Nitrogen removal and nitrous oxide emission from a step-feeding multiple anoxic and aerobic process

Abstract

The multiple anoxic and aerobic (AO) process is an advanced biological nitrogen-removal process, and nitrous oxide (N₂O) emission might affect its sustainable application. Nitrogen removal and N₂O emission in a step-feeding multiple AO sequencing batch reactor (SBR_S) was examined, in comparison with a one-feeding sequencing batch reactor (SBR_O). Nitrogen removal was enhanced by 12.6% in SBR_S compared to the removal percentage of 75.8% in SBR_O. Activated sludge in SBRs possessed a higher N₂O emission factor during nitrification, denitrification and simultaneous nitrification and denitrification (SND) than in SBR_O. A high N₂O emission factor was observed during SND in both reactors, with the emission factor of 4.38% in SBR_S and 4.66% in SBR_O. More N₂O emission occurred in the presence of nitrite. Bacteroidetes and Proteobacteria dominated in both SBR_S and SBR_O. A similar abundance of Thauera, Dechloromonas and Zoogloea possible for denitrification was observed in SBR_S and SBR_O. Moreover, nosZ from Proteobacteria dominated in both SBR_S and SBR_O, with dominating genus of Acidovorax, Ralstonia, Thauera and Marinobacter.