Effect of Ammonium Concentration on N2O Emission During Autotrophic Nitritation Under Oxygen-Limited Conditions

Nitrous oxide (N2O) is one of the most powerful greenhouse gases, emitted by ammonia-oxidizing bacteria (AOB) and denitrifier during nitrogen transformation. A laboratory-scale sequencing batch reactor with enriched nitrifiers was developed under oxygen-limited conditions with synthetic wastewater (without organic carbon) to investigate the effect of ammonium (NH4+) concentration on N2O emission. The system achieved 70% conversion of the influent NH4+ to nitrite (NO2-) and the N2O emission factor (ratio between N2O nitrogen emitted and the NH4+ oxidized) was about 17.0%. NH4+ concentration was shown to have a major impact on N2O emission. When influent NH4+ concentrations were 60, 120, and 240 mg.N/L, total N2O emissions were 3.24, 8.75, and 24.59mg.N/L, respectively. Comprehensive analysis of N2O emission rate on NO2-concentration (Fig. 5) together with the absence of a contribution from heterotrophic denitrifiers suggests that AOB denitrification is the main cause of N2O emission during oxygen-limited autotrophic nitritation processes.