Remediation of Phenanthrene-Contaminated Soil by Electrokinetics Coupled with Iron/Carbon Permeable Reactive Barrier

Conventional electrokinetics (EK) has been applied to treat phenanthrene (PHE)-contaminated soil. However, it is challenging for the conventional EK to achieve the desired outcome for the migration and degradation of PHE. Iron/activated carbon (Fe/C) particles were often used in the wastewater treatment. In the micro-electrolysis process, significant degradation of organic compounds was achieved by Fe/C galvanic cells; thus, Fe/C particles were also potential materials for permeable reaction barriers (PRBs). In this study, the surfactant-enhanced EK coupled with a Fe/C-PRB was used to treat PHE-contaminated soil. A nonionic surfactant, Tween 80, was selected as the solubility-enhancing agent. In addition, the Fe/C mixture was used as the PRB filling material. Seven sets of tests were conducted to investigate the performance of EK-PRB to remove PHE from contaminated soil. In addition, the impact of potential gradient and surfactants on the soil remediation was investigated. Furthermore, the methods including scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy were used to characterize iron in PRB and analyze the effect of EK on the micro-electrolysis in PRB. Results showed that PHE migrated toward the cathode under the driving force of electro-osmotic flow, and reacted with Fe/C-PRB. After 5 days of repair, the removal efficiency of PHE in the test group with the potential gradient of 1 V/cm and the Fe/C mass ratio of 4:1 was 3.5 times as high as that in the control group in which only EK was applied. Removal efficiency of PHE in the test group and control group were 14.4% and 4.11%, respectively. Addition of Tween 80 also improved desorption and mobility of PHE in the soil. It was noteworthy that when the potential gradient was increased from 1 to 2 V/cm, the removal efficiency of PHE was increased by 42.3% (26.9% vs. 18.9%).