Valuable phenolic compounds recovery from olive mill wastewater streams by means of cooling crystallization techniques

Abstract

Olive mill wastewater (OMW), produced during the olive oil extraction process, is a hardly degradable by-product characterized by significant high concentrations of organic compounds and complex mixtures of phenolic compounds. The treatment of OMW is considered as a very difficult task because phenolic content is highly problematic for aerobic or anaerobic treatment and at present there is no unique and affordable process for OMW treatment. On the other hand, phenolic compounds in OMW are considered as high added value constituents and their isolation, purification and recovery is related with the higher efficiency in the management and valorization of the olive mills effluents. Physicochemical treatment methods, based on membrane filtration suggested recently by several researchers, proved successful in the fractionation and isolation of phenolic compounds in the concentrated streams of either nanofiltration or reverse osmosis (RO) units. Unfortunately, rich in phenolics streams have a high content of monosaccharides or disaccharides since the molecular size of the sugars is comparable with the respective of individual phenolic compounds. The present work is associated with the development of a more sophisticated treatment process of wastewater through the application of membrane filtration, cooling crystallization and melt crystallization to enhance the isolation, recovery and purification of phenolic compounds when present at high concentrations. The experimental study was done in synthetic media simulating the RO concentrates of OMW. Glucose and most part of OMW polyphenols (including tyrosol, ferulic acid [FA] and trans-cinnamic acid [TCA]) served as model compounds for sugars and phenolic compounds, respectively. It was found that in the case of mixtures, high recovery yields of FA, tyrosol and TCA were achieved.