Synchronous Achievement of Advanced Nitrogen Removal and N₂O Reduction in the Anoxic Zone in the AOA Process for Low...

Continuous flow processes for the in situ determination of N₂O emissions during low C/N municipal wastewater treatment have rarely been reported. The anaerobic/aerobic/anoxic (AOA) process has recently shown promising potential in energy savings and advanced nitrogen removal, but it still needs to be comprehensively explored in relation to N₂O emissions for its carbon reduction advantages. In this study, a novel gas-collecting continuous flow reactor was designed to comprehensively evaluate the emissions of N₂O from the gas and liquid phases of the AOA process. Additionally, the measures of enhancing endogenous denitrification (ED) and self-enriching anaerobic ammonium oxidation (Anammox) were employed to optimize nitrogen removal and achieve N₂O reduction in the anoxic zone. The results showed that enhanced ED coupled with Anammox led to an increase in the nitrogen removal efficiency (NRE) from 67.65 to 81.96%, an enhancement of the NO₃^- removal rate from 1.76 mgN/(L h) to 3.99 mgN/(L h), and the N₂O emission factor in the anoxic zone decreased from 0.28 to 0.06%. Impressively, ED eliminated 91.46 ± 2.47% of the dissolved N₂O from the upstream aerobic zone, and the dissolved N₂O in the effluent was reduced to less than 0.01 mg/L. This study provides valuable strategies for fully evaluating N₂O emissions and N₂O reduction from the AOA process.