different metabolic pathways including direct water bio- photolysis by green algae, indirect water bio-photolysis by
cyanobacteria, photo-fermentation by photosynthetic purple non-sulfur bacteria, and dark fermentation by heterotrophic anaerobic bacteria. Dark fermentation generates hydrogen at higher rates, uses wider spectrum of substrates, and require lower energy than that of light-dependent processes [5e7].Several feedstocks such as municipal waste, livestock manure, crop residues, food waste, and wastewater have been
utilized as substrates in the dark fermentation [8e11].