Electrochemical Remediation Technologies
Electrochemical Remediation Technologies (ECRTs) use a proprietary AC/DC electrical signal to mineralize organic compounds (e.g. volatile organic compounds (VOCs)), and to mobilize and remove metal contaminants. Proprietary AC/DC converters produce a low-voltage, low-amperage electrical field that polarizes the soil or sediment (soil), causing soil particles to charge and discharge electricity. This causes redox reactions that occur at all interfaces within the soil–groundwater–contaminant–electrode system, mineralizing organics and increasing the mobilization of metals. Metals migrate to the electrodes where they are deposited and removed with the electrodes. There are several distinctions between ECRTs and traditional electrokinetics. First, relatively low energy input is required to perform remediation. Second, ECRTs generally are effective within months, instead of years, and they can be performed in-situ or ex-situ. Third, metals generally migrate to and deposit at both electrodes, unlike classical electrokinetic techniques, in which metals migrate in the direction of only one electrode. This shortens cleanup time.
Limitations and Concerns
ECRTs reaction rates are inversely proportional to grain size, so ECRTs remediate faster in clays and silts than in sands and gravels. The working depth of the technology is limited by the availability of drilling technology to install the electrodes.
ECRTs remediate metals, radionuclides, and organic compounds in soil and groundwater. Metals remediated include mercury, arsenic, lead, cadmium, chrome, copper, nickel, and zinc. Organic compounds remediated include semi-volatile organic compounds (SVOCs) such as polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs); volatile organic compounds (VOCs), and total petroleum hydrocarbons. Typically, ECRTs are implemented in-situ. In some applications they have been used ex-situ.
Technology Development Status
In more than 50 European projects, ECRTs have been applied in commercial operations. However, scientists are still learning about the range of contaminants that they can treat and the situations they can work in. In the U.S., the technology is being field tested.
Other Resources and Demonstrations
A demonstration is being conducted by the U.S. Army Corps of Engineers, the U.S. EPA Great Lakes National Program Office, and the Minnesota Pollution Control Agency to evaluate this technology’s use in removing PAHs in the fresh-water sediments of Lake Superior. The Washington State Department of Ecology and King County, WA, are cooperating with the U.S. EPA in a Superfund Innovative Technology Evaluation (SITE) program to demonstrate the technology’s ability to reduce concentrations of PAHs, mercury, and phenols in marine sediments. The U.S. Department of Energy (DOE) is considering an ECRT field test for removal of mercury and other heavy metals at the National Security Complex (Y-12) near Oak Ridge.
Over two million metric tons of soil (in the vadose zone and groundwater) and sediments have been remediated in Europe using ECRTs. Two of these projects are described below.
Ex-Situ PAH Remediation
In Enns, Austria, approximately 500 tons of excavated soil consisting of silt and fine sands contaminated with PAHs were remediated. Six electrodes were installed in a pile of contaminated material. After 70 days the average PAH concentration had been reduced to 55 mg/kg, below the cleanup objective of 100 mg/kg.
In-situ Mercury Remediation in Sediments.
A mercury remediation demonstration project was conducted in 1997 at the Union Canal in Scotland. The canal contained brackish water and is 10 m wide by 1.1 m deep. The canal sediment contained both elemental and organic mercury. Pre-remediation average mercury concentration was 243 mg/kg, with a range of 33 mg/kg to 809 mg/kg. After 26 days, average mercury concentrations dropped to 6.5 mg/kg, with a range of 0.7 mg/kg to 11 mg/kg. The cleanup objective was 20 mg/kg. A total of 76 kg (168 lbs.) of mostly mercury was deposited on both the anode and cathode electrodes.