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Olive mill wastewater (OMWW) is an extremely polluting dark liquid generated in large quantities during the extraction of olive oil. OMWW is also an interesting source of high-added value natural compounds such as biophenols, especially hydroxytyrosol (HT), a powerful antioxidant with proven nutritional and pharmaceutical properties. The main objective of this work was to explore the use of membrane technology for the treatment of OMWW in order to obtain a retentate stream rich in hydroxytyrosol and a permeate with low chemical oxygen demand (COD). Pretreatment was firstly performed by a combined centrifugation and acidification process. Then, several membrane operations were tested and phenolics rejection, HT content, COD removal and membrane fouling were examined. Best results were obtained using a single ultrafiltration process with a 10 kDa ST polyethersulfone membrane at 8 bar. Improved results were reached using a two-stage integrated system with 100 kDa US100 ultrafiltration and 200 Da NF90 nanofiltration membranes, at 5 and 10 bar, respectively. Volume reduction factor of 1.9 in ultrafiltration and 1.6 in nanofiltration yielded to 234.49 ± 26.08 mg/L of HT in the retentate (9-fold the HT content in the raw OMWW) and 94.15% COD removal.

Olive pomace, a solid residue generated during olive oil production process and a rich source of phenolic compounds, was dried and defatted to obtain a pomace oil rich in monounsaturated fatty acids with 64% oleic acid. The defatted pomace was further treated by ultrasound-assisted extraction (UAE). The optimal phenol extraction conditions of 10 min, 40% amplitude and 4% (w/v) solid:solvent ratio, yielded to 14.70 mg/g total phenols, 2.48 mg/g total flavonoids and 0.924 mmol Trolox/g antioxidant activity. In order to purify valuable biophenols, two polymeric resins (XAD4 and XAD16) and two activated charcoals (NPAC and GAC) were tested as adsorbents using a magnetic stirrer and an incubator shaker. XAD16 (100 g/L) in magnetic stirrer showed the optimal adsorption ratios with 74.36%, 39.25%, 68.79% and 100% for total phenols, hydroxytyrosol, tyrosol and oleuropein, respectively. Desorption using acidified 50% (v/v) ethanol-water at pH = 2.3 proved 57.65% recovery of total phenols, 19.27% of hydroxytyrosol and 45.73% of tyrosol. These results indicate that extraction and selective purification of biophenols from olive pomace can be achieved by the proposed UAE using 50% v/v ethanol-water as solvent, followed by adsorption-desorption stages with the XAD16 polymeric resin., Spanish Agencia Estatal de Investigación [grant number PID2019-104950RB-I00/AEI/10.13039/ 501100011033] and the Junta de Castilla y León (JCyL) and the European Regional Development Fund (ERDF) [grant numbers BU301P18 and BU050P20].

El objetivo general de esta Tesis Doctoral es la valorización de hojas de olivo y moringa mediante la recuperación y purificación de compuestos bioactivos mediante tecnologías limpias emergentes. En primer lugar, se realizó una caracterización completa de las materias primas. Se estudió la extracción de compuestos bioactivos mediante tecnologías basadas en el empleo de disolvente verdes tales como el agua presurizada en estado subcrítico. Así mismo, se realizaron extracciones convencionales y con ultrasonidos. Los extractos óptimos fueron purificados mediante procesos de adsorción empleando diferentes resinas de intercambio iónico obteniendo un extracto con una alta concentración de oleuropeina para las hojas de olivo. Además, los extractos de hoja de olivo se fraccionaron mediante procesos de membranas para separar y purificar los compuestos fenólicos y azúcares. Mediante los procesos propuestos se obtuvieron diferentes extractos liofilizados con una alta concentración de compuestos bioactivos y capacidad antioxidante con múltiples aplicaciones., The general objective of this Doctoral Thesis is the valorization of olive and moringa leaves through the recovery and purification of bioactive compounds through emerging clean technologies. First, a complete characterization of the raw materials was carried out. The extraction of bioactive compounds was studied using technologies based on the use of green solvents such as pressurized water in a subcritical state. Likewise, conventional and ultrasound extractions were performed. The optimal extracts were purified by adsorption processes using different ion exchange resins, obtaining an extract with a high concentration of oleuropein for olive leaves. Furthermore, the olive leaf extracts were fractionated by membrane processes to separate and purify the phenolic compounds and sugars. Through the proposed processes, different lyophilized extracts with a high concentration of bioactive compounds and antioxidant capacity were obtained with multiple applications.