The conductivity and redox properties of pyrolyzed carbon mediate methanogenesis in paddy soils with ethanol as substrate.

Pyrolyzed carbon such as biochar and activated carbon could influence the methanogenesis in paddy soil, which is an important process controlling methane emission. Different electrochemical properties of pyrolyzed carbon may be involved in methanogenesis, such as conductivity and redox activity. However, their different roles have not been thoroughly illustrated before. In this study, we identified the roles of pyrolyzed carbon redox property and electron conductivity in methanogenesis with ethanol as a substrate, by comparing pyrolyzed carbon samples with sequential change of electrochemical properties. Right after the addition, pyrolyzed carbon with highest electron donating capacity (0.85 mmol/g) promoted the methane generation by 33.3%; while, other pyrolyzed carbon with higher electron accepting capacity and lower electron donating capacity than B4 inhibited the methane generation. The relative abundance of electroactive bacteria and certain methanogens increased with the pyrolysis temperature. The strict linear relationship between electroactive bacteria/certain methanogens and cyclic voltammetry peak currents of paddy soil implied that microbial structure was altered due to the improved the electron transfer situation by the electron shuttle ability of pyrolyzed carbon. This study could deepen our understanding about the effect of pyrolyzed carbon on methanogenesis process.