Cyclodextrin-enhanced electrokinetic removal of phenanthrene from a model clay soil

Removal of hydrophobic organic contaminants (HOCs) from saturated low-perme ability subsurface environments using a solubility-enhanced electrokinetic remediation process is demonstrated for a model system. Phenanthrene, hydro xypropyl-beta-cyclodextrin (HPCD), and kaolinite were selected as a represe ntative HOC, HOC solubility-enhancing agent, and model clay soil, respectiv ely. Electrokinetic (EK) column experiments were conducted under various op erating conditions, and the results were interpreted in terms of the EK pro perties and expected phenanthrene solubilization of the test systems. No si gnificant effects of HPCD on the EK properties of kaolinite were observed. Initial pore solution pH values dictated the initial electroosmotic flow (E OF) and charge flow rates through the test samples. However, with increasin g EK operating times, low pH values (i.e., near or below the point of zero charge of kaolinite) dominated over most of the column length in unbuffered systems, thereby decreasing the EOF and charge flow rates with time. To mi nimize these adverse effects, pH control of the anode reservoir with a Nar CO3 buffer was used to keep EOF and charge flow rates high. EK experiments using HPCD solutions showed greater phenanthrene removal from the kaolinite samples, and the removal efficiency depended on the HPCD concentration use d. Longer EK operating times without pH control were generally not benefici al for removing phenanthrene because of the low EOF rates obtained after 3 days. The best overall phenanthrene removal was obtained by flushing the an ode reservoir with a high HPCD concentration prepared in the Na2CO3 buffer solution. The results obtained from this preliminary study show that an EK process combined with HPCD flushing and pH buffering may be a good remediat ion alternative for removing HOCs from low-permeability subsurface environm ents.