The biorefinery of lignocellulosic wastes allows decreasing the emission of greenhouse gases by the introduction of eco-friendly alternatives such as biofuels and bioproducts, reducing the cost of waste disposal and overcoming the environmental problems related to the production of first-generation biofuels by dedicated cultures. The enzymatic hydrolysis of waste biomasses is one of the crucial steps of the biorefinery process; it is aimed at obtaining fermentable sugars starting from the complex carbohydrates (cellulose and hemicellulose). Among the biomasses classified as lignocellulosic wastes, Coffee Silverskin (CSS) is one of the most abundant residues from the roasting process of the coffee industry. CSS is the external layer protecting the coffee beans and is composed almost by carbohydrates (˜40% w/w) and lignin (˜30% w/w).
The present contribution is part of a study focused on the characterization of enzymatic hydrolysis kinetics of real wastes biomass. In particular, the initial rate of glucose production has been characterized in a bench scale stirred reactor (0.5 L) using a commercial cellulase cocktail (Cellic® CTec2). The experimental procedure included an enzyme adsorption step on CSS followed by the hydrolysis step. Initial glucose production rate was assessed at 10 and 15 min at different stirring rates, the results shows that the initial rate increased at increasing stirring speed with a more evident variability than that observed for initial hydrolysis rates assessed after 60 min in previous work (Procentese et al., 2020). This result agrees with the literature (Hou et al., 2016) because is likely due to the early changes in morphology and size of biomass granules occurring during the first hour of enzymatic conversion. Further investigation of the effect of biomass morphology and size on the initial rate of glucose production has been carried out by laser scatter analysis of particle size and scanning electron microscopy.