Biogas upgrading with hydrogenotrophic methanogenic biofilms.

Hydrogen produced from periodic excess of electrical energy may be added to biogas reactors where it is converted to CH that can be utilized in the existing energy grid. The major challenge with this technology is gas-to-liquid mass transfer limitation. The microbial conversions in reactors designed for hydrogenotrophic methanogenesis were studied with microsensors for H, pH, and CO. The H consumption potential was dependent on the CO concentration, but could partially recover after CO depletion. Reactors with 3-dimensional biofilm carrier material and a large gas headspace allowed for a methanogenic biofilm in direct contact with the gas phase. A high density of Methanoculleus sp. in the biofilm mediated a high rate of CH production, and it was calculated that a reactor filled with 75% carrier material could mediate a biogas upgrading from 50 to 95% CH within 24 h when an equivalent amount of H was added.