Insight into using up-flow anaerobic sludge blanket-anammox to remove nitrogen from an anaerobic membrane reactor during mainstream wastewater treatment

A partial nitritation/anammox system treating the effluent of an anaerobic membrane bioreactor was investigated in this study with emphases on the nitrogen conversion and microbial dynamics along the up-flow anaerobic sludge blanket. An average total nitrogen concentration of 12.3 mg/L was achieved in effluent, which resulted in a total nitrogen removal efficiency of 75.9% ± 0.6%, in which the contribution of anammox was over 98%, and mainly occurred at the bottom of the up-flow anaerobic sludge blanket. Furthermore, external nitrite produced from nitrate reduction enhanced the nitrogen removal efficiency. Ca. Brocadia was the dominant anammox bacteria and was enriched at the bottom; Dokdonella and Thermomonas were identified as the denitrifiers for nitrite production and existed in the whole reactor. Findings of this study can be used in a practical model for the future development of integrating anaerobic digestion with partial nitritation/anammox in mainstream wastewater treatment.