N₂O recovery from wastewater and flue gas via microbial denitrification: Processes and mechanisms

Nitrous oxide (N₂O) is increasingly regarded as a significant greenhouse gas implicated in global warming and the depletion of the ozone layer, yet it is also recognized as a valuable resource. This paper comprehensively reviews innovative microbial denitrification techniques for recovering N₂O from nitrogenous wastewater and flue gas. Critical analysis is carried out on cutting-edge processes such as the coupled aerobic-anoxic nitrous decomposition operation (CANDO) process, semi-artificial photosynthesis, and the selective utilization of microbial strains, as well as flue gas absorption coupled with heterotrophic/autotrophic denitrification. These processes are highlighted for their potential to facilitate denitrification and enhance the recovery rate of N₂O. The review integrates feasible methods for process control and optimization, and presents the underlying mechanisms for N₂O recovery through denitrification, primarily achieved by suppressing nitrous oxide reductase (Nos) activity and intensifying competition for electron donors. The paper concludes by recognizing the shortcomings in existing technologies and proposing future research directions, with an emphasis on prioritizing the collection and utilization of N₂O while considering environmental sustainability and economic feasibility. Through this review, we aim to inspire interest in the recovery and utilization of N₂O, as well as the development and application of related technologies.