Waste to Sustainable Biohydrogen Production Via Photo-Fermentation and Biophotolysis − A Systematic Review

Considering the environmental challenges humanity faces in the 21st century, it is obvious that there is an enormous need for change of the global energy map. Under these circumstances, new energy sources and intermediates must be considered as options to limit the greenhouse gases emissions and mitigate climate crisis. Biohydrogen production is one of the most appealing options, due to hydrogen's multiple applications and zero emissions as a fuel, to empower a future hydrogen circular economy. In this review article we focus on two methods that are not widely used at industrial scale but have many future possibilities and growth margins: (a) photo-fermentation and (b) bio photolysis. Both methods are light dependent and need photobioreactors to function and produce significant amounts of biohydrogen. Based on an extensive literature search and systemic analysis of the findings, presentation of the different reactants, operating conditions and biohydrogen productions, key factors and effecting parameters were discussed. Temperature, pH, light intensity and photobioreactor operation and design are some of the most significant factors that define the biohydrogen production rates and yields. Innovative solutions and approaches are presented including biotechnological and genetic engineering modifications to microorganisms, as well as combinations of some hybrid biohydrogen producing methods, especially dark and photo fermentation. For implementing a biohydrogen circular-economy, different wastes were explored as potential feedstocks, and overcoming of major bottlenecks that biophotolysis and photo-fermentation face in the transition to a sustainable biohydrogen economy, were discussed