DIELECTROPHORESIS: APPLICATIONS TO POLLUTED SOIL REMEDIATION

DECONTAMINATION OF DENSE NONAQUEOUS PHASE LIQUIDS (DNAPLS) FROM SUBSURFACE SOILS AND GROUNDWATER FORMATIONS PRESENTS A COMPLEX ENVIRONMENTAL PROBLEM THAT HAS PROVEN EXTREMELY DIFFICULT TO REMEDIATE. THERE IS A CRITICAL NEED TO DEVELOP AND IMPLEMENT EFFECTIVE TREATMENT METHODS FOR DNAPL-CONTAMINATED SOILS AND AQUIFERS BECAUSE OF THE THREAT THAT IS POSED TO GROUNDWATER SUPPLIES. CLEANUP OF SOILS AND AQUIFERS IS ESPECIALLY DIFFICULT DUE TO THE FACT THAT THEY MAY BE PRESENT IN THE SUBSURFACE IN VARIOUS PHYSICAL PHASES: AS ORGANIC VAPORS, DISSOLVED IN GROUNDWATER, SORBED ONTO THE AQUIFER MATERIAL, OR AS AN IMMISCIBLE PHASE IN THE SOIL PORES. ELECTROKINETIC PROCESSING OF SOIL IS AN INNOVATIVE TECHNOLOGY WHICH INVOLVES ELECTRICALLY INDUCED TRANSPORT OF CONTAMINANTS (E.G., BY ION MIGRATION OR ELECTROOSMOSIS) BY THE APPLICATION OF AN ELECTRIC FIELD BETWEEN ELECTRODES INSERTED IN THE SOIL. RESEARCH HAS SHOWN THAT THIS TECHNIQUE HAS THE POTENTIAL TO BE EFFECTIVE IN FACILITATING THE REMOVAL OF CERTAIN TYPES OF HAZARDOUS WASTES FROM SOILS, PARTICULARLY HEAVY METALS. A NOVEL APPROACH FOR IN SITU ELECTROKINETIC REMEDIATION OF DNAPL POLLUTED SOILS IS BASED ON THE APPLICATION OF NONHOMOGENEOUS PULSED DC AND/OR HIGH FREQUENCY AC ELECTRIC FIELDS. THE APPROACH IS BASED ON THE FACT THAT IN NONHOMOGENEOUS ELECTRIC FIELDS, A DIELECTROPHORETIC FORCE IS INDUCED CAUSING A MIGRATION OF NON-CHARGED SPECIES OR MOLECULES, IN PARTICULAR, TOWARD REGIONS OF HIGHEST ELECTRIC FIELD STRENGTH. AMONG THE ADVANTAGES OFFERED BY THE APPROACH ARE: (1) REMEDIATION PROCESS IS AN IN SITU PROCESS; (2) REMEDIATION PROCESS TARGETS DIFFERENT PHASES OD DNAPLS DISPERSED IN SOIL, AND PARTICULARLY THE IMMISCIBLE PHASE, WHICH IS MOST DIFFICULT TO REMOVE; (3) DIRECTION OF DNAPL CONTAMINANT MOVEMENT IS STRICTLY CONTROLLED ALONG ELECTRIC FIELD LINES DEFINED BY ELECTRODE PLACEMENT IN THE SOIL; AND (4) STRONG ELECTRIC FIELD ASSURES CONTAINMENT OF DNAPLS IN THE ZONE OF DECONTAMINATION WITH NO RISK OF FURTHER DOWNWARD MOVEMENT. EMPHASIS IS PLACED ON UNDERSTANDING THE PROPOSED ORGANIC CONTAMINANT MIGRATION BY APPLICATION OF NONHOMOGENEOUS ELECTRIC FIELDS, MAXIMIZING RATES OF DNAPL REMOVAL, AND MINIMIZING TREATMENT COSTS.