[Construction and Denitrification Performance of A²/O Based on Partial Nitrification Coupled with an ANAMMOX System]

To resolve the issue of existing municipal wastewater treatment plants (WWTPs) in China with an insufficient influent carbon source, a bench-scale A²/O process based on partial nitrification coupled with ANAMMOX was constructed by controlling aeration partition ratio, dissolved oxygen (DO) concentration, and sludge retention time (SRT). In this study, the nitrogen removal performance, nitrogen removal pathway, and microbial community structure of the system under different conditions were investigated. The results showed that the system had excellent nitrogen removal efficiency at low-C/N influent (C/N=5). The A²/O reactor had experienced the co-culture stage (Phase 1), screening stage (Phase 2-3), and enrichment stage (Phase 4) successively during the 140-day experiment, and the nitrogen removal pathway changed from nitrification and denitrification to partial nitrification coupled ANAMMOX in the end. The optimal removal efficiencies of 97.69% for NH₄⁺-N and 87.83% for TN were obtained in the enrichment stage (Phase 4), and the effluent concentration of NH₄⁺-N and TN were 1.20 mg·L^-1 and 7.03 mg·L^-1, respectively. Illumina MiSeq sequencing results showed that the enrichment of AOB including Nitrosomonas and Nitrosospira and the elimination of NOB including Nitrospira, Nitrococcus, and Nitrobacter were the main causes of achieving partial nitrification in the system. The enrichment of AnAOB including Candidatus Kuenenia and Candidatus Jettenia was the key point for the occurrence of ANAMMOX in the system, and thus, played an important role in the achievement of advanced nitrogen removal.