An overview of biomethanation and the use of membrane technologies as a candidate to overcome H mass transfer limitations.

Energy produced from renewable sources such as sun or wind are intermittent, depending on circumstantial factors. This fact explains why energy supply and demand do not match. In this context, the interest in biomethanation has increased as an interesting contribution to the Power-to-gas concept (P2G), transforming the extra amount of produced electricity into methane (CH). The reaction between green hydrogen (H) (produced by electrolysis) and CO (pollutant present in biogas) can be catalysed by different microorganisms to produce biomethane, that can be injected into existing natural gas grid if reaching the standards. Thus, energy storage for both hydrogen and electricity, as well as transportation problems would be solved. However, H diffusion to the liquid phase for its further biological conversion is the main bottleneck due to the low solubility of H. This review includes the state-of-the-art in biological hydrogenotrophic methanation (BHM) and membrane-based technologies. Specifically, the use of hollow-fiber membrane bioreactors as a technology to overcome H diffusion limitations is reviewed. Furthermore, the influence of operating conditions, microbiology, H diffusion and H injection methods are critically discussed before setting the main recommendations about BHM.