Nitrogen Removal 3.0: A Pilot Study to Evaluate the Feasibility of Mainstream Deammonification

A pilot study evaluated the feasibility of applying mainstream deammonification to a wastewater treatment facility (WWTF) lacking anaerobic digestion and therefore the potential for sidestream-generated ammonia oxidizing organism (AOO) bioaugmentation. The pilot incorporates two unique stages operated in series, known as an A/B process. The A-stage includes a low solids retention time (SRT), high-rate activated (HRAS) process targeted at 50-60% influent chemical oxygen demand (COD) removal. The B-stage includes a two-sludge deammonification process incorporating a partial nitritation reactor (CSTR) with a clarifier followed by an anammox moving bed bioreactor (MBBR).This paper considers the B-Stage nitritation reactor, operated under cyclical dissolved oxygen (DO) conditions based on a control strategy applying online ammonia, nitrite and nitrate instruments. The reactor operation limited the second nitrafication reaction by suppression of nitrate oxidizing bacteria (NOB) resulting in accumulation of greater than 80% of nitrogen species as nitrite (NO2-N/NOx-N). Hypotheses on NOB repression mechanisms include cyclical DO and COD loading.