Molly Jameson, Soil Science, North Carolina State University, Raleigh, NC, Jeffrey G. White, Box 7620, North Carolina State University, Raleigh, NC and Deanna L. Osmond, PO Box 7620, North Carolina State University, Raleigh, NC
Biosolids are the largely organic, nutrient-rich, solid or semisolid residuals of wastewater treatment. Sewage sludge becomes biosolids when treated to meet federal and state standards for beneficial reuse via land application as a fertilizer and soil amendment. In North Carolina (NC) and elsewhere, land application is currently governed by biosolids plant-available N and the agronomic N needs of the crop on the receiving soil. Because of the differences between biosolids and crop N:P, N-based biosolids applications typically surpass crop P needs, create excess soil P, and increase surface water pollution potential. USDA Conservation Practice Standards mandate P budgets and in many cases, P-loss risk assessments. Many states have P-based guidelines, and the NC Department of Environment and Natural Resources is considering guidelines for some nutrient-impaired watersheds. In NC, the P Loss Assessment Tool (PLAT) will likely be used to estimate biosolids P-loss risk. To use PLAT with biosolids, however, the soluble P fraction (soluble P/total P) must be quantified. Forms and quantities of P in biosolids depend on wastewater treatment plant (WWTP) influent and treatment processes. NC WWTPs were surveyed to characterize treatment and biosolids production processes. These can vary significantly, greatly influencing water-soluble and total P. We sampled biosolids from representative WWTPs and analyzed for water-extractable and total P so that PLAT can be used to estimate P-loss risk. We are determining relationships between the P fractions and WWTP processes to ascertain whether the former can be assigned based on the latter. Land application of biosolids based on both P and N will likely decrease application rates, reduce the number of eligible receiving fields, and shorten the time soils can receive biosolids, thus making land application more costly. Hence, widespread adoption of a P-based approach may foster development of alternative beneficial uses of biosolids other than land application.