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.