Mineralization and Plant Availability of Nitrogen and Phosphorus in Land-Applied Municipal Biosolids.

Wastewater treatment generates ever-increasing quantities of biosolids, the largely organic solids, semisolids, or liquid suspensions remaining after treatment and effluent separation. Biosolids are recycled primarily via application to agricultural land. Different wastewater treatment processes produce sludge with different characteristics, and further variations arise from various final treatment processes used to transform sludge into biosolids that meet regulatory requirements for land application.  Assuming acceptable levels of toxic metals, biosolids application rates are currently regulated based on total N content and availability coefficients.  The USEPA and the North Carolina Department of Environment and Natural Resources are considering regulating application rates based on both P and N.  Research is needed to determine N and P mineralization-availability coefficients of different types of biosolids applied to North Carolina’s diverse soils in order to determine appropriate application rates. This should help optimize nutrient uptake efficiency and minimize excess N and P available to contaminate ground and surface waters. The biosolids we are studying include products of: 1) aerobic digestion, 2) anaerobic digestion, and 3) aerobic digestion, heat treatment, and pelletization.  We are evaluating several biological and chemical tests for their ability to predict N and P availability from these biosolids applied to representative soils with a range of chemical and physical properties. The tests include aerobic and anerobic incubations; extractions; and the amino sugar N test. We will conduct short-term greenhouse experiments to determine N, P, and other nutrient and metal uptake by representative receiving crops (e.g, bermudagrass  [Cynodon dactylon], tall fescue [Festuca arundinacea Schreb.], corn [Zea mais L.]).  Eventually, we will conduct field trials to correlate with laboratory and greenhouse tests.  Results from this research will be useful in determining whether multiple availability coefficients are necessary for different soils, crops, and biosolids, with an aim toward protecting water quality.