Biogas upgrading and energy storage via electromethanogenesis using intact anaerobic granular sludge as biocathode

Microbial electrochemical system is a promising CO2-to-CH4 conversion technology that can upgrade raw biogas to high calorific content for downstream applications. The development of efficient, robust, and cost-effective biocathode is the pivotal issue for its industrial application. In this study, intact anaerobic granular sludge (AGS), which was the conventional biocatalyst in anaerobic digestion processes for high-efficiency CH4 production, was for the first time employed as biocathode in electromethanogenesis system (EM) for biogas upgrading. The applied voltage (0, 3, 4, and 5 V) and biogas flow rate (5.22-23.43 mL/h) were modulated to optimize biogas upgrading performance in the AGS-EM system. The CH4 content in treated biogas could reach as high as 97.9 +/- 2.3% at an applied voltage of 4 V and a gas flow rate of 17.79 mL/h. The system showed superior stability and anti-interference ability in the continuous operation mode for 2 months. 16S rRNA sequencing results showed that Methanobacterium and Azoarcus were the dominant populations in biocathode. The AGS-EM system obtained an energy benefit of 477.3 kJ/mol(biogas), and economic benefit of 446.4 EUR/m(biogas)(3). The novel AGS-EM system showed the promising perspectives for the industrial application in the field of biogas upgrading and renewable energy storage.