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Potential found for expanding the US water supply through wastewater reuse

April 03, 2012
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Expanding water reuse — the use of treated wastewater for irrigation, industrial uses, and drinking water augmentation — could significantly increase the nation’s total available water resources, concludes a new report from the National Academy of Sciences, titled, “Water Reuse: Potential for Expanding the Nation’s Water Supply through Reuse of Municipal Wastewater.”

A portfolio of treatment options is available to mitigate water quality issues in reclaimed water, and new analysis, the report says, suggests the risk of exposure to certain microbial and chemical contaminants from drinking reclaimed water does not appear to be any higher than the risk experienced in at least some current drinking water treatment systems and may be orders of magnitude lower. Adjustments to the federal regulatory framework could enhance public health protection for both planned and unplanned — or de facto — reuse, and increase public confidence in water reuse.

Key findings in the report include the following:

• Approximately 12 billion gallons of municipal wastewater effluent is discharged each day to an ocean or estuary out of the 32 billion gallons per day discharged nationwide. Reusing these coastal discharges would directly augment available water resources — equivalent to 6 percent of the estimated total U.S. water use, or 27 percent of public supply. Inland effluent discharges may also be available for water reuse, although extensive reuse has the potential to affect the water supply of downstream users and ecosystems in water-limited settings.

• De facto reuse of treated wastewater to augment drinking water supplies — for example, when a drinking water system uses a water supply that receives upstream wastewater discharges — is common in many of the nation''s water systems. A systematic analysis of the extent of effluent contributions to potable water supplies has not been made in the U.S. for over 30 years.

• A portfolio of treatment options, including engineered and managed natural treatment processes, exists to mitigate microbial and chemical contaminants in reclaimed water. Numerous process combinations can be tailored to meet specific product water quality objectives.

• To ensure the quality of reclaimed water, treatment systems should include multiple barriers for pathogens that cause waterborne diseases to strengthen the reliability of contaminant removal, and should employ diverse combinations of technologies to address a broad variety of contaminants. Reclamation facilities should develop monitoring and operational plans to respond to variability, equipment malfunctions and operator error to ensure that reclaimed water meets the appropriate quality standards for its use.

• In nearly all current potable water reuse systems, water is discharged after treatment to an aquifer, stream, or a wetland to provide a buffer between water treatment and consumption. Environmental buffers can further remove contaminant levels such as pathogens from the water and provide additional retention time. However, the science necessary to design engineered natural systems to provide a uniform level of public health protection is not available at present.

• Modern technology allows the detection of chemical and biological contaminants at extremely low levels, but the detection of a contaminant in reclaimed water does not, in and of itself, indicate a significant risk. Information on the dose of a contaminant required to cause health effects allows scientists to determine if the level of contaminant is significant.

The committee compared the estimated risks of a conventional drinking water source that contains a small percentage of treated wastewater against the estimated risks of two different potable reuse scenarios considering 24 chemical and four microbial contaminants. The analysis suggests that the risk of contaminant exposure in the two planned potable reuse scenarios does not exceed the risk encountered from existing water supplies, and may be orders of magnitude lower.

The financial costs of water reuse vary widely because they depend on site-specific factors, the report notes, including the location, water-quality objectives, and method of treatment applied. To determine the most socially, environmentally, and economically feasible water supply option, the non-monetized costs and benefits of reuse projects should also be considered.

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