High-efficient nitrogen removal from municipal wastewater via two-stage nitritation/anammox process: Long-term stability assessment and mechanism analysis.

This study focused on the long-term stability of a novel two-stage partial-nitritation/anammox (PN/A) process treating municipal wastewater with fluctuated water quality. Specifically, two parallel sequencing batch reactors (SBRs) were used for removing organic matters and achieving complete nitritation, while the expanded granular sludge bed (ANA-EGSB) was used for anammox. With the influent ammonium concentration varying from 32 to 79 mg/L and the average hydraulic retention time of 3.39 h in this system, more than 93% of ammonium was removed and the effluent TIN was 4.8-11.8 mg/L. The partial denitrifying occurring in the anammox reactor could reduce nitrate to nitrite that was reused by anammox bacterium, enhancing the TIN removal efficiency. Further, the "overconsumption of ammonium" under anaerobic conditions was observed in ANA-EGSB. Microbial community analysis showed that Nitrosomonas (AOB) were the dominant nitrifying bacteria in the nitritation SBR and Candidatus_Brocadia with the relative abundance of 6-13% dominated in ANA-EGSB.