Biorefining for olive wastes management and efficient bioenergy production

Highlights: • A novel biorefinery was explored for biofuel production from olive wastes. • Per hectare of trees, 296 L ethanol, 137 m³ CH₄, and 347 kg lignin were produced. • Multi-products plant recovered 2.5 times higher energy than a single-product one. • Acid-catalyzed organosolv doubled yields for hydrolysis and ethanol production. • The biorefinery is promising for olive waste management and energy recovery. The potential of olive wastes for development of a multi-product biorefinery was investigated. Different parts of olive wastes, i.e., stone, pomace, leaves, and wood, were subjected to liquid hot water, organosolv, and acid-catalyzed organosolv (ACO) pretreatments prior to bioconversion through three different scenarios. The first scenario, i.e., anaerobic digestion of substrates for biogas production, yielded 219.3 m³ biomethane per hectare of olive trees, equated to 247.4 L gasoline. The highest methane production of 103.3 m³ was attributed to liquid hot water pretreated wood and ACO increased methane yield for leaf and stone samples by 200 and 33%, respectively. The second scenario, i.e., fermentation of wastes for bioethanol production, resulted in 295.9 L bioethanol per hectare of olive trees, equivalent to 196.1 L gasoline. Organosolv pretreated wood with 82.9% production yield and 152.5 L bioethanol constitutes this plan's dominant part. The ACO pretreatment improved fermentation yield for pomace and stone samples by 49% and 53%, respectively. The third scenario, included the utilization of olive wastes in bioethanol production, anaerobic digestion of fermentation residues, and lignin separation, resulted in 295.9 L bioethanol, 137.2 m³ biomethane, and 347.1 kg lignin, equated with 521.6 L gasoline. Furthermore, the remaining oil content in pomace and stone samples was 17% and 20%, respectively, which could be used for biodiesel production. Overall, olive wastes processing through an integrated biorefinery plant with multiple products significantly improved the energy recovery of the whole plant.