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

Abstract 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 / NH 4 + – N ), also known as the ‘initial complete nitrification and subsequent partial nitrification’ (CN in –PN sub ) 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 −1 Alk / NH 4 + – 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 NO 2 - – N / NH 4 + – 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 ( K B ) and maximum ammonium utilization rate ( U max ) were determined to be 5.8 and 5.4 kg m −3  day −1 , respectively.