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

• Biogas-fed MES outperformed pure CO 2 -fed MES in CH₄ conversion efficiency • Distribution density of archaea dominated the CO 2 electromethanogenesis performance • Feedstock regulated the electron transfer pathway in CO₂ electromethanogenesis Microbial electrosynthesis (MES) has shown excellent CO 2 -to-CH 4 activity with pure CO 2 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% CH 4 and 40% CO 2 was fed into biocathode MES (–1.0 V vs. Ag/AgCl) to evaluate its efficiency of biogas upgrading. Compared to pure CO 2 -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 CO 2 content under biogas condition stimulated the enrichment of electroactive- methanogens and bacteria, which primarily facilitated electron transfer during CO 2 conversion. Notably, it was proposed that the spatial consortium of “methanogens–electroactive bacteria,” rather than the methanogen abundance within the biofilm, contributed to the CO 2 -to-CH 4 performance. Overall, these results indicate that low CO 2 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.