Electrokinetic remediation of soil polluted with insoluble organics using biological permeable reactive barriers: Effect of periodic polarity reversal and voltage gradient

Abstract

This study investigated the remediation of clay soil polluted with low-solubility organics (diesel hydrocarbons) using a combined electrochemical-biological technology. Electrokinetic soil flushing was used, coupled with a biological permeable reactive barrier, which was placed into soil away from electrodes to prevent the negative effects of the acidic and basic fronts on the viability of microorganisms. Three two-week long batch experiments were performed in a lab-scale installation specifically designed to evaluate the remediation of polluted soil. The primary variable under study was the electric field applied to the soil (0.5, 1.0 and 1.5Vcm−1), and the experimental procedure included daily polarity reversal of the electrodes and the addition of anionic surfactant in the electrode wells. The polarity reversal was observed to be a key strategy, which allowed adequate experimental conditions to be maintained in the soil (especially temperature and pH) for the success of the organic biodegradation process. The surfactant was evenly distributed across the soil, which helped the pollutant be transported. The biological activity was not limited to the barrier area but extended to the entire soil portion due to the microbial transport and growth far from the central barrier position. The voltage gradient did not have a strong influence on the measured experimental conditions (soil temperature, pH and moisture) but affected the electroosmotic flow. A higher diesel removal efficiency (36%) was observed when using the higher voltage gradient (1.5Vcm−1) after two weeks, which demonstrates a promising performance of the studied technology for a future real in-situ application.