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 pre-treatment of the main wastewater stream. After this pre-treatment, 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 °C. But, anaerobically pretreated municipal wastewater is characterized by much lower nitrogen concentrations (20–100 mg L^?1) and lower temperatures (10–25 °C). We operated PN/A under similar conditions: total ammonium nitrogen concentration 50 mg L^?1 and lab temperature (22 °C). PN/A was operated for 342 days in a 4 L moving bed biofilm reactor (MBBR). At 0.4 mg O₂ 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 °C, improving the applicability of PN/A for municipal wastewater treatment.