ALN #45, Spring/Summer 1999
Water in Cities
by Martin M. Karpiscak, Roland D. Wass, Robert J. Freitas and Susan B. Hopf
"The use of constructed wetlands for treatment of wastewater is a relatively recent technological innovation in Arizona, particularly in the arid parts of the state. (...) In southern Arizona, both surface and subsurface constructed wetland systems are being built and investigated as viable wastewater treatment options. A few of these systems are discussed in more detail below along with some of the findings and observations by researchers."
Introduction(Back to top)
In many parts of the world, natural wetlands have received wastewaters for many years. Information on the quality of water exiting these natural wetlands led scientists and engineers to realize the potential benefits of wetlands in wastewater management systems. Thus, increasingly over the past 40 years, natural and constructed wetlands have been engineered for wastewater treatment (Reed et al., 1988, Hammer, 1989, Moshiri, 1993, Kadlec and Knight, 1996, Vymazal et al., 1998). The idea of using constructed wetland technology in the arid southwestern United States for urban and peri-urban wastewater treatment and habitat creation has developed in the early 1980s (Karpiscak et al., 1993, 1994, 1999). Several demonstration, research and operational facilities have been created in Arizona and over 40 systems from small residential on-site systems to large operational facilities have been built or are planned. These systems have demonstrated significant benefits in improved water quality and habitat creation, but have also encountered some problems.
Constructed wetland technology includes systems with open water surface flow (SF), subsurface flow (SSF) through a gravel or soil media, or aquatic systems with deeper water and floating aquatic plants. These have been designed to treat municipal, industrial and/or agricultural wastewaters and stormwater. Municipal wastewaters, including domestic and commercial wastewaters pretreated in lagoons, septic tanks, or conventional primary and secondary processes (screening, primary settling, trickling filters and activated sludge) are the primary sources for these systems. Industrial wastewaters discharged to wetlands for advanced treatment include food processing wastes, textile wastes, chemical facility and refinery wastes, cooling tower blow-down waters, landfill leachates, and pulp and paper effluents. Agricultural wastewaters include dairy wastes, feedlot and hog-farrowing wastewaters, and runoff from many agricultural practices.
The use of constructed wetlands for treatment of wastewater is a relatively recent technological innovation in Arizona, particularly in the arid parts of the state. Constructed wetlands treating wastewater were first built in northern and eastern Arizona in the late 1970s. Existing surface water systems such as the Show Low complex (Pintail Lake, Redhead Marsh, and Telephone Lake), Jacques Marsh at Pinetop-Lakeside, and Springerville have created valuable and important amenities to their communities and serve as examples for other communities interested in cost-effective and environmentally sound wastewater management. In southern Arizona, both surface and subsurface constructed wetland systems are being built and investigated as viable wastewater treatment options. A few of these systems are discussed in more detail below along with some of the findings and observations by researchers.(Back to top)
CERF Background and Site Description
The Constructed Ecosystems Research Facility (CERF), Tucson, Arizona, is a cooperative effort of Pima County and The University of Arizona. Research conducted by the University is and has been funded by Pima County Wastewater Management Department. The Pima County Wastewater Management Department (PCWMD) is a recognized leader in the southwestern United States in initiating and supporting research studies that define water quality criteria for effluent recharge and/or reuse while simultaneously maintaining the regional environment.
In 1983, a study was initiated by PCWMD and The University of Arizona's Office of Arid Lands Studies (OALS) to determine the feasibility of an aquatic wastewater treatment facility in Tucson's arid environment. A research and demonstration facility (CERF) was constructed in 1989 on a 1.2 ha (3 ac) site west of Interstate Highway 10 and adjacent to Pima County's Roger Road Wastewater Treatment Plant.
The CERF consists of six pilot-scale hypalon-lined ponds or raceways with an array of pumps and monitoring stations and a trailer that serves both as a sample and data collection facility and as an on-site laboratory. Five of the raceways measure 61 m x 8.2 m x 1.4 m (200 ft x 27 ft x 4.6 ft). The sixth raceway is somewhat larger in area and is 2.6 m (8.5 ft) deep. This provides a unique, controlled setting both for evaluating water quality impacts on vegetation species of the regional ecosystem and for determining water quality standards.
Thumbnail link to image of wildlife in Raceway 1, ~27K file
Original research focused on the use and survival of water hyacinth (Eichhornia crassipes) grown in the six aquatic ponds or raceways through which unchlorinated secondary effluent from the main sewage treatment plant at Roger Road flowed (Karpiscak et al., 1994). In 1991, conversion of five of the aquatic ponds into multi-species wetland ecosystems was begun. Almost all hyacinth plants were removed, gravel was added to the raceways, and selected (mostly locally available) vegetation was planted. Secondary effluent began flowing into the first system (Raceway 1) in August 1992. Raceway 6, planted with lemna sp. (duckweed), continued to receive secondary effluent. After construction of the other four raceways, potable municipal water flowed through the raceways until planting was complete. At that point, July 1994, municipal water continued to flow into Raceways 2 and 4, and the effluent from Raceway 6 was diverted into Raceways 3 and 5. The duckweed and a small pond filled with water hyacinths in Raceway 1 are used to filter the secondary effluent before it enters the respective ecosystems.
Thumbnail link to image of vegetation in raceways, ~31K file
Vegetation in the ecosystems began with the planting of two tree species, black willow (Salix nigra) and cottonwood (Populus fremontii), in Raceway 1 in 1991 along with selected herbaceous species. In March 1994, black willow and cottonwood also were planted in Raceways 2-5 as well as cattail (Typha domingensis), bulrush (Scirpus olneyi), and giant reed (Arundo donax). Over the next few months, shrubs and trees were planted in Raceways 2 and 3. Desert shrub species included seep willow (Baccharis glutinosa) and desert willow (Chilopsis linearis) and the tree species were coyote willow (Salix exigua) and sycamore (Platanus wrightii). In August 1994, black walnut (Juglans major) and ash (Fraxinus sp.) were planted in Raceways 4 and 5.(Back to top)
Originally, research focused solely on the usefulness of water hyacinths in the treatment of effluent. The more recent studies at CERF have compared the effect of both potable water and secondary effluent on a variety of native, locally tolerant plants representative of the arid west. In addition, studies are examining the plants' efficacy in treating the secondary effluent by reducing selected biological and chemical constituents and pathogens. Another research topic is the removal of organics from wastewater by plants.
Research objectives at CERF include but are not limited to:
Operation of an on-site water quality analysis laboratory and access to several laboratory facilities located both on The University of Arizona main campus and at Pima County's Ina Road Water Pollution Control Facility permits evaluation of vegetative response to effluent loading, vegetation uptake of nutrients, water quality improvements and other issues of concern.
Increasingly, CERF is acting as a central research/study facility as masters- and doctoral-level graduate students conduct individual projects on constructed and/or natural wetlands. The students are affiliated with several different departments at The University of Arizona including Soil, Water, and Environmental Science, Civil Engineering, Chemical and Environmental Engineering, and Hydrology.(Back to top)
The research conducted at CERF has proven that plants (both native and locally available varieties) can clean wastewater in a constructed wetlands setting. These studies have also proven that secondary effluent does not negatively affect native vegetation; in fact, effluent appears to stimulate the growth of most plant species. Cottonwood and willow trees were observed to grow over 3 m (10 ft) during the first year following planting into the raceways supplied with either potable municipal water or secondary effluent.
Water hyacinth plants were found to survive the winter and to provide treatment year-round in Tucson. Through the ongoing research at CERF, many new questions have been posed, and future studies promise to provide answers that will benefit the community.
Studies designed to measure the effect of effluent on plant life and to study the enhancement of water quality show promise. These multi-species wetlands have been found to remove pathogens such as Cryptosporidium parvum and Giardia lamba and to improve water quality.
University researchers are now testing whether secondary-quality effluent discharged from the Roger Road Plant can be treated further with the aid of diverse multi-species wetland. If these systems can produce cleaner effluent, the effluent can be reused within the community for a variety of irrigation purposes: watering of parks, schoolyards, and golf courses.
Water hyacinth (Eichhornia crassipes) was the first species selected for study as a biological filter. During the first years of operation (1990-92), research focused on winter survival of hyacinths and their year-round performance in enhancing water quality. Duckweed was found to be more frost-tolerant, but water hyacinths were found to be more effective in cleaning the water. Duckweed, however, unlike water hyacinth, is readily consumed by some of the avian visitors to CERF such as mallards.
CERF has an array of cottonwood, willow, ash, sycamore, desert willow, cattail, bulrush and other species of plants in various stages of growth in the gravel-filled raceways. As the wetlands facility has developed, the increase in vegetation has created a natural habitat for wildlife, including mammals, reptiles, birds and insects. In an effort to duplicate the most natural environmental conditions, researchers encourage the presence of animals and, as much as possible, avoid interfering with wildlife drawn to the facility.(Back to top)
Tres Rios Background and Site Description
In 1993, as part of the Phoenix Water Reclamation and Reuse Study, the Multi-City Subregional Operating Group (SROG) and the United States Bureau of Reclamation (BofR) wanted to evaluate methods of water reclamation and beneficial reuse utilizing municipal sewage effluent. The use of a constructed, multi-purpose wetlands near the confluence of the Salt, Gila and Agua Fria Rivers was proposed as one of four reuse options. The "Tres Rios Demonstration Wetlands" is the result of a conceptual plan developed by the BofR that recommended the construction of two demonstration wetlands and a series of pilot cells to be located at the City of Phoenix's 91st Ave. Wastewater Treatment Plant.
The free water surface demonstration wetlands consist of two 0.85 ha (2.1 ac) in-stream wetland cells (Cobble Site) and two 1.2 ha (2.9 ac) upland cells (Hayfield Site). The systems currently receive denitrified wastewater effluent from the 9lst Ave. Plant.
Thumbnail link to labeled aerial photo of Tres Rios wetlands, ~76K file
The Cobble Site consists of two parallel basins located within the channel of the Salt River. One wetland cell has been lined with topsoil to facilitate vegetation establishment and to reduce water losses due to infiltration. The other cell is unlined and represents the challenges to be faced with locating a full-sized wetland in the sand and cobble of the river bottom. Both include emergent and open-water areas. The emergent areas are typically shallow at 0.15 to 0.5 m (0.5 to 1.5 ft) and planted with emergent vegetation, whereas the open water zones are deep 1.0 to1.4 m (3.0 to 4.5 ft) and have been planted with submerged aquatic plants. Fifteen subsurface well-points are located in the unlined basin to investigate the quality of water lost through the bottom material.
The Hayfield Site is a system of two wetland cells located within a riparian/upland area on the north bank of the Salt River. The two basins can be operated both in series and parallel modes. Again, both these cells have emergent and open-water deep zones. Although both cells have an equal proportion of open water to emergent area, the northern cell has five interior open water zones while the southern basin only has two. These deep zones are important from the standpoint of re-mixing water after it transits the shallow emergent areas.
The final pilot wetland system is a series of 12 small 1,200 m2 (12,900 ft2) Research Cells located within an abandoned sludge-drying basin. Three cells have one open water deep area, three have two, three have three, and three have none.
The vegetation used is similar for all wetland sites. Emergent areas have been planted with two types of bulrush, Scirpus validus (soft-stemmed bulrush) and Scirpus olneyi (three-square). The wetland fringe (transitional marsh) has been planted with a mixture of Scirpus maritima, Cyperus, Paspalum (Knot-grass) and Juncus sp. The deep, open water areas have been planted with the submerged aquatic plant Ceratophyllum. The vegetation provides surface area for the attachment of microbes (algae, fungi and actinomycetes) as well as the absorption and uptake of nutrients, metals and other wastewater constituents. Further, emergent macrophytes can play an important role in the gas exchange between wetland sediments and the atmosphere.(Back to top)
While many aspects of wetlands design are well understood, there remain a number of design issues that require additional study. The Tres Rios Multipurpose Wetlands Research Plan is intended to verify and calibrate existing constructed wetland design models and to address some design issues that have previously not been studied in detail. Demonstration-scale wetlands can provide a realistic assessment of full-scale wetlands in terms of operations parameters, pollutant removal, wildlife use and human recreational use. The Tres Rios Demonstration Wetlands and associated upland and riparian facilities are large enough for wildlife to feel that they are within a natural system and their responses should be indicative of responses to a larger-scale constructed wetlands project.
The primary objective for the Tres Rios Constructed Wetlands Project is two-fold. First, the capability of constructed wetlands to treat effluent from the wastewater treatment plant to levels that will satisfy expected 1997 and future U.S. National Pollutant Discharge Elimination System permit requirements will be tested. Second, appropriate design criteria will be developed for a full-scale wetlands project in the Tres Rios Area.
The research objectives for the wetland systems include:
Mid-size pilot wetlands provide the best opportunity to experiment with the effect of design criteria on wetland performance. This experimentation can be used to optimize the design of full-scale wetland systems by helping to identify expected reaction rates for processes such as organic decomposition, nitrification and denitrification; optimum cell configurations and water depths to insure even flow distribution; and effects of hydraulic and mass loading on wetland effluent water quality. Pilot-scale constructed wetlands are also a suitable environment in which to quantify the effects of hydrologic regime on growth of candidate plant species.(Back to top)
To date, more than twenty bird species have been identified using the site. Included in this list are: Cinnamon Teal, Mallard and Pintail ducks, the Western and Spotted Sandpipers, the Long-Billed Marsh Wren, Great and Black-Crested Night Herons, to name a few. In addition, bobcats, raccoons, rabbits, coyotes, and ground squirrels also have been noted. Beaver have moved into the wetlands and have had to be removed and relocated because of their very intensive dam-building activity. Finally, a very healthy population of snakes, reptiles, and amphibians inhabit the site.
It took approximately six months after planting the Hayfield Site Wetlands for denitrifying conditions, e.g., anoxic zones and available carbon, to develop. The Cobble Site basins, having less suitable substrate, took almost two months longer. Results also indicate that carbon concentration in the wetland effluent, as measured by Total Organic Carbon (TOC), can be influenced by hydraulic loading rate. At high hydraulic loading rates (HLR), the TOC concentration in the influent water can be reduced. Conversely, at lower HRLs, the retention time increases permitting the concentration of organic compounds from vegetation decay. Finally, monthly biomonitoring has shown wetland-treated effluent to be non-toxic to the test organism, Cerriodaphnia dubia, whereas conventionally-treated effluent shows some toxicity.
The next phase of research begun during the late summer of 1998 focuses upon basin geometry and wetland plantings geared to minimizing mosquito production while maximizing water treatment and habitat value. A bioaccumulation study looking at heavy metals and trace organic compounds was initiated in August 1998 and has moved into its second phase. Results from this and other endeavors will be available around December 1999. More information can be obtained from the Tres Rios web site (see Additional Web Resources at the end of this article).(Back to top)
Sweetwater Background and Site Description
Thumbnail link to aerial photo of Sweetwater wetlands, ~31K file
The Sweetwater Wetlands and Recharge Project is a 24.3 ha (60 ac) operational facility built by Tucson Water to combine functional elements such as effluent treatment, recharge, and research with a natural park setting that offers educational and wildlife viewing opportunities to the community. The Wetlands was developed with significant assistance and input from citizens, students from elementary through high school grade levels, and numerous environmental and community organizations.
In May 1994, the Arizona Department of Environmental Quality (ADEQ) filed a suit against the City of Tucson alleging violations of state monitoring and reporting requirements. The City and ADEQ negotiated a settlement that among other things committed the City to designing and building an experimental wetland/recharge facility to treat backwash filter water from the City's Reclaimed Water Treatment Plant. In addition, the facility would include wildlife habitat and educational as well as recreational amenities.
Thumbnail link to photo of recharge basin, ~40K file
Backwash water from the City's Reclaimed Water Treatment Plant, as well as secondary effluent from Pima County's Wastewater Treatment Facility, are introduced into four densely vegetated settling ponds covering 0.7 ha (1.8 ac). The water flows from the ponds into two 3.0 ha (7.5 ac) free-water-surface wetland cells where natural biological processes further treat the water. The water then is released into four recharge basins (5.7 ha [14 ac]) where it filters through the ground. The recharged water is later recovered and reused to irrigate parks, golf courses, schoolyards and street medians in the Tucson area.
The project also includes extensive passive public use elements to provide the visitor with a variety of experiences relating to water management and ecological issues. There is a public parking area that was designed to accommodate cars as well as school buses. All of the public use facilities are wheelchair accessible. A six-sided kiosk is the initial focal point for visitors. A ramada provides shade, seating and a place for groups to meet. Restrooms are available near the kiosk. Extensive landscaping of the area includes the marsh of the wetland, a transitional marsh around the edge of the wetland cells, and an upland zone outside and above the transitional community. A looping trail system provides numerous viewpoints and interpretive signage to inform the visitor.
Sweetwater Research Objectives(Back to top)
The main research goal of the Sweetwater Wetlands and Recharge Project is to determine the effectiveness of a surface flow wetland as a means of pretreatment for water that is to be recharged for later removal and reuse. The source water entering the system is either secondary quality wastewater or backwash water from a tertiary treatment facility. Parameters under study include: TSS, BOD5, pathogens, organics, and nitrogen. In addition, the research efforts are focusing on the development of the entire ecosystem as habitat for wildlife. Methods to control the breeding of mosquitoes by the application of selected larvicides and wetland operations are also research priorities.
The research objectives for the Sweetwater wetland system include:
Since April 1997, the emergent plants have grown rapidly and the density has increased greatly. Additionally, new shoots have grown back after each winter. The underlying winter-kill dead and matted vegetation has enhanced the extent and quality of the mosquito habitat. The mosquitoes' natural predators, such as aquatic arthropods and dragonfly and damselfly nymphs, although numerous, have not been able to keep up with the mosquito larvae population and active measures for its control have been implemented.
A wildlife study funded by the Arizona Game and Fish Department (AGFD) and further observations by the Tucson Audubon Society have documented over 120 species of birds at the Sweetwater Wetlands since the spring of 1997. Prior to construction of the Wetlands, background surveys noted less than 20 bird species as being present at the 24.3 ha (60 ac) site. The AGFD study has documented not only seasonal species changes, but also a shift in populations with time as the Wetlands develops. Studies also have documented the nesting of species such as Black-necked Stilts and Black-bellied Whistling Ducks. Mammals observed at the site have ranged from field mice to bobcats.
Since the public opening in early 1998, the Wetlands has attracted more than 40,000 human visitors, as well as nearly two hundred species of birds, mammals, reptiles and insects.
The densely planted free water wetlands cells at Sweetwater have developed into an ideal habitat for breeding the Culex tarsalis mosquito, the primary carrier of Encephalitis virus. These mosquitoes lay their eggs predominantly in the emergent zone areas of the cells where the shallow water zones are planted with cattail and four species of bulrush. University of Arizona entomologists have been setting adult mosquito traps at the Wetlands since the summer of 1997.
In 1999, staff will apply three products to the water that hopefully will keep the mosquito larvae population in check. Methoprene, an insect growth regulator (IGR), along with Bacillus thuringiensis var. israeliensis (BTI) and Bacillus sphaericus (BS), two biological larvicides, are being applied in rotation at the site using a remote-controlled helicopter. The IGR and BS leave an effective residual in the water for a longer-acting treatment. With the help of the UA trapping program, staff will continue to assess the effectiveness of the abatement program to determine which combination of products provides cost-effective treatment.
Dairy Constructed Wetland Demonstration and Research Project(Back to top)
Dairy Background and Site Description
This program is a cooperative project between The University of Arizona's Office of Arid Lands Studies and Departments of Soil, Water, and Environmental Science; Animal Science; and Agriculture and Biosystems Engineering. Funding is provided by the Arizona Department of Water Resources, Phoenix Active Management Area, and the Arizona Department of Environmental Quality. Engineering assistance has been provided by the Natural Resources Conservation Service, USDA. Additional assistance has been provided by the City of Phoenix 9lst Ave. Wastewater Treatment Plant, the Bureau of Reclamation, US Department of the Interior, and the Rovey Dairy.
Beginning in 1994, The University of Arizona, the Natural Resources Conservation Service (NRCS-USDA), and the Paul Rovey Dairy discussed options for treating wastewater by incorporating a constructed wetland as part of a new overall wastewater treatment system. The wetland was to be designed to document and demonstrate that this technology will be able to improve the quality of the treated wastewater and possibly make it suitable for reuse and/or recharge. The University then obtained funding from the Arizona Department of Water Resources-Phoenix AMA to design, build, operate and monitor the constructed wetland component. Additional funding was obtained from the 319(h) Program of the Arizona Department of Environmental Quality for water quality monitoring of the upper subsystem.
The wastewater treatment process begins with an upper subsystem water collection sump that combines all the wastewater and stormwater runoff from the dairy. The water then goes into one of two chambers of a solid separator, which removes about 50 percent of the solids. The water from the solid separator then flows by gravity to two 200 m x 33 m x 5 m (656 ft x 108 ft x 16 ft), anaerobic ponds where the digestion of organic compounds via microbial organisms begins. The wastewater then flows from the anaerobic ponds to the aerobic ponds, which add atmospheric oxygen to the wastewater. These ponds are also 200 m (656 ft) in length and typically operate at 15 to 60 cm (6 to 24 in) in depth. Treated wastewater from the upper subsystem, comprised of the components listed above, then flows to the lower subsystem, or the constructed wetlands, for additional treatment. Both the upper and lower subsystems' components can be configured to direct water flow either in parallel or in series.
Thumbnail link to labeled aerial photo of Dairy wetlands, ~49K file.
The wetlands consist of eight individual ponds, with a total surface area of about 0.5 ha (1.2 ac) and an operating depth of 15 to 30 cm (6 to 12 in). The paired ponds currently are planted with three macrophytic emergent species of plants: cattail (Typha domingensis), soft-stemmed bulrush (Scirpus validus), and common reed (Phragmites australis). As the wastewater flows from cell to cell, the plants and microbial community transform and utilize the pollutants/nutrients for their metabolic activities, thus improving water quality. Details of the systems are presented in an article by Karpiscak et al. (1999).(Back to top)
This program monitors, tests, and evaluates the utility of various plant species for use in constructed wetlands to remove or reduce potential pollutants such as nitrates and pathogens. This is accomplished by determining changes in water quality at each stage of the treatment process. The water quality is determined by measuring the concentration of selected chemical, biological and physical parameters in the water.
The treated wastewater is collected in a 165 m3 (90,000 gal) reservoir. Several options are currently being tested and examined as possible uses for the treated wastewater. These uses include (1) direct reuse in the dairy flush system, (2) blending with irrigation water for crops grown on other areas of the Rovey farm, and (3) recharge to the aquifer to acquire water credits for later use. Options (1) and (2) are operational and option (3) has been submitted for regulatory review and approval. However, the water has not proven adequate to initiate recharge research.
The most obvious benefit is recycling and conservation of water. Since waste is a measure of inefficiency, by recycling, the dairy can derive an economic benefit by becoming more efficient and by reducing the amount of potable water used for non-potable purposes. Environmental advantages include reduction in contaminants released to the surface and groundwater. Additional environmental benefits include the creation of wetland wildlife habitat. A possible economic benefit may be found in the use of wetland plant biomass as part of the feed ration for the cows. This benefit remains to be explored.
The research objectives for the system include:
In short, the purpose of this project is to test and demonstrate more efficient use of our resources from both an economic and ecological standpoint by using biological treatment methods. The application of constructed wetlands can lead to environmental improvements in handling wastewater that then allow for opportunities in the recycling and conservation of water as well as for using the nutrient resources of nitrogen, phosphorus, and organic matter contained in the wastewater.(Back to top)
Preliminary findings have shown that significant wastewater treatment is achieved by combining wetland technology with more traditional pond and lagoon treatment of highly enriched dairy wastewater as well as by incorporation of a solids separator. Initial BOD5 and TSS approaching 5,000 mg/l were reduced by nearly 90 percent (Karpiscak et al., 1999). Microbiological parameters also were reduced significantly. Mosquitoes in the highly organic wastewater did not respond to the use of Bacillus thuringiensis var. israeliensis (BTI) and Bacillus sphaericus (BS) and were controlled only by the use of a larvicidal oil applied on a weekly basis and by physically cutting and removing the densely-growing cattail plants. The high evapotranspirational losses and thus the concentration of salts in the system during the summer also proved to adversely impact the health and survival of all the plant species originally planted.(Back to top)
The application of constructed wetland technology in arid and semi-arid parts of the world has great promise to provide wastewater treatment and habitat improvement. We must, however, more fully understand the functioning of these ecosystems if we are to benefit fully from this technology without creating unintentional adverse consequences.(Back to top)
Hammer, D.A., Ed. 1989. Constructed Wetlands for Wastewater Treatment: Municipal, Industrial and Agricultural. Lewis Publishers Inc., Chelsea, MI.
Kadlec, R.H. and R.L. Knight, Eds. 1996. Treatment Wetlands. Lewis Publishers, Inc., New York.
Karpiscak, M.M., R.J. Freitas, C.P. Gerba,L.R. Sanchez and E. Shamir. 1999. Management of dairy waste in the Sonoran Desert using constructed wetland technology. Water Science and Technology, in press.
Karpiscak, M.M., K.E. Foster, S.B. Hopf, J.M. Bancroft and P.J. Warshall. 1994. Using Water Hyacinth to Treat Municipal Wastewater in the Desert Southwest. Water Resources Bulletin 30(2):219-227.
Karpiscak, M.M., K.E. Foster, S.B. Hopf and G. W. France. 1993. Treating Municipal Effluent Using Constructed Wetlands Technology in the Sonoran Desert. Pages 45-53 in K.D. Schmidt (ed.), Proceedings of the Symposium Effluent Use Management. August 29-September 2, 1993. Tucson, Arizona, USA.
Moshiri, G.A., Ed. 1993. Constructed Wetlands for Water Quality Improvement. Lewis Publishers, Boca Raton, FL.
Reed, S.C., E.J. Middlebrooks and R.W. Crites. 1988. Natural Systems for Waste Management and Treatment. McGraw Hill Co., New York, NY.
Vymazal J., H. Brix, P.F. Cooper, M.B. Green and R. Haberl, Eds. 1998. Constructed Wetlands for Wastewater Treatment in Europe. Backhuys Publishers, Leiden, The Netherlands.
Martin M. Karpiscak is a Research Scientist, and Susan B. Hopf is a Research Specialist, at the Office of Arid Lands Studies, The University of Arizona. They can both be reached for comment at the following address:
Office of Arid Lands Studies
The University of Arizona
1955 E. 6th St.
Tucson, AZ 85719-5224
Roland D. Wass is a Research Project Manager for the City of Phoenix Wastewater Engineer Division. He can be reached for comment as follows:
Tres Rios Wetlands
91st Ave. Wastewater Treatment Plant
5615 S. 91st Ave.
Tolleson, AZ 85353
Robert J. Freitas is an Associate in Extension, Department of Agricultural and Biosystems Engineering at The University of Arizona. He can be reached for comment as follows:
Department of Agricultural and Biosystems Engineering
Forbes Building, Room 102
The University of Arizona
Tucson, AZ 85721
Tres Rios Constructed Wetlands Demonstration Project: http://www.tresrios.net/
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