Valorisation of olive mill wastewater by enhancement of natural hydroxytyrosol recovery

Summary Recovery of natural and simple phenolic compounds with high added value was performed successfully from olive mill wastewater. Three types of olive mill wastewater were assayed in bioconversion at 15 and 40 L in mechanically stirred systems for 2 h at 50 °C. Maximum hydroxytyrosol concentrations of about 1.53, 0.83 and 0.46 g L−1 were obtained in the presence of 5 IU Aspergillus niger β-glucosidase per milliliter of OMW in North OMW, MSP and MCC, which were 2.70-, 1.38- and 1.77-fold higher than the controls, respectively. Enzymatic pretreatment was followed by two tangential flow membrane separation steps, microfiltration (MF) and ultrafiltration (UF), and concentration procedures for the ultrafiltration permeate. The latter exhibited a COD level of 48.44 g L−1. The UF permeate concentration increased the hydroxytyrosol concentration to 7.2 g L−1. Hence, this innovative work described an environmently friendly process; pilot-scale has allowed producing a new and natural product which obeyed the dietary requirements; it contains some minerals beneficial to health and does not contain heavy metals or chemicals. Overall, this chemical-free large-scale process proved efficient for recovery of natural hydroxytyrosol.