Effect of anoxic to aerobic duration ratios on nitrogen removal and nitrous oxide emission in the multiple anoxic/aerobic process.

Characteristics of nitrogen removal and nitrous oxide (NO) emission in the multiple anoxic/aerobic (AO) process were examined in three sequencing batch reactors (SBRs) with different anoxic durations (50 min, SBR; 40 min, SBR; 30 min, SBR) and a fixed aerobic duration of 30 min. The highest total inorganic nitrogen removal percentage of 85.8% was obtained in SBR, while a minimum NO emission factor of 1.9% was obtained in SBR. During nitrification batch experiments, the NO emission factor and emission rate were both lower in SBR than SBR. More NO production was obtained during denitrification in SBR when denitrifiers utilized intracellular organic carbon. Nitrite reduction by heterotrophs was the main NO production pathway during simultaneous nitrification and denitrification in SBR and SBR, with the NO emission factor of 31.3% and 36.3%, respectively. Adequate anoxic duration and lowering aerobic nitrite concentrations could be adopted to mitigate NO emission in the multiple AO process. The dominant microorganisms at the phylum level in all reactors were Proteobacteria and Bacteroidetes, while the abundance of Nitrospira was the highest in SBR with relatively lowest dissolved oxygen concentrations.