Analyzing the mechanism of nitrous oxide production in aerobic phase of anoxic/aerobic sequential batch reactor from the perspective of key enzymes

Yang, Rui; Yuan, Lin-jiang; Wang, Ru; He, Zhi-xian; Lei, Lin; Ma, Yan-chen

Analyzing the mechanism of nitrous oxide production in aerobic phase of anoxic/aerobic sequential batch reactor from the perspective of key enzymes

2022

How the vast majority of nitrous oxide (N₂O) in the aerobic zone of nitrogen bio-removal process is produced is still a controversial issue. To solve this issue, this study measured the activities of two key denitrifying enzymes (nitric oxide reductase (Nor) and nitrous oxide reductase (N₂OR)) in an A/O SBR with different chemical nitrogen demand (COD)/total nitrogen (TN) ratios. By analyzing the Spearman’s correlations between the N₂O production, the enzyme activities, and the factors, the main N₂O production process was identified. By comparing the activities of these enzymes, this study analyzed the reasons for the N₂O production. Results show that Nor activities had a linear relationship with total N₂O concentrations (y = 0.34749 + 31.31365x, R² = 0.83362) and were not affected by COD (r = 0.299, N = 15, P = 0.279 > 0.05), which showed that most of the N₂O released and produced came from the autotrophic denitrification. N₂OR activities had a positive correlation with COD (r = 0.692, N = 15, P = 0.004 < 0.01), which showed that heterotrophic denitrification played a role as an N₂O consumer. Nor activities were much higher than N₂OR activities and the gap between them increased when the total N₂O concentration increased, showing that the heterotrophic denitrification was difficult to consume all the N₂O produced by the autotrophic denitrification. Reducing autotrophic denitrification is the best way to reduce N₂O production in aerobic phase.

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