A feasibility study on the bioconversion of CO2 and H2 to biomethane by gas sparging through polymeric membranes

•A hollow-fiber MBR was evaluated for the bioconversion of CO2 and H2 to biomethane.•Gas sparging resulted in kLa values up to 430 h−1for H2.•Biomethane yield reached 0.22–0.23 m3 per m3 of H2 supplied.•Biogas could be upgraded up to a 95% CH4 concentration.

In this study, the potential of a pilot hollow-fiber membrane bioreactor for the conversion of H2 and CO2 to CH4 was evaluated. The system transformed 95% of H2 and CO2 fed at a maximum loading rate of 40.2 mH23/mR3d and produced 0.22 m3 of CH4 per m3 of H2 fed at thermophilic conditions. H2 mass transfer to the liquid phase was identified as the limiting step for the conversion, and kLa values of 430 h−1 were reached in the bioreactor by sparging gas through the membrane module. A simulation showed that the bioreactor could upgrade biogas at a rate of 25 m3/mR3d, increasing the CH4 concentration from 60 to 95%v. This proof-of-concept study verified that gas sparging through a membrane module can efficiently transfer H2 from gas to liquid phase and that the conversion of H2 and CO2 to biomethane is feasible on a pilot scale at noteworthy load rates.