Determining Nutrient and Metals Contents in WI Septage to Manage Current WI Regulations

Abstract

Land application of septage from private onsite wastewater treatment systems (POWTS) is a practice used to dispose of waste that is generated from the general maintenance of POWTS. This waste source consists of wastewater and solids that contain nutrients, heavy metals, and potentially fecal pathogens. When septage is land applied, nutrients become available for beneficial reuse. An over application of these nutrients could result in environmental harm through nutrient contamination of surface water and groundwater resources. In 1992, the United States Environmental Protection Agency (EPA) regulated the land application of domestic septage through volume restrictions designed to limit the maximum nitrogen loading rates on land application sites. This formula equates to 100 lbs of available nitrogen per acre when domestic septage is applied at 39,000 gallons per acre, which was based on only a few analyzed samples to create the EPA regulation. The present nutrient and metals content of septic waste in Wisconsin is relatively novel and otherwise unknown. In this study 360 septic samples were collected from 36 counties across Wisconsin and analyzed for a complete nutrient and heavy metals characterization by the Environmental Microbial Analysis and Research Laboratory (EMARL), an extension of the University of Wisconsin Stevens Point (UWSP) College of Natural Resources (CNR). Analyses of these samples showed an increase in nitrogen contents compared to the 1992 EPA regulations, along with other inferences. In addition, a greenhouse trial was performed to evaluate the impact of different land application methods and fertilization rates on plant nitrogen yields. The results of this study will further inform management decisions by industry professionals and regulatory bodies.