Impact of gas-water ratios on N_2O emissions in biological aerated filters and analysis of N_2O emissions pathways

摘要

Biological aerated filter (BAF) is a widely applied biofilm process for wastewater treatment However, characteristics of nitrous oxide (N_2O) 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 N_2O production pathway. Results showed that N_2O production increased with increasing gas-water ratio in both BAFs: higher gas-water ratio promoted more N_2O releasing from hydroxylamine oxidation process. To improve nitrogen removal performance and reduce N_2O emission, the optimal gas-water ratios for BAF1 and BAF2 were 5∶1 and 1.5∶1, respectively. Most of N_2O was produced from ammonia oxidizing bacteria (AOB) denitrification and hydroxylamine oxidation in BAF1. and heterotrophic denitrification contributed to relieve N_2O emission. In BAF2, N_2O was emitted from AOB denitrification and hydroxylamine oxidation by 87.8% and 12.2%, respectively. Heterotrophic denitrification is a N_2O sink in BAF, causing BAF1 produced less N_2O than BAF2 with the same gas-water ratio. Enhancing heterotrophic denitrification and anaerobic ammonium oxidation (Anammox) activity could reduce the release of N_2O in BAFs.