Integrated membrane system for the production of phytotherapics from olive mill wastewaters

In this work an integrated membrane system for the valorization of OMWs through the selective recovery of valuable biophenols was investigated. Pressure driven membrane processes, such as microfiltration (MF) and ultrafiltration (UF), were used as pre-treatment steps to produce a permeate stream containing phenolic compounds, then submitted to a bioconversion step by using a biocatalytic membrane reactor. In this last system, the oleuropein is converted to oleuropein aglycon by β-glucosidase immobilized in a polymeric membrane. A multiphasic biocatalytic membrane reactor (MBMR) is also used to guide the transformation of biophenols to a specific valuable product (the isomer of oleuropein aglycon) and its simultaneous isolation in the organic phase. The pre-treatment of raw OMWs by a selected flat-sheet MF membrane (cellulose acetate with a pore size of 0.2 μm) produced a total removal of suspended solids and a permeate solution which was submitted to an UF treatment with a polysulphone flat-sheet membrane having a molecular weight cut-off of 10 kDa. In the UF permeate oleuropein was the most represented low molecular weight phenolic compound due to the low rejection (1.1) observed. In the following step two different fractions were produced by the MBMR: an organic phase containing the isomer of oleuropein aglycon and an aqueous phase containing water soluble biophenols. The maximum oleuropein conversion reached was about 45.7% and the reaction rate was about 2×10−4 mmol/min cm3. A steady-state flux was reached in all the steps of the integrated membrane system. In particular, in the MBMR this assures a constant residence time and same catalytic performance of the system in presence of pure substrate.