Metabolic pathways for microalgal biohydrogen production: Current progress and future prospectives

Microalgal biohydrogen (bioH(2)) has attracted global interest owing to its potential carbon-free source of sustainable renewable energy. Most of previous reviews which focused on microalgal bioH(2), have shown unclear differentiation among the metabolic pathways. In this review, investigation of all different metabolic pathways for microalgal bioH(2) production along with discussion on the recent research work of last 5-years have been considered. The major factors (such as light, vital nutrients, microalgal cell density, and substrate bioavailability) are highlighted. Moreover, effect of various pretreatment approaches on the constituent's bioaccessibility is reported. Microbial electrolysis cells as a new strategy for bioH(2) production is stated. Comparison between the operation conditions of various bioreactors and economic feasibility is also emphasized. Genetic, metabolic engineering, and synthetic biology as recent technologies improved the microalgal bioH(2) production through inactivation of uptake hydrogenase (H(2)ase), inhibition of the competing pathways in polysaccharide synthesis, and improving the O-2 tolerant H(2)ase.