Electron transfer from Geobacter sulfurreducens to mixed methanogens improved methane production with feedstock gases of H₂ and CO₂

In order to solve problems of poor utilization of H₂ and CO₂ in biomethane conversion with mixed methanogens due to multi-channel competition and nondirectional electron transfer, Geobacter sulfurreducens were cocultured with mixed methanogens to promote oriented metabolic pathway of H₂ and CO₂ to produce CH₄. When inoculation volume ratio of G. sulfurreducens to mixed methanogens was 2:4, CH₄ yield increased to 0.24 mL/ml H₂ (close to the maximum theoretical yield of 0.25 mL/ml H₂) and conversion efficiency of H₂ to CH₄ increased from 72 to 96%. Electrochemical detection and three-dimensional fluorescence spectra showed that the co-culture system had an increased metabolic capacity and spectral intensity of fulvic acid-like compounds was enhanced, which mediated direct interspecific electron transfer to produce CH₄. The 16S rRNA gene sequencing showed that relative abundance of G. sulfurreducens and Methanoculleus increased, indicating an established syntrophic relationship between G. sulfurreducens and Methanoculleus.