Impact of carbon source on nitrous oxide emission from anoxic/oxic biological nitrogen removal process and identification of its emission sources

Wastewater treatment is an important source of nitrous oxide (N2O), which is a strong greenhouse gas and dominate ozone-depleting substance. The purpose of this study was to evaluate the effect of carbon source on N2O emission from anoxic/oxic biological nitrogen removal process. The mechanisms of N2O emission were also studied. Long-term experiments were operated to evaluate the effect of three different carbon sources (i.e., glucose, sodium acetate, and soluble starch) on N2O emission characteristics. And batch experiments, in the presence or absence of specific inhibitors, were carried out to identify the sources of N2O emission. The ammonia-oxidizing bacteria (AOB) and denitrifiers community compositions under different circumstances were also analyzed based on which the underlying mechanisms of N2O emission were elucidated. The conversion ratios of N2O in reactors with glucose, sodium acetate, and soluble starch were 5.3 %, 8.8 %, and 2.8 %, respectively. The primary process responsible for N2O emission was nitrifier denitrification by Nitrosomonas-like AOB, while denitrification by heterotrophic denitrifiers acted as the sink. Reactor with sodium acetate showed the highest N2O emission, together with the highest nitrogen and phosphate removal ratios. Carbon source has a significant impact on N2O emission quantity and relatively minor effect on its production mechanism.