Dark fermentation for hydrogen production from cheese whey: a parametric study

Batch dark fermentation experiments were performed on mixtures of cheese whey (CW) and wastewater activated sludge (AS) to evaluate the influence of pH and the inoculum-tosubstrate ratio (ISR) on biological H2 production via dark fermentation. Factorial design experiments were conducted to derive response surfaces for the fermentation process by means of a predictive model describing the effects of the operating conditions on the main response variables (namely, H2 production yield and kinetic parameters). The specific H2 production potential was found to vary with pH and ISR by a factor of 6, from 61 L H2/kg TOCwhey at ISR = 0 and pH = 7.0 to 371 L H2/kg TOCwhey at ISR = 1.44 g VS/g TOC and pH = 5.5. The metabolic products included mainly acetate and butyrate, followed by ethanol (although at much lower concentrations), while propionate was only observed once H2 production had significantly levelled off. The presence of multiple metabolic products suggested that the process was governed by several overlapping and competing fermentation pathways, which caused the conversion yield of substrate into H2 to be reduced compared to the expected yield associated to clostridial fermentation.