Redox-active reactions in denitrification provided by biochars pyrolyzed at different temperatures

Abstract

The aim of this study was to investigate the role of redox-active components of biochar in the denitrification processes and N2O reduction. Both biochars pyrolyzed at 300 and 800°C were separated into two redox-active components (i.e., dissolved aromatic moieties and condensed aromatic structure), then applied to study the reduction process of denitrifying bacteria from a paddy soil. Results demonstrated three main pathways of the biochar redox-active components for the denitrification processes and N2O reduction. The biochar at 300°C and its redox-active components accelerated the first step of denitrification (i.e., NO3− reduction), attributable to the oxidation of reduced phenolic moities to donate electrons. The biochar at 800°C and both redox-active components decreased total N denitrified because their dominant quinone moieties and electrical conductivity structure served as alternative electron acceptors. All the biochar treatments accelerated the last step of denitrification and decreased N2O emission by 74.1%–99.9%. As electron donor, the biochar at 300 °Csignificantly increased humic acid-oxidizing and nitrate-reducing bacteria in the nosZ-harbouring bacterial community, which promoted N2O reduction. The biochar at 800°C as electron sink decreased N2O production, and as electron shuttle for nosZ-harbouring denitrifying bacteria, its electrical conductivity structure enhanced N2O reduction.