Reclaimed Water as an Alternative Water Source for Crop Irrigation Lawrence R. Parsons1 University of Florida, IFAS, Horticultural Sciences Department, Citrus Research and Education Center, 700 Experiment Station Road, Lake Alfred, FL 33850 Bahman Sheikh Bahman Sheikh Associates, 3524 22nd Street, San Francisco, CA 94114 Robert Holden Monterey Regional Water Pollution Control Agency, 5 Harris Court, Building D, Monterey, CA 93940 David W. York York Water Circle, 3158 S. Fulmer Circle, Tallahassee, FL 32303 Additional index words. recycled water, reclaimed water, irrigation, reuse, wastewater, citrus Abstract. Reclaimed water has been safely and successfully used for more than 40 years in Florida and California. Reclaimed water in these states is regulated with restrictions more stringent than World Health Organization guidelines. In the United States, Florida is currently the largest producer and California is the second largest producer of reclaimed water. Reclaimed water is more highly tested than other sources of irrigation water, and the safety of this water has been demonstrated in these and other states. Very high application rates of reclaimed water to citrus on well-drained Florida sands increased tree growth and fruit production. Although reclaimed water contains some nutrient elements, there is usually insufficient macronutrient content to meet plant nutritional requirements. Most reclaimed waters do not have high salinity levels although they are slightly more salty than the potable waters from which they originated. With an adequate leaching fraction, salts in reclaimed water can be handled with appropriate irrigation management. Use of reclaimed water has steadily increased in Florida since 1992, but other entities besides agricultural irrigation are now competing for its use. Public acceptance of reclaimed water has also increased, and crops grown with reclaimed water in Florida and California have been marketed without a negative public reaction. Recent issues of food safety have caused some to question reclaimed water, but there is no evidence of food safety problems with its use. Although reclaimed water in Florida was initially promoted as a way to improve surface water quality, it has now become an important alternate source of water to help meet water shortages and urban demand. In California, reclaimed water has become a necessary part of statewide water management.
The purpose of this article is to discuss terms of reclaimed water production. Why is are helping drive the increased production of several aspects of reclaimed water that are of this? reclaimed water. importance today. Emphasis is placed on Issues relating to water quality, popula- Recent spring droughts from 2000 through water reuse in Florida and California because tion growth, environmental regulations, and 2009 in Florida increased demand for re- they are two of the largest producers of re- saltwater intrusion are some of the primary claimed water. Severe restrictions were placed claimed water in the United States. The term reasons that Florida currently produces more on residential irrigation with potable water, but ‘‘reclaimed water’’ is commonly used in Florida. reclaimed water than other states. Florida’s fewer restrictions were placed on reclaimed California changed from ‘‘reclaimed water’’ to population increased fivefold from 1950 to water irrigation. The Water Management Dis- ‘‘recycled water’’ in 2000 (State of California, 2000, and it is now the fourth largest state in tricts in Florida are actively promoting the 2000). For the purpose of this discussion, both the nation with a 2009 estimated population use of reclaimed water as a way to reduce terms are considered to mean the same thing. of 18.5 million (U.S. Census Bureau, 2010). potable water use (Southwest Florida Water Reclaimed water in Florida is defined as ‘‘water Several major reclaimed water projects in Management District, 2009a, 2009b). that has received at least secondary treatment Florida were started for water quality reasons. With less rainfall and a larger population and basic disinfection and is reused after flowing The city of St. Petersburg brought its reclaimed than Florida, California also has strong rea- out of a domestic wastewater treatment facil- water system online in 1977 after passage sons for reclaiming water. Currently, Cali- ity’’ [Florida Department of Environmental of the Wilson-Grizzle Act (Asano et al., fornia uses nearly half of its reclaimed water Protection (FDEP), 2010c]. 2007). This act mandated that ‘‘wastewater on agriculture and the rest on landscape irri- Florida has less than half the population treatment plants discharging to Tampa Bay and gation and other uses. The two largest reclaimed of California. Statewide, Florida receives its tributaries treat their wastewater to that of water projects for food crop irrigation in Cal- an average of 1372 mm of rainfall annually drinking water standards.’’ (Tchobanoglous ifornia (and the United States) were developed (FDEP, 2010b), whereas much of southern et al., 2003). St. Petersburg became the first in response to seawater intrusion. The Monterey California receives less than half that amount, major city in the United States to reach zero County Water Recycling Projects (Asano yet Florida is the leading state in the nation in discharge of wastewater effluent into nearby et al., 2007) irrigates over 4800 ha with over surface waters. By using reclaimed water in- 18.8 billion liters per year of reclaimed water. stead of groundwater, this project reduced Crops grown include artichokes (Cynara car- Received for publication 20 Jan. 2010. Accepted demand for well water near the coast and dunculus), lettuce (Lactuca sativa), strawber- for publication 7 May 2010. thus helped slow saltwater intrusion. Another ries (Fragaria ·ananassa), celery (Apium Part of a colloquium (The Efficient Use of Alterna- project, Water Conserv II, was started in graveolens), cauliflower (Brassica oleracea), tive Water and Traditional Irrigation Sources in Horticulture) presented 25 July 2009 at ASHS-2009, 1986 to stop discharge of treated wastewater broccoli (Brassica oleracea), and spinach St. Louis, MO; sponsored by the Water Utilization from Orlando and Orange County into Lake (Spinacia oleracea). The Watsonville Area and Management (WUM) Working Group. Tohopekaliga, an important recreational bass Water Recycling Project irrigates over 800 ha 1To whom reprint requests should be addressed; fishing lake (Parsons, 2009). Now, water of similar crops with over 4.9 billion liters per e-mail [email protected]fl.edu. shortages (or water quantity issues) in Florida year of reclaimed water (Pajaro Valley Water
1626 HORTSCIENCE VOL. 45(11) NOVEMBER 2010 Management Agency, 2010). The Irvine agriculture was still the dominant user of used with overhead irrigation for citrus and Ranch Water District has been providing reclaimed water in 2001 in California (Fig. other crops that are peeled or cooked. reclaimed water for irrigation of over 400 1) and accounted for 46% of the total re- For crops that are eaten raw (called the ha of food crops for over 40 years (Irvine claimed water use, whereas golf courses and ‘‘salad crops’’), FDEP regulations currently Ranch Water District, 2010). Their crops landscaping accounted for 21%. Of the new require that there be no direct contact of the include lettuce and strawberries. The city reclaimed water projects since 2001, 84% reclaimed water with the edible part of the of Santa Rosa has used reclaimed water for convert wastewater into water that percolates crop. This means that growers of salad crops grapes (Vitis vinifera), row crops, and fodder into the drinking water groundwater system who irrigate with reclaimed water should use for over 32 years. Currently, they use 6.8 [e.g. Orange County’s Groundwater Replen- drip, bubbler, or furrow irrigation, which does billion liters per year to irrigate 2300 ha ishment Project (96.7 billion liters per year)]. not spray water directly on the crop. This (Piazza, 2010). These and other California The U.S. Environmental Protection Agency regulation also means that reclaimed water projects also produce organic certified crops (EPA) established guidelines for water reuse. cannot be used in Florida for overhead frost with reclaimed water. Rather than establishing national water reuse protection sprays onto crops such as blue- standards, the EPA decided that comprehensive berries or strawberries (Parsons, 2009). USES OF RECLAIMED WATER federal guidelines, along with state regulations, The regulation prohibiting direct contact would increase implementation of water reuse of reclaimed water with salad crops was As of 2008, Florida produced an estimated projects. Hence, states have established their created in the 1980s to encourage acceptance 921.3 billion liters per year of reclaimed water own water reuse regulations. In Florida, the of reclaimed water in Florida. At the time, (FDEP, 2010a). California is gathering data FDEP established water quality standards and there were not sufficient studies to determine for a survey of reclaimed water use, which regulates reclaimed water. In California, the whether such a precaution was necessary. they anticipate completing in 2010. The only predecessor of the California Department of Since then, studies conducted in California accurate statewide survey was conducted for Public Health established the first criteria for (Engineering Science, 1987; Sheikh et al., 2001 production and published in 2002. In crop irrigation with reclaimed water in 1918 1990) have shown that salad crops can be 2001, California’s production was 648 billion (Crook, 2002). The modern era regulations directly sprayed with reclaimed water with liters per year (California EPA, 2002; Water were established in 1968 and have been re- no health, safety, or marketing problems. Facts, 2004). vised three times since then. This finding was expected because reclaimed In 1992, Florida produced 1.098 billion water is disinfected, usually by chlorination. liters of reclaimed water per day and this more SAFETY OF RECLAIMED WATER Reclaimed water has been successfully sprayed than doubled to 2.524 billion liters per day by onto the edible portion of salad crops and 2008 (FDEP, 2010a). In 1992, agriculture was Reclaimed water has an excellent safety strawberries for over 40 years in California. the largest user of reclaimed water in Florida record. Reclaimed water has been used in Nationally, there has never been a documented and golf course irrigation was the second lar- Florida for more than 40 years with no reported case of human illness caused by reclaimed gest user. By 2008, Florida agriculture used incidence of human illness (Southwest Florida water (Crook, 2002). only 12%, whereas golf courses used 19% of Water Management District, 2009b). In Flor- the total reclaimed water (Fig. 1). In contrast, ida, reclaimed water is water that has received NUTRIENTS IN RECLAIMED WATER at least secondary treatment and basic disin- fection. Because it is disinfected (usually by Most wastewater treatment facilities do chlorination), reclaimed water can be better not monitor nutrients in detail. However, one than some other irrigation sources from a facility that has regularly monitored nutrients health and safety point of view. In fact, re- and other elements is the Water Conserv II claimed water undergoes more testing than project near Orlando, FL. Maximum average most irrigation waters. Water quality stan- concentration limits and typical concentra- dards for reclaimed water are stricter than tions of elements in this reclaimed water are standards for recreational water. Because of shown in Parsons et al. (2001b). Nutrient these strict water quality standards, there is concentration in reclaimed water, parti- essentially no risk to humans or animals from cularly advanced treated reclaimed water, is periodic contact with reclaimed water. usually low. Important macronutrients in- Reclaimed water can meet drinking water clude nitrogen (N), phosphorus (P), potas- standards for many elements, but reclaimed sium (K), calcium (Ca), and magnesium. For water is not required to meet all the drinking example, the typical concentration of total N water standards. Reclaimed water is not cur- in reclaimed water with biological nutrient rently intended to be directly used for drinking. removal is 2 to 12 mgÁL–1 (Asano et al., 2007). However, indirect potable reuse has become For advanced wastewater treatment in Florida, more common, particularly in California (Asano total N cannot exceed 3 mgÁL–1 (Florida et al., 2007). Statutes, 2010). Reclaimed water can also The National Research Council (1996) contain low levels of other essential elements concluded, ‘‘Where reclaimed water has been such as manganese, zinc, and boron (B). used for food crop production, the state Boron is an element that is essential for plant standards for wastewater treatment and reuse, growth in small quantities, but it can cause along with site restrictions and generally plant damage if too much is applied (Asano good system reliability, have insured that food et al., 2007). crops thus produced do not present a greater Along with other environmental factors, risk to the consumer than do crops irrigated the amount of nutrient uptake from reclaimed from conventional sources.’’ water by plants depends on the concentration of nutrients, amount of reclaimed water ap- IRRIGATION OF EDIBLE CROPS plied, and residence time of the reclaimed water in the root zone. With regular irrigation, For crops in Florida that are ‘‘peeled, several turfgrasses can extract some N and P cooked, or thermally processed,’’ reclaimed from reclaimed water. In those cases, reclaimed water can be directly applied to the edible part water can supply a reasonable amount of these Fig. 1. Water reuse in Florida and California. of the crop. Hence, reclaimed water can be nutrients. With other crops such as citrus,
HORTSCIENCE VOL. 45(11) NOVEMBER 2010 1627 normal irrigation with reclaimed water pro- for salt-sensitive plants such as azaleas (Rho- in the lower root zone is regulated by the vides less than 16% of the N requirement for dodendron sp.) or Chinese privet (Ligustrum leaching fraction (LF), the ratio of depth of mature trees. Although reclaimed water can sinense). If salinity is too high, the reclaimed drainage water to depth of applied water. The provide some essential elements, the concen- water may be acceptable for some lawn depth of drainage water may be obtained trations of N and K are usually too low to irrigation but not for irrigation of salt-sensitive from the difference between applied water meet plant needs completely. Hence, addi- plants. and water lost to the atmosphere from tran- tional applications of N, K, and other fertil- In California, the most common salt- spiration by plants and surface soil evapora- izer elements are necessary to ensure good sensitive crops are avocadoes (Persea amer- tion. In freely draining soils, a comparatively plant growth. icana), strawberries, and lettuce (Asano small depth of drainage may be sufficient et al., 2007). All are grown with reclaimed to keep the root zone in salt balance. A LF of SALINITY AND SODICITY water, but some actions may be necessary on 0.15 to 0.2 is usually adequate to maintain salt the grower’s part to be successful. Some balance for irrigation of most plant species and Water quality of recycled waters may municipalities have been successful in re- for typical recycled water salinities (Hanson impact plants, soils, and irrigation systems. ducing brines and salts from entering the et al., 1993). Most recycled waters do not inherently con- sewage system and thus reducing the salt in tain higher concentrations of salts although the reclaimed water. Other municipalities PERCEPTION OF RECLAIMED they typically contain 150 to 400 mgÁL–1 have encouraged the use of KCl rather than WATER more total dissolved solids than the potable NaCl in residential and commercial water waters from which they originated (Asano softeners to reduce Na while increasing K When the idea of using reclaimed water et al., 1984). In coastal areas, the incoming (a plant nutrient). for irrigation was first presented to Florida water source used to produce reclaimed water Soil permeability is affected by the com- citrus growers for the Water Conserv II pro- may already be salty. Also, the pipes carrying bined effects of sodicity and salinity in the ject in the 1980s, they initially rejected using groundwater to the wastewater treatment applied water. Sodicity is usually evaluated such water as a result of concerns about tree facility may pass through areas of salty water. by the sodium adsorption ratio (SAR), a ratio damage by heavy metals, salinity, disease If salty water infiltrates into the incoming of sodium to calcium plus magnesium, and organisms, or excessive water (Parsons et al., water pipes, the level of salt in the reclaimed salinity by electrical conductivity (EC). A 2001a). After much negotiation, water qual- water can further increase. If communities moderate level of SAR and low EC may ity standards were established, and several use sodium chloride (NaCl)-based water result in reduced soil permeability of some growers decided to take a chance with the softeners, the reclaimed water may contain soil types. In contrast, the detrimental effects reclaimed water. At the request of growers, elevated Na and Cl ions compared with the of moderate levels of SAR on soil perme- research was carried out on this water by potable water supply. Use of cleaning agents ability may be partially overcome by moder- scientists at the University of Florida (Parsons such as detergents may also elevate B con- ate levels of EC. In some treatment processes et al., 2001a). The research showed that very centrations in recycled waters. Many water for recycled waters, additives are used that high quantities of this water could be applied reclamation facilities monitor salts (i.e., chlo- elevate SAR (e.g., using sodium hypochlorite to citrus on well-drained soils with no negative rides). If the salt concentration gets too high for disinfection) and/or bicarbonate and car- effects (Parsons et al., 2001b). Tree growth (more than 350 to 400 mgÁL–1), they will bonate concentrations (e.g., using lime to neu- and fruit production were greater at rates of typically divert the salty reclaimed water to tralize water pH). Nearly all recycled waters 2500 mm/year than at lower irrigation rates. another discharge point. produced in California have a combination of Although the concentration of juice soluble Plants have a wide range of tolerance to salinity and sodicity that puts them in the safe solids in the fruit was lowered by the high salinity, and many of them can be irrigated range in terms of impacts on soil permeability. irrigation rate, total soluble solids per hectare with recycled water without impact. Sensi- A second sodicity parameter known as were significantly higher as a result of the tive plants typically exhibit foliar leaf dam- residual sodium carbonate, the difference be- greater fruit production caused by the greater age, slower growth, and, in more severe cases, tween the sum of bicarbonate and carbonate tree canopy growth. defoliation and death. Excessive levels of ions minus sodium ion, is used to evaluate Water quality standards were maintained, Na may also cause an imbalance in mineral detrimental effects that cause dispersal of soil and more growers agreed to accept reclaimed nutrition of plants such as Ca deficiency. The organic matter resulting, for instance, in dark water. Now, citrus growers who initially op- presence of dissolved mineral salts has an unsightly matting on turf in golf courses and posed the use of reclaimed water are enthusi- osmotic effect on plants, and some constituents reduced water infiltration rates into turf soils. astic supporters of this water. In addition, over like Na, Cl, and B cause specific ion toxicities Another constituent of concern in recycled 800 parks and 477 golf courses are currently to plants (Hanson et al., 1993). waters is excessive N in the form of dissolved irrigated with reclaimed water (FDEP, 2010a). Salts have a tendency to build up on the ammonia or ammonium ions and nitrates. The With fewer irrigation restrictions on reclaimed root zone of actively transpiring plants be- presence of these forms of N is highly de- water during droughts, public acceptance has cause more or less pure water is lost to the pendent on the wastewater treatment processes also increased noticeably. atmosphere through evaporation and transpira- used. Ammonia or ammonium ions in applied However, perception issues still exist. For tion, whereas dissolved mineral salts in the waters are eventually oxidized to nitrate ions in example, many Florida tomato growers do applied water are left behind in the soil solution. the soil. Nitrogen in recycled water used for not want to use reclaimed water because of It is necessary to maintain a salt balance in the irrigation can be an issue because nitrates not perceived, but scientifically unfounded, con- root zone to obtain satisfactory plant perfor- taken up by plant roots may run off or leach cerns over food safety. This attitude devel- mance, especially under semiarid climatic con- below the root zone. This can contribute to oped because Florida tomato growers were ditions when natural rainfall may be insufficient nitrate contamination of surface waters or un- economically hurt by a Salmonella incident to leach salts out of the root zone. In surface- derlying groundwater basins. Nitrate leaching (Sutton, 2008). Because of a Salmonella irrigated soils (e.g., sprinklers) with no drainage losses may be minimized if N content in the outbreak in 2008, the U.S. Food and Drug impediments, the upper root zone is the zone of recycled water is taken into account as con- Administration initially recommended that salt leaching, whereas the lower root zone is the tributing to the N requirement of plants. people not eat certain types of raw tomatoes. zone of salt accumulation. Fortunately, most landscape plants have It was later found that tomatoes were not the In inland Florida locations, salt in re- a denser rooting system in the surface depths source of Salmonella, but Florida growers lost claimed water is not usually a problem. How- where soil salinity tends to be lowest. Soil an estimated $50 to $100 million because of the ever, in coastal regions, whether the result of water is extracted from the more saline negative publicity. Although reclaimed water infiltration into the incoming water source deeper root zone only when the available soil has no association with Salmonella,Florida or naturally high levels of Na and Cl, salts in water becomes limiting in the less saline tomato growers are reluctant to use it because reclaimed water can sometimes be a problem portions. The extent of accumulation of salts of perceived issues related to food safety.
1628 HORTSCIENCE VOL. 45(11) NOVEMBER 2010 In California, the 2006 spinach Escher- Pettygrove, G.S. and T. Asano (eds.). Irrigation 20 July 2010.
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