Conversion of H(2) and CO(2) to CH(4) and acetate in fed-batch biogas reactors by mixed biogas community: a novel route for the power-to-gas concept

BACKGROUND: Applications of the power-to-gas principle for the handling of surplus renewable electricity have been proposed. The feasibility of using hydrogenotrophic methanogens as CH(4) generating catalysts has been demonstrated. Laboratory and scale-up experiments have corroborated the benefits of the CO(2) mitigation via biotechnological conversion of H(2) and CO(2) to CH(4). A major bottleneck in the process is the gas–liquid mass transfer of H(2). RESULTS: Fed-batch reactor configuration was tested at mesophilic temperature in laboratory experiments in order to improve the contact time and H(2) mass transfer between the gas and liquid phases. Effluent from an industrial biogas facility served as biocatalyst. The bicarbonate content of the effluent was depleted after some time, but the addition of stoichiometric CO(2) sustained H(2) conversion for an extended period of time and prevented a pH shift. The microbial community generated biogas from the added α-cellulose substrate with concomitant H(2) conversion, but the organic substrate did not facilitate H(2) consumption. Fed-batch operational mode allowed a fourfold increase in volumetric H(2) load and a 6.5-fold augmentation of the CH(4) formation rate relative to the CSTR reactor configuration. Acetate was the major by-product of the reaction. CONCLUSIONS: Fed-batch reactors significantly improve the efficiency of the biological power-to-gas process. Besides their storage function, biogas fermentation effluent reservoirs can serve as large-scale bio CH(4) reactors. On the basis of this recognition, a novel concept is proposed, which merges biogas technology with other means of renewable electricity production for improved efficiency and sustainability.