Fast start-up and enhancement of partial nitritation and anammox process for treating synthetic wastewater in a sequencing bath biofilm reactor: Strategy and function of nitric oxide

• Pre non-aeration is critical for fast start-up and enhancement of PN-A process. • NO produced by AOB might induce AnAOB during the start-up stage. • NO accumulation could indicate the synergetic state between AOB and AnAOB. • Low N 2 O emission (＜0.51%) was obtained due to low NO 2 – and low NO accumulation. In this study, the partial nitritation and anammox (PN-A) process was initiated within 30 days in a sequencing batch biofilm reactor (SBBR) by employing pre non-aeration and post non-aeration with fixed aeration rates. The average ammonia removal efficiency (ARE), total nitrogen removal efficiency (TNRE) of 98.5 ± 1.5% and 89.5 ± 1.6% were achieved. By doubling aeration rate and agitation rate and adopting pre non-aeration, the TNRR was promoted from 0.135 ± 0.013 kg N·m −3 ·d −1 to 0.285 ± 0.015 kg N·m −3 ·d −1 , obtaining an average ARE and TNRE of 97.5 ± 1.5% and 85.5 ± 2.6%. Nitric oxide might induce anaerobic ammonia oxidation bacteria (AnAOB) during the start-up stage, and could be an indicator for synergetic state between ammonia oxidation bacteria (AOB) and AnAOB. Lower nitrous oxide emission factor of 0.51% was obtained. The abundance of AOB, AnAOB and nitrite oxidation bacteria (NOB) accounted for 1.6%, 19.3% and 0.3%, respectively.