Enhancing NosZ Activity to Reduce N 2 O Emissions from Biological Wastewater Treatment Systems
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Nitrous oxide (N 2 O) emissions from wastewater treatment plants, with a warming potential 298 times that of CO 2 , pose a significant challenge to lowering their carbon footprint. Current mitigation strategies focus on limiting N 2 O formation during nitrification and denitrification but overlook microbial reduction mechanisms. This study examines the potential for enhancing nitrous oxide reductase (NosZ) activity to reduce N 2 O to N 2 . We hypothesize that strategic oxygen manipulation can enhance N 2 O 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 N 2 O emission. Intermittent aeration with periodic anoxic exposure significantly reduced N 2 O 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 N 2 O emissions due to suppressed NosZ activity and higher N 2 O production from Methylobacillus , which uses nitric oxide as an alternative electron acceptor. Our finding that strategic oxygen manipulation can energize N 2 O destruction lays the foundation for developing next-generation wastewater treatment technologies for mitigating N 2 O emissions.
