New insight on the regulation of N2O production in aerobic condition: An N2O metabolic perspective based on enzymatic analysis of nitrous oxide reductase

Abstract Nitrous oxide reductase (N2OR) (EC 1.7.2.4) is the only enzyme that can catalyze nitrous oxide (N2O) decomposition to nitrogen gas, which connects tightly with N2O accumulation. But it is known little about N2O metabolism based on the enzyme in biological nitrogen removal of wastewater, especially in aerobic conditions. This paper studies the biosynthesis and metabolism of N2O through the analysis of the activity of the enzyme in aerobic conditions. It is revealed that the main metabolic mechanism of N2O was heterotrophic denitrification, which was mainly affected by electron supply (the amount of organic matter) and the external environment (pH value), while the escaped N2O mainly came from nitrifiers. This indicates that the primary reason for the emission of N2O in the aerobic phase was that the N2O consumption rate of heterotrophic denitrifiers was lower than the N2O production rate of nitrifiers. Considering the removal efficiency of nitrogen, the enzyme activity and the reduction of N2O emissions, it is feasible to keep the C/N ratio of inflowing around 6.5 in A/O SBR.