Hydrogen Production by Dark Fermentation

Dark fermentation, photo-fermentation, hybrid system, direct bio photolysis, and indirect bio photolysis are all types of biological processes used to produce bio hydrogen. Dark fermentation involves bio hydrogen production by anaerobic bacteria from carbohydrate-rich substrates in the absence of light, whereas in photo-fermentation, photosynthetic bacteria use light energy to produce bio hydrogen from various organic acids, food processing and agricultural wastes Dark fermentation and photo-fermentation are complementary technologies and can be used sequentially in a hybrid system. In direct bio photolysis solar energy is used by algae and cyanobacteria to convert water into oxygen and bio hydrogen. On the other hand, indirect bio photolysis involve separation of the bio hydrogen and oxygen evolution reactions into separate stages, coupled via carbon dioxide (CO2) fixation/evolution. Dark fermentation present advantages when compared to other biological processes because it is light-independent and different raw materials can be used as a carbon source to the microorganisms, which have both a high rate of bio hydrogen production and growth rate to supply the system. Furthermore, strict and facultative anaerobic microorganisms can be used in the form of pure cultures and mixed cultures. Unlike mixed cultures, pure cultures require a sterile environment to prevent contamination, which is difficult and expensive to achieve in industrial scale. For this reason, mixed cultures have been preferred in scaled-up applications.