Three Cost-effective Public Domain On-site Sewage Treatment Technologies Verified for Their Ability to Denitrify

Sewage typically contains high levels of nitrogen. Even with new technologies, on-site sewage (septic) treatment systems typically do not reduce nitrogen levels in treated wastewater. Cost effective on-site sewage systems with adequate denitrification capabilities are needed for areas where nitrogen has been determined a contaminant of concern. A collaborative effort between the Washington State Department of Health and the University of Washington Civil and Environmental Engineering Department was undertaken to design and evaluate cost effective, reliable, and low maintenance public domain treatment technologies that have high nitrogen removal efficiencies. The systems were installed and tested at the Snoqualmie Wastewater Treatment Plant. In addition to meeting low effluent biochemical oxygen demand and low total and volatile suspended solids concentrations and bacteriological reduction, a major treatment objective was to produce an effluent TN concentration below 20 milligrams per liter (mg/L). A total nitrogen (TN) concentration of less than 20 mg/L is the Washington State technology-based standard for on-site nitrogen removal. Using the EPA Environmental Technology Verification protocol for nutrient reduction, three novel systems were evaluated for performance and denitrification capability. All three systems met the objective of reducing total nitrogen concentrations to less than 20 mg/L. This presentation will summarize the system designs, evaluation protocols, results, and next steps