Nitrous oxide emission in low-oxygen simultaneous nitrification and denitrification process: Sources and mechanisms

摘要

This study attempts to elucidate the emission sources and mechanisms of nitrous oxide (N_2O) during simultaneous nitrification and denitrification (SND) process under oxygen-limiting condition. The results indicated that N_2O emitted during low-oxygen SND process was 0.8±0.1mgN/gMLSS, accounting for 7.7% of the nitrogen input. This was much higher than the reported results from conventional nitrification and denitrification processes. Batch experiments revealed that nitrifier denitrification was attributed as the dominant source of N_2O production. This could be well explained by the change of ammonia-oxidizing bacteria (AOB) community caused by the low-oxygen condition. It was observed that during the low-oxygen SND process, AOB species capable of denitrification, i.e., Nitrosomonas europaea and Nitrosomonas-like, were enriched whilst the composition of denitrifiers was only slightly affected. N_2O emission by heterotrophic denitrification was considered to be limited by the presence of oxygen and unavailability of carbon source.