Effect of the dissolved oxygen concentration on the N2O emission from an autotrophic partial nitritation reactor treating high-ammonium wastewater

• The effect of DO on N2O emission quantity from macroscopic view was investigated.
• N2O production inside sludge aggregates were quantified by using microelectrodes.
• At a lower DO concentration N2O production enhanced from denitrification pathway.

A laboratory-scale sequencing batch reactor (SBR) fed with synthetic high-ammonium wastewater was operated for partial nitritation, and the effect of the dissolved oxygen (DO) concentration on the N2O emission was investigated. From a macroscopic viewpoint, as the DO concentration increased from 0.35 to 0.60 and 0.85 mg l−1, the N2O emission factor (the ratio between N2O nitrogen emitted and the influent total nitrogen) decreased from 2.35% ± 0.32% to 1.81% ± 0.16% and 0.57% ± 0.08%, respectively. When air was replaced with N2 for blowing, N2O emission was also observed, demonstrating the N2O production pathway of denitrification. A higher ammonia oxidation rate (AOR) led to a lower N2O emission rate, and the concentration of free nitrous acid (FNA) had no obviously effect on the N2O emission. From a microscopic viewpoint, nitrogen transformation inside sludge aggregates under different DO concentrations was investigated by using microelectrodes. It demonstrated that N2O production increased with decreasing DO concentration, and at lower DO concentrations (0.35 and 0.60 mg l−1) N2O production enhanced from denitrification pathway.