Use of Reclaimed Water and Sludge in Food Crop Production (1996) / Chapter Skim
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Executive Summary
Executive Summary
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Executive Summary BACKGROUND The use of treated municipal wastewater effluent for irrigated agriculture offers an opportunity to conserve water resources. Water reclamation can also provide an alternative to
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An estimated 5.3 million metric tons per year dry weight of sludge are currently produced in the United States from publicly owned treatment plants. This amount will surely increase as a larger population is served by sewers and as higher levels of wastewater treatment are introduced.
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In this context, sewage sludge traditionally regarded by many groups as an urban waste requiring careful disposal is now viewed by the wastewater treatment industry, the regulatory agencies, and participating farmers as a beneficial soil amendment. EPA believed that both water reclamation and sludge beneficial use programs could benefit from an independent assessment of the public health and environmental concerns that have been raised by the food processors concerning land application of treated municipal wastewater and sludge.
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In general, modern wastewater treatment procedures incorporate monitoring and technical redundancies that provide system reliability and protection against exposure to pathogens. The strategy for regulating pathogens in the agricultural use of sludge is similar.
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Potentially harmful trace elements, such as arsenic, cadmium' cobalt, copper, lead, mercury, molybdenum, nickel, selenium, and zinc are found in treated municipal wastewater effluents. In 1973, the National Academy of Sciences issued a report on water quality criteria that recommended limits on the concentration of trace elements in irrigation water with regard to their effects on crop production.
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Chemical production and use bans, industrial pre-treatment programs, and municipal wastewater treatment have been effective in reducing the levels of toxic constituents in wastewater effluents to acceptable levels. Wastewater treatment processes also remove many toxic organic chemicals in the wastewater stream through volatilization and degradation.
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Recent studies suggest that plant tissues may absorb volatile toxic organic chemicals from the vapor phase of volatile compounds; however, the aeration that occurs during treatment of wastewater and during many sludge treatment processes removes most of the volatile organic chemicals at the treatment plant. This study revealed some inconsistencies in EPA's approach to risk assessment and its technical interpretation for development of the Part 503 Sludge Rule, although the inconsistencies do not affect food safely.
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, reclaimed water that has received a minimum of secondary treatment will normally meet these recommended limits for irrigation water quality. While the plant nutrients in treated effluents are generally considered a supplemental fertilizer source, the application rates are not easily controlled compared to commercial fertilizer operations.
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Treated Municipal Sludge Municipal sewage sludge is a source of nitrogen and phosphorus in crop production. The addition of organic matter through successive sludge applications improves the physical properties and productivity of soils.
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Where excess phosphorus is of concern, soil phosphorus levels should be monitored and sludge application rates should be adjusted to correspond to crop phosphorus rather than nitrogen needs. · As more croplands are treated with municipal sludges and reach their regulatory limit of chemical pollutant loading from sludge applications, additional infonnation will be needed to assess potential, long-term Impacts of sludge on ground water quality and on the sustainability of soils for crop production.
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, potential risks could lead to liability, and the negative public perception of food crops produced using these materials could have a detrimental impact on consumer demand. Even though the value of the water and nutrients represents only a small percentage of total farm production costs, there are many cases of clear economic incentives for society as a whole as well as for municipal wastewater treatment plants to pursue cropland reuse options.
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In addition, the utility should be prepared to indemnify fanners against potential liabilities when farmers' financing by banks or other lenders may hinge on this assurance. Other Regulations Art Institutional Controls From a regulatory perspective, it is important to remember that EPA's Part 503 Sludge Rule augments a wide array of existing institutional programs and controls over the disposition of municipal wastewater and sludge For example, federal and state regulations govern the handling and treatment of toxic waste and the protection of surface and ground waters These regulatory mandates appear adequate to manage most of the risks associated with land application, but they must be funded and implemented to be meaningful safeguards Sludges that do not meet beneficial use criteria standards as defined by the Part 503 Sludge Rule must be disposed of according to federal and state regulations as applicable Both the general public and state and local regulators should be aware that the Part 503 Sludge Rule is not the only control over agricultural use of sewage sludge Recommendation · Management of sludge for beneficial use should be more visibly linked to existing regulations governing its disposal.
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Established numerical limits on concentration levels of pollutants added to cropland by sludge are adequate to assure the safety of crops produced for human consumption. In addition to health and environmental concerns, institutional barriers such as public confidence in the adequacy of the regulatory system and concerns over liability, property values, and nuisance factors will play a major role in the acceptance of treated municipal wastewater and sewage sludge for use in the production of food crops.
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