Drivers of nitrous oxide accumulation in denitrification biofilters with low carbon:nitrogen ratios.

Heterotrophic denitrification is usually inhibited by insufficient carbon sources; however, the underlying mechanisms responsible for nitrous oxide (N 2 O) accumulation within denitrification at low carbon:nitrogen (C/N) ratios have not been quantified from a molecular level. In this study, five denitrification biofilters were developed and exhibited efficiency (total nitrogen: 18.5%–92.2%; nitrate nitrogen: 42.9%–99.5%; chemical oxygen demand: 50.5%–93.7%) in remediating micro-polluted water with C/N ratios ranging between 0.65 and 3.0. A combined analysis revealed that the coupling of anaerobic ammonium oxidation (ANAMMOX) and denitrification accounted for N 2 O accumulation in the biofilters, and the key drivers of the N 2 O accumulation rates were qnorB/nirK , nosZ/(narG + napA) , amx/(nirS + nirK) , narG/bacteria and qnorB/bacteria . Our study demonstrated that genetic association was indicative of microbial processes relative to nitrogen cycling and reflected N 2 O flux within denitrification biofilters at low C/N ratios. [ABSTRACT FROM AUTHOR]