Enhancing phenolic compound recovery from olive oil mill wastewater through optimized cryoconcentration

This work aims to develop a process for treating olive mill wastewater (OMW) using cryoconcentration. The experiments are carried out in two stages: the freezing stage, producing an ice at temperatures between −16 °C and −24 °C, and the sweating stage, conducted at room temperature. This second step consists in purifying in depth the ice by melting the impure zones of concentrated solutions pockets. Three to five liquid fractions with decreasing concentrations of solute were then collected. The physicochemical analysis indicates that as the initial concentration of the solution increases, the concentration efficiency in the first fraction decreases, and the final ice block is less pure. The parametric study, conducted using the Response Surface methodology (RSM), highlighted the effects of initial concentration, freezing temperature and the number of liquid fraction applied during the partial melting of the ice on the concentration of total phenols in the first liquid fraction obtained. The initial concentration and the fractional partial melting step have a very significant impact. However, within the studied range of cooling temperatures, −16 °C results in a slight increase in the recovery efficiency of phenolic compounds compared to −24 °C. Overall, the results demonstrate the feasibility of the process, which enables the recovery of cryoconcentrated solutions rich in total phenols and the production of good-quality water.