Enhancement of Biohydrogen Production by Two-Stage Systems: Dark and Photofermentation

Abstract

Hydrogen is an attractive, clean, future renewable energy carrier. Biological H2 production from wastes could be an environmentally friendly and economically viable way to produce hydrogen compared with present production technologies. Hydrogen yields in dark fermentation are rather low since carbohydrates are converted into hydrogen and volatile fatty acids with a maximal theoretical yield of 4 mol H2/mol glucose when acetate is the sole end product. Photofermentation is theoretically capable of the complete conversion of substrate to hydrogen, but the main substrates are expensive organic acids. Therefore combining these systems is a good alternative to improve overall hydrogen yields. By using the acetate produced in dark fermentation with photofermentation, the yield can be theoretically increased to 12 mol H2/mol glucose. Here we review the current research on biohydrogen production using two-stage systems that combine dark fermentation by mixed cultures and photofermentation by purple non-sulfur bacteria.