Quantitative responses of nitrous oxide accumulation to genetic associations across a temperature gradient within denitrification biofilters

- NO2−-N accumulation limited TN removal at the temperature of 5-15 °C.
- The major mechanism for nitrogen removal at low temperatures were revealed.
- DNRA accounted for 0.43-1.74% of NO3−-N removal.
- The key driver of N2O accumulation rate was (nirK + nirS)/nosZ.

Increased nitrous oxide (N2O) in the atmosphere is of global concern. Biofiltration has been studied for gaseous nitrogen treatments in drinking water environments; however, the molecular mechanisms mediating N2O accumulation in denitrification biofilters have not been quantified. Five denitrification biofilters were developed in this study and all achieved high removal efficiencies for total nitrogen (TN: 72.4-92.7%), nitrate nitrogen (NO3−-N: 88.6-98.2%) and chemical oxygen demand (COD: 79.3-90.0%) across a low-temperature gradient (5-25 °C). Denitrification coupling with anaerobic ammonium oxidation (ANAMMOX) and dissimilatory nitrate reduction to ammonium (DNRA) processes yielded the presently robust treatment performance. Nitrite availability limited TN removal at 5-15 °C. Our findings indicate that temperature affected N2O accumulation indirectly by controlling the balance of nitrite versus N2O reductase carrying microorganisms. In addition, our results demonstrated that genetic association was an important index reflecting the relative intensity of N2O accumulation at low temperatures.

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