Electrokinetics

Description

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 Technology™. 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.

Recent tests at the Livermore National Laboratory have indicated problems when electrokinetics is applied to dense non-aqueous phase liquid (DNAPL), because the system gets clogged.

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.

Applicability

Electrokinetics helps to remove metals, radionuclides and organics in low permeability soils.

Technology Development Status

This technology is being field demonstrated at several locations. Bioremediation in Lasagna^TM 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. 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.

Web Links

http://www.frtr.gov/matrix2/section4/4-4.html

http://www.em.doe.gov/plumesfa/intech/lasagna/index.html

http://www.sandia.gov/Subsurface/factshts/ert/ek.pdf

http://aec-www.apgea.army.mil:8080/prod/usaec/et/restor/insitu.htm

http://www.estcp.org/projects/cleanup/199605v.cfm

Other Resources and Demonstrations

See http://www.epa.gov/swertio1/download/remed/electro.pdf for a description of current research projects.

The Bay Area Defense Conversion Action Team (BADCAT), in cooperation with several parties including the U.S. Navy, demonstrated electrokinetics at the former Alameda Naval Air Station in March, 1998. Information is available from BADCAT at http://www.cedar.ca.gov/badcat/12envtec.htm.

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 “Emerging Technologies for the Remediation of Metals in Soil: Electrokinetics,” Interstate Technology and Regulatory Cooperation Work Group (ITRC), December, 1997. Contact http://www.itrcweb.org/common/default.asp (See Guidance Documents).

See also “In Situ Remediation Technology Status Report: Electrokinetics,” EPA 542-K-94-007, April, 1995 (http://www.gwrtac.org/html/tech_status.html#ELECTRO). Three pilot studies were also conducted under the EPA Superfund Innovative Technology Evaluation (SITE) program.