Towards the integration of dark- and photo-fermentative waste treatment. 3. Potato as substrate for sequential dark fermentation and light-driven H2 production

The goal of the study was to characterize H2 production in an integrated process utilizing potato homogenate (PH) for dark, fermentative H2 production followed by H2 photoproduction using purple non-sulfur bacteria. Emphasis was placed on (a) examining potato fermentation effluent (FE) as substrate for H2 photoproduction, (b) estimating the yield and efficiency of both processes, and (c) elucidating the physiological factors influencing the integrated system as a whole. In the dark stage maximal production of gas (11.5 L L−1 of the culture) and VFA (350 mM) were observed with a PH concentration of 400 g L−1 of medium, but higher yields (0.05 L g−1 PH; 1.9 mmol g−1 PH) were obtained at PH concentrations of 50–100 g L−1. H2 photoproduction by purple bacteria was inhibited at high FE content. Upon suitable dilution, adequate illumination, and supplementation with Fe/Mg/phosphate nutrients, H2 photoproduction reached 40 L L−1 of non-diluted FE, with a total H2 yield of 5.6 mol mol−1 glucose equivalent for the two-stage integrated process.