Immobilized Purple Bacteria for Light-Driven H2 Production from Starch and Potato Fermentation Effluents

The goal of the study was to show that immobilized purple bacteria could photoproduce H ₂ using dark fermentation effluent (FE) as substrate. Simple pretreatment of an inexpensive glass-fiber matrix accelerated the immobilization process. Photobioreactors (PhBR) containing immobilized Rhodobacter sphaeroides GL produced 0.128 L H ₂ h ^-1 L ^-1 of PhBR volume (0.570 L h ^-1 L ^-1 of matrix) for up to 3 months when continuously fed artificial media with volatile fatty acids (VFAs) or FE from potato and starch fermentations. Hydrogen production was insensitive to NH ₄ ⁺ up to 1 mM and saturated at 8 mM lactate or 1.5% potato FE (diluted in water and supplemented with critical micronutrients). The efficiency of VFA transformation to H ₂ was 50-70% of theoretical. At nonlimiting substrate concentrations in artificial media or FE, acetate was utilized before butyrate. High volumetric rates of continuous H ₂ photoproduction and stability of the process are advantages of using immobilized cultures. Use of H ₂ photoproduction as a polishing step in the treatment of FEs from dark fermentations increased the total amount of H ₂ produced from 0.9 to 4.7 mol mol ^-1 glucose equivalent in the original potato homogenate.