Enhanced CO₂ electromethanogenesis using biogas over pure CO₂ as MES feedstock: Performance and microbial mechanisms

Microbial electrosynthesis (MES) has shown excellent CO₂-to-CH₄ activity with pure CO₂ stream. However, its performance and electron transfer pathway has not been deeply unveiled when biogas was used as MES feedstock. In this work, mimic biogas composed of 60% CH₄ and 40% CO₂ was fed into biocathode MES (–1.0 V vs. Ag/AgCl) to evaluate its efficiency of biogas upgrading. Compared to pure CO₂-fed MES, the faradaic efficiency of biogas-fed MES was increased by 15.1% with 1.34-fold of conversion rate. Metagenomic sequencing and qPCR analysis revealed that the lower CO₂ content under biogas condition stimulated the enrichment of electroactive- methanogens and bacteria, which primarily facilitated electron transfer during CO₂ conversion. Notably, it was proposed that the spatial consortium of “methanogens–electroactive bacteria,” rather than the methanogen abundance within the biofilm, contributed to the CO₂-to-CH₄ performance. Overall, these results indicate that low CO₂ partial pressure in biogas enhances the activity of the methanogenic biocathode for biogas upgrading, rather than inhibiting methanogenesis. This study provides comprehensive insights into the mechanism of electromethanogenesis using biogas as MES feedstock. Future efforts should focus on the development of large-scale, practical continuous-flow systems to advance this technology.