Trace Metal Retention in the Incorporation Zone of Land-Applied Sludge

Recycling nutrients in wastewater sludge (biosolids) via land application is a desirable goal. However, potential movement of sludge-applied trace metals is of concern and an area of ongoing research. In this paper, we examine the first-order model used by the United States Environmental Protection Agency (U.S. EPA) for predicting losses from the zone of incorporation as part of the risk assessment that undergirded the development of Part 503 regulations ( , ). We found that when empirical adsorption partition coefficients from the site are used as model inputs, the U.S. EPA model for the incorporation zone is similar to that derived from preferential flow theory and simulates well the loss of metal from the surface soil layer at an orchard site where sludge was applied 15 years earlier.