Researchers have known since the early 1990s that application of a low-voltage electrical current can be used to manipulate and accelerate migration of ionically charged reagents to treat contaminants in low-permeability geologic matrices such as clays and silts. In this process, electrokinetics (EK) is used to induce the movement of water, ions, and charged particles by electroosmosis, electromigration, and electrophoresis, respectively, along with soil heating. EK-based remediation offers special promise for remediation of low-permeability silts and clays, as it has been demonstrated to increase groundwater flow rates (and ionic amendment delivery rates) that are 100 to 1000X greater than can be achieved by pumping. For EK, however, the road to technology scale-up and maturity has been a long one. Initial success with EK in bioremediation was reported in the 1990s in bench studies which showed that EK could achieve acetate propagation rates in clay of 2.5 - 3.0 cm/day, stimulating biological activity within the clay matrix. At the same time, significant EK research focused on use of electrical currents to facilitate extraction of metals from soil and groundwater. Several EK pilot tests for metals remediation were performed in the late 1990s and early 2000, but when the results of these tests showed that EK failed to achieve significant metals removal, general interest in EK diminished significantly for the next several years. Keen to find a solution to the problem of chlorinated solvent contamination in clay till, in 2009 the Danish government initiated research on use of EK to deliver organic substrates and bacteria to stimulate reductive dechlorination in chlorinated solvent source areas in clay till (K &lt; 10-9 cm/s). Column tests demonstrated that EK applied in clay from a chlorinated solvent site could achieve lactate transport rates of 3 - 5 cm/day, and promote migration of dechlorinating Dehalococcoides bacteria, achieving complete dechlorination of tetrachloroethene (PCE) to ethene within the clay column. Based on the success of this bench test, field demonstrations of EK for bioremediation of chlorinated solvent source areas have been implemented at test sites in Denmark and Naval Air Station Jacksonville. Field results have demonstrated EK-stimulated high rates of PCE dechlorination to ethene, and growth and migration of Dehalococcoides in clay till. This presentation will describe key findings from the EK field demonstrations.

From infancy to full-scale demonstration: The twenty year development of electrokinetically-enhanced bioremediation for successful treatment of chlorinated solvents in clays and silts

253rd National Meeting (2017)

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