High Solids Loading Pretreatment of Olive Tree Pruning with Dilute Phosphoric Acid for Bioethanol Production by Escherichia coli

This paper deals with a new approach for using olive tree pruning biomass as raw material for ethanol and other chemical production. This process includes a water extraction step, followed by a high solids loading dilute phosphoric acid pretreatment and an ethanologenic Escherichia coli fermentation for the conversion of all of the sugars released. Results show that the operational conditions leading to the maximal hemicelullosic sugar recovery in the liquid fraction (near 70%) are 170 degrees C and 0.5% (w/v) phosphoric acid concentration. The fermentation of the mixed sugars found in the detoxified prehydrolysates by ethanologenic E. coli MS04 led to an ethanol concentration of 23 g/L and an ethanol yield of 0.46 g of ethanol/g of sugars consumed. When the ethanol production from the pretreated solids after enzymatic hydrolysis is also taken into account, 13.2 g of ethanol/100 g of original material was obtained. The production of other interesting compounds is also considered.