[Effects of Temperature and Substrate Concentration on N₂O Release of ANAMMOX Process]

The greenhouse gas N₂O is released during the biological nitrogen removal process. ANAMMOX (anaerobic ammonium oxidation) is regarded as a promising nitrogen removal process for treating municipal wastewater, and the N₂O emission patterns and mechanisms need further investigation. In this study, batch tests were performed to study the release of N₂O at different temperatures and substrate concentrations, and the microbial mechanisms of N₂O emission were discussed. The results showed that the increase of the influent substrate concentration of the ANAMMOX process promoted the release of N₂O. At 35℃, when the influent nitrite increased from 40 mg·L^-1 to 60 mg·L^-1, 120 mg·L^-1, the maximum accumulated concentration of N₂O increased from 0.5 mg·L^-1 to 1.5 mg·L^-1 and 2.4 mg·L^-1, accounting for 0.85%, 1.43%, and 1.11% of the total nitrogen removal, respectively. Lowering temperature had an obvious inhibitory effect on ANAMMOX activity. The specific ANAMMOX activity at 15℃ was only 6% of that at 30℃. Furthermore, the intracellular ATP concentration was reduced. At 15℃, the intracellular ATP concentration was 4% of that at 30℃. The decrease in temperature led to a decrease in the release of N₂O in the ANAMMOX process. When the temperature decreased, the denitrification rate would decrease, leading to a lower N₂O production rate and lower N₂O accumulation. 16S rRNA amplicon sequencing showed that ANAMMOX bacteria Candidatus Brocadia and Ca. Jettenia were enriched, accounting for 6.9%-13.8% and 1.4%-2.6% of microbial community, respectively. Abundant heterotrophic bacteria were also found in the microbial community. The accumulation of N₂O in the ANAMMOX process was mainly attributed to denitrifying bacteria producing and consuming N₂O. This study provides support for controlling N₂O emission during the ANAMMOX process for treating municipal wastewater.