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

Abstract

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.

Current Status of Biological Biogas Upgrading Technologies

“…Since flow-through reactors are optimized to maximum H 2 conversion efficiency, generally low hydrogen injection rates are applied that limit methane production rates. In spite of the intermittent operation of the fed-batch reactor, a remarkable 1000 mL L −1 d −1 H 2 consumption rate was attained, while methane was enriched up to 95% [86].…”

Biohydrogen production through dark fermentation from waste biomass: Current status and future perspectives on biorefinery development

“…The key methanogens involved depend on how the P2M process is achieved, i.e., mixed anaerobic communities are required for in-situ P2M. At the same time, pure cultures are essential for ex-situ P2M, which could be enriched from full-scale anaerobic digestion plants [246,247]. Further, the converted methane from H2 could be either utilized directly to replace natural gas or converted back to hydrogen.…”

Effect of Inoculum Microbial Diversity in Ex Situ Biomethanation of Hydrogen

“…Another study found that psychrophilic conditions can inhibit methanogenic activity but either mesophilic or psychrophilic conditions can enrich homoacetogens [ 45 ]. To better understand the microbial communities and their functioning, omics techniques such as metagenomics and metatranscriptomics have been exploited to unravel in more detail the community members and their metabolic functions during biomethanation of hydrogen [ 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 ].…”