Impact of gas-water ratios on N2O emissions in biological aerated filters and analysis of N2O emissions pathways

Biological aerated filter (BAF) is a widely applied biofilm process for wastewater treatment. However, characteristics of nitrous oxide (N2O) production in BAF are rarely reported. In this study, two tandem BAFs treating domestic wastewater were built up, and different gas-water ratios were controlled to explore N2O production pathway. Results showed that N2O production increased with increasing gas-water ratio in both BAFs; higher gas-water ratio promoted more N2O releasing from hydroxylamine oxidation process. To improve nitrogen removal performance and reduce N2O emission, the optimal gas-water ratios for BAF1 and BAF2 were 5:1 and 1.5:1, respectively. Most of N2O was produced from ammonia oxidizing bacteria (AOB) denitrification and hydroxylamine oxidation in BAF1, and heterotrophic denitrification contributed to relieve N2O emission. In BAF2, N2O was emitted from AOB denitrification and hydroxylamine oxidation by 87.8% and 12.2%, respectively. Heterotrophic denitrification is a N2O sink in BAF, causing BAF1 produced less N2O than BAF2 with the same gas-water ratio. Enhancing heterotrophic denitrification and anaerobic ammonium oxidation (Anammox) activity could reduce the release of N2O in BAFs. © 2020