Contribution of nitrous oxide to the carbon footprint of full-scale wastewater treatment plants and mitigation strategies- a critical review.

Nitrous oxide (NO), a potent greenhouse gas, significantly contributes to the carbon footprint of wastewater treatment plants (WWTPs) and contributes significantly to global climate change and to the deterioration of the natural environment. Our understanding of NO generation mechanisms has significantly improved in the last decade, but the development of effective NO emission mitigation strategies has lagged owing to the complexity of parameter regulation, substandard monitoring activities, and inadequate policy criteria. Based on critically screened published studies on NO control in full-scale WWTPs, this review elucidates NO generation pathway identifications and emission mechanisms and summarizes the impact of NO on the total carbon footprint of WWTPs. In particular, a linear relationship was established between NO emission factors and total nitrogen removal efficiencies in WWTPs located in China. Promising NO mitigation options were proposed, which focus on optimizing operating conditions and implementation of innovative treatment processes. Furthermore, the sustainable operation of WWTPs has been anticipated to convert WWTPs into absolute greenhouse gas reducers as a result of the refinement and improvement of on-site monitoring activities, mitigation mechanisms, regulation of operational parameters, modeling, and policies.