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

• Published in: Energies (Basel) 2021-11, Vol.14 (21), p.7336
• Main Authors: Szuhaj, Márk, Wirth, Roland, Bagi, Zoltán, Maróti, Gergely, Rákhely, Gábor, Kovács, Kornél L.
• Format: Article
• Language: English
• Subjects: Acetic acid; Alternative energy sources; Batch culture; Batch reactors; Biogas; Biomass; Bioreactors; Carbon dioxide; Climate change; Deoxyribonucleic acid; DNA; Effluents; Electricity; Fed batch; fed-batch reactor; Fermentation; Gas chromatography; Gas mixtures; Gases; Headspace; Homoacetogenesis; Injection; metagenome; Methane; Methanothermobacter; Microbiota; Microorganisms; power-to-gas; Process parameters; Reactors; Renewable resources; Sensors; Solar energy; starvation; Stoichiometry; thermophilic biogas
• ISSN: 1996-1073; 1996-1073
• DOI: 10.3390/en14217336

The performance of a mixed microbial community was tested in lab-scale power-to-methane reactors at 55 °C. The main aim was to uncover the responses of the community to starvation and stoichiometric H2/CO2 supply as the sole substrate. Fed-batch reactors were inoculated with the fermentation effluent of a thermophilic biogas plant. Various volumes of pure H2/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 N2 prior to the daily H2/CO2 injection. Total DNA samples, collected at the beginning and end (day 71), were analyzed by metagenome sequencing. Low levels of H2 triggered immediate CH4 evolution utilizing CO2/HCO3− dissolved in the fermentation effluent. Biomethanation continued when H2/CO2 was supplied. On the contrary, biomethane formation was inhibited at higher initial H2 doses and concomitant acetate formation indicated homoacetogenesis. Biomethane production started upon daily delivery of stoichiometric H2/CO2. The fed-batch operational mode allowed high H2 injection and consumption rates albeit intermittent operation conditions. Methane was enriched up to 95% CH4 content and the H2 consumption rate attained a remarkable 1000 mL·L−1·d−1. The microbial community spontaneously selected the genus Methanothermobacter in the enriched cultures.