Effective partial nitritation of dewatered liquor from dry methane fermentation using the submerged aerobic fixed film reactor (SAFFR)

• The nitritation-based process was first applied for treating dewatered liquor from dry fermentation. • Severe inhibition during the transition was observed as loss of nitritation and nitratation booming. • Integrated strategies were developed to recover nitritation and suppress NOB activity. • Nitrite conversion rate (NCR) reached 1.42 gN/L/d and effluent qualities satisfied anammox process. Characterized as more concentrated wastewater, the treatment of dewatered liquor from dry methane fermentation via the nitritation process was investigated in the present study. The transition from synthetic to the dewatered liquor has gone through severe deterioration: a loss of nitritation capacity and increased nitration. Several modifications were implemented: replacing the fixed beds to remove accumulated sludge and refresh the biofilm, adjusting the aeration rate based on Ammonia versus Nitrite (AvN) control, and maintaining free ammonia (FA) concentration to inhibit NOB. Through continuous monitoring and incremental adjustments, nitrite conversion rate (NCR) was gradually improved to 1.4 gN/L/d, with effluent nitrate levels below 42 mgN/L. The effluent ratio of NO 2 – /NH 4 + fluctuated within the range of 0.96–1.41, indicating successful partial nitritation of the target wastewater for the downstream anammox process. This acclimation experience underscores the importance of early adaptation to actual wastewater and the implementation of integrated strategies to effectively suppress nitrite oxidizing bacteria (NOB).