Monitoring of soil contamination from olive mill wastewater (OMW) using physico-chemical, geotechnical analysis and electrical resistivity tomography (ERT) investigation

Mediterranean countries are known worldwide by their significant contribution in the olive oil production. This generates large quantities of olive mill wastewater (OMW) which degrade land and aquatic environments near to the OMW storage sites. It contains the organic substances with high phenolic compounds concentrations as well as inorganic particles. In Tunisia, uncontrolled OMW disposal sites cause enormous problems that harm the environment in general and human health. Due to its production of olive oil in Tunisia, its OMW production and in particular its underground resources, the Sidi Bouzid region was chosen to carry out this multidisciplinary research. The aim of this study focuses on environmental characterization and the evaluation of these waste zones which are faced with significant environmental pollution. Using geophysical mapping (electrical resistivity tomography—ERT method), the OMW subsurface infiltration can be monitored. The spatial distribution of these wastes is defined and localized through the resistivity signature (ERT method), who’s lower resistivity values correspond to the OMW zones infiltration. Several ERT lines were located inside and outside the OMW pond of Ben Aoun, Sidi Bouzid region, Tunisia. Multiple ERT surface lines are measured to build the subsurface resistivity models. Published results of lithologic and IP geophysic are complementary with our ERT results which the flow of the wastes within the porous layers was manifested with conductive target surrounded by resistive levels. The movement of these contaminants was released based on numerous geochemical (pH, electrical conductivity—EC, organic matter—OM and the water content—W) and geotechnical analyzes (X-ray diffraction—XRD and Atterberg limits) to characterize any potential infiltration in the basement or the neighboring terrain. The results show that ERT can be provided us an efficient and a powerful method to control and monitor the movement of contaminants in OMW disposal sites.