THF co-solvent pretreatment prevents lignin redeposition from interfering with enzymes yielding prolonged cellulase activity

Background Conventional aqueous dilute sulfuric acid (DSA) pretreatment of lignocellulosic biomass facilitates hemicellulose solubilization and can improve subsequent enzymatic digestibility of cellulose to fermentable glucose. However, much of the lignin after DSA pretreatment either remains intact within the cell wall or readily redeposits back onto the biomass surface. This redeposited lignin has been shown to reduce enzyme activity and contribute to rapid enzyme deactivation, thus, necessitating significantly higher enzyme loadings than deemed economical for biofuel production from biomass. Results In this study, we demonstrate how detrimental lignin redeposition on biomass surface after pretreatment can be prevented by employing Co-solvent Enhanced Lignocellulosic Fractionation (CELF) pretreatment that uses THF–water co-solvents with dilute sulfuric acid to solubilize lignin and overcome limitations of DSA pretreatment. We first find that enzymatic hydrolysis of CELF-pretreated switchgrass can sustain a high enzyme activity over incubation periods as long as 5 weeks with enzyme doses as low as 2 mg protein/g glucan to achieve 90% yield to glucose. A modified Ninhydrin-based protein assay revealed that the free-enzyme concentration in the hydrolysate liquor, related to enzyme activity, remained unchanged over long hydrolysis times. DSA-pretreated switchgrass, by contrast, had a 40% drop in free enzymes in solution during incubation, providing evidence of enzyme deactivation. Furthermore, measurements of enzyme adsorption per gram of lignin suggested that CELF prevented lignin redeposition onto the biomass surface, and the little lignin left in the solids was mostly integral to the original lignin–carbohydrate complex (LCC). Scanning electron micrographs and NMR characterization of lignin supported this observation. Conclusions Enzymatic hydrolysis of solids from CELF pretreatment of switchgrass at low enzyme loadings was sustained for considerably longer times and reached higher conversions than for DSA solids. Analysis of solids following pretreatment and enzymatic hydrolysis showed that prolonged cellulase activity could be attributed to the limited lignin redeposition on the biomass surface making more enzymes available for hydrolysis of more accessible glucan.

Prediction of the fixed-bed reactor behavior for biotransformation with parallel enzyme deactivation using dispersion model: A case study on hydrogen peroxide decomposition by commercial catalase

The problems of process costs and pollution of residual waters in the textile industry require increasing attention due to the new ecological regulations and also those resulting from an economic point of view. Hence, the behavior of non-isothermal fixed-bed reactor applied for hydrogen peroxide decomposition by immobilized Terminox Ultra catalase attached onto the outer surface of glass beads was studied to determine the operational conditions at which hydrogen peroxide decomposition is most effectively. A dispersion model for bioreactor applied in this work, and verified experimentally, took into account the coupled mass and heat balances as well as the rate equation for parallel enzyme deactivation. The effect of feed temperature, feed flow rate, feed hydrogen peroxide concentration, and diffusional resistances were analysed. In the calculations the global effectiveness factor based on the external mass-transfer model developed previously was employed to properly predict the real bioreactor behavior.