N2O emission during wastewater nitrification with enriched nitrifying bacteria

Nitrifying bacteria were enriched in a sequencing batch reactor and used to quantify N2O emission specifically by wastewater nitrification while minimizing or preventing the chances of denitrification during the experiment. Batch wastewater nitrification was carried out in a reactor (working volume 0.5L) at different aeration rates (10 and 20mL/min) and -N concentrations (25, 50, and 100mg/L). Wastewater nitrification efficiencies were more than 97% in all the cases except at 100mg/L with 10mL/min aeration rate (92%). Cumulative N2O emission reached 0.2, 1.15, and 2.67mg (aeration: 10mL/min) and 0.37, 2.18, and 3.08mg (aeration: 20mL/min) at the initial -N concentration of 25, 50, and 100mg/L, respectively. N2O emission yields (kg N2O-N per kg processed -N) were 0.016-0.058 and 0.029-0.088 at 10 and 20mL/min aeration rate, respectively. The yields were higher than that of denitrification. The results showed that cumulative N2O emission and the yield increased at higher ammonium concentration and aeration rate. Accumulated nitrite during nitrification also contributed and played a pivotal role in N2O emission.