Perfluorocarbon nanoemulsions as hydrogen carriers to promote the biological conversion of hydrogen and carbon dioxide to methane

The formation of methane (CH4) via a biomethanation process using hydrogen (H2) and carbon dioxide (CO2) as feedstock is impeded by H2 gas-liquid mass transfer limitations. To address these limitations and improve the CH4 production rate in H2/CO2 biomethanation, perfluorocarbon (PFC) nanoemulsions exhibiting a high solu-bility for gases were proposed as H2 transfer carriers to promote the H2 utilization rate and methanogenesis kinetics. The presence of PFC nanoemulsions in a volume fraction of 1.5% increased the peak rate of CH4 pro-duction by 30.6% and decreased the lag time by 84.5%. These nanoemulsions, composed of PFC and surfactants, efficiently transported H2 molecules to alleviate gas-liquid transport limitations in biological solutions. Furthermore, lipophilic PFC, which is nonspecifically bound to cell membranes of Methanosarcina barkeri (M. barkeri) cells, also provided the transport of H2 molecules from PFC nanoemulsions to the cells. The PFC nanoemulsions separated from these cell membranes primarily through physical oscillations. However, physical separation was difficult when using 2 vol% PFC nanoemulsions due to their strong combination with M. barkeri cells, which hindered H2 transmission and utilization.