A comprehensive model of N₂O emissions in an anaerobic/oxygen-limited aerobic process under dynamic conditions

A comprehensive model for nitrous oxide (N₂O) emissions in an anaerobic/oxygen-limited aerobic (A/OLA) process is proposed here. This paper includes the following main innovations: (i) adding the phosphorus-accumulating organism (X_PAO) denitrification pathway to the contribution of N₂O emissions; (ii) considering the biological removal of organic matter and phosphorus and predicting the effect of influent phosphorus concentration on N₂O emissions via an increase in the influent phosphorus concentration; and (iii) determining the effect of X_PAO on N₂O production in a simultaneous nitrification, denitrification and phosphorus removal (SNDPR) system by sensitivity analysis. The results suggested that the simulated data matched the measured data well. The predominant pathways of N₂O emissions in the process of A/OLA were the ammonium-oxidizing bacterium (X_AOB) denitrification pathway and the heterotrophic bacterium (X_H) denitrification pathway, while the incomplete hydroxylamine (NH₂OH) oxidation pathway and the X_PAO denitrification pathway contributed less to N₂O emissions. The metabolic activity of X_PAO had a significant effect on N₂O emissions, and increasing the influent phosphorus concentration was beneficial for reducing the release of N₂O. This study is expected to provide a meaningful reference for reducing N₂O emissions in wastewater treatment engineering.