Continuous dark-photo fermentative H2 production from synthetic lignocellulose hydrolysates with different photoheterotrophic cultures: sequential vs. co-culture processes

In this study, sequential and co-culture dark-photo fermentation were compared in terms of hydrogen production, substrate consumption and by-products formation during continuous process. Anaerobic digester sludge was a source of microorganisms for dark fermentation. Two different bacterial culture was used for photofermentation: pure culture of Rhodobacter sphaeroides and mixed heterotrophic culture. The highest substrate consumption and hydrogen yields were obtained for sequential dark-photo fermentation. Acetate and butyrate produced from sugars during dark fermentation were consumed by photofermentative bacteria resulting in higher H2 production. R. sphaeroides (4.15 mol H2/molsugar) showed higher yields compared to mixed heterotrophic culture (3.07 mol H2/molsugar). A stable co-culture of R. sphaeroides and dark-fermentative microorganisms were observed during one-step process.