Agricultural Utilization of Sewage Sludge

Project Background

Finding environmentally acceptable, socially responsible, and economically feasible ways of using municipal sewage sludge has received much attention from both research and regulatory agencies, as well as the general public. Daily processing of large quantities of sewage sludge under increasingly rigid water and air quality standards, has forced municipal officials, environmental engineers, and wastewater treatment operators to look beyond the conventional systems of treatment and disposal (i.e., incineration, landfilling, and ocean dumping). Land application of sewage sludge and effluent is an alternative that provides a means of returning the materials to a natural cycle that could be agriculturally useful and environmentally sound.

The nationwide environmental movement in the early 1970’s heightened our concerns about the need for proper disposal of sewage sludges. From 1973 to 1993, intense world-wide research efforts were conducted to better understand the reaction of sludge constituents in soils. A large part of this research effort has been due to the commitment and support of the U. S. Environmental Protection Agency (USEPA). These research efforts have generated a credible technical database that has led to the development of comprehensive sludge management regulations. As a result, the USEPA can now use regulations that set limits based on risk to human health and the environment (USEPA, 1993).

The USDA and land-grant agricultural universities must also be credited for their research and progress in utilization of sludge on land. Much of the leadership and financial support for the Rosemount Watershed study came from these organizations.

In 1973, when the Rosemount Watershed study was begun, most researchers were in agreement that sludges could be useful soil conditioners and sources of plant nutrients (N, P, and micronutrients), but information was needed to properly assess potential long-term hazards associated with its application to land. The potential for nitrate leaching, food chain transfer of toxic chemicals, pathogens, and phytotoxicity of trace elements were the primary concerns.

Background on Sludge

More than $2 billion are spent annually treating and disposing of nearly 5.4 million dry tons of municipal sewage sludge in the United States (Jewell, 1994). Depending upon the treatment alternative used, sludge generation rates are equivalent to an average production of 47 lbs (dry) person-1 yr-1 (21.4 kg person-1 yr-1). The quantities of sewage sludge applied to land in the United States has steadily increased over the last two decades (Lue-Hing et al., 1994).

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