CO2-free biohydrogen production by mixed dark and photofermentation bacteria from sorghum starch using a modified simple purification and collection system

•A modified simple collection system is described for CO2-free bio-H2 production.•The collection system allows to monitor both hydrogen and CO2 production.•Crude sorghum starch showed a high potency as a substrate for H2 production.•Combined dark and photo-fermentation showed higher yield than dark one.•Mixed photo-heterotrophic bacteria was better for H2 production than each alone.

In this study two tasks were accomplished. First, a modified simple purification and collection lab system is described for CO2-free bio-hydrogen production. Second, the efficiency of hydrogen production was investigated by mixed dark and photo-fermentative hydrogen producing bacteria Escherichia coli, Clostridium acetobutylicum, Rhodobacter capsulatus and Rhodobacter sphaeroides from sorghum grains crude starch. The crude starch of white sorghum grains showed a higher potency as a carbon source for fermentative hydrogen production than that of red sorghum grains although both varieties are quite applicable for industrial scale hydrogen production. Using mixed R. capsulatus and R. sphaeroides showed a higher efficiency for hydrogen production than using each alone in the combined dark and photo-fermentation due to their varying efficiencies of converting various volatile fatty acids produced by dark fermentation into hydrogen gas. For enhanced hydrogen production, this study suggests using mixed strains of non-oxygenic photosynthetic purple non-sulfur bacteria in the combined dark and photo-fermentation. The high efficiency of hydrogen production from sorghum starch suggests that using this cheap crop in future industrial application of biological H2 production would increase its economic feasibility in developing countries of arid climate where sorghum is no longer widely used as human food.