in water reuse, including 15 years with the California Department of Health Services. .... Bakersfield, California, has used its effluent for irrigation since 1912.
April I O , 1996 The Friday Center Chapel Hill, North Carolina Sponsored by North Carolina A W A / WEF
James Cmok
Biographical Information
James Crook is an internationally-recognized expert in the area of water reclamation and reuse. He is the Director of Water Reuse for the firm of Black & Veatch. Dr. Crook received his B.S. degree in civil engineering from the University of Massachusetts and his M.S. and Ph.D. degrees in environmental engineering from the University of Cincinnati. He has 24 years of experience in water reuse, including 15 years with the California Department of Health Services. Dr. Crook has authored more than 60 articles and technical papers. He was the principal author of water reuse guidelines published by the U.S. Environmental Protection Agency and a water reuse assessment report published by the Water Environment Research Foundation.
Dr. Crook is a member of AAEE, ASCE, AWWA, IAWQ, and WEF. He currently is Chairman of the WEF Water Reuse Committee and is a member of the AWWA Water Reuse Committee and the IAWQ Water Reuse Group. He also serves on the National Research Council Committee on the Evaluation of the Viability of Augmenting Potable Water Supplies with Reclaimed Water, the National Water Research Institute Research Advisory Board, the Santa Ana River Health Effects Committee, and the Florida Department of Environmental Protection Reuse Rule Technical Advisory Committee. Dr. Crook has been an advisor to the National Sanitation Foundation, Pan American Health Organization, United Nations Development Programme, and U.S. Agency for International Development. He is a certified as a Diplomate by the AAEE and a Grade 5 Water Treatment Plant Operator in California and is a Registered Professional Engineer in California and Florida.
WATER REUSE EXPERIENCE IN THE U.S. James Crook Black & Veatch 100 Cambridgepark Drive Cambridge, MA 02140
Introduction Water reclamation and reuse is well-established in the United States. While many of the early projects were implemented as a least-cost means of wastewater disposal, water reuse is now recognized as an important integral component of water resources management in many parts of the country. As droughts and population increases continue to stress the availability of fresh water supplies, reuse of municipal wastewater will play an ever-increasing role in helping to meet water demands. Reclaimed water is used for many purposes, ranging frem pasture irrigation to augmentation of potable water supplies. Although many regulatory agencies do not advocate the use of reclaimed water for potable purposes, indirect potable reuse via groundwater recharge and surface water augmentation is occurring and will likely increase in the future. Depending on the intended use of reclaimed water, considerations may include health protection, user water quality and quantity requirements, irrigation effects, environmental effects, aesthetics, and public anqor user perception of the reuse concept. Making reclaimed water suitable and safe for reuse applications is achieved by eliminating or reducing the concentrations of pathogenic microorganisms and chemical constituents of concern through wastewater treatment and/or by limiting public or worker exposure to the water via design and operational controls. The impacts or constraints on nonpotable reuse from physical parameters, e.g., pH, color, temperature, and particulate matter, and chemical constituents, e.g., chlorides, sodium, heavy metals, and some trace organic compounds, are well known and recommended limits have been established for many of them (National Academy of Sciences-National Academy of Engineering, 1973; U.S. Environmental Protection Agency, 1981; Westcot and Ayers, 1985; Water Pollution Control Federation, 198%U.S.Environmental Protection Agency, 1992). The health risks associated with pathogenic "organisms are more difficult to assess. Indirect potable reuse presents additional concerns regarding the fate and long-term health effects of contaminants in reclaimed water. Historical Perspective
Sewage farms were established in several parts of the United States in the late 1800's, where they served as a popular land -sal method. By 1904, there were about 14 sewage farms in the U.S., serving a population of about 200,000 (Fuller, 1912). Early municipal sewage irrigation projects near Chicago and Los Angeles were abandoned due, among other reasons, to rapid growth of the cities in the direction of sewage-irrigated lands. Solids and grease in the raw sewage tended to create nuisances, and increased sewage flows resulted in over-application of the sewage causing anaerobic soil conditions. Odor problems and public health concerns, particularly the possible transmission of disease from vegetable crops irrigated with untreated sewage, were largely responsible for the decline of sewage farming. -1-
The advent of biological treatment processes that require much less land accelerated the decline of sewage farms in the U.S. Diversity in the types of water reuse developed along with technology advances in wastewater treatment.
Not all of the early projects were developed out of a necessity to meet water shortages. Some were developed to take advantage of the wastewater as a resource that was available a t a reasonable cost or as a least-cost means of disposal. Historically, the largest-volume uses of reclaimed water were for those that do not require a high quality effluent, e.g,, pasture irrigation, and were often perceived as a method of wastewater disposal. Reclaimed water is now perceived as a resource, and, in conjunction with advances in wastewater treatment technology, the trend has shifted toward higher level uses, e.g., urban irrigation, toilet flushing, industrial uses, and groundwater recharge. Status of %use
Reclaimed water has been used successfully for many purposes, including all types of agricultural and landscape irrigation, toilet and urinal flushing, industrial cooling and process water, groundwater recharge, chiller water in commercial air conditioning systems, vehicle washing, fire protection, street cleaning, recreational impoundments, and decorative ponds and fountains. Table 1 lists water reuse applications currently practiced in the U.S. Agricultural irrigation water and cooling water for thermoelectric power generation each represent about 40 percent of the keshwater used in the U.S. (van der Leeden et al., 1991). The use of reclaimed water for agricultural irrigation and cooling provides significant opportunities for reuse, particularly at sites near urban areas where large volumes of reclaimed water are generated. Although commercial and domestic water use constitutes only about 10 percent of the total water demand, water reuse is more Likely to be cost-effective in or near urban areas where reclaimed water is used to conserve or replace potable water for various applications. Although most of ,the water reuse projects in the U.S. currently are located in the southeast (Florida), southwest (Texas and New Mexico) and west (Arizona, California, and Nevada), diminishing potable water supply sources and increasingly stringent requirements for wastewater discharges to surface waters has made water reuse an attractive alternative in other parts of the country. Advanced wastewater treatment (AWT) processes necessary to achieve water quality goals are not needed to produce reclaimed water for many uses, thus making water reuse an economically viable option. While up-to-date statistical information on water reuse in the U.S. has not been compiled, it has been estimated that the use of reclaimed water approached 5.7 x lo6 cubic metedday (m3/d) (1.5 billion gallodday) in 1990 (Crook, 1992). An average of approximately 930,000 m3/d [ B O million gallons/day (mgd)] of municipal wastewater was reclaimed in California in 1987, representing about 12 percent of the total wastewater produced in the state. Sixtythree percent of the reclaimed water was used for agricultural irrigation, 14 percent for groundwater recharge, 13 percent for landscape irrigation, and 10 percent for industrial and other uses (California State Water Resources Control Board, 1990).
In Florida, 1.1x lo6m3/d (290 mgd), or about 30 percent of the state's municipal wastewater, was reused in 1992. Thirty-eight percent of the reclaimed water was used for landscape irrigation, 30 percent for agricultural irrigation, 14 percent for groundwater recharge, and 18 percent for industrial purposes, environmental enhancement, and other uses (Florida -2-
Department of Ehvironmental Regulation, 1992). Other water-short states also use large quantities of reclaimed water. For example, Arizona reuses about 35 percent of the municipal wastewater produced in the state, and Nevada reclaims more than 85 percent of its wastewater for agricultural and landscape irrigation, industrial uses, and environmental enhancement (WateReuse Association of California, 1993).
Examples of Reuse in the U.S.
Agricultural Irrigation In many parts of the US.,the demand for irrigation water is nearing or exceeds the supply of freshwater supplies. Reclaimed water provides a constant and reliable source of water, even during drought conditions. Agricultural irrigation currently represents the largest use of reclaimed water. In California alone, almost 570,000 m3/d (150 mgd) of reclaimed water is used for agricultural purposes at over 200 sites (California State Water Resources Control Board, 1990). Because agricultural irrigation with reclaimed water has a long history, the technology and suitability of the practice are relatively well understood. The chemical composition of reclaimed water that has received secondary or higher levels of treatment, although highly variable, normally meets existing guidelines for irrigation water (National Research Council, 1996). Regulatory controls directed at assuring an adequate level of health protection address reclaimed water treatment and quality, method of irrigation, type of crops to be irrigated, and operation and management of the distribution system and use area. The nitrogen, phosphorus, and potassium in reclaimed waters provide valuable nutrients to plants that would otherwise have to be provided by the use of fertilizers and can result in considerable cost savings. In Florida, the value of the nitrogen, phosphorus, and potassium in reclaimed water is about $0.03 to $0.04 per m3 ($0.11 to $0.13 per 1,OOO gallons) (Baldwin and Comer, 1986). The cost of reclaimed water is often less than the real cost of subsidized agricultural irrigation water or the cost of potable water used for irrigation. There are numerous examples of successful agricultural irrigation projects in the U.S. Bakersfield, California, has used its effluent for irrigation since 1912. During the early years, first raw sewage and then primary effluent was used for irrigation. Approximately 2,200 hectares (ha) [5,100 acres (ac)] of corn, alfalfa, cotton, barley, and sugar beets are irrigated with more than 64,OOO m3/d (17 mgd) of primary and secondary effluent from three treatment plants (Boyle Engineering Corporation, 1981). With the exception of cotton, crop yields exceed the county averages without the addition of supplemental fertilizer. The cotton yields have been lower than normal because the high nitrogen content of the wastewater directed growth to the plant rather than to the cotton bolls. To solve that problem, the cotton crop is irrigated with wastewater only early in the growing season, and well or canal water is used during the setting of the bolls. The long-term application a t Bakersfield has resulted in changes in soil chemical properties. There are increased concentrations of surface adsorbed and/or precipitated heavy metals in the soil surface, although only zinc and lead levels are markedly different from those in soils irrigated with well water. Concentrations of extractable phosphorus have increased markedly throughout the soil profile. The City of Tallahassee, Florida, has been using reclaimed water for irrigation since 1966. About 68,000 m3/d (18 mgd) of secondary effluent produced by the city's Thomas P. Smith Wastewater Renovation Plant is pumped approximately 13.7 kilometers (km) (8.5 miles) and distributed via 13 center-pivot irrigation units to about 700 ha (1,750 ac). The activated sludge effluent meets water quality requirements of 20 mg/L biochemical oxygen demand
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(BOD) and total suspended solids ("SS) and 200 fecal coliform organisms per 100 mL (payne et al., 1989). The major crops produced include corn, soybeans, coastal Bermuda grass, and rye. Corn is stored as high-moisture grain prior to sale, and soybeans are sold upon harvest. Both the rye and Bermuda grass are grazed by cattle. harvested as hay.
Some of the Bermuda grass is
In Orange County, Florida, a project known as WATER CONSERV I1 has been supplying reclaimed water for citrus irrigation and groundwater recharge through rapid infiltration basins (RIBS)since 1986. The project is jointly owned by the City of Orlando and Orange County. M a i m e d water h m the City's McLRod Water Reclamation Plant and the County's South Water Reclamation Facility are sent via a 34-km (21-mi) transmission pipeline to a distribution center, from which 70 percent of the water is sent through a 69-km (46-mi) distribution network serving 71 agricultural and commercial customers; the remaining 30 percent is sent to 4 RIB sites (Cross et al., 1996). Daily flows to the distribution center average 102,000 m3/d (27 mgd). Because the reclaimed water is provided to citrus growers free of charge, the growers have been able to irrigate at proper agronomic rates and have realized increased crop yields of 10 to 30 percent. Environmental benefits include eliminating surface water dischruges, reducing groundwater withdrawals, accelerating recharge of the Floridan aquifer, and establishing a preserve within the RIB sites for endangered and threatened species of plants and animals. Trickling filter effluent fi-om the City of Lubbock, Texas, has been used to irrigate approximately 1,200 ha (3,000 ac) of cotton, grain sorghum, and wheat on a local farm since 1938 (George et al., 1985). The use of reclaimed water has reportedly increased crop yields without commercial fertilizer and has improved soil conditions. Increasing flows through the years eventually led to hydraulic overloading at the farm, which was remedied by expanding the system in 1982 by an additional 1,000 ha (2,700 ac) at another site, allowing a total of 57,000 m3/d (15 mgd) of reclaimed water to be used for agricultural purposes (Schoening and Pohren, 1992).
A 7-year agricultural reuse demonstration study conducted at Castroville, California, and completed in 1987, determined that filtered, secondary effluent meeting a total coliform limit of 2.YlOO mL was acceptable for the spray irrigation of food crops eaten raw (Engineering-Science, 1987). During the study no pathogenic organisms were detected in the reclaimed water, and spray irrigation with reclaimed water did not adversely affect soil permeability, did not result in heavy metal accumulation in the soil or plant tissue, and did not adversely affect crop yield, quality, or shelf life. As a result of this study, an 110,000m3/d (30-mgd) wastewater reclamation plant is under construction, with the intent of utilizing the effluent for crop irrigation in the Salinas Valley.
Landscape Irrigation Landscape irrigation involves the spray irrigation of golf courses, parks, cemeteries, school grounds, fi-eeway medians, residential lawns, and similar areas. The concern for microorganisms is somewhat different than for agricultural irrigation in that landscape irrigation frequently takes place in urban areas where control over the use of the reclaimed water is more critical. The chemical composition of the irrigation water is not usually limiting. Depending on the area being irrigated, its location relative to populated areas, and the extent of public access or use of the grounds, the microbiological requirements and operational controls placed on the system may differ. Irrigation of areas not subject to public access have limited potential for creating public health problems, whereas microbiological -4-
requirements generally increase as the expected level of human contact with the reclaimed water increases. Golden Gate Park in San Francisco, California, was the first site in the U.S. to use reclaimed water for landscape irrigation and has been using disinfected, activated sludge effluent periodically since 1932. Approximately 4,000 m3/d (1 mgd) is discharged to ornamental lakes where it is mixed with well water and subsequently used to supply about 25 percent of the park water needs for horticultural purposes. The reclaimed water is low in solids and oxygen-consuming substances. It contains 40-60 mg/L of total nitrogen and an appreciable amount of phosphate, making it desirable for general irrigation when mixed with fresh water. Landscape irrigation with reclaimed water is well-accepted and widely practiced in the U.S. Secondary or tertiary effluent is used to irrigate more than 500 landscape irrigation sites in California and Florida alone. The sites include golf courses, parks, school grounds, cemeteries, freeway landscapes, and other open green space.
Dual system8 Increasing use of reclaimed water in urban areas has resulted in the development of several large dual water systems that distribute two grades of water to the same service area - one potable and the other nonpotable reclaimed water. A dual water system can provide water for most of the uses listed in Table 1. Many of these applications are currently part of dual systems in the U.S. Dual water systems that make reclaimed water available throughout a community for irrigation and other uses where significant portions of the population will be exposed to the reclaimed water should be microbiologically safe such that inadvertent contact o r ingestion does not constitute a health hazard. Chemical -constituents in tertiary-treated effluent are generally not a problem for most types of nonpotable urban reuse, but, if necessary, can be removed by specific advanced wastewater treatment unit processes. The American Water Works Association has published guidelines for the design and operation of dual water systems (American Water Works Association, 1994). Important considerations include identification of reclaimed water lines and appurtenances by color-coding and labeling, cross-connection control, reclaimed water quality, monitoring, storage, distribution system design and construction, use area controls, and management.
h areas where local governments have imposed sewer moratoriums o r sewer-capacity restrictions, onsite wastewater reclamation and recycling systems have been used successfully in schools and office buildings (Irwin,1990). At least 25 individual onsite wastewater treatment systems in the US. provide reclaimed water for outside irrigation or for toilet and urinal flushing in office buildings, schools, shopping centers, and manufacturing plants (Thetford Systems, Inc., 1988). Some of the landmark and better k n o w n comprehensive dual distribution systems in the U.S., where the predominant use of reclaimed water is for irrigation, are described below.
Grand Canyon Village, Arizona. This represents the oldest dual water system in the U.S., begun in 1926. Approximately 110 m3/d (0.03 mgd) of filtered activated sludge effluent is used for landscape irrigation, toilet flushing, vehicle washing, and construction uses when needed (Fleming, 1990). -5-
Colorado Springs, Colorado. An extensive nonpotable water distribution system provides reclaimed water to various locations in the city for the irrigation of parks, cemeteries, golf courses, grounds a t Colorado College, other green space, and for industrial cooling water. Fire hydrants are located on the pressure lines. Of the 76,000 m3/d (20 mgd) given secondary treatment, approximately 19,000 m3/d (5 mgd) receives filtration prior to chlorination and storage in a series of reservoirs (Water Pollution Control Federation, 1983).
Imine Ranch Water District, California. The 57,000-m3/d (15 mgd) Michelson Water Reclamation Plant provides tertiary treatment (biological oxidation, chemical coagulation, filtration, and disinfection) that produces an effluent essentially free of pathogens. The district reuses wastewater treated at the reclamation plant through an extensive dual distribution system. Beginning with crop irrigation in 1968, the system has been expanded to include ornamental impoundments, and the irrigation of parks, golf courses, school grounds, common areas around condominiums, roadway medians, and other open space. A n ordinance was enacted in 1990 requiring all new buildings over 16.8 meters (m) 155 feet (ft)] high to install a dual distribution system for flushing toilets and urinals in areas where reclaimed water is available (l[rvine Ranch Water District, 1990). The use of reclaimed water for toilet and urinal flushing in office buildings began in 1991. St. Petamburg, Florida. Reclaimed water of equivalent quality to that produced by the
Irvine Ranch Water District is distributed throughout the city from four treatment plants for irrigation, industrial uses, air conditioning chiller water in commercial buildings, and as a backup source of water for fire protection. This dual water system, in operation since 1977, is the largest in the US.and carries 85,000 m3/d (25 mgd) of reclaimed water through 400 km (250 miles) of pipeline ranging in size from 10 to 120 centimeters (2 to 48 inches) in diameter. In 1992, the water was used by more than 7,000 customers to irrigate more than 2000 ha (5,000 ac) of parks, school grounds, golf courses, and industrial, commercial, and residential neighborhoods (US. Environmental Protection Agency, 1992). It is estimated that St. Petersburg's reclaimed water system will have the potential to serve approximately 17,000 customers and irrigate almost 3600 ha (9,000 ac). Hose bibbs are prohibited, and backflow prevention devices are required on the potable water supply to each irrigation user, including residences.
Industrial Reuse Reclaimed water that has been treated by conventional wastewater treatment processes is of adequate quality for many industrial applications that can tolerate water of less than potable quality, and the reliability of supply is an important advantage. Industries are often located near populated areas that generate large volumes of wastewater. Industrial uses of reclaimed water include cooling, processing, stack scrubbing, boiler feed, washing, transport of material, and as an ingredient in a product. Cooling is the predominant reuse application, resulting in over 90 percent of the total volume of industrial use of reclaimed water.
Cooling Water. In 1985, there were at least 17 steam electric generating plants in the US. that used municipal wastewater as plant makeup water (Breitstein and Tucker, 1986). In general, the major problems unique to power plants employing municipal effluents as makeup water consist of scale formation, corrosion, and biological fouling due to high residual organic substrate and nutrient concentrations in the wastewater.
In most cases, disinfected secondary effluent is supplied to power plants for cooling water, and additional treatment by the industry is often required for recirculating cooling systems. -6-
.
Additional treatment may include lime or alum treatment, filtration, ferric chloride precipitation, ion exchange, and reverse osmosis. In some cases, only additional chemical treatment is necessary. Sulfuric acid may be added for pH and alkalinity control, polyphosphates for corrosion control, phosphonates or calcium phosphate for destabilization, polyacsylates for suspended solids dispersion, chlorine' for biological control, and anti-foaming agents for dispersion of foam caused by phosphates and some organic compounds. Advanced treatment, consisting of oxidation, alum coagulation, filtration, and disinfection to achieve a total coliform level of 12.2/100 mL is used for power plant cooling a t the City of Burbank, California, power generating plant. The 8,000 m3/d (2 mgd) used for cooling receives additional chemical treatment at the power plant. The City of Glendale, California, receives about 23,000 m3/d (6 mgd) of similar quality effluent for use in the Glendale Steam Electric Generating Plant.
Las Vegas, Nevada and Clark County Sanitation District provide 340,000 m3/d (90 mgd) of reclaimed water to supply 35 percent of the water demand in power generating stations operated by the Nevada Power Company. The Nevada Power Company receives unfiltered secondary effluent and provides lime softening, fdtration, and disinfection on site (Water Pollution Control Federation, 1989). The Palo Verde Nuclear Generating Station (PVNGS) is the largest nuclear power plant in the nation. The plant is located in the desert, approximately 89 km (55 miles) west of Phoenix, Arizona. The facility uses reclaimed water for cooling purposes and has zero discharge. The source of the cooling water is two secondary wastewater treatment plants, located in Phoenix and Tolleson, Arizona. About 340,000 m3/d (90mgd) of reclaimed water is received at the PVNGS and receives additional treatment by trickling filters to reduce ammonia, limqsoda ash softening to reduce scale- and corrosion-causing constituents, and fdtration to reduce suspended solids. Two 189-ha (467-ac) evaporation ponds were constructed to dispose of liquid waste from blowdown. (US.Environmental Protection Agency, 1992). The largest industrial reuse application in the US. is at the Bethlehem Steel Corporation's Sparrow Plant in Baltimore County, Maryland, which uses approximately 405,000m3/d (107 mgd) for cooling and steel production. Because of the once-through nature of cooling, a relatively low quality secondary effluent h m Baltimore's Back River Wastewater Treatment Plant has been successfully used with chlorination being the only additional treatment provided at the plant (Water Pollution Control Federation, 1983). Other uses of reclaimed water at the plant include roll cooling, descaling, sluicing, gas scrubbing, pickle liquor diluting, slab and coil cooling, and indirect cooling in heat exchangers. The process water receives additional treatment prior to reuse.
Boiler Feed Water. The use of reclaimed water for boiler feed water often requires extensive additional treatment and usually is not recommended. Reclaimed water must be treated to remove hardness. Calcium and magnesium salts are the principal contributors to scale formation and deposits in boilers. Ejrcessive alkalinity contributes to foaming and results in deposits in heater, reheater, and turbine units. Silica and aluminum form a hard scale on heat-exchanger surfaces, while high concentrations of potassium and sodium can cause excessive foaming in the boiler. In order to use reclaimed water for boiler feed make-up, extensive advanced treatment may be necessary. -7-
The Wyodak Power Plant near Gillette, Wyoming uses up to 1,600 m3/d (0.4 mgd) of reclaimed water for boiler make-up, dust suppression, and other small-volume plant uses. Secondary effluent b m Gillette is piped approximately 8 km (5 miles) to a water treatment facility that includes chlorination, softening, activated carbon adsorption, pH adjustment, sand filtration, cartridge filtration, reverse osmosis, dechlorination, recarbonation, and ion exchange demineralization (Breitstein and Taylor, 1986). Three industries in Odessa, Texas have used approximately 9,500 m3/d (2.5 mgd) of municipal wastewater effluent for cooling tower make-up and boiler feed for over 20 years. Secondary effluent is treated by lime softening prior to use by the industries. The reclaimed water is used directly for cooling tower make-up, and water use for boiler feed is treated by two-bed demineralization before use (Water Pollution Control Federation, 1989).
Roceee Water. The acceptability of reclaimed water for industrial process water is dependent on the specific application and is highly variable. Whereas relatively low quality secondary effluent may be acceptable for some applications, e.g., secondary effluent has been used in the manufacture of concrete, exceptionally high quality water is required for certain industrial applications, e.g., water used to wash circuit boards in the electronics industry often receives reverse osmosis treatment. ?Fvo paper mills use tertiary treated effluent from the Los Angeles County Sanitation Districts' Pomona Water Reclamation Plant as process water. The Garden State Paper Company uses 11,OOO m3/d (3 mgd) of reclaimed water during newsprint reprocessing, and the Simpson Paper Company uses 4,000 m3/d (1 mgd) during the manufacture of high quality paper for stationery and wrappings. The treatment includes biological oxidation, alum coagulation, filtration, and disinfection to achieve a total coliform of 52.2 total coliform organisms/100 mL (Sanitation Districts of Los Angeles County, 1993).
Stack Gas Scrubbing. The Tampa Electric Company has been using reclaimed water since 1984 for stack gas scrubbing at its Big Bend Station. Approximately 760 m3/d (0.2 mgd) of tertiary-treated effluent from the Sun City Wastewater Treatment Plant is stored in two 23,000-m3(6-milJion gallon) storage tanks at the treatment plant and rechlorinated prior to being pumped 19 k m (12 mi) to the Big Bend facility for scrubbing in the flue gas desulfurization system. A minimum chlorine residual of 0.1 mg/l in conjunction with a turbidity of 5.0 NTU is used as a guideline to provide reasonable assurance that the reclaimed water is adequately disinfected. Wastewater generated &om the flue gas desulfurization system enters the in-plant recycle system for further reuse within the plant for floor and equipment washdown and other uses (Rogers et al., 1992).
Impoundments Reclaimed water impoundments, which are often used for system or seasonal storage, can be categorized as aesthetic or recreational. Recreational impoundments can be subdivided into either nonbody contact or body contact impoundments. Nonbody contact includes activities such as boating and fishing where there is only incidental contact with the reclaimed water, while body contact impoundments allow full body immersion. At present there are no reclaimed water recreational impoundments in the U.S. that are used for full body contact activities, although such use is acceptable in some states. Recreational impoundments should not contain chemical substances that are toxic on ingestion or irritating to the eyes or skin and should be safe from a microbiological -8-
standpoint. Other concerns are temperature, pH, chemical composition, aquatic growths, and clarity. Clarity is important for several reasons, including safety, visual appeal, and recreational enjoyment. Recreational lakes ,composed entirely of reclaimed water are prone to eutrophication. The nutrients in the wastewater can cause excessive growth of algae, and nutrient removal may be necessary. Phosphorus is generally the nutrient limited as a means of controlling algae in hshwater impoundments. If fish, shellfish, or plants are harvested from reclaimed water for human consumption, both the microbiological and chemical quality of the source water should be thoroughly assessed for possible bio-accumulation of toxic contaminants through the food chain. The recreational lakes in Santee, California, have been used since 1961 for several activities, limited initially to picnicking and boating and progressing through a "fish for fun"program to a normal fishing program. At Santee, activated sludge effluent is percolated through 120 m (400 fi) of sand and gravel and disinfected prior to discharge to five lakes, which have a total surface area of about 12 ha (30 ac). Because of the high nutrient levels in the reclaimed water, there is considerable algal growth in the lakes, which average 300 m (1,000 ft) in length and 0.6-3 m (2-10 ft) in depth. Algae control via chemicals or mechanical harvesting is practiced. The lakes have been incorporated into an extensive recreational area widely used by the local populace (Water Pollution Control Federation, 1989).
A basin adjacent to one of the Santee lakes was built and used for swimming during the summer of 1965 but was discontinued for economic reasons. The reclaimed water for swimming required additional treatment for turbidity and iron and manganese control consisting of chemical coagulation, fdtration, and disinfection. It was less costly to supply potable water for swimming than to treat reclaimed water (Merrell et al., 1967). Approximately 30,000 m3/d (8 mgd) of tertiary-treated reclaimed water from the l"an Water Reclamation Plant in Los Angeles, California, is used to fill the 11-ha (26-ac) Sepulveda Wildlife Lake. The lake was created to provide a way station for migratory birds traveling through the Los Angeles area. A walking path has been provided along the lake for wildlife viewing. When the lake is full,the amount of reclaimed water discharged to the lake is reduced to 20,000 m3/d (5 mgd) (City of Los Angeles Office of Water Reclamation, 1991).
In Las Colinas, Texas, the design for a 4,800 ha (12,000 ac) planned development included a series of 19 man-made lakes covering 110 ha (270 ac) for aesthetic enhancement. Lake levels are maintained with reclaimed water supplemented by water from the Elm Fork of the Trinity River. Wastewater treatment includes activated sludge secondary treatment, filtration, carbon adsorption (as needed), and chlorine disinfection. The finished water is consistently less than 10 mg/L BOD and 15 mgL TSS. Six fountain type aerators were installed to enhance and maintain lake water quality (Smith et al., 1990). Approximately 15,000 m3/d (4 mgd) of reclaimed water is used for recreational lakes in the Yellowstone Canyon Lakes Park in Lubbock, Texas (Water Pollution Control Federation, 1989). The canyon, formerly used as a dump, was restored through the use of reclaimed water to provide water-oriented recreational activities. Four lakes, which include man-made waterfalls, are utilized for fishing, boating, and water skiing. Swimming is restricted.
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Habitat R e s t m a t i o m a n c e m e n t Reclaimed water is used for several types of environmental enhancement, some of which are commonly associated with wastewater disposal. Reclaimed water has been applied to wetlands to: create, restore, and/or enhance wetlands systems; provide additional treatment of wastewater prior to discharge to a receiving water body; and provide a wet weather disposal alternative for a water reuse system. Application of reclaimed water to wetlands that have been altered hydrologically serves to restore and enhance the wetlands. The primary intent of most wetland projects is to provide additional treatment of effluent prior to discharge. However, this focus does not negate the need for design considerations that will maximize wildlife habitats, thereby resulting in an environmentally valuable system. Wetlands enhancement to provide wildlife habitats as well as treatment are illustrated by systems developed in Arcata, California, and Orlando, Florida. One of the main goals of the Arcata project was the enhancement of the beneficial uses of the downstream surface waters. A wetlands system was selected because the wetlands serve as nutrient sinks and buffer zones, have aesthetic and environmental benefits, and can provide cost-effective treatment through natural systems. The Arcata system also was designed to function as a wildlife habitat (U.S. Environmental Protection Agency, 1988). The Arcata wetland system consists of three 4-ha (10-ac) marshes and has attracted more than 200 species of birds, provided a fish hatchery for salmon, and was a direct contributor t o the development of the Arcata Marsh and Wildlife Sanctuary (Gearheart, 1988). In Orlando, Florida, a 76,000 m3/d (20 mgd) expansion of the Iron Bridge Regional Wastewater Treatment Facility in 1981 resulted in the creation of a wetland system to handle the additional flow. Since that time, reclaimed water has been pumped 20 k m (16 miles) to the wetland that was created by diking approximately 480 ha (1,200 ac) of improved pasture. The system is further divided into smaller cells for flow and depth management. The system includes approximately 170 ha (420 ac) of a shallow marsh containing mainly cattails and bulrush, 150 ha (380 ac) of a variety of mixed marsh species, and 160 ha (400 ac) of hardwood swamp containing a variety of tree species. The reclaimed water then flows through approximately 240 ha (600ac) of natural wetland prior to discharge to the St. Johns River (US.Environmental Protection Agency, 1992). Wetlands application of reclaimed water has been integrated with urban reuse on Hilton Head Island, South Carolina. While there are plans to substantially expand the reclaimed water urban irrigation system that began with golf course irrigation in 1983, an alternative disposal system is necessary during the rainy season. Due to the natural cycling, wetlands typically are drier in the summer than in the winter, thus making a perfect complement to the irrigation system. A three-year pilot study initiated in 1983 proved the acceptability of wetlands augmentation with reclaimed water, and the Boggy Gut wetland project in the Sea Pines Forest Preserve has since become operational (Hirsekorn and Ellison, 1988). Approximately 67,000 m3/d (18 mgd) of treated wastewater from the Columbia, Missouri, Regional Wastewater Treatment Plant is discharged to a constructed wetlands having about 37 ha (19 ac) of surface area. Wastewater entering the wetlands is a blend of primary and secondary effluent. Effluent from the constructed wetlands then enters a nearby 1,460-ha (3,600-ac) riverine area known as the Eagle Bluffs Wildlife Area for natural wetland management @runner and Kadlec, 1993). San Diego County, California, is evaluating a "live stream concept" in which reclaimed water -10-
would be discharged to streams for the purpose of maintaining a constant high quality flow of water to enhance the aquatic and wildlife habitat and maintain the aesthetic value of the water courses. Effluent discharged into these systems would receive the benefit of additional treatment by natural purification processes.
Other Nonpotable Uses of Reclaimed Water Other current uses include livestock water, frost protection of crops, construction uses such as soil compaction and dust control, fire protection, equipment washdown, vehicle washing, and ornamental fountains and water features. Snow-making at ski resorts, aircraft washing, use in washing machines at laundromats, street cleaning, fish-rearing ponds, and process water a t food processing plants are some of the uses for which reclaimed water has been considered.
Indirect Potable Reuse Groundwater Recharge. The purposes of groundwater recharge include: (1) to establish saltwater intrusion barriers in coastal aquifers; (2)to provide further treatment for future reuse; (3) to augment potable and nonpotable aquifers; (4) to provide storage of reclaimed water; and (5) to control or prevent ground subsidence. The constraints on groundwater recharge are conditioned by the use to which the abstracted water w i l l be put, and include health concerns, economic feasibility, physical limitations, legal restrictions, water quality constraints, and reclaimed water availability. The health concerns pervade almost all recharge projects, because boundaries between potable and nonpotable aquifers are rarely well-defmed. The lack of knowledge about the fate and long-term health effeds of contaminants in reclaimed water dictates a conservative approach in setting water quality standards for groundwater recharge. Because of these uncertainties, some states have set stringent water quality standards and require high levels of treatment - in some cases processes to remove organic constituents - where recharge affects potable aquifers, while some states prohibit groundwater recharge under any circumstances. Reclaimed water has been used to recharge potable groundwater aquifers by surface spreading since 1962 in Los Angeles County, California. At the present time, 170,000 m3/d (45 mgd) of highly disinfected tertiary (secondary treatment plus filtration) effluent from three wastewater reclamation plants operated by the Sanitation Districts of Los Angeles County are spread at Whittier Narrows in the Montebello Forebay area of Los Angeles County. Reclaimed water accounts for more than 30 percent of the inflow into the basin (Crook et d.,1992). Local stormwater runoff and imported surface water are also used for recharge. Extensive monitoring of groundwater in the Montebello Forebay indicates that there has been no degradation of the groundwater quality in terms of total dissolved solids, nitrogen, trace organics, heavy metals, or microorganisms (Hartling, 1993). Sampling and analysis indicate that the reclaimed water does not contain measurable levels of viruses, contains less than 2.2 total coliform organisms/100 mL, and has an average turbidity of less than 2 NTU (Bookman-Edmonston Engineering, Inc., 1992).
In 1978, the Sanitation Districts of Los Angeles County initiated a 5-year health effects study to determine whether the Whittier Narrows groundwater recharge project has had an -11-
adverse effect on the groundwater or the health of individuals ingesting the groundwater. The study included extensive microbiological and chemical water quality characterization, percolation studies, toxicological studies, and epidemiological studies. The Whittier Narrows health effects study did not demonstrate any measurable adverse effects on the areals groundwater or the health of the population ingesting the water. The reclaimed water and groundwater complied with all federally prescribed drinking water standards, and no pathogenic organisms were detected in either the reclaimed water or groundwater (Nellor et al., 1984). The cancer-related epidemiological study findings are somewhat weakened by the fact that the minimum observed latency period for human cancers that have been linked to chemical agents is about 15 years. Due to the relatively short time period that groundwater containing reclaimed water had been consumed, it is unlikely that any positive effects of exposure to the reclaimed water would have been detected (State of California, 1987). A recently-completed follow-up epidemiological study provided no evidence that populations being served reclaimed water at the concentrations used in the Montebello Forebay are at a higher risk of caner, mortality, or infectious disease than those being served other water (Sloss et al., 1996). L
Currently, there are only two projects in the US. involving groundwater recharge of reclaimed water by injection. Since 1976, reclaimed water produced at the Orange County Water District's Water Factory 21 in Fountain Valley, California, has been hjected into a series of 23 injection wells to form a seawater intrusion barrier. The 57,000 m3/d (15 mgd) facility receives secondary effluent from the adjacent Orange County Sanitation District's wastewater treatment plant and provides additional treatment by lime clarification, recarbonation, mixed media filtration, granular activated carbon (two-thirds of the flow), reverse osmosis (one-third of the flow), and chlorination. Water Factory 21 reliably produces high-quality water. Chemical oxygen demand (COD) concentrations averaged 8 mg/L in 1988, and total organic carbon (TOC) averaged 2.6 mg/L. The average turbidity of filter effluent was 0.22 FTLJ and did not exceed one FTZT during 1988. Virus sampling has indicated that the effluent is essentially free of measurable levels of viruses (McCarty et al., 1982). The product water is blended 2:l with deep well water prior to injection. Once underground, some of the injected water flows toward the ocean forming the seawater barrier, but the majority of the water flows into the groundwater basin to augment the potable groundwater supply (Argo and Cline, 1985).
A prototype injection project has been in operation in El Paso, Texas, since 1985, supplying more than 15,000 m3/d (4 mgd) of reclaimed water to the underground aquifer. At the Fred Hervey Water Reclamation Plant, primary effluent enters a two-stage biophysical process which combines activated sludge with powdered activated carbon adsorption ( P A C F system). This step of the treatment is designed for organics removal, nitrification, and denitrification. Methanol is added to the second stage to provide a carbon source for the denitrifiers. The wastewater effluent advances to a lime treatment step to remove phosphorus and heavy metals, to inactivate viruses, and to soften the effluent. Turbidity removal is provided by sand filters, and disinfection is provided by ozonation. The final product water is passed through a granular activated carbon filter for final polishing before release to storage. Ultimately, the treated wastewater returns to the city's potable water system after an estimated two- t o six-year travel time in the underground (Reich and Belliew, 1992). While the reclaimed water currently recharged represents a small percentage of the total aquifer volume, the long-term goal is to provide 25 percent of El Paso's future water needs with reclaimed water.
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The total capital cost for the El Paso recharge project was approximately $33,000,000, and the actual per unit cost of the reclaimed water in 1991-92 was $0.36/m3 ($1.35/1,000 gallons) (Morgan et al., 1993). Surface Water Augmentation. The Upper Occoquan Sewage Authority (UOSA) water reclamation plant in Virginia discharges 80,000 m3/d (20 mgd) of highly treated wastewater to Bull Run for indirect potable reuse. The discharge point is about 32 km (20 miles) upstream of the water supply intake. The treatment unit processes include conventional primary and secondary treatment followed by five advanced waste treatment processes: chemical clarification and two-stage recarbonation with intermediate settling; multi-media filtration; activated carbon adsorption; ion exchange for nitrogen removal; and brehkpoint chlorination. Typical constituent concentrations in the UOSA plant product water are as follows: BOD
