[NO Generation, Key Influencing Factors, and Emission Reduction Strategies of AO Process in Municipal Wastewater Treatment Plant].

To achieve non-carbon dioxide greenhouse gas emission reduction and control in municipal wastewater treatment plants （WWTPs）, this study conducted one-year long-term monitoring of nitrous oxide （NO） in the anaerobic-anoxic-aerobic （AO） process of a large-scale municipal wastewater treatment plant in Beijing. The experimental results showed that the anaerobic and anoxic zones of the AO process could effectively remove dissolved NO contained in the return sludge, while the aerobic zone was the main area for NO generation and emission, and its generation pathway may have been dominated by ammonia oxidizing bacteria （AOB） denitrification. A significant difference was observed between winter and summer NO production, and the difference in the average NO release flux was up to 7.6 times, and the average monthly NO emission in winter was 32.75 kg, which was significantly higher than that in summer （6.06 kg）. The accumulation of nitrite （NO-N） and the concentration of dissolved oxygen （DO） had a significant impact on NO production. Therefore, to achieve NO reduction in the AO process, the concentration of NO-N in the aerobic zone should be controlled below 0.40 mg·L in winter and 0.10 mg·L in summer, while the DO concentration should be maintained above 1.2 mg·L.