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

The multiple anoxic and aerobic (AO) process is an advanced biological nitrogen-removal process, and nitrous oxide (N2 O) emission might affect its sustainable application. Nitrogen removal and N2 O emission in a step-feeding multiple AO sequencing batch reactor (SBRS ) was examined, in comparison with a one-feeding sequencing batch reactor (SBRO ). Nitrogen removal was enhanced by 12.6% in SBRS compared to the removal percentage of 75.8% in SBRO . Activated sludge in SBRs possessed a higher N2 O emission factor during nitrification, denitrification and simultaneous nitrification and denitrification (SND) than in SBRO . A high N2 O emission factor was observed during SND in both reactors, with the emission factor of 4.38% in SBRS and 4.66% in SBRO . More N2 O emission occurred in the presence of nitrite. Bacteroidetes and Proteobacteria dominated in both SBRS and SBRO . A similar abundance of Thauera, Dechloromonas and Zoogloea possible for denitrification was observed in SBRS and SBRO . Moreover, nosZ from Proteobacteria dominated in both SBRS and SBRO , with dominating genus of Acidovorax, Ralstonia, Thauera and Marinobacter.