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.

Automated summary

The study focused on the performance of a mixed microbial community in lab-scale power-to-methane reactors at 55°C, revealing the community's response to different levels of H2 supply. Low H2 triggered immediate CH4 evolution, while high H2 doses inhibited biomethane formation. However, biomethane production continued steadily with the daily delivery of stoichiometric H2/CO2.