Enzymatic Hydrolysis of Olive Industry Solid Waste into Glucose, the Precursor of Bioethanol

Olive industry solid waste (OISW) is a by-product generated in the process of olive oil extraction. It is a lignocellulosic material consisting of cellulose, hemicelluloses, lignin and other extractives. In this work, a process for hydrolyzing the OISW into its monomers glucose, the precursor of bioethanol was developed.  The hydrolysis process involves two stages: in the first stage, the OISW was activated by treating it with a material that opened the cellulose structure and made it more accessible for chemical reagents.  Several activating materials were evaluated among them are water, NaOH, Ca(OH)₂ and acetic acid.  In the second stage, the OISW was subjected to an enzymatic treatment which hydrolyzed it into sugar. A combination of the two enzymes cellulase (endo-1,4-β-glucanase) and β-glucosidase was used in the hydrolysis. Best hydrolysis results were obtained at enzymes dose of 15.0 mg of cellulase and 20.0 mg/g of β-glucosidase per one gram of OISW at 45 oC and a pH of 4.8. A yield of 85.02% sugar was obtained from the hydrolysis of 10% NaOH pre-treated OISW under a positive pressure of air.  Whereas, hydrolysis of cellulose extracted from OISW by the Kraft pulping process and bleached using DEHP beaching sequence produced about 95.30% sugar.