Single-chamber microbial electrochemical cell for CH₄ production from CO₂ utilizing a microbial consortium

We report the first single-chamber microbial electrochemical cell for conversion of CO₂ to CH₄, with an average CH₄ production rate of 0.47 ± 0.05 mL day⁻¹ cm⁻² at an applied potential of 600 mV, utilizing a methanogenic microbial community collected from the formation water in the San Juan coal basin (Colorado, USA). CH₄ production was only observed at the graphite rod cathode after an electrochemical pre-treatment that facilitates biofilm formation. The carbon contained within the CH₄ arose predominantly from the CO₂ source, as verified by experiments during which the CO₂ source was repeatedly turned off and on. Modest quantities of acetic acid and ethanol were also produced. DNA extraction and sequencing from the microbial community showed that from the Archaea kingdom, only 2 species survived prolonged exposure to CO₂ and CH₄ production, methanobacterium sp. (81.4%), and methanoculleus sp. (18.6%), while in the bacterial kingdom, anaerobaculum thermoterrnum (67.1%) was the predominant surviving species.