Fermentative H2 production from food waste: Parametric analysis of factor effects

Factorial fermentation experiments on food waste (FW) inoculated with activated sludge (AS) were conducted to investigate the effects of pH and the inoculum-to-substrate ratio (ISR [g VSAS/g TOCFW]) on biohydrogen production. The two parameters affected the H-2 yield, the fermentation rate and the biochemical pathways. The minimum and maximum yields were 41 L H-2/kg TOCFW (pH = 7.5, ISR= 1.74) and 156-160 L H-2/kg TOCFW (pH = 5.5, ISR = 0.58 and 1.74). The range of carbohydrates conversion into H-2 was 0.37-1.45 mol H-2/mol hexose, corresponding to 9.4-36.2% of the theoretical threshold. A second-order predictive model for H-2 production identified an optimum region at low pHs and high ISRs, with a theoretical maximum of 168 L H-2/kg TOCFW at pH = 5.5 and ISR = 1.74. The Spearman's correlation method revealed several relationships between the variables, suggesting the potentially governing metabolic pathways, which turned out to involve both hydrogenogenic pathways and competing reactions.