Experimental and theoretical investigation of diffusion processes in a membrane anaerobic reactor for bio-hydrogen production

This paper explores the potential for advanced membranes to act as a sink for hydrogen generated during anaerobic digestion thereby maintaining very low hydrogen concentrations and more favorable conditions for fermentative and possibly acetate oxidative pathways. This necessitates that the membranes function when submerged in water.Permeation of hydrogen through submerged membranes was measured at fluxes of 1.31×10−9 mol m−2 s−1 Pa−1, and 74.1×10−9 mol m−2 s−1 Pa−1 for Carbon Template Molecular Sieve Silica (CTMSS) and polytetrafluoroethylene (PTFE) membranes, respectively. A γ-alumina membrane showed no permeability to hydrogen when submerged. Fermentation experiments with high hydrogen yielding cultures fed with glucose and settled onto the CTMSS membrane verified that hydrogen will preferably flow through the membrane, although the membrane failed after 24 h of operation. In the absence of the membrane, microprobe measurements demonstrate dissolved hydrogen concentrations are supersaturated by a factor of over 100.Diffusion modeling shows that the hydrogen permeability of a submerged PTFE membrane is sufficient to maintain thermodynamically feasible conditions for acetate oxidation providing the organisms are in direct contact with the membrane surface.