Stability of ex situ biological methanation of H 2 /CO 2 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 H /CO was converted into methane at 4NL.L .d . 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 reached 0.7 bar. The MMC withstood a storage period of 34d at room temperature indicating its suitability for industrial constraints.