N2O emission from a nitritation double-sludge system treating wastewater with a high concentration of ammonium

A high efficient nitrite based double-sludge system combining sequential denitrification and nitritation reactors has been developed to remove nitrogen from wastewaters containing high concentrations of ammonium. System performance was examined and also nitrous oxide (N₂O) emission was measured under different aeration rates with or without the addition of nitrite nitrogen (NO₂-N). The nitritation efficiency (the ratio of NO₂-N to the oxidized nitrogen, NO_X-N) reached to 99.8% at the ammonium loading rate of 1.47 g l^-1 d^-1. With increasing the aeration rate, ammonium oxidizing rate increased, indicating that the activity of ammonia oxidizing bacteria was enhanced. However, N₂O emission decreased with increasing the aeration rate. N₂O emission was high with the addition of NO₂-N. The aeration rate had a high effect on N₂O emission at high initial NO₂-N concentrations, with the N₂O emission factor ranged from 0.59% to 1.64%. While the effect of aeration rate on N₂O emission was not significantly without the addition of NO₂-N, with the emission factor of only around 0.20% to 0.27%.