Effects of system variables on surfactant enhanced electrokinetic removal of polycyclic aromatic hydrocarbons from clayey soils

Numerous polycyclic aromatic hydrocarbon (PAH)-contaminated sites threaten public health and the environment because PAHs are commonly toxins, mutagens, and/or carcinogens. PAHs are hydrophobic and resistant to degradation; therefore, conventional remediation methods are often costly or inefficient, especially when the PAHs are present in low permeability clayey soils. Electrokinetically enhanced in-situ oil flushing is an innovative technology that has the potential to greatly increase soil-solution-contaminant interaction and remedial efficiency, even under low permeability soil conditions. Although this technique is promising, many system variables may affect remedial efficiency, such as the surfactant concentration, pH control and voltage gradient. The objective of this investigation was to evaluate the effects of these system variables. Bench-scale electrokinetic experiments were conducted using various operating conditions, which included deionized water or a 3% or a 5% surfactant concentration flushing solution. Additional tests were also conducted using the 5% surfactant concentration along with a higher pH solution or a larger voltage gradient. The experiments employing the surfactant flushing solution had a lower electroosmotic flow but exhibited greater contaminant desorption, solubilization and migration. The benefits of using a higher pH solution or a larger voltage gradient were difficult to discern because changing these process variables did not significantly improve remedial efficiency. Overall, the results indicated that the surfactant flushing solution was advantageous for treating the soil near the anode region, but contaminant migration was limited by changes in the soil and/or solution chemistry that occurred with time and/or distance from the anode.