Hydrogen production via dark fermentation

Dark fermentation is an alternative method for biological hydrogen production from biomass. It is a process which is carried out in the dark, under anaerobic conditions, and it is directly related to the acidogenic stage of anaerobic digestion process. It has been considered as a viable and effective method, since it is carried out at ambient temperatures and pressures, without photoenergy, so that the cost of hydrogen production is estimated as 340 times lower than that of the photosynthetic processes (Morimoto, 2002). The hydrogen-producing enzymes (hydrogenases) can be utilized in dark fermentations by using pure microbial cultures or by a mixture of anaerobic microorganisms. Since no oxygen is produced or consumed in these reactions, hydrogenase is less likely to be inactivated by oxygen. Organic wastes from agriculture or sewage can be fed into large anaerobic bioreactors, achieving the dual goals of waste management and hydrogen production. Dark fermentation as a method of hydrogen production does not have the demand of expensive photo-bioreactors, which are necessary for direct biophotolysis and photo-fermentation. Fermentative hydrogen production is focused on this handbook, since it is considered as the most promising compared to all biological hydrogen production methods. Brief comparison of biomass materials that can be used for biohydrogen production, microorganisms available, factors limiting biohydrogen production, modelling and process optimization and lastly strategies for process improvement will be highlighted in the next chapter section.