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 H2 production and build a related predictive model. ISR and pH affected H2 potential and rate, and the fermentation pathways. The specific H2 yield varied from 61 (ISR =0, pH=7.0) to 371 L H2/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 H2 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 H2 compared to that expected with clostridial fermentation.