Biogas upgrading technologies have
received widespread attention recently and are researched extensively.
Microbial biogas upgrading (biomethanation) relies on the microbial performance
in enriched H2 and CO2 environments. In this
review, recent developments and applications of CH4 enrichment
in microbial methanation processes are systematically reviewed.
During biological methanation, either H2 can
be injected directly inside the anaerobic digester to enrich CH4 by
a consortium of mixed microbial species or H2 can be injected
into a separate bioreactor, where CO2 contained in biogas is
coupled with H2 and converted to CH4, or a
combination hereof. The available microbial technologies based on
hydrogen-mediated CH4 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 H2 injection are thoroughly discussed.
Finally, the summary of
existing demonstration, pilot plants and commercial CH4 enrichment
plants based on microbial biomethanation are critically reviewed.