Impact of N2O Emissions on Nitritation in Two Sequencing Batch Reactors: Activated Sludge Reactor and Biofilm System

The objective of this study was to evaluate nitrous oxide (N2O) emissions on nitritation in activated sludge sequencing batch reactor (ASSBR) and sequencing batch biofilm reactor (SBBR) treating ammonium-rich wastewater at two different influent ammonium concentrations. During stable operation, there was no significant difference of [GRAPHICS] removal efficiencies between the two reactors. At the end of nitrification, both nitrite accumulation rates were above 85%. However, SBBR had a better total nitrogen (TN) removal efficiency (81.7% +/- 1.5%) than that of ASSBR (66.5% +/- 5.7%). According to typical cycles, when influent [GRAPHICS] concentrations were 120 mg/L and 240 mg/L, N2O emissions during nitritation in SBBR accounted for 2.3% +/- 0.4% and 6.5% +/- 0.9% of the TN removed, respectively, which were 1/3-1/2 of that in ASSBR (6.6% +/- 0.6%, 14.1% +/- 1.6%). In addition, N2O production increased with increase of feed ammonia concentration in both reactors. These results contribute to further understanding of N2O emission in partial nitrifying system.