Wastewater Technology Fact Sheet

A significant nutrient load can be generated internally by publicly owned treatment works (POTWs). These nutrients can be found in the reject water, also known as side streams, of many municipal wastewater and sewage sludge treatment processes. These side streams include the reject stream from membranes, supernatant liquid from sludge digesters, and the centrate/filtrate return stream from sewage sludge dewatering processes, among others. Most of these side streams are conventionally returned to the headworks of the POTW, where they are combined with the normal influent. Estimates of the nitrogen load from this side stream return are between 15 and 30 percent of the total nitrogen load on the process (Solley, D. 2000).