Upscaling the Zeolite-Anammox Process: Treatment of Secondary Effluent

Water quality in San Francisco Bay is reportedly adversely affected by nitrogen loading from the wastewater treatment plants (WWTPs) discharging around the periphery of the Bay. Here, we consider a zeolite-anammox system to remove ammonia and nitrate from secondary-treated wastewater at ambient temperatures (12-30 degrees C). Until now, use of anammox bacteria has been largely limited to treatment of high-ammonia content wastewater at warm temperatures (30-40 degrees C). Specifically, we investigate upscaling the zeolite-anammox system to nitrogen removal from relatively low-ammonia content (similar to 35 NH3-N mg/L) effluent using gravity-fed 0.7 m wide and 0.17 m deep linear-channel reactors within pilot plants located at either the WWTP or some eight kilometers away. Following establishment, we monitored ammonia and nitrate concentrations along one reactor bi-weekly and only inflow-outflow concentrations at the other for more than a year. We found nearly complete ammonia removal within the first 22 m of reactor consistent with the theoretical 89% nitrogen removal capacity associated with the nitrogen-conversion stoichiometry of anammox bacteria. We also determined degradation parameters of a constant 1.41 mg NH3-N/L per hour in the first 15 m, or 20.7 g NH3-N/m(3)/day for overall reactor volume. At the higher flowrate of the second reactor, we achieved a removal rate of 42 g NH3-N/m(3)/day. Overall, the linear-channel reactors operated with minimal maintenance, no additional energy inputs (e.g., for aeration) and consistently achieved NH3-N discharge concentrations similar to 1 mg/L despite fluctuating temperatures and WWTP effluent concentrations of 20-75 mg NH3-N/L.