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

Comparison of methane yield of a novel strain of Methanothermobacter marburgensis in pure and mixed adapted culture derived from a methanation bubble column bioreactor

The ongoing discussion regarding the use of mixed or pure cultures of hydrogenotrophic methanogenic archaea in Power-to-Methane (P2M) bioprocess applications persists, with each option presenting its own advantages and disadvantages. To address this issue, a comparison of methane (CH4) yield between a novel methanogenic archaeon belonging to the species Methanothermobacter marburgensis (strain Clermont) isolated from a biological methanation column, and the community from which it originated, was conducted. This comparison included the type strain M. marburgensis str. Marburg. The evaluation also examined how exposure to oxygen (O2) for up to 240 min impacted the CH4 yield across these cultures. While both Methanothermobacter strains exhibit comparable CH4 yield, slightly higher than that of the mixed adapted culture under non-O2-exposed conditions, strain Clermont does not display the lag time observed for strain Marburg.

Syngas biomethanation: Current state and future perspectives

In regions highly dependent on fossil fuels imports, biomethane represents a promising biofuel for the transition to a bio-based circular economy. While biomethane is typically produced via anaerobic digestion and upgrading, biomethanation of the synthesis gas (syngas) derived from the gasification of recalcitrant solid waste has emerged as a promising alternative. This work presents a comprehensive and in-depth analysis of the state-of-the-art and most recent advances in the field, compiling the potential of this technology along with the bottlenecks requiring further research. The key design and operational parameters governing syngas production and biomethanation (e.g. organic feedstock, gasifier design, microbiology, bioreactor configuration, etc.) are critically analysed.

Stability of ex situ biological methanation of H2/CO2 with a mixed microbial culture in a pilot scale bubble column reactor

Biological methanation is a promising technology for gas and carbon valorisation. Therefore, process stability is required to allow its scale up and development. A pilot scale bubble column reactor was used for ex situ biological methanation with Mixed Microbial Culture (MMC). A 16S rRNA high throughput sequencing analysis revealed the MMC reached a stable composition with 50-60% Methanobacterium in closed liquid mode, a robust genus adapted to large scale constraints. Class MBA03 was identified as an indicator of process stability. Methanogenic genera moved toward 50% of Methanothermobacter when intensifying the process, and proteolytic activity was identified while 94% of H₂/CO₂ was converted into methane at 4NL.L^-1.d^-1. This study gives clarifications on the origin of volatile fatty acids (VFA) apparitions. Acetate and propionate accumulated when methanogenic activity weakened due to nutritive deficiency, and when P_H2 reached 0.7 bar. The MMC withstood a storage period of 34d at room temperature indicating its suitability for industrial constraints.

Physiological Effects of 2-Bromoethanesulfonate on Hydrogenotrophic Pure and Mixed Cultures

Mixed or pure cultures can be used for biomethanation of hydrogen. Sodium 2-bromoethanesulfonate (BES) is an inhibitor of methanogenesis used to investigate competing reactions like homoacetogenesis in mixed cultures. To understand the effect of BES on the hydrogenotrophic metabolism in a biomethanation process, anaerobic granules from a wastewater treatment plant, a hydrogenotrophic enrichment culture, and pure cultures of Methanococcus maripaludis and Methanobacterium formicicum were incubated under H₂/CO₂ headspace in the presence or absence of BES, and the turnover of H₂, CO₂, CH₄, formate and acetate was analyzed. Anaerobic granules produced the highest amount of formate after 24 h of incubation in the presence of BES. Treating the enrichment culture with BES led to the accumulation of formate. M. maripaludis produced more formate than M. formicicum when treated with BES. The non-inhibited methanogenic communities produced small amounts of formate whereas the pure cultures did not. The highest amount of acetate was produced by the anaerobic granules concomitantly with formate consumption. These results indicate that formate is an important intermediate of hydrogenotrophic metabolism accumulating upon methanogenesis inhibition.

Seasonal Energy Storage with Power-to-Methane Technology

To have a sustainable society, the need to use renewable sources to produce electricity is inevitable [...]