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 CH₄ 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 H₂, pH, and CO₂. The H₂ consumption potential was dependent on the CO₂ concentration, but could partially recover after CO₂ 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 CH₄ production, and it was calculated that a reactor filled with 75% carrier material could mediate a biogas upgrading from 50 to 95% CH₄ within 24 h when an equivalent amount of H₂ was added.