Recovery of Polyphenols from Olive Mill Wastewaters by Membrane Operations

Olives contain an appreciable amount of bioactive compounds such as polyphenols with remarkable health benefits. They are potent antioxidants and exhibit various other physiological activities including antiinflammatory, antimicrobial, antiallergic, anticarcinogenic, and antihypertensive activities (Obied et al. 2005). The biophenolic fraction of olive oil comprises only 1-2 % of the total phenolic content of the fruits; the remaining 53%and 45%are lost in olive mill wastewaters (OMWs) and the olive cake, respectively. Typical biophenols occurring in OMWs are benzoic acid derivatives (4-hydroxybenzoic, protocatechuic, vanillic acids), hydroxycinnamic acid derivatives (ferulic, caffeic acids), tyrosol, homovanillyl alcohol, hydroxytyrosol, and oleuropein. These compounds represent a precious resource of potentially useful chemical substances (after their direct recovery or chemical transformation) for cosmetic and pharmaceutical industries and in food processing and food product conservation. Several techniques have been proposed individually or in integrated forms to recover phenolic compounds from OMWs including solvent extraction, supercritical fluid extraction, and chromatographic separation. Membrane operations such as microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO), mostly in sequential form, represent useful Technologies for the recovery, purification, and concentration of polyphenols with regard to their molecular weight cutoff values. They offer significant advantages over conventional methodologies in terms of low energy consumption, no additive requirements, and no phase change. Integrated membrane processes based on the use of these operations permit to obtain purified water which can be discharged in aquatic systems according to national regulations or to be used for irrigation. NF is typically employed for the separation of most part of phenolic compounds (Paraskeva et al. 2007).