Biogas fermentation has two general problems

low production rate and low methane concentration. From the reaction mechanism for methane formation

if external H2 is supplied

CO2 in the biogas can be converted into CH4

leading to increased yield and concentration of methane. Recently published experimental studies reported that biogas could be purified and upgraded to a quality as biomethane with the addition of hydrogen gas. However

to make this technology practical

two key problems should be resolved. One is to intensify H2 transfer from gas phase to aqueous phase at low mixing speeds. The other is to obtain hydrogen gas with economical methods. A scheme is suggested for biogas upgrading through the integration of H2 generation by photoelectrocatalysis and CH4 production by anaerobic fermentation.