Intermittent Perturbation with High-Frequency Aerobic-Anoxic Cycling Enhances N2O Reductase Activity during Wastewater Treatment

Nitrous oxide (N2O) emissions from wastewater treatment plants, with a warming potential 298 times that of CO2, pose a significant challenge to lowering their carbon footprint. Current mitigation strategies focus on limiting N2O formation during nitrification and denitrification but overlook microbial reduction mechanisms. This study examines the potential for enhancing nitrous oxide reductase (NosZ) activity to reduce N2O to N2. We hypothesize that strategic oxygen manipulation can enhance N2O destruction by continuous NosZ expression and enable NosZ activation in microorganisms with superior NosZ capabilities. We assess microbial community function and metabolic regulation using metagenomics and metaproteomics to clarify the effect of intermittent aeration regimes on N2O emission. Intermittent aeration with periodic anoxic exposure significantly reduced N2O emissions with 71% nitrogen removal by enhancing the metabolic activity of Hyphomicrobium. NosZ activity increased by 4- to 6.5-fold after system adaptation to oxygen modulations, compared to continuous oxic-anoxic cycling without the anoxic phase. The latter resulted in increased N2O emissions due to suppressed NosZ activity and higher N2O production from Methylobacillus, which uses nitric oxide as an alternative electron acceptor. Our finding that strategic oxygen manipulation can energize N2O destruction lays the foundation for developing next-generation wastewater treatment technologies for mitigating N2O emissions.