The Effect of DO on N2O Production in Simultaneous Nitrification and Denitrification Process

N
₂
O formation was studied using Sequencing Biofilm Batch Reactor (SBBR) by applying different DO (Dissolved Oxygen) gradient in the system. Simultaneous nitrification and denitrification (SND) process was achieved at different DO concentrations. Total N
₂
O productions were 0.495, 0.423, 0.843 and 2.01 mg-N/L respectively in accordance with DO concentrations, which were controlled at 1.0, 2.0, 2.5 and 3.0mg/L. Nitrite accumulation increased with the increasing of DO concentration. The activity of N2O reductase was inhibited by higher nitrite, which resulted in N
₂
O emission. Besides, nitrifier denitrification process during which nitrite as electron acceptor and ammonium as electron donor was responsible for part of N
₂
O emission. When DO was controlled at 2.0 mg/L, more than 97% of ammonium was removed by SND process and N
₂
O emission was lower than any other processes. It showed that both lower and higher DO concentrations could suppress SND process and a balanced SND may reduce N
₂
O production.