Inhibition of fermentative H2 production by hydrolysis byproducts of lignocellulosic substrates

Lignocellulosic materials are potential renewable substrates for fermentative H2 production; however, most of the methods available to hydrolyze these materials produce fermentation inhibitors. This study assessed the effect of three different groups of inhibitors on fermentative H2 production by a mixed culture: (1) acetic acid; (2) furan derivatives, such as furfural and 5-hydroxymethylfurfural (HMF); and (3) phenolic monomers, such as vanillin, syringaldehyde, and 4-hydroxybenzoic acid (HBA). Conduction of batch assays in the presence of glucose and different concentrations of inhibitors helped to assess how the inhibitors affected the kinetic parameters of the modified Gompertz model (Rm, Hmax, and λ). The concentrations of inhibitors that reduced 50% of the maximum H2 production rate (IC50) were estimated. In terms of IC50, HBA provided the largest inhibition, 0.38 g L−1, which is a novel result in the literature. HBA was followed by HMF and furfural, 0.48 and 0.62 g L−1, respectively. Vanillin, syringaldehyde, and acetic acid at 0.71; 1.05; and 5.14 g L−1 provided the same inhibition level, respectively. Knowledge about the degree of inhibition of these compounds shall contribute to sustainable H2 production from lignocellulosic substrates.