Nitrifier denitrification dominates nitrous oxide production in composting and can be inhibited by a bioelectrochemical nitrification inhibitor

Targeted options to reduce nitrous oxide (N2O) emission from composting is scarce due to challenges in disentangling the complex N2O production pathways. Here, combined approaches of nitrogen form analysis, isotopocule mapping, quantitative PCR, and Illumina MiSeq sequencing were used to differentiate N2O production pathways and decipher the underlying biochemical mechanisms. Results suggested that most N2O was produced at the latter stage through nitrifier denitrification. The bioelectrochemical assistance through applying an electric potential reduced N2O emissions by 28.5–75.5%, and the underlying mitigation mechanism was ammonia oxidation repression, as evidenced by the observed reduction in the proportion of the amoA containing family Nitrosomonadaceae from 99% to 83% at the lower voltage and to a negligible level at the higher voltage assessed, which was attributed to their depressed competitiveness for oxygen with heterotrophs. The findings provide evidence that the bioelectrochemical assistance could function as a nitrification inhibitor to minimize compost derived N2O emissions.