Effects of extraction processes on the physicochemical characteristics and phenolic compound content of olive mill wastewater: a comparative study

The olive oil industry generates two types of olive liquid waste, i.e., olive mill wastewater (OMWW) and olive washing wastewater (OWW), which are considered a major environmental issue, particularly in Mediterranean areas. This study was designed to assess the influence of trituration systems on OMWW physicochemical characteristics, and of the olive pressing seasons on OMWW and OWW. The results showed that olive trituration systems had a significant impact on OMWW quality, with the traditional system producing the most polluting effluent in terms of chemical oxygen demand, total suspended solid, total solids, ash and metal levels. The phenolic compound study revealed high tyrosol concentrations in all OMWW (384 ± 71 mg/L, 370 ± 70 mg/L, and 286 ± 54 mg/L for traditional, semi-traditional and modern three-phase systems, respectively), while no gallic acid was noted within our detection limit (< 0.4 mg/L). The OWW results revealed that its pollution load was lower than that of OMWW, yet it still exceeded the limits authorized by wastewater discharge legislation for total suspended solid, total solid, oil and grease, and chemical oxygen demand. Finally, our findings showed that the olive pressing season factor did not induce significant variations in most of the OMWW and OWW physicochemical components. Regardless the olive mill wastewater origin, this study revealed the need for pretreatment steps before application of a wastewater purification system to avoid hindering the system performance.