Optimization of Microwave-Assisted Organosolv Pretreatment for Enzymatic Hydrolysis of Cherry Tree Pruning and Pistachio Shells: a Step to Bioethanol Production

The overall purpose of this research work was to apply a microwave-assisted digestion process combined with ethanol organosolv as pretreatment for pistachio shells (PS) and cherry tree pruning (CTP) biomasses for cellulose production. This process would reduce the technical and environmental disadvantages of the accumulation of these agricultural wastes. A central composite design based on the Response Surface Methodology was applied to check the effect of reaction time, temperature, and concentration of ethanol acid solution. Adequate models have been obtained for the contents of cellulose and lignin of the treated solids as well as for solubilized cellulose percentage. Best conditions implied 67% ethanol and 30 min at 150 ◦C, involving the production of a cellulose-enriched material (81.1% and 90.1% for treated CTP and PS, respectively). Finally, enzymatic hydrolysis of these materials was carried out, reaching glucose concentrations of 70 and 100 kg/m3 for CTP and PS, resulting in enzymatic hydrolysis yields at 12 h of 97.2% and 76.9%. These high values are one of the main novelties and strengths of this work, as show the ease of the process and can have a beneficial influence on its scale-up, reducing both costs and environmental impact.