Effect of aeration rate on the emission of N2O in anoxic–aerobic sequencing batch reactors (A/O SBRs)

Nitrous oxide (N₂O) is a significant greenhouse gas, and biological nitrogen removal systems have been shown to be a significant N₂O source. To evaluate the control parameters for N₂O emission in the wastewater treatment process, N₂O emissions were compared in the activated sludge from anoxic–aerobic sequencing batch reactors (A/O SBRs) acclimated under different aeration rates, and fed with synthetic wastewater. Results showed that a higher aeration rate led to a smaller N₂O emission, while reactors acclimated under mild aeration performed the best in terms of nitrogen removal efficiency. Most of the N₂O was produced during the aerobic phase, regardless of the aeration rate. Trace studies showed that incomplete denitrification appeared to be the major process responsible for high N₂O emission at a low aeration rate (Run 1), while incomplete nitrification was the reason for N₂O emission at a higher aeration rate (Run 2 and Run 3). For enhancing the efficiency of nitrogen removal while lowering energy consumption and reducing N₂O emission, the optimal aeration rate would be 2.7 L_air/(L_reactor · h), in terms of the synthetic wastewater used.