A parametric response surface study of fermentative hydrogen production from cheese whey

Batch factorial experiments were performed on cheese whey + wastewater sludge mixtures to evaluate the influence of pH and the inoculum-to-substrate ratio (ISR) on fermentative H-2 production and build a related predictive model. ISR and pH affected H-2 potential and rate, and the fermentation pathways. The specific H-2 yield varied from 61 (ISR = 0, pH= 7.0) to 371 L H-2/kg TOCwhey (ISR = 1.44 g VS/g TOC, pH = 5.5). The process duration range was 5.3 (ISR = 1.44 g VS/g TOC, pH = 7.5) - 183 h (ISR = 0, pH= 5.5). The metabolic products included mainly acetate and butyrate followed by ethanol, while propionate was only observed once H-2 production had significantly decreased. The multiple metabolic products suggested that the process was governed by several fermentation pathways, presumably overlapping and mutually competing, reducing the conversion yield into H-2 compared to that expected with clostridial fermentation.