The United States Environmental Protection Agency (EPA) has developed guidelines and regulations for the use and disposal of sewage sludge (40 CFR 503). Compliance with the standards in 40 CFR 503 took full effect in February 1994. State and local governments are expected to enforce these regulations (or impose more stringent regulations than the requirements of EPA). Land applied biosolids in California must at least meet Class B pathogen standards as required in 40 CFR 503 and must be non-hazardous in accordance with the procedures that are specified in Title 22, Division 4.5, Chapter 11, Article 3 of California Code of Regulations or by other permits issued by the Regional Water Quality Control Board (RWQCB). Biosolids must also meet 40 CFR 503.13 Tables 1-4 for trace element limits and maximum loading rates.
Land application is one of the most effective methods of disposal of sewage sludge. Land application of sewage sludge and dewatered biosolids may also be beneficial in improving soil physical and chemical conditions, water holding capacity, and water penetration rate. However, the presence of heavy metals and pathogens in sewage sludge may make their use undesirable in lands used for the production of fruits and vegetables. Disposal of sewage sludge will be more likely on lands planted to field crops. California EPA and local county governments are the permitting authorities in California. Several attempts have been made by Publicly Owned Treatment Works (POTWs) to explore the possibility of applying biosolids to agricultural lands in California. Local county governments across the state have expressed concern about health and environmental issues associated with bulk application of sewage sludge despite the fact that sludges meet the general requirements of 40 CFR 503.12 and the management practices in 40 CFR 503.14.
Biosolids contain considerable amount of nitrogen (Kelling et al., 1977). Biosolids have been primarily used as a source of nitrogen, the amount of sludge nitrogen varies from 4 to 50% (Magdoff and Amadon, 1980). Most of the published research on biosolids has dealt with nitrogen availability from sewage sludge (Sommers, 1977) and plant uptake of metals in corn and wheat. A considerable amount of work has been done on the rate of accumulation of Se and other heavy metals in field crops in the San Joaquin Valley (SJV) in California (Severson and Gough, 1992). Drainage water from part of the SJV was transported to Kesterson Reservoir via the San Luis drain canal. Evaporation of water at Kesterson resulted in a high concentration of Se and other metals in Kesterson soil. Research has been done on the distribution of Se and other elements in soils (Tidball et al., 1989) and in groundwater (Deverel and Gallanthine, 1989), and their uptake by alfalfa and other crops (Wan et al., 1988). The uptake of heavy metals and trace elements by plants depends on the concentration of theses elements in soil as well as on complex sets of other factors related to soil geochemistry (Tidball et al., 1989). The most important soil factors that influence plant uptake of elements are pH, clay content, soil texture, root depth, organic matter content and the presence of competitive ions (such as S for Se uptake). In addition, plant species vary in their ability to accumulate and tolerate trace elements and heavy metals. The beneficial uses of sewage sludge and the other aspects such as nutrients, trace metals, organic compounds, and public health has been discussed in detail by Page et al. (1983).
Dewatered biosolids contains nitrogen, macro and micro nutrients, and organic matter with a high fertilizer value. Issues such as quality of drainage and surface water, groundwater pollution, and plant uptake of metals such as Mo, As, Se, and Cr are of great concern to the general public. Little is known about the environmental issues, such as quality of drainage and surface water, associated with the application of dewatered biosolids in irrigated regions in the United States. Sludge materials may contain heavy metals and trace elements such as lead (Pb) and selenium (Se). However, in the Imperial Valley and elsewhere, selenium has been found in drainage water in California at concentrations that already exceed the EPA standard for wetlands. Field crops account for almost 80% of the 500,000 acres of irrigated land in the Imperial Valley. Alfalfa and sudangrass ranked 1st and 2nd in total acreage, respectively in 1993 in Imperial Valley (Imperial County Agricultural Crop and Livestock report). These two major field crops were grown on more than 236,000 acres of irrigated lands in Imperial Valley in 1993. This proposed research will apply Class B biosolids at 0, 4, 8, 12 dry tons per acre of dewatered biosolids. This research will be directed toward evaluating the effect of different application rates of biosolids on soil physical characteristics, groundwater quality, plant uptake of metals that are identified in part 40 CFR 503.13 Table 4, and hay yield and quality aspects. No work has been done addressing the above issue after the full implementation of 40 CFR 503 in February of 1994 regarding the uses of sewage sludge or the environmental aspects associated with biosolids applications on irrigated lands. This project is designed to address these issues in addition to providing information relative to some of 40 CFR 503 data gaps.
Since soil salinity and water management are affected by biosolids application, part of this study will be to quantify soil salinity, water infiltration rates, and heavy metal accumulations in soil and groundwater. To observe cumulative aspects of dewatered biosolids application on soil characteristics, this study is proposed for three years. A comprehensive guide to the application and management of dewatered biosolids in agricultural soils, video materials, and a slide set of 40 CFR 503 requirements will be developed. Several field days, seminars and short courses will be conducted by the PI's during the project. Findings from this research project will be published in local, statewide, and national agricultural magazines and scientific journals.
The specific objectives of this research and demonstration project are to: