Preliminary Assessment of Electrokinetic Remediation of Soil and Sludge Contaminated with Mixed Waste

ABSTRACT

In order to avoid the effects of complex soil composition or contaminant interaction, previous bench-scale electrokinetic experiments were generally performed using simplified conditions. An ideal soil such as kaolinite was often used, and testing was frequently restricted to an individual contaminant or a small group of contaminants. However, actual waste sites consist of soils that are usually quite different from ka-olinite, and many sites are polluted by a large number of mixed contaminants. Therefore, this preliminary study was undertaken to assess electrokinetic performance on a site-specific field soil and a simulated sludge mixture containing mixed wastes in the form of metals, organic compounds, and radionuclides. Bench-scale experiments showed that the field soil had a high buffering capacity that resulted in high pH conditions throughout the soil, whereas the simulated sludge had a low buffering capacity that resulted in low pH conditions except near the cathode. The high pH conditions in the soil allowed the migration of anionic metallic contaminants, such as hexavalent chromium, but inhibited the migration of cationic metallic contaminants, such as cadmium. The low pH conditions in the sludge allowed simultaneous migration of both anionic and cationic contaminants in opposite directions, respectively, but the synergistic effects of co-contaminants retarded contaminant removal. The removal of organic compounds and radionuclides from both the soil and the sludge were achieved. However, additional research is warranted to systematically investigate the synergistic effects and the fate of different contaminants as well as to develop electrode-conditioning systems that enhance contaminant migration.