Removal of hydrophobic organic contaminants (HOCs) using electrokinetic method was studied in a model system. Kaolinite and phenanthrene were selected as the model clay soil and representative HOC. Three different types of surfactants, APG (alkyl polyglucoside), Brij30 (polyoxyethylene 4 lauryl ether), and SDS (sodium dodecyl sulfate), were used to enhance the solubility of HOCs.
Electrokinetic (EK) column experiments were performed using aqueous, surfactant, and acetate buffer solutions under a constant current condition. Voltage and flow through the soil system were interpreted with time. Electrolytes pH at the anode and cathode compartments was observed for operation time. Removal efficiencies of phenanthrene were examined after the end of EK operation during 2, 4, and 6 weeks.
As time passed by, low pH values due to acid fronts from the anode part dominated over the model system. Then the electroosmotic flow (EOF) and electrical potential gradually decreased. When an acetate buffer solution was applied to EK system, the EOF kept constant slopes and the electrical potential had constant values. So after a certain period of time, the EOF of buffer solution exceeded that of aqueous solution.
Removal efficiency of phenanthrene in EK process using surfactant solution depended upon characteristics of surfactant under electric field; solubility, desorption ability, and mobility. Brij30 was known as a good surfactant in the removal of HOCs. In the present work on EK experiment, however, the EOF of Brij30 in aqueous solution turned out to be lower than that of other two surfactants. Removal efficiency of phenanthrene in an experiment with Brij30 was also lower than that with other surfactants. In order to increase the EOF, an acetate buffer could be added to the washing solution. Brij30 in buffer solution showed a high removal efficiency of phenanthrene. APG was known to be an environmentally compatible and non-toxic surfactant. When APG was applied to EK experiment, it showed a high EOF and removal efficiency.
The results obtained from this study show that EK process combined with surfactant washing and pH buffering is a promising technology for HOCs removal in low-permeability.