The synergistic effects of dissolved oxygen and pH on N2O production in biological domestic wastewater treatment under nitrifying conditions
2015
Li, Pengzhang | Wang, Shuying | Peng, Yongzhen | Liu, Yue | He, Janzhong
Nitrous oxide (N ₂O) is a potent greenhouse gas, which is produced during nitrifying and denitrifying processes. Some factors and mechanisms affecting N ₂O emission have been reported in previous literature, but wastewater biological nitrification is accompanied by a dynamic process of dissolved oxygen (DO) consumption and pH reduction, it is more meaningful to study the synergistic effects between DO and pH on N ₂O production. In this study, the synergistic effects between DO and pH on N ₂O production were investigated with real domestic wastewater. The results showed that high DO levels and a high pH could improve the oxidation ratio of and the production ratio of while effectively reducing the accumulation ratio of N ₂O. The was a prerequisite for nitrifier denitrification; when was oxidized completely, there would be no N ₂O production and an even higher concentration of The pH factor is shown to directly affect N ₂O emission, although free ammonia and free nitrous acid which changed with pH had no correlation with N ₂O emission. There were two reasons: (1) pH can influence the flow direction of electrons afforded by NH ₂OH oxidation; at high pH, electrons were mainly used for combining H ⁺ and O ₂ (O ₂ + 4H ⁺ + 4e ⁻ = 2H ₂O), the accumulation of cannot be a result of denitrification, and a higher DO can get more electrons to prefer and (2) was the prerequisite for NH ₂OH oxidation, since NH ₂OH oxidation process was the way to provide electrons for nitrifier denitrification.
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