Mechanistic investigation of seasonal climate effects on greenhouse gas emissions from biological nitrogen removal systems

Abstract

evenness: p = 0.96), analysis of the relative abundance of nitrifiers based on ASVs using NMDS plots revealed significant clustering changes of nitrifying bacteria at 25℃ compared to 15℃ (stress < 0.2). Based on these findings, this study suggests that temperature control corresponding to seasonal and climatic variations should be implemented in WWTPs to mitigate excessive N$_2$O emissions resulting from biological activity.

NH4$^+$: R = 0.53, p = 0.042). (3) Microbial community analysis was performed over reaction time to investigate the causes of temperature-dependent differences in N$_2$O emissions using the nitrifier target cultured samples. Identified nitrifiers belonged to the genera Nitrospira and Nitrosomonas. While no significant differences were observed in the overall microbial community composition between two temperature conditions (diversity: p = 0.79

The biological activity-induced emissions of nitrous oxide (N$_2$O) have a significant impact on the acceleration of global warming, making research on this topic essential. Wastewater treatment plants (WWTPs), which are directly impacted by external temperature variations, are recognized as major sources of anthropogenic N$_2$O due to the continuous influx of nitrogen compounds. However, the microbial perspective regarding the temperature-dependent mechanisms of N$_2$O generation in these treatment plants remains largely unknown. Moreover, the significance of studying N$_2$O production through nitrification, which accounts for a higher proportion of N$_2$O emissions than denitrification, is underscored by the incomplete understanding of the N$_2$O generation mechanism during nitrification. Therefore, this study aimed to analyze the N$_2$O emissions resulting from nitrification at different temperature within the biological nitrogen removal (BNR) system in a WWTP. (1) The activated sludge samples from an oxic tank were inoculated and subsequently cultured at 15℃ and 25℃, which are the range of nitrification optimal temperature and the WWTP temperature. The results revealed significantly higher N$_2$O emissions at 25℃ when an equal amount of ammonium was oxidized (p < 0.05). (2) To gain deeper insights into the temperature-dependent differences in N$_2$O emissions at 15℃ and 25℃ from a kinetic perspective, the chloramphenicol-treated sludge samples were injected with 50 µmol of NH4$^+$ and reacted at the temperature of wastewater. Consequently, the subtle positive correlations were observed between the NH4$^+$ oxidation rate with respect to temperature (N$_2$O: R = 0.47, p = 0.078