The distillers grains with solubles as a perspective substrate for obtaining biomass and producing bio-hydrogen by Rhodobacter sphaeroides

• Distillers grains with solubles (DGS) waste can serve as an effective source for bio-hydrogen.
• On diluted DGS media H2 production by Rhodobacter sphaeroides started at 24 h growth.
• DGS enhanced (∼6 fold) H2 photo-production.

The photosynthetic purple non-sulfur bacterium Rhodobacter sphaeroides MDC6521, isolated from Armenian mineral spring, and distillers grains with solubles (DGS) (by-product of bio-ethanol fermentation) were applied for obtaining biomass and producing bio-hydrogen (H2) upon illumination. During growth on diluted DGS media H2 production was started at 24 h growth, whereas H2 photoproduction by R. sphaeroides cells, grown on Ormerod medium, was detected after 48 h. Moreover, the R. sphaeroides produced considerably more H2 during DGS photo-fermentation: the H2 yields from 2- fold and 5-fold diluted media were ∼4.6–5.5-folds higher in comparison with control. H2 yield has decreased at higher dilution. The growth yields of R. sphaeroides cells, grown in the 2–5-folds diluted DGS media, were considerably higher than those of control cells, grown in Ormerod medium. The results can provide with new cheaper and more effective source of biomass and bio-hydrogen and as well as solve the problem of ethanol by-product utilization.