Energetic Valorisation of Olive Biomass: Olive-Tree Pruning, Olive Stones and Pomaces

Abstract

Olive oil industry is one of the most important industries in the world. Currently, the land devoted to olive-tree cultivation around the world is ca. 11 × 106 ha, which produces more than 20 × 106 t olives per year. Most of these olives are destined to the production of olive oils. The main by-products of the olive oil industry are olive-pruning debris, olive stones and different pomaces. In cultures with traditional and intensive typologies, one single ha of olive grove annually generates more than 5 t of these by-products. The disposal of these by-products in the field can led to environmental problems. Notwithstanding, these by-products (biomasses) have a huge potential as source of energy. The objective of this paper is to comprehensively review the latest advances focused on energy production from olive-pruning debris, olive stones and pomaces, including processes such as combustion, gasification and pyrolysis, and the production of biofuels such as bioethanol and biodiesel. Future research efforts required for biofuel production are also discussed. The future of the olive oil industry must move towards a greater interrelation between olive oil production, conservation of the environment and energy generation.

Biodiesel and Other Value-Added Products from Bio-Oil Obtained from Agrifood Waste

“…The major chemical components of lignocellulose biomass are cellulose, hemicelluloses and lignin. All of them have shown great potential as raw materials for energy generation [14]. For instance, cellulose can be described as a long-chain homopolymer consisting of D-glucose units with cellobiose as a repeating unit.…”

“…Hemicelluloses are also essential for the production of biofuels because they can represent up to 35% of the weight of biomass on a dry basis [14]. To be specific, the production of bioethanol from hemicellulose-rich biomasses, such as olive stones and olive tree-pruning residues, requires the use of non-conventional yeasts capable of fermenting not only D-glucose, but also pentoses (mainly D-xylose) [14,15,18]. Lignin has received less attention than the other lignocellulose constituents in biofuels production due to its composition, which is mainly based on aromatic compounds.…”

“…This includes a wide range of techniques, including pyrolysis, liquefaction, gasification and combustion. Among all the thermochemical conversion techniques, the differences among them are based on their oxidation range and temperature [14,20].…”

Environmental Assessment of Olive Mill Solid Waste Valorization via Anaerobic Digestion Versus Olive Pomace Oil Extraction

“…1 Net electricity production after subtracting the total electricity consumed from the electricity produced. 2 Net heat production after subtracting the total heat consumed from the heat produced. 3 Natural gas employed as fuel for drying.…”

“…In general, the olive mill solid waste obtained from the two-outlet decanters is transported to the pomace extraction plants to extract the crude pomace oil from them, mainly by extraction with organic solvents (technical hexane) [2]. Before extraction, a drying phase is necessary to reduce the moisture and volatile matter of the olive mill solid waste (between 65 and 75%) to less than 8%.…”