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2 Current State of Water Reuse Historical Perspectives on Sewage and Municipal This chapter provides the background needed Wastewater Treatment to understand the role of water reuse in the nation’s water supply. After presenting a brief overview of Prior to the installation of piped water supplies, how sewage collection and treatment developed dur- most cities did not have sewers or centralized systems ing the 19th and 20th centuries, the chapter describes for disposing of liquid waste. Feces and urine were the ways in which reclaimed water has been used for collected in privy vaults or cesspools (Billings, 1885). industrial applications, agriculture, landscaping, habitat W hen the vaults were filled, wastes were removed and restoration, and water supply. Through descriptions of applied to agricultural fields, dumped in watercourses current practices and case studies of important water outside of the city, or the vault was abandoned (Tarr et reclamation projects, the chapter provides a means of al., 1984). Other liquid wastes, from cooking or clothes understanding the potential for expansion of different washing, were discharged to gutters or unlined dry types of water reuse and identifies factors that could wells. Sewers were only employed to a limited extent in limit future applications. densely populated areas to prevent flooding by convey- ing runoff to nearby rivers. In many cities, it was illegal CONTEXT FOR WATER REUSE to discharge human wastes to sewers (Billings, 1885). To understand the potential role of water reuse in the nation’s water supply, it is important to consider Emergence of Sewer Collection Systems the infrastructure that has been developed to enable With the advent of pressurized potable water, per the collection, treatment, and disposal of municipal capita urban water use increased from approximately 5 wastewater because these systems serve as the source of gal/d (20 L/d) to over 105 gal/d (400 L/d; Tarr et al., reclaimed water. By understanding the ways in which 1984). When ample freshwater supplies became avail- wastewater collection and treatment systems developed able, the popularity of the flush toilet grew and the and are currently operated, it is possible to gain insight resulting large volumes of liquid waste overwhelmed into many of the technical issues discussed in later sec- the capacity of privy vaults, cesspools, and gutters. The tions of the report. In particular, this section describes public health and aesthetic problems associated with the practice of unplanned, or de facto, water reuse (see the liquid wastes led to the widespread construction Box 1-1), which is an important but underappreciated of sewer systems in populated areas. During the initial part of our current water supply, as well as the different phase of sewer system construction, in the late 1800s, types of systems that have been developed as part of most cities in the United States built combined sewers planned water reclamation projects. to convey sewage and stormwater runoff from the city 21
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22 WATER REUSE to nearby waterways (Tarr, 1979). Separate sanitary consistent quality of the waste. In some communities, sewers (that conveyed mainly waste from homes and sewage was applied directly to orchards or farms (in a businesses) were built in several dozen cities because practice known as sewage farming (Anonymous, 1893; they were less expensive and the concentrated wastes see Box 2-1). Sewage farming led to high crop yields, could be used as fertilizers (Tarr, 1979). By 1890, ap- especially in locations where water was limited. The proximately 70 percent of the urban population lived in nutrients in the sewage made sewage farming attrac- areas that were served by one of the two types of sewer tive to farmers, but the practice eventually died out in systems (Figure 2-1). the 1920s as public health officials expressed concerns Throughout this period, the wastes conveyed by about exposure to pathogens in fruits and vegetables combined sewer systems were usually discharged to grown on sewage farms. surface waters without any treatment because the avail- As downstream communities became aware of the able treatment methods (e.g., chemical precipitation) impact that upstream communities were having on were considered to be too expensive (Billings, 1885). As their water supplies, there were debates about the ob- a result of the rapid growth of cities and the relatively ligations of communities to remove contaminants from large volumes of water discharged by sewers, drinking sewage prior to discharge. Leading engineers, such as water supplies of cities employing sewers and their Allen Hazen, advocated for downstream cities to install downstream neighbors were compromised by water- drinking water treatment systems (Hazen, 1909) while borne pathogens, resulting in increased mortality due public health scientists, like William Sedgwick (1914), to waterborne diseases (Tarr et al., 1984). For example, advocated a requirement for cities to treat sewage. severe outbreaks of typhoid fever in Lowell and Law- Many sanitary engineers supported their assertion that rence, Massachusetts, in 1890 and 1891, in which over wastewater treatment was unnecessary by a belief that 200 people died, were traced back to the discharge of flowing water undergoes a process of self-purification. sewage by communities located approximately 12 miles They asserted that as long as a water supply was located (20 km) upstream of Lawrence (Sedgwick, 1914). at a sufficient distance downstream of the sewage dis- In cities with separate sanitary sewers, treatment charge, the water would be safe to drink. In fact, this was more common because of the smaller volumes and concept was instrumental in the state of Massachusetts’ policy of allowing sewage discharges to rivers if the outfall was located more than 20 miles (32 km) from a drinking water intake (Hazen, 1909; Sedgwick, 1914; Tarr, 1979). As a result of these debates, downstream communities often took the responsibility for ensuring the safety of their own water supply by building drink- ing water treatment plants or relocating their water supplies to protected watersheds. Emergence of Wastewater Treatment In 1900, less than 5 percent of the municipal wastewater in the United States was treated in any way prior to discharge (Figure 2-1). However, increases in population density, especially in cities, coupled with the growth of the progressive movement, which cre- ated a greater awareness of natural resources, led to increased construction of wastewater treatment systems FIGURE 2-1 Comparison of total U.S. population with urban (Burian et al., 2000). Coincident with these trends population, population served by sewers, population served by was the development of more cost-effective methods water treatment plants, and population served by wastewater treatment plants. of biological wastewater treatment, such as activated SOURCES: Tarr et al. (1984), (EPA, 2008b). R02129 Figure 2-1 bitmapped
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23 CURRENT STATE OF WATER REUSE BOX 2-1 Sewage Farming Throughout history, farmers have recognized the potential benefits of applying human wastes to agricultural land. With the widespread popular- ity of the water closet (i.e., the flush toilet) in the latter part of the 19th century, the water content of wastes increased and the traditional system for transporting waste to agricultural fields became impractical. To obtain the benefits of land application of wastes, scientists in Europe began evaluating the potential for using pipelines to transport sewage to farms where the water and nutrients could be used to grow plants. Eventually, large sewage farms were built and operated in Edinburgh, Paris, and Berlin where they produced fodder for cattle, fruits, and vegetables (Hamlin, 1980). At the turn of the century, the majority of the sewage produced in Paris was being treated on sewage farms (Reid, 1991). In the United States, sewage farming was especially popular in arid western states because water supplies were limited (see figure below). For example, in California the practice of irrigating food crops with raw sewage reached a peak in 1923 with 70 municipalities applying their sew- age to food crops (Reinke, 1934). In some locations, chemical treatment followed by settling was used prior to irrigation (Tarr, 1979). Eventually sewage farming became less prevalent as cities expanded, fertilizers became less expensive, and modern wastewater treatment plants provided an alternative means of sewage disposal. Sewage farming continued in France and Germany until the second half of the 20th century. Despite the public health risks associated with potential exposure to pathogens in raw sewage, almost all of the wastewater produced in Mexico City is sent to sewage farms (Jiménez and Chavez, 2004). A sewer farm near Salt Lake City, Utah. SOURCE: Utah Historical Society, circa 1908. sludge. By 1940, 55 percent of the urban population of of $24.6 billion in construction and research grants the United States was served by wastewater treatment for wastewater treatment plants as part of the Clean plants (EPA, 2008b). Concerns associated with raw Water Act of 1972 (Burian et al., 2000). Most of the sewage discharges increased during the postwar period, municipal wastewater treatment plants built in the with the passage of the Water Pollution Control Acts United States during the late 1960s and early 1970s of 1948 and 1956, which provided federal funding for were equipped with primary and secondary treatment wastewater treatment plant construction (Everts and (see Box 2-2 and Chapter 4), which are capable of Dahl, 1957; Melosi, 2000). By 1968, 96.5 percent of removing from wastewater over 90 percent of the total the urban population of the United States lived in areas suspended solids and both oxygen-demanding organic where wastewater was treated prior to discharge (EPA, wastes (i.e., biochemical oxygen demand [BOD] and 2008b), but the extent of treatment varied consider- chemical oxygen demand [COD]). By 2004, only 40 of ably, with many plants only removing suspended solids more than 16,000 publicly owned wastewater treatment through primary treatment. plants in the United States reported less than secondary Concerns associated with sewage pollution grew treatment (see Table 2-1; EPA, 2008b). during the 1960s and culminated with the allocation The increased number of wastewater treatment
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24 WATER REUSE sources, ammonia concentrations often reached levels BOX 2-2 that were toxic to aquatic organisms. In other locations, Stages of Wastewater Treatment wastewater effluent discharges caused excessive growth of algae and aquatic macrophytes due to the elevated Primary Removal of a portion of the suspend- concentrations of nutrients (i.e., nitrogen and phospho- ed solids and organic matter form the rus) in the effluent. To address these issues, treatment wastewater. plants were often retrofitted or new treatment plants were built with technologies for removing nutrients Secondary Biological treatment to remove biodegradable organic matter and (see Chapter 4 for detailed descriptions). These nutri- suspended solids. Disinfection is ent removal processes, which are sometimes referred typically, but not universally, included to as tertiary treatment processes, became increasingly in secondary treatment. popular in the 1970s. To protect downstream recreational users, waste- Advanced treatment Nutrient removal, filtration, disinfec- water effluent is often disinfected before discharge. tion, further removal of biodegradable organics and suspended solids, The most common means of disinfection in the United removal of dissolved solids and/ States is effluent chlorination, a process in which a or trace constituents as required for small amount of dissolved chlorine gas or hypochlorite specific water reuse applications. (i.e., bleach) is added to the effluent prior to discharge. However, concerns about potential hazards associated SOURCE: Adapted from Asano et al. (2007). with handling of chlorine coupled with the need to minimize the formation of disinfection byproducts that are toxic to humans and aquatic organisms have caused plants built during the postwar period had immedi- some utilities to switch to other means of effluent dis- ate and readily apparent impacts on the aesthetics of infection (Sedlak and von Gunten, 2011). In particular, surface waters and the integrity of aquatic ecosystems. disinfection with ultraviolet light has become more However, effluent from wastewater treatment plants common as the technology has become less expensive. sometimes caused problems. In locations where efflu- Ozone also is being used for effluent disinfection in ent was insufficiently diluted with water from other some locations because it also oxidizes trace organic TABLE 2-1 Treatment Provided at U.S. Publicly Owned Wastewater Treatment Plants Treatment Facilities in Operation in 2004a Number of Existing Flow Present Design Number of Percent of U.S. Level of Treatment Facilities (MGD) Capacity People Served Population Less than Secondaryb 40 441 570 3,306,921 1.1 Secondary 9,221 14,622 19,894 96,469,710 32.4 Greater than Secondary 4,916 16,522 23,046 108,506,467 36.5 No Dischargec 2,188 1,565 2,296 14,557,817 4.9 Partial Treatmentd 218 507 632 — — Totale 16,583 33,657 46,438 222,840,915 74.9 aAlaska, American Samoa, Guam, the Northern Mariana Islands and the Virgin Islands did not participate in the CWNS 2004. Arizona, California, Georgia, Massachusetts, Michigan, Minnesota, North Dakota, and South Dakota did not have the resources to complete the updating of their data. All other states, the District of Columbia, and Puerto Rico completed more than 97 percent of the data entry or had fewer than 10 facilities that were not updated. bLess-than-secondary facilities include facilities granted or pending section 301(h) waivers from secondary treatment for discharges to marine waters. cNo-discharge facilities do not discharge treated wastewater to the Nation’s waterways. These facilities dispose of wastewater via methods such as industrial reuse, irrigation, or evaporation. dThese facilities provide some treatment to wastewater and discharge their effluents to other wastewater facilities for further treatment and discharge. The population associated with these facilities is omitted from this table to avoid double accounting. eTotals include best available information from states and territories that did not have the resources to complete the updating of the data or did not participate in the CWNS 2004 in order to maintain continuity with previous reports to Congress. Forty operational and 43 projected treatment plants were excluded from this table because the data related to population, flow, and effluent levels were not complete. SOURCE: EPA (2008b).
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25 CURRENT STATE OF WATER REUSE contaminants (see Chapter 4 for details). It is worth nation’s potable water supply, monitoring efforts (e.g., noting that effluent disinfection is not practiced at all the U.S. Geological Survey [USGS] Toxic Substances wastewater treatment plants because of variations in Hydrology Program) have documented the presence local regulations. of wastewater-derived contaminants in watersheds throughout the country (Kolpin et al., 2002). In a recent study of drinking water supplies, one or more Increasing Importance of De Facto Water Reuse prescription drugs was detected in approximately 25 Irrespective of the treatment process employed, percent of samples collected at the intakes of drinking municipal wastewater effluent that is not directly re- water treatment plants in 25 states and Puerto Rico used is discharged to the aquatic environment where (Focazio et al., 2008). it reenters the hydrological cycle. As a result, almost Although detection of wastewater-derived organic every municipal wastewater treatment plant, with the compounds demonstrates the occurrence of de facto exception of coastal facilities, practices a form of water reuse, making precise estimates of the contribution of reuse, because the discharged treated wastewater is effluent to a water supply is more challenging. Aside made available for reuse by downstream users. In many from anecdotal reports from watersheds such as the cases, effluent-impacted surface water is employed for Trinity River (Box 2-3), it is challenging to find good nonpotable applications, such as irrigation. However, estimates of effluent contributions to water supplies. there are numerous locations where wastewater effluent Attempts to quantify the fraction of the overall flow accounts for a substantial fraction of a potable water of a river that was derived from wastewater effluent supply (Swayne et al., 1980). This form of reuse, which require detailed information about the hydrology of the is also referred to as de facto reuse (Asano et al., 2007), watershed and the quantity of effluent discharged. In is important to the evaluation of water reuse projects 1980, EPA conducted a scoping study to characterize and may be a useful source of data on potential public the contribution of wastewater effluent to drinking wa- health risks. In many cases, the degree of treatment that ter supplies (see Box 2-4). Results indicated that more this municipal wastewater receives prior to entering the than 24 major water utilities used rivers from which potable water supply is less than that applied in planned effluent accounted for over 50 percent of the flow under reuse projects. low-flow conditions (Swayne et al., 1980). Rivers and lakes that receive wastewater efflu- Since that time, the urban population of the United ent discharges are sometimes referred to as effluent- States has increased by over 35 percent (U.S. Census, impacted waters.1 Box 2-3 describes an example of 2010c, 2011), with much of the growth occurring in the a watershed where wastewater effluent accounts for southeastern and western regions. As a result, it is likely about half of the water in a drinking water reservoir. that the contribution of wastewater effluent to water The concentration of wastewater-derived contaminants supplies has increased since the 1980 EPA scoping in a drinking water treatment plant water intake from study. In 1991, data from EPA indicated that 23 per- an effluent-impacted source water depends upon the cent of all permitted wastewater discharges were made wastewater treatment plant, the extent of dilution, resi- into surface waters that consisted of at least 10 percent dence time in the surface water, and the characteristics wastewater effluent under base-flow conditions. More of the surface water (including depth and temperature, recently, Brooks et al. (2006) estimated that 60 percent which affect the rates of natural contaminant attenu- of the surface waters that received effluent discharges in ation processes). Although it is currently difficult to EPA Region 6 (i.e., Arkansas, Louisiana, New Mexico, estimate the total contribution of de facto reuse to the Oklahoma, and Texas) consisted of at least 10 percent wastewater effluent under low-flow conditions.2 1 Effluent-impacted surface waters can also discharge to ground- water. As a result, groundwater wells located proximate to effluent- 2 The committee recognizes that temporal variations in dilution impacted surface waters can be a route for de facto potable water flows will affect surface water quality, but it was beyond the com- reuse. The number of people who acquire their drinking water from mittee’s charge to assess specific flow criteria (e.g., average flow, wells under the influence of effluent-dominated waters that are not 7Q10 [average low-flow over 7 consecutive days with a 10-year intentionally operated as potable water reuse systems is unknown. return frequency]) that should be used to evaluate the extent and
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26 WATER REUSE BOX 2-3 De Facto Reuse in the Trinity River Basin The Trinity River in Texas is an example of an effluent-dominated surface water system where de facto potable water reuse occurs. The section of the river south of Dallas/Forth Worth consists almost entirely of wastewater effluent under base flow conditions (Fono et al., 2006; TRA, 2010). In response to concerns about nutrients, the wastewater treatment plants in Dallas/Fort Worth that collectively discharge about 500 million gallons per day (MGD; 2 million m3/d) of effluent employ nutrient removal processes (Fono et al., 2006). Little dilution of the effluent-dominated waters occurs as the water travels from Dallas/Fort Worth to Lake Livingston, which is one of the main drinking water reservoirs for Houston (see figure below). Once the water reaches Lake Livingston, it is subjected to conventional drinking water treatment prior to delivery to consumers in Houston. Results from hydrological models and contaminant monitoring indicate that contaminant attenuation takes place in the river and reservoir. During the estimated 2-week travel time between Dallas/Fort Worth and Lake Livingston, many of the trace organic contaminants undergo trans - formation by microbial and photochemical processes (Fono et al., 2006). Additional contaminant attenuation and pathogen inactivation also may occur during the water’s residence time in the reservoir. On an annual basis, about half of the water flowing into Lake Livingston is derived from precipitation. Therefore, water entering the drinking water treatment plant consists of approximately 50 percent wastewater effluent that has spent approximately 2 weeks in the Trinity River and up to a year in the reservoir before it becomes a potable water supply. The potable water from the Trinity River meets all of the Environmental Protection Agency’s water quality regulations and this de facto potable reuse system is an important element in the region’s water resource planning. Trinity River Basin, showing Dallas/Fort Worth in the headwaters of the water supply for the city of Houston. SOURCE: http://wapedia.mobi/en/File:Trinity_Watershed.png. R02129 Figure 2-3 Improved integration of hydrological data and bitmapped of conditions. For example, Andrew Johnson and bet- range ter watershed models make it possible to estimate the Richard Williams (Centre for Ecology and Hydrology, fraction of wastewater effluent in surface waters under a personal communication, 2009) used readily available data on river flows and volumes of wastewater effluent discharged by individual treatment plants to develop significance of de facto reuse. The existing regulatory structure for a hydrological model that predicts the fraction of drinking water addresses this issue through requirements for peri- odic monitoring. For chemicals where the risk is based on lifetime wastewater effluent in different surface waters in and exposure, average concentrations of contaminants are used. For around Cambridge, UK, under base-flow conditions pathogens and chemicals where risks are based on shorter exposures, (Figure 2-2). Such hydrological data are available in low-flow measures might be appropriate, although it is beyond the committee’s charge to evaluate.
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27 CURRENT STATE OF WATER REUSE BOX 2-4 The Presence of Wastewater in Drinking Water Supplies Circa 1980 A survey of wastewater discharges upstream of drinking water intakes was conducted on behalf of EPA, reflecting water systems that collec- tively served 76 million persons (Swayne, et al., 1980). Data are shown in the below figure for average flow conditions and low flow (i.e., 7-day, 10-year low flow) conditions. Utilities serving 32 million people (of the 76 million total reflected in the survey) reported that no wastewater was discharged upstream of the water intakes. However, of the remaining 44 million people served by the utilities surveyed, more than 20 million relied upon source water with a wastewater content of 1 percent or more under average flow conditions, and a similar number relied on source water with a wastewater content of 10 percent or more during low-flow conditions. No comparable more recent data are available, but these percentages have likely increased significantly since the EPA data were collected, given the population growth and increasing water use over the last 30 years. Although some of the supplies represented by the data on the right side of the figure below are controversial, most of these urban water supplies are considered safe, conventional water supplies by the public. Millions of Persons Served 12,000,000 10,000,000 8,000,000 Low Flow Avg Flow 6,000,000 4,000,000 2,000,000 - Wastewater discharges upstream ÷ flow at point of withdrawal Persons served by a water supply with wastewater content according to EPA’s 1980 survey of wastewater discharged upstream of drinking water intakes. SOURCE: Data from Swayne et al. (1980). the United States through the EPA’s Better Assess- USGS maintains stream gauging stations and ment Science Integrating Point and Nonpoint Sources has an active research and monitoring program for (BASINS) system3 and have been adapted by scientists wastewater-derived contaminants. EPA has consider- working for the pharmaceutical industry to make such able experience in the development and application of calculations for 11 watersheds serving as drinking water surface water quality models. Through a collaborative supplies for 14 percent of the U.S. population (Ander- effort drawing upon the expertise of both agencies, son et al., 2004). Maps that show the contribution of agency scientists could provide water resource planners wastewater under current and future scenarios could be with a better understanding of the extent of de facto extremely useful to water resource planners and public reuse in their catchment and provide data useful to health experts as part of efforts to manage the nation’s estimating contaminant attenuation between effluent water resources in a safe and reliable manner. discharge and potable water intakes (e.g., residence time, water quality, depth). 3 S ee http://water.epa.gov/scitech/datait/models/basins/index. cfm.
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28 WATER REUSE FIGURE 2-2 Estimated Contribution of wastewater effluent to overall river flow in the River Ouse (UK). SOURCE: Andrew Johnson and Richard J. Williams, CEH, personal communication, 2009. R02129systems currently provide reclaimed water for PLANNED NONPOTABLE WATER reuse Figure 2-5 irrigation, decorative water features, toilet REUSE APPLICATIONS landscape bitmapped flushing, fire protection, cooling water for and urinal As an alternative to releasing wastewater effluent air conditioners, commercial uses (e.g., car washes, into the environment, reclaimed wastewater can be laundries), dust suppression, and street washing, among reused for a variety of purposes (Table 2-2). Currently, others. For example, in Florida, urban nonpotable ap- most reclaimed water is used for nonpotable applica- plications (i.e., industrial uses, public access irrigation) tions, such as agricultural and landscape irrigation. represented at least 68 percent of total reclaimed water (Data on the extent of various reuse applications use by flow volume in 2010 (FDEP, 2011). Industrial in several states is presented toward the end of this and landscape irrigation reuse applications are dis- chapter.) The following section discusses a variety of cussed in more detail below, along with dual distribu- nonpotable reuse applications and associated technical tion systems that enable these applications. and water quality considerations. Economics, the regu- latory framework, and public acceptance also influence Landscape Irrigation planning decisions about nonpotable reuse, and these factors are examined in Chapters 9 and 10. Landscape irrigation is the most widely used ap- plication of reclaimed water in urban environments and Urban Reuse Applications typically involves the spray irrigation of golf courses, parks, cemeteries, school grounds, freeway medians, A wide array of uses for nonpotable reclaimed residential lawns, and similar areas. Because public water have been identified in urban areas. Urban water contact with the applied water presents potential health
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29 CURRENT STATE OF WATER REUSE TABLE 2-2 Uses of Reclaimed Water Category of Use Specific Types of Use Limitations Landscape Parks, playgrounds, cemeteries, golf courses, roadway • Dual distribution system costs irrigation rights-of-way, school grounds, greenbelts, residential and • Uneven seasonal demand other lawns • High–total dissolved solids (TDS) reclaimed water can adversely affect plant health Agricultural Food crops, fodder crops, fiber crops, seed crops, nurseries, • Use and source are often some distance apart irrigation sod farms, silviculture, frost protection • Dual distribution system costs • Uneven seasonal demand • High-TDS reclaimed water can adversely affect plant health Nonpotable Toilet and urinal flushing, fire protection, air conditioner • Dual distribution system costs urban uses (other chiller water, commercial laundries, vehicle washing, street • Building-level dual plumbing may be required than irrigation) cleaning, decorative fountains and other water features • Greater burden on cross-connection control Industrial uses Cooling, boiler feed, stack scrubbing, process water • Dual distribution system cost to industrial sites varies based on proximity • Treatment required depends on end use Impoundments Ornamental, recreational (including full-body contact) • Dual distribution system costs • Nutrient removal required to prevent algal growth • Potential ecological impacts depending on reclaimed water quality and sensitivity of species Environmental Stream augmentation, marshes, wetlands • Nutrient and ammonia removal may be required. uses • Potential ecological impacts depending on reclaimed water quality and sensitivity of species Groundwater Aquifer storage and recovery, seawater intrusion control, • Appropriate hydrogeological conditions needed recharge ground subsidence control • High level of treatment may be required • Potential for water quality degradation in subsurface Potable Water supply treatment • Very high level of treatment required water supply • Requires post-treatment storage augmentation • Can be energy intensive Miscellaneous Aquaculture, snow making, soil compaction, dust control, equipment washdown, livestock watering SOURCE: Adapted from Washington State Department of Health (2007). risks if microbial pathogens are present in the water, microbiological requirements become more restrictive reclaimed water typically is subjected to high doses of as the expected level of human contact with reclaimed disinfectants. Chemical contaminants usually are not a water increases (e.g., parks, golf courses, schoolyards). major concern in landscape irrigation projects. When Operational considerations include limiting aerosol used for landscape irrigation, reclaimed water usually formation and dispersal, managing application rates does not have adverse impacts on plants, although in to avoid ponding and runoff, and maintaining proper some cases high levels of salts or constituents such as disinfection (EPA, 2004). boron can adversely affect vegetation (see Chapter 8). Landscape irrigation with reclaimed water is well Furthermore, the potential for ingestion of irrigation accepted and widely practiced in the United States. For water is limited. example, in 2005 there were more than 200 water recla- Depending on the area being irrigated, its location mation facilities that provided reclaimed water to more relative to populated areas, and the extent of public than 1,600 individual park, playground, or schoolyard access or use of the grounds, the microbiological re- sites for irrigation (Crook, 2005b). The majority of the quirements and operational controls placed on the sites were in California and Florida. Irrigation of golf system may differ. Irrigation of areas not subject to courses is one of the most common uses of reclaimed public access (e.g., highway medians) have limited water, and 525 golf courses in Florida alone used re- potential for creating public health problems, whereas claimed water for irrigation in 2010 (FDEP, 2011).
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30 WATER REUSE Industrial Applications quantities of makeup water and extensive treatment required, reclaimed water is typically a poor candidate Effluent from conventional wastewater treatment for boiler feed. However, reclaimed water is used at a plants is of adequate quality for many industrial ap- few facilities that provide additional treatment (e.g., plications. Major industrial uses of reclaimed water reverse osmosis). include cooling, process water, stack scrubbing, boiler feed, washing, transport of material, and as an ingre- Process Water. The acceptability of reclaimed water dient in industrial products (MCES, 2007). When for industrial process water depends on the specific used for these applications, reclaimed water has the application. Whereas secondary treatment effluent important advantage of being a reliable supply. This is may be acceptable for some applications (e.g., concrete particularly advantageous for industries located near manufacturing), advanced treatment is needed for ap- populated areas that generate large volumes of waste- plications such as carpet dyeing because water used in water effluent. textile manufacturing must be nonstaining and the iron, manganese, and organic matter in secondary effluent Cooling Water. The predominant application of re- could compromise the quality of the final product. claimed water by industry is for cooling water. There Divalent metal cations cause problems in some of the are more than 40 power plants in the United States dyeing processes that use soap, and nitrates and nitrites that use municipal wastewater as plant makeup water may also cause problems (WPCF, 1989). Exceptionally ( Veil, 2007). Examples of a steam electric generating high-quality water is required for some other industrial plant and a nuclear plant that use reclaimed water for process uses (e.g., water used to wash circuit boards in cooling are provided in Boxes 2-5 and 2-6. In general, the electronics industry often requires reverse osmosis the major problems experienced by power plants em- treatment to remove salts). ploying reclaimed water for cooling are scale formation, Reclaimed water is used in the paper and pulp biological growth, and corrosion. industry, although higher quality paper products are Power plants often use disinfected secondary ef- more sensitive to water quality. Certain metal ions, such fluent for cooling, but in recirculating cooling systems, as iron and manganese, can cause discoloration of the additional treatment, such as filtration, chemical pre- paper, microorganisms can affect its texture and uni- cipitation, ion exchange or reverse osmosis, is often formity, and suspended solids may affect its brightness necessary. In some cases, only additional chemical (Rommelmann et al., 2004). The use of reclaimed water treatment is necessary (e.g., antifoaming agents, poly- in the manufacture of paper products used as food wrap phosphates to control corrosion, polyacrylates to dis- or beverage containers is prohibited in some states (e.g., perse suspended solids, chlorine to control of biological F lorida) to prevent the possibility of contaminants that growth; see EPA, 2004). pose health risks leaching into consumable products. In the chemical industry, water requirements vary Boiler Feedwater. W hen used as feedwater in boil- widely depending on the processes involved. In gen- ers, reclaimed water requires extensive treatment with eral, water that is in the neutral pH range (6.2 to 8.3), quality requirements that increase with the operating moderately soft (i.e., low calcium and magnesium), pressure of the boiler. Typically, both potable and re- and relatively low in silica, suspended solids, and color claimed water need to be treated to remove inorganic is required (WPCF, 1989). Total dissolved solids and constituents that can damage the boilers (EPA, 2004). chloride content generally are not critical. For example, calcium, magnesium, silica, and alumi- num contribute to scale formation in boilers, while Dual Distribution and Distributed Systems for Urban excessive alkalinity and high concentrations of potas- Water Reuse sium and sodium can cause foaming (WPCF, 1989). Bicarbonate alkalinity can lead to the release of carbon Increasing use of reclaimed water in urban areas dioxide, which can increase the acidity in the steam and has resulted in the development of large dual-water corrode the equipment. Because of the relatively small systems in several communities that distribute two
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31 CURRENT STATE OF WATER REUSE BOX 2-5 Xcel Energy Cherokee Station, Denver, Colorado The Xcel Energy Cherokee Station (pictured below) is a coal-fired, steam electric generating station with four operating units that can produce 717 MW of electricity. The plant, located just north of downtown Denver, Colorado, also is capable of burning natural gas as fuel. The power plant uses 7.1–9.0 MGD (27,000 to 34,000 m3/d) of water for cooling towers. Historically, all cooling tower feedwater originated from ditch systems that provided raw water to the plant. The Xcel Energy Cherokee Station began using reclaimed water from Denver’s Water Recycling Plant as one of its sources of cooling water in 2004 to reduce the plant’s freshwater consumption. The Cherokee Station is the largest customer of Denver Water’s Recycling Plant, using up to 4.7 MGD (18,000 m3/d) of reclaimed water. Raw water and reclaimed water are brought to the site and mixed in a large reservoir before feeding the cooling towers. The blend of reclaimed and raw water is also used onsite for ash silo washdown and fire protection. The major benefit of reclaimed water to the power plant is the availability of a new water source and an overall increased water supply to ensure that Xcel Energy will be able to obtain needed water even in dry or drought years. Denver Water’s Recycling Plant, which currently has a treatment capacity of 30 MGD (110,000 m3/d) and is designed for expansion to 45 MGD (170,000 m3/d), receives secondary effluent from the Metro Wastewater Treatment Plant. Treatment at the Water Recycling Plant, which is located in close proximity to the Cherokee Station, includes the following • Nitrification with biologically aerated filters • Coagulation with aluminum sulfate for phosphorus reduction • Flocculation and high rate sedimentation • Filtration with deep-bed anthracite filters • Chlorine disinfection with free chlorine or chloramines depending on season and need The cooling towers typically run four to five cycles, and sodium hypochlorite is used as a biocide. Blowdown from the cooling towers is treated with lime and ferric chloride to ensure discharge permit compliance before it is discharged into the South Platte River. The Xcel Energy Cherokee Station. SOURCE: Photo courtesy of Xcel Energy (www.XcelEnergy.com) grades of water to the same service area: potable waR02129 here significant portions of the population could be - w Figure 2-6 ter and nonpotable reclaimed water. The nonpotable exposed to the reclaimed water. bitmapped Dual-water distribution systems vary considerably reclaimed water can be used for residential irrigation, toilet flushing, and fire protection, among other appli- in aerial extent, reclaimed water uses, volumes, and cations (see Table 2-2). To minimize microbial health complexity of the systems. Infrastructure requirements risks associated with inadvertent contact or ingestion vary but often include storage facilities, pumping facili- of reclaimed water (see also Chapter 6), dual-water ties, transmission and distribution pipelines, valves and systems generally provide filtered, disinfected effluent meters, and cross-connection control devices. There
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44 WATER REUSE amount of time that the water remains in the subsurface for removal of particle-associated contaminants (e.g., prior to abstraction. pathogens, mineral particles). In addition, contami- The composition of reclaimed water and geology of nants may be transformed by microbes as they undergo the aquifer are important considerations in groundwa- infiltration. Recharge basins are attractive to water ter recharge projects. Highly treated reclaimed water is utilities because they are relatively inexpensive to build often depleted with respect to calcium, magnesium, and and do not require extensive maintenance (EPA, 2004). other common ions. As a result, minerals in the aqui- However, compared to other means of introducing fer may dissolve as the reclaimed water is recharged. water into the subsurface (e.g., direct injection, vadose Alternatively, elevated concentrations of certain ions wells) recharge basins take up more space. As a result, could lead to the formation of new mineral phases they are often impractical in dense urban settings. Fur- in aquifers. Over time, these processes can alter the thermore, spreading basins cannot be used in locations permeability of the aquifer or result in the release of with shallow water tables or where local geological toxic trace elements, such as arsenic and chromium. To conditions (e.g., impermeable zones close to the land prevent such changes, post-treatment processes are fre- surface) limit rates of water infiltration. quently employed before introducing reclaimed water In the United States, many of the pioneering ef- into an aquifer. However, the long-term responses of forts associated with aquifer recharge with reclaimed an aquifer to reclaimed water are not always completely water have occurred in Southern California. The first understood when a project is initiated. major recharge project was conducted by the County Sanitation Districts of Los Angeles County and the Surface Spreading Via Recharge Basins. S urface Water Replenishment District of Southern California spreading is a method of groundwater recharge in when they established a spreading basin in Whittier, which reclaimed water moves from the land surface to California, in 1962. The 570-acre (220-ha) complex the aquifer, usually through unsaturated surface soils. of spreading basins recharges a mix of reclaimed water, Generally, surface spreading is accomplished in large local stormwater runoff, and imported water to an bermed basins with sand or permeable soil above an aquifer that serves as a potable water supply for resi- unconfined aquifer where reclaimed water can percolate dents located as close as approximately 65 ft (20 m) into the subsurface (see Figure 2-5). This practice is downgradient of the spreading basins. On an annual also called soil aquifer treatment or rapid infiltration. basis, reclaimed water accounts for approximately 60 In terms of water quality and contaminant attenu- percent of the water recharged at this site. ation, the process of infiltration provides opportunities Surface spreading basins also are used to recharge water from an effluent-dominated river into a potable aquifer in a community located south of Los Angeles. Since 1933, the Orange County Water District has diverted water from the nearby Santa Ana River into a series of spreading basins in the city of Anaheim. At this location, Santa Ana River water typically con- sists of over 90 percent wastewater effluent from the upstream communities of the Inland Empire Region during the dry season (i.e., April through October). Prior to reaching the location where the water is di- verted, about half of the flow of the river passes through an engineered treatment wetland that has a hydraulic residence time of approximately 3 days (Lin et al., 2003). The remaining half of the dry season, Santa Ana River flow travels from the upstream advanced-treated FIGURE 2-5 Rapid infiltration basins at the Water CONSERV II wastewater effluent outfalls to the infiltration basins, in facility in Orlando, Florida, which recharged 31 MGD (120,000 m3/d) of reclaimed water in 2006. some cases with slightly less than 1-day transport time. SOURCE: Alley et al. (1999). R02129 Figure 2-14
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45 CURRENT STATE OF WATER REUSE After percolating through the soil, the water enters an BOX 2-11 aquifer that is used as the potable supply for a well field Orange County Water District, California located downgradient of the infiltration basins. Groundwater withdrawals make up about 70 percent of Subsurface Injection. Reclaimed water can also be the water supply in the Orange County Water District’s service directly injected into the subsurface to replenish an area, with the remaining demand being met by imported water aquifer. Direct injection usually requires more treat- from the Colorado River and Northern California. Histori- ment of wastewater effluent than is required for surface cally, imported water from the Colorado River and Northern California and water from the Santa Ana River have been the spreading because the injected water is pumped directly source waters for groundwater recharge in Orange County. into the aquifer without the benefit of soil aquifer treat- Seawater intrusion has been a problem since the 1930s as ment. A high level of treatment also is needed to reduce a consequence of groundwater basin overdraft. Injection of the potential for aquifer clogging. Direct injection can reclaimed water from an advanced wastewater treatment facil- occur via direct-injection wells, deep vadose zone wells ity (Water Factory 21) to form a seawater intrusion barrier in that discharge water into the unsaturated zone, or aqui- the Talbert Gap area of the groundwater basin began in 1976. The project served the dual purpose of seawater intrusion fer storage and recovery wells, which are designed for barrier and potable supply augmentation. Agency leaders both injection and withdrawal. acknowledged both of these purposes and did not encounter The first project in the United States that employed public opposition to the potable augmentation. direct injection of reclaimed water into a potable aqui- A recharge project called the Groundwater Replenishment fer started in Orange County, south of Los Angeles, in (GWR) System was conceived in the 1990s to replace Water 1976. The Orange County Water District’s Water Fac- Factory 21 and provide additional water to recharge the Orange County Groundwater Basin. The GWR System consists of three tory 21 facility employed a state-of-the-art treatment major components: the Advanced Water Purification Facility system for water reclamation prior to injection into a (AWPF); the Talbert Gap Seawater Intrusion Barrier; and the seawater intrusion barrier. Water Factory 21 injected Miller and Kraemer spreading basins. The AWPF began two-thirds reclaimed water and one-third groundwater, producing reclaimed water in January 2008 for injection at obtained from a deep aquifer, into the barrier. The sea- the Talbert Gap and spreading at Kraemer and Miller basins. water barrier was a potable water reuse project because The source water for the 70-MGD (260,000-m3/d) ad- vanced treatment facility is secondary effluent from the the water in the seawater intrusion barrier also flowed adjacent Orange County Sanitation District Plant No. 1. The toward nearby potable water supply wells. For example, AWPF provides further treatment by microfiltration, reverse water supply wells located approximately 0.3 mile (500 osmosis, and advanced oxidation. The treated water is stabi- m) from a seawater intrusion barrier in Orange County, lized by decarbonation and lime addition to raise the pH and California, exhibit chloride concentrations equal to add hardness and alkalinity to make the water less corrosive those of the water injected into the barrier (Fujita et and more stable. In 2009, production of reclaimed water averaged 54 MGD al., 1996), indicating that most of the water delivered (200,000 m3/d). Plans are under way to increase the capac- by these wells originated in the injection well. Subse- ity of the GWR System in phases, with an ultimate capacity quent to the success of Water Factory 21, the Orange of 130 MGD (490,000 m3/d). Half of the water produced by County Water District developed the new Groundwa- the advanced treatment plant is injected into the Talbert Gap ter Replenishment System, which expanded the utility’s Seawater Intrusion Barrier and half is pumped approximately potable reuse capacity from 16 MGD (61,000 m3/d) 13 miles (21 km) to the Kraemer and Miller basins in Ana- heim, which are deep spreading basins in the Orange County to 70 MGD (260,000 m3/d) in 2008 (see Box 2-11). Forebay area. The nearest downgradient extraction well is Other projects that use a combination of advanced more than 5,200 ft (1,580 m) from the percolation basins, and treatment processes similar to those practiced at Or- the retention time underground prior to extraction in excess ange County’s Groundwater Replenishment System of 6 months. have been built in Southern California and Arizona. The West Basin Water District’s Recycling Plant was SOURCES: Crook (2007); Alan Plummer Associates (2010). built near Los Angeles Airport in 1993. The project initially used deep wells to inject a mixture of equal volumes of reclaimed water and water imported from
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46 WATER REUSE the Colorado River into the West Coast Barrier (see traction wells, the peak concentrations of contaminants Figure 2-4). Projects in Scottsdale, Arizona, Los Ange- sometimes encountered in water supplied from rivers or les, and Denver were initiated in 1999, 2005, and 2009, lakes are moderated. In addition, physical and biologi- respectively. The Scottsdale and Los Angeles projects cal processes in the subsurface result in decreases in the employ reverse osmosis prior to groundwater injection concentrations of many contaminants as water flows whereas the Denver project applies reverse osmosis to toward the extraction wells (Sontheimer and Nissing, the abstracted groundwater. 1977; Sontheimer, 1980; Sontheimer, 1991; Kühn and In light of the trend to employ reverse osmosis Müller, 2000; Wang et al., 2002; Schmidt et al., 2004; prior to groundwater injection, it is noteworthy that the Hoppe-Jones et al., 2010). groundwater recharge project operated by El Paso Wa- Riverbank filtration has been used for public and ter Utilities since 1985 employs activated carbon and industrial water supply in Europe (Kühn and Müller, ozonation as barriers against waterborne pathogens and 2000; Grischek et al., 2002; Ray et al., 2002a,b) for chemical contaminants in a potable reuse project. By more than a century. Riverbank filtration has been avoiding the use of reverse osmosis, the El Paso facility practiced to a lesser extent in the United States for does not produce a brine waste that requires disposal. more than 50 years in communities along the Ohio, The reclaimed water produced by the advanced treat- Wabash, and Missouri Rivers (Weiss et al., 2002). In ment plant is injected into the aquifer, where it spends Europe, it provides 50 percent of potable supplies in the approximately 6 years underground before abstrac- Slovak Republic, 45 percent in Hungary, 16 percent in tion. According to estimates from the operators of the Germany, and 5 percent in The Netherlands (Hiscock system, reclaimed water accounts for approximately 1 and Grischek, 2002). For example, Berlin obtains ap- percent of the water abstracted in the nearest down- proximately 75 percent of its drinking water supply gradient wells (Ed Archuleta, El Paso Water Utilities from riverbank filtration of effluent-dominated rivers. Public Service Board, personal communication, 2010). Düsseldorf has been using riverbank filtration of an Given the rapid growth in population in com- effluent-impacted section of the Rhine River water as munities that do not have access to ocean outfalls for a potable water supply since 1870. brine disposal, projects such as the system in El Paso Site-specific factors can affect the performance of may become more common in the near future. For riverbank filtration systems (see Chapter 4 for addi- example, the 190-MGD (720,000-m3/d) potable re- tional discussion of treatment performance). As a result, use project initiated in Aurora, Colorado, near Denver riverbank filtration is mainly practiced in locations with (see Table 2-3) in 2010 employs advanced treatment the appropriate geological characteristics (e.g., high- after groundwater recharge and extraction, without permeability sediments located adjacent to a river). In reverse osmosis. In situations where salt removal is not addition, riverbed characteristics and operational con- required, similar projects may offer distinct advantages ditions (e.g., well type, pumping rates, travel time in the over reverse osmosis followed by direct injection. subsurface) are important factors affecting water yields and water quality. Although some of these factors can be influenced by engineering design, others depend on Riverbank Filtration the individual site and local hydrogeological conditions. Riverbank filtration is a process that has been In the context of water reclamation, riverbank used to treat surface waters that have been subject to filtration offers a means of improving the quality of contamination from upstream sources. During riv- effluent-dominated surface waters (e.g., systems in erbank filtration, aquifer sediments act as a natural which de facto reuse is practiced). The process also filter removing contaminants as river water recharges has the potential to serve as a means of attenuating groundwater. The hydraulic gradient driving the flow contaminants in planned potable reclamation systems. of water through the riverbank is often induced by However, additional research is needed to develop a pumping nearby water supply wells (Hiscock and better understanding of factors affecting the perfor- Grischek, 2002; Kim and Corpcioglu, 2002). Because mance of riverbank filtration systems. water follows different flow paths as it moves into ex-
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47 CURRENT STATE OF WATER REUSE Recent Trends with Respect to Environmental Buffers plant, energy consumption for the reclamation project is approximately equal to that of other available water As discussed previously, environmental buffers sources. were important features of potable water reuse projects While the surface water reservoir employed by the constructed in the United States between 1960 and Colorado River Water District or the blending pond 2009. Over the five decades, treatment technologies used by the Gwinett County Water Authority have have improved and their costs have decreased. In addi- characteristics of environmental buffers, a recently built tion, the continued success of an environmental-buffer- project in the community of Cloudcroft, New Mexico, free potable reuse project in Windhoek Namibia (see in which 0.1 MGD (380 m3/d) of reclaimed water is Box 2-12) has provided evidence that environmental blended with local spring water in a covered reservoir buffers are not always necessary in potable reuse proj- does not have many attributes normally associated with ects. As utilities have become more confident in their environmental buffers (see Box 2-13). This project ability to meet potable water standards and guidelines, was approved by the local community and underwent potable reuse projects have been proposed, designed, review without a requirement for an environmental and in several cases built in the United States without buffer. environmental buffers. The characteristics of an environmental buffer af- The increasing interest of utilities in operating fect the impacts on public acceptance and contaminant potable reuse projects without environmental buf- attenuation. For example, a wetland populated with fers is driven by a number of factors, including water healthy plants, birds, and fish is likely to be more ac- rights, lack of suitable buffers near the locations where ceptable to the public than a sandy-bottomed river with reclaimed water is produced, potential for contamina- steeply sloped concrete flood control levees. Likewise, tion of the reclaimed water when it is released into the percolation of reclaimed water through 16 ft (5 meters) environmental buffer, and costs associated with main- of soil followed by mixing with local groundwater tenance, operation, and monitoring of environmental and a year in the subsurface is more likely to result buffers. For example, recent controversies about water in contaminant attenuation than direct injection with rights in Lake Lanier, Georgia, could jeopardize the no dilution followed by days or weeks in an aquifer Gwinett County Water Authority’s rights to the re- consisting of fractured bedrock. Environmental buf- claimed water that it currently discharges to the lake. fers used in IPR projects fall along a continuum and As a result, it is considering the possibility of piping each should be judged within the context of the entire the reclaimed water directly to a blending pond that is water system. Manufactured water storage structures, not connected to the reservoir, thereby allowing them such as blending ponds or artificial aquifers, employed to maintain ownership of the water. Because the blend- in direct potable water reuse systems, can provide many ing pond would be a manmade structure that does not of the same benefits as natural environmental buffers, receive water from other sources, this potable reuse both in terms of public perception and contaminant project would not include an environmental buffer. attenuation. Another example of this trend is the potable reuse The direct connection of an advanced water recla- project being built by the Colorado River Municipal mation plant to a water distribution plant, without an Water District in Texas in which a series of water intermediate water storage structure for blending with reclamation plants will return reclaimed water directly water from other sources, would provide none of the to its drinking water reservoir (Sloan et al., 2010). The aforementioned benefits related to public acceptance or first of these projects, which is scheduled to begin op- contaminant attenuation. As a result, such structures erating in 2012, will deliver 2.5 MGD (9,500 m3/d) of are unlikely to be built in the near term. After the na- reclaimed water to its surface water reservoir through a tion has more experience with potable reuse systems transmission canal. In addition to decreasing the water that employ blending structures, decisions can be made district’s reliance on the Colorado River, the reuse of about the merits of direct “pipe-to-pipe” potable reuse water avoids the need to pump water up to the reservoir systems (see also Chapter 5 discussions on quality from water sources lower in the watershed. As a result, assurance). after including energy used by the advanced treatment
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48 WATER REUSE BOX 2-12 Windhoek, Namibia, Potable Reuse System The Windhoek, Namibia, advanced wastewater treatment plant returns reclaimed water directly to the city’s drinking water system. The aver- age rainfall is 14.4 inches (37 cm) while the annual evaporation is 136 inches (345 cm), and this city of 250,000 people relies on three surface reservoirs for 70 percent of its water supply. First implemented in 1968 with an initial flow of 1.3 MGD (4,900 m3/d; Haarhof and Van der Merwe, 1996), the Goreangab water reclamation plant, which receives secondary effluent from the Gammans wastewater treatment plant, has been upgraded through the years to its current capacity of 5.5 MGD (21,000 m3/d). Industrial and potentially toxic wastewater is diverted from the wastewater entering the plant. There have been four distinct treatment process configurations since 1968. The current treatment train was placed in operation in 2002 and includes the following processes: • Primary sedimentation • Activated sludge secondary treatment with nutrient removal • Maturation ponds (4 days) • Powdered activated carbon, acid, polymers (used when required) • Preozonation • Coagulation/flocculation with ferric chloride (FeCl3) • Dissolved air flotation • Rapid sand/anthracite filtration preceded by potassium permanganate (KMnO4) and sodium hydroxide (NaOH) addition • Ozonation preceded by hydrogen peroxide (H2O2) addition • Biological and granular activated carbon • Ultrafiltration (0.035-micrometer [μm] pore size) • Chlorination • Stabilization with NaOH • Blending prior to distribution Blending occurs at two locations. The first blending takes place at the Goreangab water treatment plant, where reclaimed water is blended with conventionally treated surface water. This mixture is then blended with treated water from other sources prior to pumping to the distribution system. Prior to recent upgrades in 1991 the percentage of reclaimed water in the drinking water averaged 4 percent (Odendaal et al., 1998). Following the plant upgrades, reclaimed water represents up to 35 percent of the drinking water supply during normal periods, and as much as 50 percent when water supplies are limited (Lahnsteiner and Lempert, 2005; du Pisani, 2005). Extensive microbial and chemical monitoring is performed on the product water, with continuous monitoring of several constituents. Both in vitro and in vivo toxicological testing has been conducted on product water from the Goreangab treatment plant (such as Ames test, urease enzyme activity, bacterial growth inhibition, water flea lethality, and fish biomonitoring). An epidemiological study (1976 to 1983) was also conducted, which found no relationships between cases of diarrheal diseases, jaundice, or deaths to drinking water source (Isaacson and Sayed, 1988; Odendaal et al., 1998; Law, 2003). However, a prior NRC committee concluded that because of limitations in the Windhoek epidemiological studies and its “unique environment and demographics, these results cannot be extrapolated to other populations in industrialized countries” (NRC, 1998). There was some initial public opposition to the Windhoek project, but over time, opposition has faded, and no public opposition to the project has emerged in recent years. United States EXTENT OF WATER REUSE The current extent of reuse is summarized in the Statistics on the extent of water reuse in the United following section, focusing on the United States, with States remain somewhat limited. Every 5 years, the additional information on other countries with large USGS releases data on U.S. water use, and for 1995, reuse initiatives. Available reuse data, however, are the last year for which reclaimed water use data were sparse, and most of the figures cited below should be included, 1,057 MGD (4 million m3/d) of wastewater considered estimates. was reused. This amount represented approximately
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49 CURRENT STATE OF WATER REUSE estimated that water reuse was growing at a rate of 15 BOX 2-13 percent per year. Potable Reuse in Cloudcroft, New Mexico As of 2002, EPA estimated that Florida reused the largest quantities of reclaimed water, followed by The village of Cloudcroft, New Mexico, is a mountain California, Texas, and Arizona. At that time, these four community at 8,600-ft (220-m) elevation with a permanent states accounted for the majority of the nation’s water population of 750. As a winter resort community, population reuse, although EPA reported that at least 27 states had can increase during holidays and weekends to more than water reclamation facilities as of 2004, with growing 2,000 with a peak demand of 0.36 MGD (1,400 m3/d). Recent drought conditions had resulted in a reduction of spring flows programs in Nevada, Colorado, Washington, Virginia, and groundwater tables. Because of limited local supplies and and Georgia (EPA, 2004). Three of the four states Cloudcroft’s elevation, which limit use of water sources from with the largest reclaimed water use are located in the outside the community, the village decided to reuse their local arid southwest where population growth and climate wastewater to augment their drinking water supply. In 2009, variability have created recent water supply challenges. an advanced water treatment plant with a capacity of 0.10 Water reuse in these states has become commonplace MGD (380 m3/d) was established to treat the community’s wastewater and blend it with natural spring and well water (up as a means to expand the water supply portfolio and to 50 percent wastewater) prior to consumption. provide an additional drought-resistant supply. Florida The wastewater generated in the community is treated by a originally launched its water reuse program to address membrane bioreactor. After disinfection using chloramination, nutrient pollution concerns in its streams, lakes, and the filtered effluent is treated by reverse osmosis followed by estuaries, but increasingly, new projects are being con- advanced oxidation (ultraviolet radiation/hydrogen peroxide). sidered for their water supply benefits as well. The ultrafiltration and reverse osmosis units are located away from the membrane bioreactor at a lower elevation, allowing The end uses of reclaimed water are not well docu- gravity feed to the reverse osmosis units. The plant effluent mented on a national scale. The WateReuse Founda- is subsequently blended with other source water from local tion is working on a national database of reuse facilities springs and wells in a covered reservoir that provides a reten- that could help address this data gap, although as of tion time of 40 to 60 days. The blended water is then treated early 2011, the database was still being refined. Some by ultrafiltration followed by ultraviolet radiation and granular states have additional inventory data, described below, activated carbon prior to final disinfection. The reverse os- mosis concentrate with a TDS concentration of approximately that reflect the varied uses of reclaimed water across 2,000 mg/L is currently blended with membrane bioreactor different states. filtrate and held in storage ponds for use in snow making, irrigation of the ski area, and dust control. The operations and maintenance cost for the production of this water was $2.40/ Florida kgal ($0.63/m3) during its first year of operation. The state of Florida conducts a comprehensive The community provided input through public meetings, and the state regulator has approved the project. inventory of water reuse each year and reports that approximately 659 MGD (2.5 million m3/day) of SOURCE: Livingston (2008). wastewater was reused for beneficial purposes in 2010 (FDEP, 2011). Over half of Florida’s reclaimed water is used for public access irrigation, with additional uses in agricultural irrigation, groundwater recharge, and industrial applications (Figure 2-6). In Florida, groundwater recharge consists largely of rapid infiltra- 2 percent of wastewater discharged and less than 0.3 tion basins and absorption field systems that are not percent of total water use in 1995 (Solley et al., 1998).5 specifically designated as indirect potable reuse projects. In the 2004 EPA Guidelines for Water Reuse (EPA, In several Florida counties, nonpotable reuse accounts 2004), total water reuse in the United States was es- for 30–60 percent of the freshwater supplied for public timated at 1,690 MGD (6.4 million m3/d), and they water supply, industry, agriculture, and power genera- tion (FDEP, 2006; Marella, 2009). 5 Solleyet al. (1998) reported that in the United States, 155 × 106 m3/d of treated water were discharged in 1995, and total water use was approximately 1.5 × 109 m3/d.
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50 WATER REUSE International Reuse Other 7% Industrial Crook et al. (2005) and Jiménez and Asano (2008) 13% recently reviewed international reuse practices. Ac- cording to their findings, major water reuse facilities are in place in at least 43 countries around the world, including Egypt, Spain, Syria, Israel, and Singapore. Landscape Groundwater Irrigation Recharge Based on the statistics given by Jiménez and Asano, 55% 14% approximately 13 BGD (50 million m3/d) of waste- water are reused worldwide. The authors identified 47 countries that engaged in reuse. Of these, 12 engaged in reuse of untreated municipal effluent, 7 engaged in Agricultural Irrigation the reuse of both treated and untreated effluent, and 11% 34 reuse wastewater only after treatment. Of the total volume, 7.7 BGD (29 million m3/d) or 58 percent was FIGURE 2-6 Water reuse in the state of Florida as of 2010, by flow volume and by application. untreated (raw) sewage used for irrigation, mostly in SOURCE: Data from FDEP (2011). China and Mexico (see Figure 2-8). Jiménez and Asano (2008) reported that 5.5 BGD (21 million m3/d) of treated municipal wastewater was California reused globally in 43 countries. The United States was The California State Water Resources Control first among them in total volume of water reused (see Board reported 646 MGD (2.44 million m3/day) of Figure 2-9). Although the United States reused the water reuse in California in 2009.6 California’s end largest volume of treated wastewater, per capita water uses, depicted in Figure 2-7, appear more diverse than F lorida’s, including recreational impoundments and geothermal energy. In general, agricultural irrigation makes up a larger percentage of water reuse in Califor- nia compared with Florida, while landscape irrigation Recreational and industrial reuse represent smaller portions of the Impoundment Landscape 7% Habitat overall portfolio. Both states have comparable extents Irrigation 4% 18% of reuse in the area of groundwater recharge (including Groundwater seawater intrusion barriers in California). Neverthe- Recharge (incl. seawater intr. less, the California data include a large percentage (20 barriers) percent) of unclassified (“other”) reuse applications that 13% may affect these comparisons. Texas Agriculture Other 29% 20% A recent report for the Texas Water Development Board estimated 320 MGD (1.2 million m3/day) of water reuse in Texas in 2010 (Alan Plummer Associ- Geothermal Industrial 2% ates, 2010). No additional details are provided on how 7% this reclaimed water is used. FIGURE 2-7 Water reuse in the state of California as of 2009, by flow volume and application. SOURCE: Data from California Environmental Protection Agen- cy http://www.waterboards.ca.gov/water_issues/programs/ 6 S ee http://www.waterboards.ca.gov/water_issues/programs/ grants_loans/water_recycling/munirec.shtml. grants_loans/water_recycling/munirec.shtml.
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51 CURRENT STATE OF WATER REUSE Although statistics on international reuse prac- Peru All others Chile 0.2 0.5 tice provide insight into global trends, it should be 0.5 recognized that local history, geography, and cultural influences have played an important role in the types of reuse practices pursued in different countries. To illustrate these differences, Israel, Australia, and Sin- gapore are considered here—three leading practitioners China of reuse where differences in climate, population den- 14.1 sity, water resources, and history have led to different outcomes with respect to water reuse. Reuse practices Mexico 13.6 in other developed countries follow similar patterns. However, the acute need for water in these three coun- tries has led them to embrace innovative water resource management approaches that are particularly relevant to the consideration of reuse in the United States. FIGURE 2-8 Countries with the most reuse of untreated waste- water in millions of cubic meters per day. SOURCE: Data from Jiménez and Asano (2008). Israel Since the time of its founding in 1948, Israel has reuse in the United States ranked 13th globally. In at relied upon agricultural water reuse as part of its water least five countries—Kuwait, Israel, Qatar, Singapore, supply portfolio. Initially, wastewater from urban areas and Cyprus—water reuse represented more than 10 was used directly for irrigation. In recognition of po- percent of the nation’s total water extraction ( Jiménez tential health risks associated with this practice, Israel’s and Asano, 2008). 8 Global Reuse of Treated Treated Wastewater Use 7 Wastewater = 21 million m3/d 6 (million m3/d) 5 4 3 2 1 0 FIGURE 2-9 Countries with the greatest volume of water reuse using treated wastewater. SOURCE: Data from Jiménez and Asano (2008).
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52 WATER REUSE nonpotable reuse practices were upgraded through United States. After the drought ended, the projects in the construction of wastewater treatment plants and Brisbane and Canberra were put on hold. groundwater recharge basins near agricultural areas. Today, approximately 75 percent of Israel’s wastewater Singapore is reused, with almost all of it going for agricultural irrigation. This outcome was likely affected by several The high population density, near absence of ag- factors. First, Israel’s arid climate and sparse water re- ricultural water demand, and heavy reliance on water sources have made the public aware of the need to use imported from a neighboring country has led to a water efficiently. Second, the relatively high population different outcome for water reuse in Singapore. In par- density and proximity of the country’s cities to its farms ticular, early recognition that the country’s population makes it efficient to reuse municipal wastewater for growth would soon outstrip its local water resources led agricultural irrigation. Finally, Israel’s concerns about Singapore to pursue an approach that they refer to as food security and uncertainty associated with its water the “four taps”: (1) local runoff, (2) imported water from resources have made agricultural reuse a national prior- Malaysia, (3) desalinated seawater, and (4) reclaimed ity (Shaviv, 2009). water. As a result of its frequent rain and high popula- tion density, there is little irrigation water demand for reclaimed water. Instead, the country’s water reuse pro- Australia gram has focused on industrial and potable reuse. Given Like Israelis, Australians are highly aware of their Singapore’s access to seawater for cooling purposes and nation’s limited water resources. However, Australia’s its growing high-tech industry, the Public Utilities population density is much lower, and much of its Board recognized the need for high-quality reclaimed agricultural activity occurs far from urban centers (e.g., water. The resulting advanced water treatment system most of the farming in the Murray-Darling Basin (see Box 2-14) delivers reclaimed water to industrial us- takes place hundreds of miles from coastal cities). As a ers and local reservoirs. As was the case in Brisbane and result, agricultural reuse has not played a major role in Canberra, groundwater recharge or aquifer storage and the country’s water reuse planning process. In contrast, recovery were not viable options because of Singapore’s nonpotable reuse projects, such as landscape irrigation local geology and geography. and industrial reuse, are quite popular, as epitomized by Sydney’s high-profile reuse project at the facility built as CONCLUSIONS AND RECOMMENDATIONS part of the Olympic Park for the games in 2000. Cur- rently, approximately 10 percent of the water used in Water reuse is a common practice in the United Australia’s mainland capital cities is reused, mainly for States with numerous approaches available for reus- landscaping and industrial applications. Until recently, ing wastewater effluent to provide water for industry, potable water reuse was not considered a viable option agriculture, and potable supplies. However, there are by most water managers in Australia, but the extreme considerable differences among the approaches em- drought that lasted from 2003 to 2009 coupled with ployed for water reuse with respect to costs, public ac- high rates of urban population growth forced several of ceptance, and potential for meeting the nation’s future Australia’s biggest cities to reconsider (Radcliffe, 2010). water needs. At the height of the drought, Brisbane (C. Rodriguez Water reclamation for nonpotable applications is et al., 2009), Canberra (Radcliffe, 2008), and Perth (C. well established, with system designs and treatment Rodriguez et al., 2009) were all considering potable technologies that are generally accepted by communi- water reuse projects. A distinctive aspect of the planned ties, practitioners, and regulatory authorities. Non- water reuse projects in Brisbane and Canberra was potable reuse currently accounts for a small part of blending of reclaimed water directly in drinking water the nation’s total water use, but in a few communities reservoirs—a practice that deviated from the estab- (e.g., several Florida cities), nonpotable water reuse ac- lished soil aquifer treatment and groundwater injection counts for a substantial portion of total water use. New projects that had been pioneered in the southwestern developments and growing communities provide op-
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53 CURRENT STATE OF WATER REUSE BOX 2-14 Singapore Public Utilities Board NEWater Project, Republic of Singapore The Republic of Singapore has a population of about 5 million people. Although rainfall averages 98 inches (250 cm) per year, Singapore has limited natural water resources because of its small size of approximately 270 square miles (700 km2). Reclaimed water (referred to by the local utility as NEWater; see figure below) is an important element of Singapore’s water supply portfolio. Currently, there are five NEWater treatment plants in operation, all of which include nearly identical treatment processes. Feedwater to the treatment plants is activated sludge secondary effluent. The advanced water treatment processes included microscreening (0.3-mm screens), microfiltration (0.2-mm nominal pore size) or ultrafiltration, reverse osmosis, and ultraviolet disinfection. Chlorine is added before and after microfiltration to control membrane biofouling. The reclaimed water is either supplied directly to industry for nonpotable uses or discharged to surface water reservoirs, where the water is blended with captured rainwater and imported raw water. The blended water is subsequently treated in a conventional water treatment plant of coagulation, flocculation, sand filters, ozonation, and disinfection prior to distribution as potable water. The NEWater factories all produce high-quality product water with turbidity less than 0.5 nephelometric turbidity units; TDS less than 50 mg/L; and total organic carbon less than 0.5 mg/L. The water meets all Environmental Protection Agency and World Health Organization drinking water standards and guidelines. Additional constituents monitored include many organic compounds, pesticides, herbicides, endocrine-disrupting com - pounds, pharmaceuticals, and unregulated compounds. None of these constituents have been found in the treated water at health-significant levels. The NEWater facilities at the Bedok and Kranji went into service in 2003 and have since been expanded to their current capacities of 18 MGD and 17 MGD (68,000 and 64,000 m3/d), respectively. A third NEWater factory at the Seletar Water Reclamation Plant was placed in service in 2004 and has a capacity of 5 MGD (19,000 m3/d). The fourth NEWwater factory (Ulu Pandan) has a capacity of 32 MGD (121,000 m3/d) and went into operation in 2007. A fifth facility, the Changi NEWater Factory, is being commissioned in two stages: the first 15 MGD (57,000 m3/d) phase was commissioned in 2009, with an additional 35 MGD (130,000 m3/d) phase to be commissioned in 2010. Once completed, these five plants will have a combined capacity of 122 MGD (462,000 m3/d). Schematic of the Singapore NEWater system. SOURCE: Ong and Seah, 2003. Most of the reclaimed water from the NEWater Factories is supplied directly to industries. These industries include wafer fabrication, electron- ics and power generation for process use, as well as commercial and institutional complexes for air-conditioning cooling purposes. Less than 10 MGD (38,000 m3/d) of NEWater currently is used for potable reuse via discharge to raw water reservoirs, accounting for slightly more than 2 R02129 percent of the total raw water supply in the reservoirs. However, the contribution of NEWater to the potable water supply is expected to increase Figure 2-19 in the coming decades. bitmapped The capital costs for all of the NEWater factories averaged about $6.03/kgal per year capacity (or $1.59/m3 per year). Annual operation and maintenance costs for the water are about $0.98/kgal ($0.26/m3) produced. The Public Utilities Board charges industries and others $2.68/kgal ($0.71/m3) for NEWater on a full cost recovery approach. This includes the capital cost, production cost, and transmission and distribution cost. SOURCE: A. Conroy, Singapore Public Utilities Board, personal communication, 2010.
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54 WATER REUSE portunities to expand nonpotable water reuse because health agencies understand the extent and importance it is more cost-effective to install separate nonpotable of de facto water reuse. Furthermore, an analysis of de water distribution systems at the same time the pri- facto potable reuse may spur the additional develop- mary drinking water distribution system is installed. In ment of contaminant prediction tools and improved existing communities nonpotable water reuse is often site-specific monitoring programs for the betterment restricted by the high costs associated with constructing of public health. USGS and EPA have the necessary the distribution system and retrofitting existing plumb- data and expertise to conduct this analysis on large ing (see also Chapter 9). watersheds that serve as water supplies for multiple The use of reclaimed water to augment potable states. For smaller watersheds or watersheds with exist- water supplies has significant potential for helping to ing monitoring networks, state and local agencies may meet the nation’s future needs, but potable water reuse have additional data to contribute to these analyses. Environmental buffers can play an important projects only account for a relatively small fraction of role in improving water quality and ensuring public the volume of water currently being reused. However, acceptance of potable water reuse projects, but the potable reuse becomes more significant to the nation’s historical distinction between direct and indirect current water supply portfolio if de facto or unplanned water reuse is included. T he de facto reuse of waste- water reuse is not meaningful to the assessment of water effluent as a water supply is common in many the quality of water delivered to consumers. Potable of the nation’s water systems, with some drinking reuse projects built in the United States between 1960 water treatment plants using waters from which a and 2010 employed environmental buffers in response large fraction originated as wastewater effluent from to concerns about public health risks and the possibil- upstream communities, especially under low-flow ity of adverse public reaction to potable water reuse. In conditions. the last few years, a potable reuse project was built and An analysis of the extent of de facto potable another is being built without environmental buffers, water reuse should be conducted to quantify the and the trend toward operating potable reuse projects number of people currently exposed to wastewa- without buffers is likely to continue in the future. An ter contaminants and their likely concentrations. environmental buffer should be considered as one of Despite the growing importance of de facto reuse, a several design features that can be used to ensure safe systematic analysis of the extent of effluent contribu- and reliable operation of potable reuse systems. As a re- tions to potable water supplies has not been made in sult, they need to be designed, evaluated, and monitored the United States for over 30 years. Available tools and like other elements of the water treatment and delivery data sources maintained by federal agencies would en- system. See Chapters 4 and 5 for additional details on able this to be done with better precision, and such an the treatment effectiveness of environmental buffers analysis would help water resource planners and public and their role in quality assurance.