Insights on biological hydrogen production routes and potential microorganisms for high hydrogen yield

Considering the present energy demand and industrial growth, finding a potential sustainable energy source is crucial. Among renewable fuels, hydrogen is considered to be the primary choice as it offers substantial benefits over other conventional fuels. Hydrogen can be generated from waste substrates, is cleaner, and has the highest energy density when compared to conventional fuels. Hydrogen production, particularly biological hydrogen production, is believed to be cost-efficient as it can be successfully performed in ambient conditions with easy operational techniques in an environmental-friendly manner. This review summarizes the different routes of biological hydrogen production including biophotolysis, indirect photolysis, dark fermentation, photofermentation, and microbial electrolysis. Further, leading microorganisms involved in biohydrogen production, such as Clostridium spp., Enterobacter spp., Bacillus spp., Escherichia coli, thermophilic lactic acid bacteria, and Klebsiella spp., along with the molecular approaches employed for the enhancement of biohydrogen production are discussed. In addition, a thorough techno-economic analysis of factors involved in the scale-up of hydrogen production is carried out.