Development of Stable Mixed Microbiota for High Yield Power to Methane Conversion

The performance of a mixed microbial community was tested in lab-scale power-to-methane reactors at 55 & DEG;C. The main aim was to uncover the responses of the community to starvation and stoichiometric H-2/CO2 supply as the sole substrate. Fed-batch reactors were inoculated with the fermentation effluent of a thermophilic biogas plant. Various volumes of pure H-2/CO2 gas mixtures were injected into the headspace daily and the process parameters were followed. Gas volumes and composition were measured by gas-chromatography, the headspace was replaced with N-2 prior to the daily H-2/CO2 injection. Total DNA samples, collected at the beginning and end (day 71), were analyzed by metagenome sequencing. Low levels of H-2 triggered immediate CH4 evolution utilizing CO2/HCO3- dissolved in the fermentation effluent. Biomethanation continued when H-2/CO2 was supplied. On the contrary, biomethane formation was inhibited at higher initial H-2 doses and concomitant acetate formation indicated homoacetogenesis. Biomethane production started upon daily delivery of stoichiometric H-2/CO2. The fed-batch operational mode allowed high H-2 injection and consumption rates albeit intermittent operation conditions. Methane was enriched up to 95% CH4 content and the H-2 consumption rate attained a remarkable 1000 mL & BULL;L-1 & BULL;d(-1). The microbial community spontaneously selected the genus Methanothermobacter in the enriched cultures.