Organosolv pretreatment of olive tree biomass for fermentable sugar production

Abstract

Olive tree pruning biomass is one of the main agricultural residues available in Mediterranean countries and is currently lacking commercial applications. For taking advantage of its sugar content, a pretreatment is necessary to enhance enzyme accessibility of the residue‟s cellulose fraction. This work describes for the first time the use of organosolv pretreatment for this purpose. The main process variables such as pretreatment temperature, residence time and solvent composition (aqueous ethanol) are studied. Results show that organosolv pretreatment causes delignification and hydrolysis of hemicelluloses and improves the enzymatic digestibility of olive tree pruning biomass. A higher pretreatment severity and ethanol content of the solvent were found to increase delignification (up to 64% at 66% w/w aqueous ethanol, 210°C, 60 min). On the other hand, xylan hydrolysis was promoted by a lower ethanol content (maximum 92%). The highest enzymatic hydrolysis yield (90% of the structural glucan present in the raw material) has been obtained after pretreatment with 43% w/w aqueous ethanol at 210°C for 15 min. Organosolv was found to be the most effective pretreatment method for enzymatic hydrolysis of olive tree pruning biomass studied thus far.