An overview of microbial biogas enrichment.

Biogas upgrading technologies have received widespread attention recently and are researched extensively. Microbial biogas upgrading (biomethanation) relies on the microbial performance in enriched H and CO environments. In this review, recent developments and applications of CH enrichment in microbial methanation processes are systematically reviewed. During biological methanation, either H can be injected directly inside the anaerobic digester to enrich CH by a consortium of mixed microbial species or H can be injected into a separate bioreactor, where CO contained in biogas is coupled with H and converted to CH, or a combination hereof. The available microbial technologies based on hydrogen-mediated CH enrichment, in particular ex-situ, in-situ and bioelectrochemical, are compared and discussed. Moreover, gas-liquid mass transfer limitations, and dynamics of bacteria-archaea interactions shift after H injection are thoroughly discussed. Finally, the summary of existing demonstration, pilot plants and commercial CH enrichment plants based on microbial biomethanation are critically reviewed.