2. Energy for water supply and wastewater facilities Out of 200,000 drinking water treatment systems in U.S., about25% of the systems serve 25 or more people throughout the year[8]. About 85% of the U.S. population is served by nearly 5% of large-scale drinking water systems; the remaining 95% include alarge number of small and very small systems serving 3300persons or fewer. Most of these systems are owned and operatedby Public agencies while a small number are privately operated.On the other hand, over 75% of the U.S. population (  223Millions) is served by nearly 16,583 public wastewater treatmentplants [9]. Nearly 70% of the facilities are small, serving only 10% of the U.S. population and 22% are large (with  󿬂 ow greater than1 million gallons per day, MGD) and serve over 85% of thepopulation. Both water and wastewater systems require energyin the form of electricity for collection, conveyance, treatment, anddistribution for end use or consumption and disposal.Fig. 1 shows the range of energy requirements for treatingdifferent water sources. Conventional water treatment processvia coagulation- 󿬂 occulation-sedimentation- 󿬁 ltration involves energyconsumption between 0.25 and 1.0 kW h/m 3 from river water andgroundwater sources and most of it accounted for pumping, trans-portation and distribution. It is interesting to note that the waste-water treatment requires energy in the range of 0.5 – 2.0kW h/m 3 , Fig. 1.  Energy requirements for water production from different water sources (1 kW h/m 3 ¼ 12,922 BTU/1000 gal). V.G. Gude / Renewable and Sustainable Energy Reviews 45 (2015) 52 – 68  53  most commonly, and less than 0.5 kWh/m 3 for processes withoutnutrient removal. On the other hand, the regions with adverse waterscarcity depend on brackish and saline water sources. These desali-nation processes consume large quantities of thermal and/or elec-trical energies for separation of freshwater from saline waterreserves, which are between 2 and 20kW h/m 3 [10]. These regionsoften recycle wastewater by processing it through an advancedtreatment process for nutrient, contaminant, and pathogen removal.Again, these processes are energy intensive with speci 󿬁 c energyconsumption between 0.5 and 2.0kW h/m 3 .  2.1. Energy for clean water production (conventionalwater treatment) Provision of clean water may not be possible without anyenergy investment (see Fig. 1). Even if freshwater is readilyaccessible under the ground level, energy is required to pumpthe freshwater from its source. Freshwater drawn from thegroundwater source requires 0.14 – 0.24 kW h/m 3 (0.5 – 0.9 kJ/kg)for a pumping head of 100 – 200 ft. Conventional treatment of surface waters to potable quality requires 0.36 kW h/m 3 (1.3 kJ/kg)[3]. Conventional treatment of water sources (direct chlorination, 󿬁 ltration or chemical coagulation- 󿬂 occulation, sedimentation,  󿬁 l-tration) is only applicable in areas where adequate surface andground water resources are available. It is interesting to note fromFig. 2a that some water treatment plants consume as much energyas needed to treat equivalent amount of seawater through desa-lination process like reverse osmosis. In Canada, the energyrequirements for  󿬁 rewater supply vary between 0.25 and3 kW h/m 3 while in Mexico, it is between 0.1 and 4.5 kW h/m 3 [11]. This intense energy consumption stems from the longdistances that the resource needs to travel prior to treatment atthe plant and distribution or from the deep wells that water needsto be pumped from. Transporting the water from a remote sourcealso involves capital costs for creating appropriate infrastructure.Smaller utilities use more electricity and pay more per unit of water produced than do medium and large utilities, due toeconomies of scale. Nearly all of the energy consumed is electri-city, about 80% of which is used by motors for pumping andtransporting [12].  2.2. Energy for desalination (thermal and membrane desalination) Desalination of saline water sources has been sought as analternative to  󿬁 ll the gap between demands and supply for fresh-water in many areas severely challenged by the scarcity of fresh-water sources. Desalination is a nonconventional water treatmenttechnology applied to recover freshwater from surface and groundwaters that have high dissolved solids (TDS) concentrations. In theearly 1950s, thermal desalting technologies such as multi-stage 󿬂 ash (MSF) desalination, multi-effect evaporation desalination(MED) and mechanical vapor compression (MVC) were commer-cialized, which consumed enormous amounts of thermal energywith speci 󿬁 c energy requirements between 30 and 120 kW h th /m 3 (10.5 and 42 kW h e /m 3 ) [13]. With the advent of reverse osmosis(RO) technology and remarkable improvements in the membraneperformance and associated reductions in energyconsumption, ROtechnology has increased its visibility compared to thermal desa-lination technologies due to its much less speci 󿬁 c energy con-sumption between 3.5 and 5 kW h e /m 3 [10]. Desalination by ROprocess is recognized as a feasible option particularly in areaswhere transportation cost of freshwater and high living standardsoverride the negative impacts of desalination such as energy- andcost- intensiveness. For instance, a recent evaluation for the city of Los Angeles, California concluded that freshwater supply based onRO desalination technology requires the same amount of energy(2.8 kW h/m 3 ) that would be required to transport surface water(2 – 3 kW h/m 3 ) from the delta region or from other surface watersources [10].  2.3. Energy for bottled water production Bottled water market has seen an unprecedented growth all overthe world with rapid industrialization. For example, 200 billion litersof bottled water was sold globally in 2007 [14]. Bottled water supplyinvolves averylarge energy footprint, for instance, energy is requiredto make, package, transport, cool, use and recycle bottled water andits packaging material. The total energy required for all these stepsvaries largely for various scenarios. Plastic bottles manufacturingrequires 4.0MJ th /L (0.39 kW h e /L) of energy with water treatment atbottle plant between 0.0001 – 0.02MJ th /L (0.002kW h e /L),  󿬁 lingoperations up to 0.01 MJ th /L (0.001kW h e /L, transportation between1.4 and 5.8 MJ th /L (0.14 – 0.56kW h e /L) and cooling between 0.2(0.019 kW h e /L) and 0.4MJ th /L (0.039kW h e /L) respectively. In com-parison,producingtapwatertypicallyrequiresaboutthan0.005MJ/L for treatment and distribution [14,15].  2.4. Energy for wastewater treatment  Water and wastewater treatment plants account for 3 to 4%(56 billion kW of electricity) of total nationwide (U.S.) electricityutilization which in some communities measures anywherebetween 20 and 40% of total energy consumption. This energyconsumption is in similar range for other developed countries.Apart from the greenhouse gas emissions related to the energyconsumption, they also emit 45 million tons of carbon dioxideannually in U.S. (this is not usually counted as GHG emission) dueto organic waste degradation [16]. In addition, water and waste-water systems representing a second major cost item for utilitieswith expenditures nearly $4 billion a year. It is also estimated thatover the next twenty years an additional $45 billion will need tobe expended to maintain and improve the infrastructure [17].Reducing energy consumption for wastewater treatment willavoid environmental degradation involved in energy production.The energy autarky of the wastewater treatment systems isimportant from many perspectives such as elimination of air Fig. 2.  (a) Speci 󿬁 c energy consumption for drinking water production from groundwater and surface water sources; (b) for wastewater treatment for different plantcapacities. V.G. Gude / Renewable and Sustainable Energy Reviews 45 (2015) 52 – 68 54   Table 1 Bene 󿬁 ts of improving energy ef  󿬁 ciency in water and wastewater facilities [91 – 111].  Advantage Description ExampleReduce air pollution andGHG emissions GHG emissions and criteria air pollutants can be signi 󿬁 cantlyreduced by decreasing consumption of fossil fuel-based energy.Fossil fuel combustion for electricity generation accounts forapproximately 40% of the nation ’ s emissions of carbon dioxide (CO 2 ),a principal GHG. It also accounts for 67% and 23% of the nation ’ ssulfur dioxide (SO 2 ) and nitrogen oxide (NO  x ) emissions,respectively. These pollutants can lead to smog, acid rain, andairborne particulate matter that can cause respiratory problems formany peopleThe Green Bay, Wisconsin Metropolitan Sewerage District has twotreatment plants that together serve more than 217,000 residents.One of the treatment plants installed newenergy-ef  󿬁 cient blowersin its  󿬁 rst-stage aeration system, reducing electricity consumptionby 50% and saving 2144,000 kW h/year  –  enough energy to power126 homes  –  and avoiding nearly 1,480 metric tons of CO 2 equivalent, roughly the amount emitted annually by 290 cars Reduce energy costs  Local governments can achieve signi 󿬁 cant cost savings by increasingthe ef  󿬁 ciency of the pumps and aeration equipment at a water orwastewater treatment plant. A 10% reduction in the energy use of U.S. drinking water and waste-water systems would collectively saveapproximately $400 million and 5 billion kW h annually. otherapproaches to reduce energycosts are shifting energy use away frompeak demand times to times when electricity is cheaper or (forwastewater plants) using CHP systems to generate their ownelectricity and heat from biogasWaste Water Treatment Plant in Albert Lea, Minnesota developeda 120-kW mictroturbine CHP system, which saves the plant about$100,000 in annual energycosts. About 70% of the savings resultedfrom reduced electricity and fuel purchases, and the remainderfrom reduced maintenance costs. The installation of the CHPsystem raised awareness at the plant about energy use in general,and led to a number of other energy ef  󿬁 ciency improvements andadditional cost savings Support economic growththrough job creation andmarket development The energy ef  󿬁 ciency services sector accounted for an estimated830,000 jobs in 2010, and the number of jobs was growing by 3%annually. Most of these jobs are performed locally by workers fromrelatively small local companies. Furthermore, facilities that reducetheir energy costs through ef  󿬁 ciency upgrades can spend thosesavings elsewhere, often contributing to the local economyIn an initiative led by the city ’ s current mayor when he was atalderman, a group of residents and city staff led an initiative in2008 to develop a plan to make the City of Franklin, Tennessee,more environmentally sustainable. This group created the city ’ s2009 Sustainability Community Action Plan, which called forreductions in energy use and GHG emissions, and directedFranklin ’ s utilities to become more involved in energy ef  󿬁 ciencyaudits. As part of its effort to meet the action plan ’ s energy goals,Franklin participated in the Tennessee Water and WastewaterUtilities Partnership, co-sponsored by EPA Region 4. Thepartnership helped Franklin ’ s water department identify andimplement opportunities to reduce energy costs by more than$194,000 per year  –  a 13% reduction  –  through changes inoperations and installing energy-ef  󿬁 cient lighting. Theimprovements have avoided more than 1280 metric tons of GHGemissions, equivalent to the annual emissions from powering 125homes Demonstrate leadership  Investing in energy ef  󿬁 ciency epitomizes responsible governmentstewardship of tax dollars and sets an example for others to follow.By implementing energy ef  󿬁 ciency and water ef  󿬁 ciency projects atwater and wastewater facilities, a local government candemonstrate not only the dollars saved, but the environmentalbene 󿬁 ts that are obtained from reducing energy and water use.Installing energy-ef  󿬁 cient products (e.g., more ef  󿬁 cient pumps),water-ef  󿬁 cient products (e.g., WaterSense products), andrenewable energy technologies (e.g., solar panels) may facilitatebroader adoption of these technologies and strategies by theprivate sector — particularly when communities publicize theeconomic and environmental bene 󿬁 ts of their actions Improve energy and water security  Improving energy ef  󿬁 ciency at a water or wastewater treatmentfacility reduces electricity demand, avoiding the risk of brownouts orblackouts during high energy demand periods and helping to avoidthe need to build new power plants. Water ef  󿬁 ciency strategiesreduce the risk of water shortages, helping to ensure a reliable andcontinuous water supplyThe East Bay Municipal Utility District (EBMUD), which providesdrinking water to 1.3 million customers and handles wastewaterfor 650,000 customers in the San Francisco Bay Area, transformeditself from an energy consumer to a net energy producer. By 2008the district had brought its GHG emissions back to their 2000 leveland then reduced them by an additional 24% the following year, allwhile insulating itself from energy price  󿬂 uctuations and supplyuncertainties. EMBUD started its energy transformation by cuttingits energy use requirements to the point where its facilities nowuse 82% less energy than the California average for delivering1 million gallons of drinking water from source to tap. Itaccomplished these improvements through design features, suchas delivering drinking water via downhill pipes rather than usingelectric pumps, and through energy ef  󿬁 ciency upgrades such asinstalling microturbine CHP units. EBMUD ’ s remaining energyneeds are met by renewable energy systems, includinghydropower, solar, and biogas. Excess power produced by therenewables provides a source of income through sales of electricity into the grid Extend the life of infrastructure/equipment Energy-ef  󿬁 cient equipment often has a longer service life andrequires less maintenance than older, less ef  󿬁 cient technologies.Efforts to improve water ef  󿬁 ciency or promote water conservationcan also extend the life of existing infrastructure due to lowerdemand, and can avoid the need for costly future expansionsMillbrae, California implemented a program to divert inediblekitchen grease from the city ’ s wastewater system, where it couldclog sewer lines and cause releases of raw sewage into theenvironment, posing risks to public health. Waste haulers collectthe grease daily from area restaurants and deliver it to thewastewater treatment facility, where it is processed in digestertanks to create biogas. Before the program was implemented, thegrease ended up in area land 󿬁 lls where its decompositionproduced methane emissions. The treatment plants digestersystem produces enough biogas to generate about 1.7 millionkW h of electricity annually, meeting roughly 80% of the plant ’ spower needs Protect public health  Improvements in energy ef  󿬁 ciency at water and wastewaterfacilities can reduce air and water pollution from the power plantsthat supply electricity to those facilities, resulting in cleaner airand human health bene 󿬁 ts Equipment upgrades may also allowfacilities to increase their capacity for treating water orwastewater or improve the performance of treatment processes,reducing the potential impacts of sea level rise, treatment failures,and risk of waterborne illness Country Energy/water ef  󿬁 ciency measure Achieved bene 󿬁 ts (savings) Australia Applying new coating to pump casing volute and impeller to reducewater friction loss20% — energy costAustralia Active leakage control through pressure management, combinedwith water main renewal and  󿬂 ow meter upgrade45% — waterAustralia Reduced energy intensity V.G. Gude / Renewable and Sustainable Energy Reviews 45 (2015) 52 – 68  55
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