The buffer composition impacts the hydrogen production and the microbial community composition in non-axenic cultures

Hydrogen obtained from biomass via dark fermentation is considered a sustainable and clean energy carrier. Batch fermentations with cheese whey powder were performed to assess total hydrogen production (Hmax), volumetric hydrogen production rate (VHPR), maximum lactose consumption (Smax), maximum lactose consumption rate (Rmax,S), hydrogen molar yield (HMY) and the bacterial species present using two mineral media formulation (A, B). The highest VHPR was 304.8 cm3 dm−3 h−1 and the HMY was 1.8 mol mol−1. Medium B yielded around twice the VHPR than the attained with medium A, but HMY only had a slight increment with the use of medium B. The values reached for Smax (17.3 g dm−3), Hmax (4.863 dm3) and Rmax,S (2.7 g dm−3 h−1) were also enhanced with medium B. Results suggest that butyrate levels and lower pH are the reasons for diminished hydrogen production with medium A. The microbial communities were analyzed using polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE). Only one band was observed in the experiments with medium A, the sequence retrieved from this band presented a closest relative match to the sequence from Citrobacter freundii JCM (100% identity); whereas for medium B, three bands were detected. Sequences from these bands presented high homology to sequences from Clostridium perfringens W11 (95% identity), uncultured Lachnospiraceae bacterium clone MS146A1 E12 (100% identity) and Enterobacter cloacae GH1 (100% identity). From the results obtained it is clear that the formulation of culture media had a strong effect on hydrogen production, kinetics and also on the microbial diversity.

► Formulation of culture media had a strong effect on hydrogen production.
► Medium B yielded around twice the VHPR than the attained with medium A.
► Formulation of culture media had a strong effect on kinetics and microbial diversity.
► Deviations from metabolic hydrogen-production pathways occurred.
► Improvement of the hydrogen production is critical for the scaling-up process.