Nitrous oxide (N2O) is a very potent greenhouse gas, and mentioned as the dominant ozone-depleting substance of the 21st century. This compound has a 300 times higher climate warming potential than CO2 and it is one of the main contributors to the greenhouse footprint of wastewater treatment plants (WWTP). N2O is an intermediate of denitrification and its accumulation can be due to incomplete denitrification by heterotrophic denitrifying bacteria, byproduct formation of ammonia oxidizing bacteria or abiotic metal-mediated reactions. Although N2O emission in WWTPs mainly occurs in aerated nitrification zones, the origin of the stripped N2O in this process is unclear. A better understanding of factors influencing the N2O-emission might provide more insight into the N2O source and possible N2O-mitigation strategies. The novel database of WWTP-specific high quality metagenome-assembled genomes (MAGs) might provide new insights into the N2O producers and consumers responsible for N2O emission.
Here were present N2O-emission and community time-series data of two full-scale Danish WWTPs in combination with a metagenome-centered metabolism study. We were able to identify statistically significant correlations between the N2O-emission patterns of the WWTPs and community members (figure 1). Community members of interest were further investigated on their potential N2O-production or –consumption abilities using previously obtained MAGs. Some of these species belonged to previously uncharacterized, but abundant species. N2O-production or –consumption potential was determined based on the prediction of the canonical norBC and nosZ genes, and conversion of hydroxylamine to N2O by cytochrome P460. The combination of time-series community and N2O data with a metagenome-centered study showed that N2O-potential alone did not explain the observed seasonality. This combined approach provided novel insights into the microbiology of nitrogen transformations in full-scale plants, which may be important for N2O-emission mitigation.
