Soil contamination with hazardous substances can be in solid or liquid forms such as petrochemicals or chlorinated solvents hydrocarbons. Contaminants in soil can be physically or chemically adsorbed to soil grains or only trapped in pore space. Soil contamination usually occurs through spillage or burial directly at the contaminated area or migration from a spillage or burial source occurred elsewhere. Some of most occurring sources of soil pollution are petrochemical and chemical contamination. This study investigates the use of electromagnetic (EM) waves with various radiation patterns to induce a controlled transportation of a nonhazardous dye (used as contamination simulant). The medium in this study is aqueous (i.e., water), which helps to monitor the contaminant simulant transport under EM stimulated conditions. EM waves can be launched into the medium at proper frequencies to minimize the heat generation and temperature increase, yet induce a transport according to the EM radiation pattern. Then, the contaminant-simulant transport under EM-stimulated and unstimulated conditions were studied, and the results suggest that dielectrophoresis can be the underlying mechanism of observed EM-induced flow of the contaminant Simulant in the aqueous medium. This is consistent with numerical results as well
Air sparging is a popular soil remediation technique that enables the removal of contaminants through diffusing air into soil. The removal process is, however, slow. The goal of this work is to study the effect of electromagnetic (EM) waves -with minimal heat generation-on transport mechanisms such as diffusion, in order to improve airflow or contaminant transport in order to expedite the cleanup process using air sparging or similar technologies. This effect is studied through an experimental setup that examines the diffusion of a nonreactive dye in water under EM waves at a range of frequencies (50-200 MHz). The electric field was simulated using COMSOL Multiphysics for better three-dimensional (3D) visualization and analysis and then validated using the experimental measurements. A dielectrophoretic study was then performed using the simulated electric field. Various dye flows under EM stimulation at different frequencies were compared. At 65 MHz and 76 MHz, the dye flow was in the direction of the dielectrophoretic forces, which are believed to be the governing mechanism for the EM-stimulated dye transport.
Hydraulic conductivity is a measure of the rate at which water flows through porous media. Because of the dipole properties of water molecules, electric field can affect hydraulic conductivity. In this study, the effect of radio-frequency (RF) waves on hydraulic conductivity is investigated. This is important both for the geophysical measurement of hydraulic conductivity as well as remediation using electromagnetic waves. Bentonite clay and sandy samples are tested in rigidwall, cylindrical permeameters and stimulated using a CPVC-cased monopole antenna vertically centered in the permeameters. The permeameters are encased within RF cavities constructed of aluminum mesh in order to prevent interference from the outside and to confine the RF wave to the medium. Falling-head and constant-head tests are performed to measure the hydraulic conductivity of the clayey and sandy soil samples, respectively. The results show a correlation between the change in the hydraulic conductivity and various characteristics of the RF stimulation. The change is, however, different for sandy and clayey soils.
Air sparging is a technique that uses the injection of a gas (e.g., air, oxygen) into the subsurface to remediate saturated soils and groundwater contaminated with volatile organic compounds (VOCs). During air sparging, air or oxygen is injected into the subsurface below the lowest known depth of chemical contamination. The injected air will rise through the contaminated zones by buoyancy. Contaminant removal efficiency and air sparging performance are highly dependent on the pattern and type of airflow. Airflow, however, suffers from air channel formation (i.e., preferential paths for airflow), limiting remediation to smaller contaminated zones. This paper presents the results of experimental work investigating the possibility of controlling and improving airflow patterns through a saturated glass-bead medium using electromagnetic (EM) waves to enhance air sparging. The test setup consists of a resonant cavity made of an acrylic tank covered with transparent, electrically conductive films. Experimental measurement of the electric field component of EM waves is performed at different frequencies. Airflow pattern is also studied at different air-injection pressure levels with/without EM stimulation. The zone of influence (ZOI) during air sparging is monitored using digital imaging. A quantitative approach is then taken to correlate the characteristics of EM waves and airflow patterns.
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