Light-dependent biohydrogen production: Progress and perspectives.

The fourth industrial revolution anticipates energy to be sustainable, renewable and green. Hydrogen (H) is one of the green forms of energy and is deemed a possible solution to climate change. Light-dependent H production is a promising method derived from nature's most copious resources: solar energy, water and biomass. Reduced environmental impacts, absorption of carbon dioxide, relative efficiency, and cost economics made it an eye-catching approach. However, low light conversion efficiency, limited ability to utilize complex carbohydrates, and the O sensitivity of enzymes result in low yield. Isolation of efficient H producers, development of microbial consortia having a synergistic impact, genetically improved strains, regulating bidirectional hydrogenase activity, physiological parameters, immobilization, novel photobioreactors, and additive strategies are summarized for their possibilities to augment the processes of bio-photolysis and photo-fermentation. The challenges and future perspectives have been addressed to explore a sustainable way forward in a bio-refinery approach.