N2O Production Pathways in Partial Nitrification Based on Isotope Technology

Abstract

Batch experiments were conducted under normal temperature conditions to study the generation of N2O in the partial nitrification process under different dissolved oxygen concentrations and their production pathways. When dissolved oxygen was 0.5, 1.5, and 2.5 mg·L-1, the proportion of N2O released into the total nitrogen input was 4.35%, 3.27%, and 2.63%, respectively. With increase dissolved oxygen, the proportion of N2O released to total influent nitrogen was reduced. Isotope measurements showed that when dissolved oxygen was 0.5 mg·L-1, only denitrification by ammonia-oxidizing bacteria (AOB) produced N2O. However, when dissolved oxygen increased to 1.5 mg·L-1, the activity of nitrifying bacteria increased, and 4.52% of N2O was generated through a hydroxylamine oxidation process, whereas the N2O generated by AOB denitrification accounted for 95.48%. When dissolved oxygen continuously increased to 2.5 mg·L-1, the proportion of N2O produced by hydroxylamine oxidation increased to 9.11%, and the N2O generated by AOB denitrification accounted for 90.89%. The change in dissolved oxygen concentration affects the N2O production pathway in the short-cut nitrification process, and avoiding excessive NO2--N accumulation can reduce the production of N2O.