Recovery of biophenols from olive mill wastewaters by integrated membrane operations

The olive oil manufacturing process yields large quantities of aqueous wastes, collectively known as 'olive mill wastewaters' (OMWs) that are considered one of the most polluting effluents produced by agro-food industry due to their high concentration of organic matter and nutrients. However, OMWs represent a rich source of several biopolyphenols widely recognized as valuable molecules in several fields, particularly pharmaceutical and nutraceutical. Membrane operations represent promising technologies for the recovery of biophenols from OMWs due their advantages over conventional technologies (solvent extraction, centrifugation, chromatography, etc.) in terms of low energy consumption, no additive requirements and no phase change. In this work, a combination of conventional and innovative membrane techniques including microfiltration (MF), nanofiltration (NF), reverse osmosis (RO) and direct contact membrane distillation (DCMD) for the recovery, purification and concentration of biophenols from OMWs has been investigated. In particular, OMWs were at first pre-treated by MF in order to remove suspended solids and then concentrated directly by MD, or through a combination of NF and RO. The performance of the investigated membranes was evaluated in terms of productivity (permeate fluxes) and efficiency in the concentration of target compounds as well as in the preservation of their biological activity. The experimental results showed that the investigated integrated processes offer interesting perspectives for the treatment of OMWs through the recovery of biophenols for a potential use in pharmaceutical, nutraceutical, and cosmeceutical industries and purified water with good characteristics for irrigation or for recycling. Overall, they turn up as clean and low-cost methods to valorize OMWs through the recovery of natural antioxidant compounds and the reduction of the polluting load within the logic of both process intensification and zero discharge strategies.