The types of waste generated in the olive-oil sector were identified and quantified, including olive pomace, olive cake, olive stones, leaves, small branches, and wastewater. Focus was given to olive pomace and olive cake. The main wastes in the sector, as well as the olive oil produced, were quantified for the main producing countries. Their yearly evolution was studied. Current practices to manage olive pomace in the EU, with a focus on Spain, was investigated. Industrial visits and communication with an industrial partner served to further collect data and stay up to date with the current status of the sector. Its relevant legislation was studied to make sure the possible ways to valorise olive pomace can be implemented at an industrial scale.
Several Waste Valorisation Options (WVOs) were explored. Next, a specific waste valorisation option was designed. The main objectives were to recover compounds of interest (WVO2) and produce bioenergy (WVO4). The use of chemicals as reagents was eliminated, being able to use only water as well as the olive cake as starting materials. This waste valorisation option was based on sequential hydrothermal treatments at increasing temperatures, followed by pyrolysis of the final solid. This allowed obtaining a low-cost adsorbent material that can be used for the removal of contaminants (WVO3). Several combinations of reaction time, temperature and solid/liquid ratios were trialled for each hydrothermal treatment. A neuro-fuzzy approach was used to identify the ideal process conditions and optimise the overall process. All steps were fully trialled and implemented at laboratory scale.
The environmental impact of the valorisation process designed was quantified by LCA. A range of environmental impact categories at midpoint and endpoint level was considered. Several process configurations were trialled. Environmental hotspots were identified, allowing further optimisation of the environmental performance. This environmental performance was compared against that of the conventional process. Opportunities to improve these results (e.g. purification of the polyphenols extracted, following by commercialisation and consequent market substitution) were identified.
Possibilities for upscaling of the waste valorisation solutions and the biorefinery approach proposed were explored. Broad economic constraints and overall challenges were identified. Potential social benefits were also identified.
