Exploitation of olive tree pruning biomass through hydrothermal pretreatments

The conversion of lignocellulosic materials into renewable products is performed through a process including pretreatment, enzymatic hydrolysis and fermentation, being the first one a key step in both technical and economic terms. As two of the most widely used pretreatment methods, liquid hot water (LHW) and steam explosion (SE) were compared in this work using olive tree (Olea europaea L.) pruning biomass (OTPB), an especially relevant lignocellulosic residue, largely available at low cost with no practical applications. Moreover, to achieve the best results in terms of bioproducts (e.g., antioxidants, bioethanol, oligosaccharides and the most complete use of the material) previous steps of aqueous extraction and dilute phosphoric acid treatment were added. Results show that LHW and SE performed similarly, although the former yielded the highest overall sugar recovery, 92%, at lower operation temperature (180 degrees C) versus 80.4% for SE at 220 degrees C. Ethanol production in selected conditions was however slightly better in the case of SE-pretreated samples, resulting in 72% yield compared with 63% in LHW-samples, but at different temperatures (220 degrees C versus 200 degrees C) although both pre treatments resulted in an ethanolic solution of about 4.4% (v/v).