Nitrogen Removal Design, Startup, and 6 Years of Operation in Scituate, Massachusetts

Scituate Massachusetts, located on the coast of eastern Massachusettts, is a 1.6 mgd average flow plant with stringent total nitrogen (TN) permit limits and discharge to shellfish waters. Nitrogen removal is achieved using activated sludge for nitrification and Tetra Denit Fitlers for denitrification. Winter monthly temperatures drop to 9°C. Plant effluent averaged 3 mg/L TN, 3 mg/L carbonaceous biochemical oxygen demand (CBOD) and 4 mg/L total suspended solids (TSS) over the 6 year period following startup. Performance of the Tetra filters exhibited continuous improvement over the first 5 years. Full scale testing of an alternative carbon source for methanol provided problematic. This paper presents design considerations, startup issues, and 6 years of operational data.