Application of Statistical Methods for the Comparative Study of the Degree of Pollution of Wastewater Collected from Three Olive Mills in Tangier-Tetouan-Al Hoceima Region (Northern Morocco)

Olive mill wastewaters represent a severe environmental problem, especially in Mediterranean countries. Indeed, the treatment and recovery processes developed so far remain very limited and their cost is very high. However, treatment by shallow evaporation ponds in the open air remains, until now, the most used technique despite the efforts made. The volume and characteristics of this liquid effluent depend, among other things, on the nature of the extraction process used. In this context, this work aims to evaluate the effect of the mode of trituration and storage in the evaporation ponds on the quality of olive oil mill wastewaters. These effluents were collected from three olive mills located in two different provinces in Northern Morocco during the 2021–2022 olive growing season. The sampling has considered different points according to different steps of the process. The analytical work corresponded to the measurement of in-situ parameters (Temperature (T°), Dissolved Oxygen (DO), Electrical Conductivity (EC) and pH degree (pH)) and other laboratory analysis (Suspension Matter (SM), Dry Matter (DM), Fatty Matter (FM), biochemical (BOD5) and chemical (COD)demands in oxygen). Results showed a high degree of environmental degradation. Indeed, these effluents are characterized, on average, by elevated concentrations of biological and chemical oxygen demands and suspended solids reaching up to 0.43 g/L ± 0.87, 1.69 g/L ±0.71 and 30.78 g/L ±25.1, respectively. This study also showed, except for two-phase olive mill BNANDA, a slightly alkaline nature of the vegetable waters (7.81<pH<8.52), as opposed to what was reported in the literature, and high levels in fat content (4.73 g/L ±3.85). Moreover, the estimated volume of vegetable water released in the study area during the 2019/2020 olive growing season (350×10³ m³) is very high considering its equivalence to domestic water. Normalized Principal Component Analysis (ACPN) and Hierarchical Principal Component Classification (HCPC) indicate that differences in the composition of this wastewater were more pronounced between the extraction processes than by the origins of the vegetable waters (fresh or stored in the natural evaporation pond).