The goal of the study was to characterize H-2 production in an integrated process utilizing potato homogenate (PH) for dark, fermentative H-2 production followed by H-2 photoproduction using purple non-sulfur bacteria. Emphasis was placed on (a) examining potato fermentation effluent (FE) as substrate for H-2 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. H-2 photoproduction by purple bacteria was inhibited at high FE content. Upon suitable dilution, adequate illumination, and supplementation with Fe/Mg/phosphate nutrients, H-2 photoproduction reached 40 L L-1 of non-diluted FE, with a total H-2 yield of 5.6 mol mol(-1) glucose equivalent for the two-stage integrated process. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.