Low Level DO Operation: Impacts on Energy, Nutrients, and Ecology

Operating activated sludge system at low dissolved oxygen (DO) setpoints can have significant impacts on both energy conservation and nutrient recovery, two key components of our shift towards a resource recovery paradigm. Performance from two facilities operating at DO setpoints of 1 mg/L or less were evaluated for treatment performance and microbial ecology. Based on full scale results, full nitrification and biological phosphorus removal were achievable at low DO setpoints. In addition, significantly more nitrogen removal was achieved at the low DO setpoints. Microbial ecology investigation indicated that the low DO setpoints had minimal impact of the total ammonium oxidizing bacteria (AOB) in the system, and minimal impact on the phosphate accumulating organisms (PAO) population when operated in a biological nutrient removal (BNR) configuration (i.e. aeration tanks with selectors). The microbial ecology investigation also indicated little impact on the overall filamentous population due to low DO setpoints when a selector zone was included in the aeration basins.