Olive Mill Wastewater as a Source of Bio-Derived Active Ingredients: Process Development and Scale-Up for Agricultural and Industrial Applications

One of the main characteristics of the “Mediterranean diet” is the regular consumption of olive oil, which is renowned for its health benefits, primarily due to its high content of unsaturated fatty acids. However, in recent years, its minor components have also been the subject of extensive research. Polyphenols are particularly noteworthy due to their remarkable antioxidant, anti-inflammatory, antiatherogenic and antiproliferative biological activities. Nevertheless, due to their high hydrophilic structure, only a small proportion of polyphenols found in olive fruits end up in olive oil; the vast majority are present in by-products of oil production, particularly liquid waste. Therefore, the recovery of polyphenols from olive mill wastewaters (OMW) and their valorization could be a promising starting point for developing bio-pesticides or fertilisers and other high-value products. In this context, the present PhD thesis investigates an integrated and scalable strategy for the valorization of olive mill wastewater as a source of bio-derived active ingredients. The proposed approach combines an acidification pre-treatment with sulfuric acid to stabilize phenolic compounds and promote solid–liquid separation, thereby enhancing the removal of suspended solids and generating a clarified stream suitable for downstream processing. The supernatant was subsequently treated through an integrated cascade of membrane filtration processes (microfiltration, nanofiltration, diafiltration and reverse osmosis), achieving effective concentration and fractionation of soluble phenolic compounds while reducing organic load. Downstream purification was performed through adsorption on strong anionic resins and electrodialysis, desalting and refining of phenolic-rich fractions while preserving their antioxidant activity. Finally, to overcome the intrinsic hydrophilicity of OMW-derived phenolics and facilitate their incorporation into lipid-based formulations, an enzymatic lipophilization step was developed using immobilized lipases. The most promising resulting products obtained from the different process streams were successfully formulated for potential applications both in agricultural and industrial fields. In particular, the sludge was tested as a feed supplement for black soldier fly (Hermetia illucens) larvae and together with the liquid fractions, after determining their cytotoxicity and phytotoxicity, were formulated for potential applications in fertilizers and biopesticides formulations. Moreover, preliminary investigations explored their incorporation into cosmetic products, such as antioxidant-enriched serums and gels. Preliminary techno-economic assessments of the main technologies investigated were presented as a basis for the future development of full life cycle assessment (LCA) and life cycle costing (LCC) analysis. Finally, based on the results obtained during this study, two main pathways were suggested for transferring the proposed technologies to real-scale applications.