Emission and control of nitrous oxide from biological denitrification treatment of wastewater

The substantial emission of nitrous oxide (N₂O), which has strong greenhouse effect and thus huge environmental impact, from wastewater treatment has attracted widespread attention. Accurate assessment of environmental impacts and effective mitigation of N₂O emission are urgently needed. Reliable prediction and effective control of N₂O emission depend heavily on mathematical modeling, which in turn requires accurate determination of N₂O yield and emission factors. Although numerous studies have investigated mechanism and pathways of N₂O generation in different biological processes, reported N₂O yields vary significantly due to differences in the regions and operational conditions. Elucidating the pathways and influencing factors of N₂O generation are the key to developing reliable models and implementing effective mitigation strategies. This study reviewed current advances on N₂O generation and emission from typical biological processes. The pathways of N₂O generation were summarized comprehensively, and the factors affecting N₂O production were discussed quantitatively. Key factors including water quality and operation conditions were identified for representative processes (e.g., AAO and SBR), and the mechanism are discussed. Based on quantitative analysis of the roles of those key factors, strategies for N₂O abatement in practical wastewater treatment processes are proposed. This study advances the understandings on the mechanism of N₂O generation in biological wastewater treatment and also support the accurate assessment and effective control of N₂O emissions.