Effect of system variables on surfactant-enhanced electrokinetic remediation of clayey soil contaminated with PAHs

Abstract

Surfactant-enhanced electrokinetic (EK) process was investigated to remove polycyclic aromatic hydrocarbons (PAHs) from low-permeable soils. Phenanthrene and kaolinite were selected as a representative PAH and a model soil, respectively. Four different surfactants, alkyl polyglucosides (APG), Calfax 16L-35, Tergitol 15-S-7 and 15-S-12, were used to enhance the solubility of phenanthrene. The solubilization capacity of phenanthrene was in order of Tergitol 15-S-7 > Tergitol 15-S-12 > Calfax 16L-35 and APG. Tergitol 15-S-7 was greatly influenced by adsorption on soil while Calfax 16L-35 and Tergitol 15-S-12 were not affected. Relatively low electrical potential gradients were maintained in electrokinetic tests with APG and Calfax 16L-36. However, experimental results of Tergitol 15-S-7 and 15-S-12 showed similar trends to the control test, in which electrical potential gradient rapidly reached to the limited value. As surfactant concentration increased, the amount of electroosmotic flow decreased, but the removal efficiency of phenanthrene was enhanced except in the case of Calfax 16L-35. At the end of experiment, most of APG was detected in effluent whereas only little amount of surfactant remained in soil. Phenanthrene removal was improved due to transport of APG micelles containing phenanthrene. On the other hand, most of Calfax 16L-35 remained in soil and little amount existed in effluent because of its ionic characteristic. As a result, Calfax 16L-35 did not enhance the removal efficiency even at the highest concentration of surfactant. In the tests of Tergitol 15-S-7, surfactant adsorption on soil occurred severely, so that only a small portion of surfactant seemed to contribute in the removal of phenanthrene. Therefore, the removal efficiency increased just slightly, especially at low concentration. However, when Tergitol 15-S-12 was applied, the problem of adsorption on soil was not severe and most of them were detected in effluent transported by electr...