FEATURE
Reclaimed Wastewater Continues Flow Toward Tap Potable reuse of water is growing, despite remaining scientific uncertainties and public resistance. STEPHEN COLE unicipal wastewater is no one's preferred source of drinking water. But for an increasing number of communities in the United States with water scarcity problems, adding highly treated wastewater to natural drinking water supplies is receiving serious consideration, although questions about potential health risks remain unresolved. Major new projects are under review this year in San Diego, Calif., and Tampa, Fla. The Los Angeles area is set to expand its well-established "recharging" of groundwater aquifers with reclaimed wastewater. Public opposition to diese projects remains a barrier in some communities, however. And a National Research Council (NRC) report released mis spring (i), which many wastewater officials hoped would give a clear stamp of approval to potable reuse, has ended up supporting both sides of the debate. The report states that studies have shown no harmful health effects from drinking reclaimed water, but it recommends better toxicity testing to reduce the uncertainty. Opponents have jumped on the report's concern about remaining potential risks and its description of potable reuse as "an option of last resort" to attack new projects. James Crook, chair of the NRC report committee and director of water reuse at the environmental engineering firm Black & Veatch, said "the current state of the art in treatment technology can produce safe water." The report's language is more neutral: "The several indirect potable reuse projects currendy operating in the United States generally produce reclaimed water that meets or exceeds the quality of the raw waters those systems would use otherwise Our general conclusion is mat planned, indirect potable reuse is a viable application of reclaimed water."
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Safe, but a "last resort" The report acknowledges that the degree of certainty about reclaimed waters safety could be im4 9 6 A • NOV. 1, 1998 / ENVIRONMENTAL SCIENCE & TECHNOLOGY / NEWS
proved, stating that "a number of methodological issues make it difficult to definitively determine the public health risks of drinking reclaimed water." Because potable reuse introduces some risk, the report states "indirect potable reuse is an option of last resort. It should be adopted only if other measures— including omer water sources, nonpotable reuse, and water conservation—have been evaluated and rejected as technically or economically infeasible." A key recommendation of the report is the use of multiple treatment barriers, both engineered and natural, to remove the complex suite of chemical and microbiological contaminants in municipal wastewater. Existing and proposed project designs use different arrays of treatment systems and environmental barriers. In Los Angeles County, wastewater that has received tertiary treatment is released to a "spreading basin," where it percolates through the soil before joining the groundwater aquifer (2). lliis "soil-aquifer treatment" constitutes the primary barrier in the system, which does not include advanced (and expensive) engineered treatment such, as reverse osmosis and microfiltration. The system can add up to 50 000 acre feet of reclaimed water to the aquifer per year, according to Margaret Nellor division engineer with the County Sanitation Districts of Los Angeles County. Neighboring Orange County is planning a system with twice that capacity that would use soil-aauifer vanced treatment technology. Proposed projects in San Diego and Tampa rely on the construction of new advanced treatment plants, as well as storage and mixing of reclaimed water with natural waters in surface reservoirs. The San Diego "water repurification" project would pipe treated water 20 miles to a reservoir, where it would be stored for at least a year before being pumped to a drinking water plant. Tampa's "Water Resource Recovery Project" would treat denitrified effluent prior to disinfection with high-pH lime treatment, recarbonation, mixed media filtra0013-936X/98/0932-496AS15.00/0 © 1998 American Chemical Society
tion, granular activated carbon adsorption, and ozone before piping water to the Tampa Bypass Canal where it would mix with natural water and be stored several weeks before use. Advanced treatment and storage in an aquifer are being used in a system nearing completion in California's Alameda County, east of San Francisco (see photo at right). Reclaimed water from a new treatment plant would be piped directly into the aquifer at several injection wells. On the basis of numerical modeling results, the reclaimed water will reside in the aquifer for a minimum of 8-10 years before being pumped out for drinking water treatment, according to Dave Requa, the district's engineering manager. The Dublin San Ramon Services District will treat wastewater formerly piped to the San FranHow valuable are environmental cisco Bay at a facility that uses advanced treatment processes such as reverse osmosis and mibarriers? crofiltration units shown here under construction. Engineers plan to turn on their 1100-acre-footThe NRC report notes that environmen- per-year system this year. (Courtesy Bruce Presser, The Covello Group, Walnut Creek, Calif.) tal banners reduce the risk in potable reuse systems, but by exactly how much "cannot presently be assessed with any confidence." A as a last resort is but one more reason why San Diego scientific panel reviewing Tampa's proposed system this shouldn't spend $168 million on its toilet-to-tap project. spring concluded that while the treatment train would . . . Repurified water might not be safe." Ronald Linsky, executive director of the Naproduce an "endproduct that is of acceptable quality," the environmental barrier of a mere two-week re- tional Water Research Institute, believes the NRC report "strongly supports the San Diego project." He tention time in the bypass canal "cannot be relied upon criticizes the Union-Tribune's opposition of the plan as a major barrier to contamination." A major research project is underway at ground- as an appeal to emotion rather than to reason. "It's water recharge sites in Arizona and California to quan- very difficult for scientists and engineers to deal with tify the effectiveness and long-term performance of soil- that kind of tactic," said Linsky, who points out that aquifer treatment. "Our hope is that this research will the Sierra Club has endorsed the project. yield some general performance measures applicable Public opposition may not be an insurmountto all projects so that we will know, once and for all, able barrier, however, according to Ron Kaiser, wawhether these systems can meet standards into the fu- ter specialist at Texas A&M University. Kaiser and ture," Nellor said. Led by Arizona State University and graduate student Michele Foss surveyed residents of the County Sanitation Districts of Los Angeles County, San Antonio, Tex., last year. "Aversion to using wastethe project will also seek to identify more than 90% of water was not as strong as we thought," said Kaiser. the complex suite of organic compounds found in mu- He believes an incremental approach to potable renicipal wastewater, most of which cannot be charac- use is needed, such as starting with using reterized with existing analytical techniques. A final re- claimed water for nonpotable purposes such as irport is expected in 2000. rigation. San Antonio began construction last year But removing scientific uncertainties and validat- of a system to distribute reclaimed water for irrigaing technological performance alone may not be tion, cooling towers, and manufacturing. enough to win public approval of potable reuse projects. Despite public resistance to potable reuse, the Crook acknowledges that public resistance to these practice is expected to become more common as projects poses a major obstacle. Take the recent case growing communities in arid regions continue to outin San Diego, where opposition surfaced after a Destrip available drinking water sources. "Groundwacember 1997 public hearing on the project. In March, ter recharge is going to continue to grow, but it's gothe San Diego City Council voted for an independent ing to be a slow process," Nellor said. scientific review of the project, which is being conducted by the National Water Research Institute. The panel will review results of the city's three-year pilot References (1) National Research Council. Issues in Potable Reuse: The Viproject; its conclusions will be incorporated into the ability of Augmeniing Drinking Water Supplies With Reproject's environmental impact statement. claimed Water, National Academy Press: Washington, DC, 1998. The San Diego Union-Tribune (3) )ame eut against (2) Pinholster, G. Environ. Sci. Technol. 1995, 29(4), 174Athe "toilet-to-tap" project, as the paper refers to it, us179A. ing the NRC report to support its case. According to the (3) San Diego Union-Tribune, March 15, 1998, p G2 (editorial). paper, "The National Research Council's conclusion that repurified sewage should be used as drinking water only Stephen Cole is the former managing editor o/ES&T. NOV. 1, 1998/ENVIRONMENTAL SCIENCE & TECHNOLOGY / NEWS • 4 9 7 A
