INFLUENCE OF SHORT-TERM pH FLUCTUATIONS ON NITROUS OXIDE EMISSIONS IN A SEQUENCING BATCH REACTOR FOR PARTIAL NITRIFICATION

Abstract

This study aimed to evaluate the impact of short-term pH fluctuations on nitrous oxide (N₂O) emissions in a sequencing batch reactor used for partial nitrification. Despite variations in operational conditions, the reactor consistently demonstrated high nitritation efficiency, with optimal performance at pH 7.0. The highest N₂O emission factor was observed at pH 7.6 (0.46%), followed by pH 7.0 (0.38%), while lower emissions were recorded at pH 8.2 and pH 6.4. High-throughput sequencing of 16S rRNA gene amplicons revealed significant temporal shifts in the microbial community, with Nitrosomonas becoming dominant during steady-state partial nitrification, and no nitrite-oxidizing bacteria detected. In the batch cycle, N₂O emissions predominantly occurred in the early phase, peaking between 5 and 15 minutes, likely due to rapid ammonium oxidation. These insights highlight the importance of pH control for minimizing N₂O emissions in wastewater treatment systems.