Applicability of one-stage partial nitritation and anammox in MBBR for anaerobically pre-treated municipal wastewater

Energy consumption of municipal wastewater treatment plants can be reduced by the anaerobic pretreatment of the main wastewater stream. After this pretreatment, nitrogen can potentially be removed by partial nitritation and anammox (PN/A). Currently, the application of PN/A is limited to nitrogen-rich streams (>500 mg L-1) and temperatures 25-35 degrees C. But, anaerobically pretreated municipal wastewater is characterized by much lower nitrogen concentrations (20-100 mg L-1) and lower temperatures (10-25 degrees C). We operated PN/A under similar conditions: total ammonium nitrogen concentration 50 mg L-1 and lab temperature (22 degrees C). PN/A was operated for 342 days in a 4 L moving bed biofilm reactor (MBBR). At 0.4 mg O-2 L-1, nitrogen removal rate 33 g N m(-3) day(-1) and 80 % total nitrogen removal efficiency was achieved. The capacity of the reactor was limited by low AOB activity. We observed significant anammox activity (40 g N m(-3) day(-1)) even at 12 degrees C, improving the applicability of PN/A for municipal wastewater treatment.