Olive mill wastewater treatment and valorization by extraction/concentration of hydroxytyrosol and other natural phenols

Abstract

Olive mill wastewater (OMW) is a by-product generated from olive oil extraction systems. It contains high concentrations of organic compounds mainly phenols which cause environmental problems for the ecosystem, such as soil contamination and water pollution. Therefore, treatment of OMW is very much needed. Some of the naturally present chemicals in OMW have a positive economic value. In this investigation, liquid/liquid extraction using ethyl acetate (EA) as a solvent to recover such valuable compounds was investigated. Several parameters were studied namely, time of extraction, pH, EA/OMW volumetric ratio, and initial concentration of total phenols. Based on UHPLC analysis, hydroxytyrosol (HT) was the most abundant phenol in EA extracts from OMW. Many other phenols (tyrosol, oleuropein, p-coumaric acid, syringic acid, and 4-hydroxybinzoic acid) were also identified. Percentage recovery of HT reached 62 % after 2 h of extraction, at an EA/OMW ratio of 2/1 (v/v) and a pH of 2. Distribution coefficient of HT in EA was evaluated and was found to be around 0.8. The above process is envisioned to ultimately produce clean water which may be used in irrigation or in olive mills in a sustainable way. In addition, the extract is expected to have a high economic value.