Influence of operational modes and aeration rates on N2O emission from urban sewage treatment using a pilot-scale sequencing batch reactor

•Most of N2O emission (>90%) occurred during the aeration period.•Insufficient O2 supply during nitrification was major reason for N2O emission.•O2-inhibiting denitrification was another contributor for N2O emission.•A higher aeration and a longer denitrification could reduce the emission.

Pilot-scale experiments were carried out in a sequencing batch reactor to study the effect of operational modes/conditions of aeration on the emission of N2O during sewage treatment. The results showed that the flow-based emission factor of N2O under the aeration mode of 60-min anoxic/60-min aeration decreased from 0.75 to 0.42 g (ton of wastewater)−1 with the aeration rate increasing from 0.6 to 1.2 m3 h−1. This emission factor was lower than that under the aeration mode of 30-min anoxic/90-min aeration, which was 0.61-1.57 g (ton of wastewater)−1 within the same studied range of aeration rate. When the aeration rate was lowered to 0.3 m3 h−1, a smallest emission rate of N2O of 0.16-0.28 g (ton of wastewater)−1 was observed because of decreased removal efficiencies of NH4+-N (54.3%-57.8%) with insufficient O2 supply.