Rapid start-up of PN/A process and efficient enrichment of functional bacteria: A novel aerobic-biofilm/anaerobic-granular nitrogen removal system (OANRS)

[Display omitted] •A denitrification system consists of a reactor and a corresponding control strategy.•PN/A process was quickly started within 41 days.•Candidatus Kuenenia relative abundance was as high as 43.13% at 98 d.•The single-stage and two-stage PN/A processes were contained in one reactor.•NOB was inhibited through matrix competition between microorganisms. Reactor configuration, control strategy and inoculation method were key factors affecting the rapid start-up of partial nitrification/anammox (PN/A) process and the efficient enrichment of functional bacteria (anammox and ammonia oxidizing bacteria). At present, PN/A process was generally operated through single factor rather than forming a system. In this study, a novel aerobic-biofilm/anaerobic-granular nitrogen removal system (OANRS) was constructed, which consisted of a multi-stage aerobic-biofilm/anaerobic-granular baffle reactor (MOABR) and a control strategy on pH/aeration time. PN process was started within 10d, and PN/A process was started on the basis of stable PN process within 41d. The simultaneous enrichment of functional bacteria was achieved by combining the advantages of single-stage and two-stage PN/A process. The results of high-throughput sequencing showed that Candidatus Kuenenia (20.42 ± 15.88%) was highly enriched in each compartment at day 98, and the relative abundance of Candidatus Kuenenia in the anaerobic compartment R4 was as high as 43.13%.