Valorization of olive tree pruning. Application for energy storage and biofuel production

Abstract This work addresses the valorization and integral use of an abundant agro-industrial waste in sustainable production routes. Olive tree pruning residues were used to obtain bioethanol and activated carbon. This was latter applied to supercapacitor electrodes preparation and also as a detoxifying agent. On the bioethanol route, the residue was pretreated with lime, hydrolyzed and subsequently fermented with native yeasts. The maximum ethanol concentration was obtained by Candida sake BCs88 (3.3 g/l). Prior to fermentation, the liquor was detoxified with activated carbon, achieving removal percentages of inhibitor compounds of 89.2 %, 32.6 % and 91.8 % for polyphenols, hydroxymethylfurfural and furfural, respectively. Detoxification stage improved markedly the performance of all yeasts. KOH was used to obtain the activated carbon, reaching a BET surface of 4083 m2/g. It was applied as supercapacitor electrode generating a high specific capacitance of 264.38 F/g at a current density of 0.5 A/g, and delivering elevated values of energy density (17.83 Wh/kg) and power density (65 W/kg).