The Use of On-Off Aeration to Achieve Nitrification and Denitrification in a Municipal Wastewater Treatment Plant

A lab-scale study was conducted to determine whether on-off aeration could be successfully applied to the Sioux Falls Water Reclamation Facility (SFWRF) activated sludge system to achieve an effluent total nitrogen concentration under 15 mg/L as N. The lab-scale reactor modeled the existing facility and was operated at a hydraulic retention time of 5.9 hours and a solids retention time of 15 days. The use of 100% primary clarifier effluent with one hour on aeration followed by three hours off aeration provided enough organic carbon to achieve target effluent ammonia-nitrogen concentrations at 20 C and 10 C. The effects of mixing during the off aeration period was examined and it was determined that mixing is required during the off period in order to provide total nitrogen removal. During all testing the need for the addition of alkalinity was eliminated due to the recovery of alkalinity through the denitrification process.