Light fermentation of dark fermentation effluent for bio-hydrogen production by different Rhodobacter species at different initial volatile fatty acid (VFA) concentrations

Three different Rhodobacter sphaeroides (RS) strains (RS–NRRL, RS–DSMZ and RS–RV) and their combinations were used for light fermentation of dark fermentation effluent of ground wheat containing volatile fatty acids (VFA). In terms of cumulative hydrogen formation, RS–NRRL performed better than the other two strains producing 48 ml H2 in 180 h. However, RS–RV resulted in the highest hydrogen yield of 250 ml H2 g−1 TVFA. Specific hydrogen production rate (SHPR) with the RS–NRRL was also better in comparison to the others (13.8 ml H2 g−1 biomass h−1). When combinations of those three strains were used, RS–RV + RS–DSMZ resulted in the highest cumulative hydrogen formation (90 ml H2 in 330 h). However, hydrogen yield (693 ml H2 g−1 TVFA) and SHPR (12.1 ml H2 g−1 biomass h−1) were higher with the combination of the three different strains. On the basis of Gompertz equation coefficients mixed culture of the three different strains gave the highest cumulative hydrogen and formation rate probably due to synergistic interaction among the strains. The effects of initial TVFA and NH4–N concentrations on hydrogen formation were investigated for the mixed culture of the three strains. The optimum TVFA and NH4–N concentrations maximizing the hydrogen formation were determined as 2350 and 47 mg L−1, respectively.