| Summary: | 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 °C). Until now, use of anammox bacteria has been largely limited to treatment of high-ammonia content wastewater at warm temperatures (30–40 °C). Specifically, we investigate upscaling the zeolite-anammox system to nitrogen removal from relatively low-ammonia content (~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/m3/day for overall reactor volume. At the higher flowrate of the second reactor, we achieved a removal rate of 42 g NH3-N/m3/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 ~1 mg/L despite fluctuating temperatures and WWTP effluent concentrations of 20–75 mg NH3-N/L.
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