Start-up and stable operation of partial nitritation prior to ANAMMOX in an internal-loop airlift reactor

The feasibility of implementing a novel strategy to start up and stably operate a partial nitritation (PN) process in an internal-loop airlift reactor was investigated. The results suggested that the PN process was successfully set up through initial complete nitrification followed by adjusting the alkalinity-to-ammonium ratio (Alk/NH4+-N), also known as the 'initial complete nitrification and subsequent partial nitrification' (CNin-PNsub) strategy. A high nitrite accumulation ratio of approximately 98% and a maximum nitrite production rate of 0.91 kg N m−3 day−1 were attained under the conditions of 1.0 mol mol−1Alk/NH4+-N, 1.24 ± 0.71 mg L−1 dissolved oxygen, 3.99 ± 2.29 mg L−1 free ammonia and 0.69 ± 0.30 mg N L−1 free nitrous acid. The stabilized effluent with an NO2--N/NH4+-N ratio of 1.15 ± 0.06 was suitable for subsequently feeding the anaerobic ammonium oxidation (ANAMMOX) process. The modified Stover-Kincannon model was used to analyze the kinetic parameters, and the saturation constant (KB) and maximum ammonium utilization rate (Umax) were determined to be 5.8 and 5.4 kg m−3 day−1, respectively.