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Wastewaters such as landfill leachate and anaerobically digester effluent are usually contain high concentrations of ammonium (NH4-N) and low concentrations of biodegradable organic matters. A high efficient nitrite (NO2-N) based double-sludge system combining sequential denitrification and nitritation reactors has been developed to remove nitrogen from such types of wastewater. Denitrification process could fully utilize the limited low carbon source, and nitrite accumulation was achieved in the nitritation reactor. By this means, enhanced biological nitrogen removal could be realized. However, nitrous oxide (N2O), a potent greenhouse gas, can be produced and emitted during biological nitrogen removal. In this study, nitrite accumulation was achieved under low dissolved oxygen (DO) concentrations, high free ammonia (FA) concentrations and high NH4N/DO ratios in the nitritation reactor. The nitritation efficiency (the ratio of NO2-N to the oxidized nitrogen, NOX-N) reached to 99.8% at the ammonium loading rate of 1.47 g/(L·d). N2O emission was measured under different aeration rates (0.24 L/min, 0.36 L/min and 0.48 L/min, respectively). With increasing the aeration rate, ammonium oxidizing rate increased, indicating that the activity of ammonia oxidizing bacteria was enhanced with increasing the aeration rate. However, N2O emission decreased with increasing the aeration rate. In addition, the effect of initial NO2-N concentrations on N2O emission under different aeration rates (0.24 L/min, 0.36 L/min and 0.48 L/min, respectively) was also examined. N2O emission was high with the addition of NO2-N and a high initial NO2-N concentrations led to a high emission of N2O. The aeration rate had a high effect on N2O emission under high initial NO2-N concentrations, with the N2O emission factor ranged from 0.61% to 1.82%. While the effect of aeration rate on N2O emission was not obvious without the addition of NO2-N, with the emission factor of around 0.24%.

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