Aerobic N₂O emission for activated sludge acclimated under different aeration rates in the multiple anoxic and aerobic process

Nitrous oxide (N₂O) is a potent greenhouse gas that can be emitted during biological nitrogen removal. N₂O emission was examined in a multiple anoxic and aerobic process at the aeration rates of 600 mL/min sequencing batch reactor (SBR_L) and 1200 mL/min (SBR_H). The nitrogen removal percentage was 89% in SBR_L and 71% in SBR_H, respectively. N₂O emission mainly occurred during the aerobic phase, and the N₂O emission factor was 10.1% in SBR_L and 2.3% in SBR_H, respectively. In all batch experiments, the N₂O emission potential was high in SBR_L compared with SBR_H. In SBR_L, with increasing aeration rates, the N₂O emission factor decreased during nitrification, while it increased during denitrification and simultaneous nitrification and denitrification (SND). By contrast, in SBR_H the N₂O emission factor during nitrification, denitrification and SND was relatively low and changed little with increasing aeration rates. The microbial competition affected the N₂O emission during biological nitrogen removal.