Time domain reflectometry (TDR) for dielectric characterization of olive mill wastewater (OMW) contaminated soils

Abstract. Olive mill wastewater (OMW) is a compound originating from oil mills during oil extraction processes. In the Mediterranean area, more than 30 million m³ of OMW are produced each year, which represents 95–97 % of world production. Such volumes of untreated OMW are usually directly disposed of into drainage systems, water bodies (such as streams, lagoons and ponds), or else are sprinkled on soils, causing potentially severe environmental problems to soils and groundwater. There is thus a serious waste management problem related to the olive oil industry, such practices no longer being acceptable. In the case of on-land OMW disposal, characterization and identification of this contaminant in soils is a fundamental task especially with a view to maintaining the integrity and quality of agroecosystems. In recent years, soils have been extensively studied to detect contaminants by using various geophysical methods. Among such techniques, time domain reflectometry (TDR) has shown, in different contexts, evident sensitivity and resolution capability for characterizing contaminated soil sites. In order to further exploit the potential of the TDR technique, in the present study we conducted a series of laboratory-controlled tests to explore how OMW influences the dielectric response of contaminated soils. The research led to the development of an empirical dielectric model to estimate the presence of OMW in variably saturated-contaminated soils with different textures and pedological features.