Strengthening the cathodic CO2 adsorption on the MIL-88B(Fe) to enhance methane production

Abstract

Direct interspecies electron transfer (DIET), as a new metabolic pathway for methanogenesis, is difficult to establish in common anaerobic digesters due to the lack of electroactive methanogens, syntrophic electroactive bacteria, and conductive proteins. In this study, a synthetic CC/MIL-88B electrode was used to accelerate the establishment of DIET in a microbial electrolysis cell (MEC)-based anaerobic digester. Results showed that the CC/MIL-88B electrode had a strong dispersive attraction generated by its three-dimensional aromatic ring structure, which benefited the capture of CO2 in the biofilm attached to the electrode and further increased the reduction of CO2 to produce methane via DIET. Electrochemical and metaproteomics analysis indicated that the MIL-88B(Fe) stimulated the secretion of conductive proteins (such as e-pili and cytochrome C). The abundances of electroactive methanogen Methanosarcina and other electroactive bacteria increased to 4.89 and 1.37 times, respectively. In addition, the expression of the key enzymes related to DIET-based methanogenesis (Fpo and Rnf) of Methanosarcina and the pathway of CO2-reduction methanogenesis were enhanced significantly. These results indicated that the synthetic CC/MIL-88B electrode helped the establishment of DIET in the MEC system, which provided a new perspective to establish DIET during anaerobic digestion by accelerating the utilization of CO2.