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.