Integrative biological hydrogen production: an overview.

Biological hydrogen (H2) production by dark and photo-fermentative organisms is a promising area of research for generating bioenergy. A large number of organisms have been widely studied for producing H2 from diverse feeds, both as pure and as mixed cultures. However, their H2 producing efficiencies have been found to vary (from 3 to 8 mol/mol hexose) with physiological conditions, type of organisms and composition of feed (starchy waste from sweet potato, wheat, cassava and algal biomass). The present review deals with the possibilities of enhancing H2 production by integrating metabolic pathways of different organisms-dark fermentative bacteria (from cattle dung, activated sludge, Caldicellulosiruptor, Clostridium, Enterobacter, Lactobacillus, and Vibrio) and photo-fermentative bacteria (such as Rhodobacter, Rhodobium and Rhodopseudomonas). The emphasis has been laid on systems which are driven by undefined dark-fermentative cultures in combination with pure photo-fermentative bacterial cultures using biowaste as feed. Such an integrative approach may prove suitable for commercial applications on a large scale.