High hydrogen yield from a two-step process of dark- and photo-fermentation of sucrose

We demonstrate a two-step process used to increase the hydrogen yield from sucrose and to relieve the pollution threat caused by resultant fatty acids in dark-fermentation. In batch tests of dark-fermentation using microflora, the maximum hydrogen production rate was > 360 mL H 2 / L h and the maximum hydrogen yield was 3.67 mol H 2 / mol sucrose. The fatty acids produced in dark-fermentation were mainly butyrate and acetate with a small amount of propionate, valerate, n-butyl alcohol, and caproate. Photo-fermentation with Rhodobacter sphaeroides SH2C was then employed to convert these small molecular fatty acids into hydrogen. The total hydrogen yield from sucrose increased from the maximum of 3.67 mol H 2 / mol sucrose in dark-fermentation to 6.63 mol H 2 / mol sucrose by using the two-step process. No butyrate, acetate, propionate, or valerate was detected in the final fermentation effluent after photo-fermentation. Our results suggest that a two-step process of combining dark- and photo-fermentation may increase hydrogen production capacity from biomass and prevent the environmental problems associated with untreated fermentation effluents.