Electrokinetic remediation is a process in which a low-voltage direct-current electric field is applied across a section of contaminated soil to move contaminants. The principle of electrokinetics remediation is similar to a battery. After electrodes (a cathode and anode) are introduced and charged, particles (e.g., ions) are mobilized by the electric current. Ions and water move toward the electrodes.
Each electrode assembly contains water, a pump, and an electrode. The outer casing of the electrode is made of porous ceramic that allows electrical current and water to pass. The porous casing contains water, which is held under pressure so it does not flow out and saturate adjacent soils. The ions flow through the casing, where they are then removed for treatment.
Another similar process for transporting contaminants through the soil using electrical current is called electroosmosis. In contrast to electrokinetics, electroosmosis is the movement of a liquid containing ions. As the electric current is applied to the soil, water in the soil pores flows between the electrodes. Sometimes these two processes are used together to enhance removal.
This basic electrokinetic technology is sometimes combined with in-situ treatment technology, such as the Lasagna Technologyª. In this process, the contaminants are moved by electroosmosis through treatment zones. As the electric charge is varied, the contaminants reverse direction. Chemical oxidation could occur, with chemical additives delivered by fracturing in conjunction with oxidant solution injection.
Limitations and Concerns
The effectiveness is sharply reduced for wastes with a moisture content of less than 10 percent.
In unsaturated soils, the addition of water could potentially wash contaminants out of the area of influence.
The presence of buried metallic or insulating material can induce variability in the electrical conductivity of the soil.
Metallic electrodes may dissolve as a result of electrolysis and introduce corrosive products into the soil. Electrodes made of inert materials such as carbon, graphite, or platinum should be used.
Electrokinetics is most effective in clays because clay particles have a negative surface charge.
The solubility and desorption potential of the contaminants may limit the success of the technology.
Electrokinetics is primarily used to remove metals and radionuclides in low permeability soils. It may also be used for organic compounds, including VOCs and pesticides, although as noted above, there have been some problems with this application.
Technology Development Status
This technology is being field demonstrated at several locations. Bioremediation in LasagnaTM treatment zones has been demonstrated in the laboratory, but it requires further development. Electrokinetic remediation has been applied successfully to soils with high soil moisture. It has been used commercially in Europe, but there are no commercial applications in the U.S. Sandia National Laboratories (SNL) is trying to extend electrokinetic remediation technology to unsaturated soils. The SNL electrode design allows water to enter the soil at the anode, replenishing the pore water adjacent to the electrode casing, but never saturating the soil. The SNL design for low-moisture soils is in the pilot stage.
Other Resources and Demonstrations
See http://www.epa.gov/swertio1/download/remed/electro.pdf for a description of current research projects.
Also see the Remediation Technologies Development Forum (RTDF) at http://www.rtdf.org/public/lasagna/lastechp.htm for a current list of relevant publications. Also see ÒEmerging Technologies for the Remediation of Metals in Soil: Electrokinetics,Ó Interstate Technology and Regulatory Council (ITRC), December, 1997 at http://www.itrcweb.org/Documents/MIS-4.pdf.
See http://costperformance.org/profile.cfm?ID=246&CaseID=246 for an SNL demonstration in an unlined chromic acid pit.