Nitrous Oxide Production Within Sludge Aggregates in a Full-Scale A2/O Wastewater Treatment Plant: A Microscopic Investigation

Mitigating nitrous oxide (N2O) emissions from municipal wastewater treatment plants (WWTPs) requires a clear understanding of their in situ production. This study employed microelectrodes to perform in situ profiling of N2O dynamics within sludge aggregates across anaerobic, anoxic, and aerobic tanks of a full-scale WWTP. The results showed that N2O production was heterogeneous: highest in the anoxic tank, lower in the aerobic tank, and minimal in the anaerobic tank. Specifically, the inlet section of the anoxic tank exhibited the maximum net production (1380.99 µmol·cm−2·h−1), 1.4 times that of the front aerobic section (986.09 µmol·cm−2·h−1). Denitrification (anoxic zone) and ammonia oxidation (aerobic zone) were identified as the two dominant pathways. Optimizing substrate availability, dissolved oxygen levels, and nitrite concentration can effectively reduce N2O production potential. This study provides novel insights into the source identification of N2O in full-scale WWTPs, forming an important basis for the sustainable optimization and greenhouse gas mitigation of wastewater treatment.