Thermophilic Biohydrogen Production

Dark fermentative hydrogen production at thermophilic conditions is attractive process for biofuel production. From thermodynamic point of view, higher temperatures favor biohydrogen production. Highest hydrogen yields are always associated with acetate, or with mixed acetate- butyrate type fermentation. On the contrary the hydrogen yield decreases, with increasing concentrations of lactate, ethanol or propionate. Major factors affecting dark fermentative biohydrogen production are organic loading rate (OLR), pH, hydraulic retention time (HRT), dissolved hydrogen and dissolved carbon dioxide concentrations, and soluble metabolic profile (SMP). A number of thermophilic and extreme thermophilic cultures (pure and mixed) have been studied for biohydrogen production from different feedstocks - pure substrates and waste/wastewaters. Variety of process technologies (operational conditions such as temperature and pH, fermentation modes and reactor types applied) are currently utilized at lab and pilot scale, for biohydrogen production. Although the process has strong potential for the production of energy from organic residues and wastes, the major challenge is to determine whether the economics and reliability of dark fermentative hydrogen production are sufficiently attractive for commercial application to be installed. Furthermore, storage and utilization of the produced hydrogen still faces challenges.