Overview of Membrane Processes for the Recovery of Polyphenols from Olive Mill Wastewater

Abstract

Problem statement: Olive Mill Wastewater (OMW) is an ambivalent by-product of the olive oil production, which appears in huge amounts every year after the olive-harvest in the production countries, mainly in the Mediterranean region. OMW is characterized by a high organic load and i.a. contains considerable amounts of phytotoxical polyphenols, which cause important environmental problems. Approach: Due to their antioxidant properties the use of these polyphenols is also popular in several industry branches, which results in high sale values for this group of chemicals. The removal of polyphenols from biological wastewaters like OMW does not only reduce the pollutant load but also shows great potential for a beneficial recovery of these antioxidants. This is the reason why a growing number of studies deal with a combined wastewater treatment, which, besides water purification, also regards the ability of recovering polyphenols. This article is an overview of reports concerning polyphenol recovery from OMW via membrane technologies. Results: Patents and studies, which appeared in literature, are reviewed in order to identify the potential of membranes as well as making comparisons possible. Some pretreatments, feasible for membrane processes, are covered. Depending on the initial wastewater and its polyphenol content the concentration in the obtained solution ranges from 0.5-19.3 g L^-1 polyphenols. An example mentioned in WO2005/123603 even obtains a concentration of 30 g L^-1. Polyphenols such as hydroxytyrosol, protocatechuic acid, tyrosol, caffeic acid and oleuropein were found in this concentrate and make it suitable for the use in industry. Conclusion: The membrane processes in sequential design in particular show good results and offer an alternative to other OMW treatments especially in terms of polyphenol recovery.