Hydrogen biorefinery: Potential utilization of the liquid waste from fermentative hydrogen production

In terms of greenhouse gas emission reduction potential, hydrogen is superior to commercial biofuels and fossil fuels because it has high energy density and it generates only water as major emission. Biohydrogen production has additional environmental benefit as different organic wastes can be valorized during the process; however, because of high process cost, its commercial production is not yet there. During dark fermentation, in addition to hydrogen, around 60% of the feedstock may convert to various industrial chemicals including ethanol, 1, 3 propanediol and butyric acid. If these products are not recovered, the liquid waste generated during the process can be used as the feedstock for production of polyhydroxyalkanoates, lipid, methane, hydrogen and electricity. The liquid waste is also a potential substitute of phosphate solubilizing bio-fertilizers. Thus, in this review, biohydrogen production process is evaluated as a potential biorefinery producing biofuels, fine chemicals and biomaterials. The strategy could be useful to reduce overall cost of the process by generating revenue from multiple sources.