Sulfide-driven nitrous oxide recovery during the mixotrophic denitrification process

We propose a novel sulfide-driven process to recover N 2 O during the traditional denitrification process. The optimum initial sulfide concentration was 120 mg/L, and the N 2 O percentage in the gaseous products (N 2 O + N 2 ) was up to 82.9%. Moreover, sulfide involved in denitrification processes could substitute for organic carbon as an electron donor, e.g., 1 g sulfide was equivalent to 0.5-2 g COD when sulfide was oxidized to sulfur and sulfate. The accumulation of N 2 O was mainly due to the inhibiting effect of sulfide on nitrous oxide reductase (N 2 OR), which was induced by the supply insufficiency of electrons from cytochrome c (cyt c ) to N 2 OR. When the initial sulfide concentration was 120 mg/L, the N 2 OR activity was only 36.8% of its original level. According to the results of cyclic voltammetry, circular dichroism spectra and fluorescence spectra, significant changes in the conformations and protein structures of cyt c were caused by sulfide, and cyt c completely lost its electron transport capacity. This study provides a new concept for N 2 O recovery driven by sulfide in the denitrification process. In addition, the findings regarding the mechanism of the inhibition of N 2 OR activity have important implications both for reducing emissions of N 2 O and recovering N 2 O in the sulfide-driven denitrification process. (c) 2022 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V.