Bioethanol from Brewer's Spent Grains: Acid Pretreatment Optimization

Abstract

This study performs a parametric study aiming at the optimization of the acid pretreatment step of brewer'sspent grains (BSG) simultaneously with the enzymatic hydrolysis for conversion into simple sugarsfermentable to bioethanol. For this purpose three acids and five enzymes were tested, by adding each twoacids (HCl with H2SO4 or HCl with HNO3) either in mixture (in one step) or sequentially (in two steps), to 25g of dry BSG, together with varying quantities of the enzymes. Results show that when using Viscozyme Lor the mixture of Cellulase and Hemicellulase by action of two acids in mixture, the total sugars conversionranges between 20-27 wt%, in which the mixture of HCl and H2SO4 promotes a greater release of glucoseplus maltose, while the mixture of HCl and HNO3 promotes the release of higher amount of xylose andarabinose. Results also show that when Glucanex 100g and Ultraflo L are used simultaneously with thesequential addition of HCl and H2SO4, the highest total sugars conversion (54.5 wt%) is obtained using2.30 mL of Ultraflo L and 1.67 g of Glucanex 100g. Furthermore, by increasing the amount of Glucanex100g (from 1.67 to 2.48 g) to the same amount of Ultraflo L (2.30 mL) the total sugars conversiondecreased from 54.5 wt% to 40.5 wt%. Moreover, a greater release of glucose was verified by increasingthe amount of Ultraflo L (from 1.75 mL to 2.30 mL), while by increasing the amount of Glucanex 100g(from 1.67 to 2.48 g) the release of arabinose and maltose was enhanced. Also, when using Glucanex100g and Ultraflo L simultaneously with the acids HCl and HNO3, the best method to obtain highconversions of sugars is by the sequential addition of the acids, instead of in mixture. In this work, itresulted in the best conversion of BSG to simple sugars (72.1 wt%), corresponding to about 720 g ofsugars per kg of dry BSG.