DC Electro-Thermal Remediation

(The integration of DC electrical heating, electroosmosis and in-situ zero-valent iron technologies)

What is it?

DC Electro-thermal Remediation is the integration of direct current (DC) electrical heating and in-situ treatment to treat solvent contamination from low permeability soils totally in place (below grade). The DC electricity provides two primary functions. The first is heating the soil to about 90 °C helping to disperse residual DNAPL pools or ganglia and possibly creating vapor phase transport. The second function is to induce electroosmotic flow. Electroosmosis is the directional movement of pore water in soil, from anode to cathode, providing a flushing action even in the tightest clays. This electroosmotic flow is the proven advantage of using DC electricity over AC (3 or 6-phase resistive heating) or steam and allows the addition of in-situ reactive treatment zones (or curtains) perpendicular to the electroosmotic flow.  In-situ destruction means no extraction or above ground treatment is necessary and keeps O&M to a minimum.  The treatment zones consist of zero-valent iron suspended in kaolin clay (similar to reactive barriers) typically spaced about 5-10 feet apart.

How is it used?

Electro-thermal remediation is used to treat solvent contaminated low permeability (less than 1x10^-5 cm/sec) or heterogeneous soils. When applied to the source zones, 99% or more removals are achieved. Even DNAPL areas can be treated to levels below 1 mg/kg for about one third the cost of excavation and disposal. This technology can be applied above or below the water table.

Lasagna^TM is the patented and trademarked name for this integration of DC electricity and in-situ treatment. Typically, a series of planar electrodes are emplaced at the outer edge of a source zone with a spread of between 20 and 100 ft apart. Treatment zones consisting of iron filings and clay are emplaced between and parallel to the electrode zones. When the power is on, the soil is heated and pore water travels from the anode toward the cathode uniformly and predictably.

Lasagna was extremely successful in reducing trichloroethylene (TCE) contamination at a DOE facility in Paducah, KY from levels indicative of DNAPL to well below the Record of Decision (ROD) mandated level.

Installing electrodes at Paducah	Installing electrodes  at Paducah	Electrode Wiring	Completed Lasagna  site at Paducah

Principles of Lasagna movie (0.4 MB)
Lasagna Installation movie (1.1 MB)
Phase IIa Installation movie (3.2 MB)

Lasagna^TM is a registered trademark of Monsanto Company (now Pfizer though acquisition of Pharmacia)

Mini-Lasagna

Mini-Lasagna, installed using a Geoprobe system, was used to reduce the area of a PCE source in Indiana for $100,000.

Mini Lasagna installed with a Geoprobe	Site after Lasagna installation	Completed site in Indiana

How much does it cost?

A Lasagna system typically costs about $100 per cubic yard treated. Very deep sources (>40 ft) and very small sites (<0.1 acres) usually cost more whereas larger, shallower sites cost less. Call Chris Athmer at Terran (937-320-3601) for a cost estimate for your site.

DC Electro-Thermal Remediation (Lasagna) advantages:

• Most thorough in-situ remediation process,
• System is emplaced using sheet pile techniques resulting in NO WASTE to dispose of,
• Completely installed and operated below grade,
• Not constrained by vapor or hydraulic permeabilities,
• No extraction equipment to operate,
• Reductive in nature - compatible with most naturally occurring reductive dechlorination processes (MNA),
• Treatment walls are left in place and will continue to polish the site for years after the power is turned off,
• DC power is 30% more efficient than AC power.

How does it work?

Electroosmosis has been known since the 1930s as an efficient means of dewatering clays and silts for soil stability. It can also be used to move pore water and contaminants through all types of soils. This attribute, plus the resistive soil heating that occurs makes it a useful tool for reclaiming solvent contaminated soils.

When a DC electric field is applied to soil, cations begin to move toward the cathode and anions move toward the anode. Since soil typically has a negative surface charge there are more cations than anions in the pore water (conservation of charge). These extra cations, lined up along the pore walls and moving toward the cathode, drag the pore water along causing a net pore water flow to the cathode that is uniform and predictable. In low permeable soils (clays and silts), this process is much more efficient and thorough than conventional hydraulic or diffusion based processes. The application of DC energy also results in the heating of the soil, which is a bonus when dealing with VOC contamination. The soil heating can be harnessed to assist in the efficient mobilization of DNAPL pools and residuals much like a thermal technology. The combination of heat and pore water movement (flushing) gives EK a one-two punch for dealing with VOC contamination in low permeable soils.

Terran has prepared a short paper about electroosmosis.
A Case for Electroosmotic Remediation (PDF)

Terran also has two short presentations about electroosmosis.
Principles of Electrokinetics
The Latest on Lasagna

Example of Application

Lasagna was developed by a consortium of industrial partners (Monsanto, DuPont and General Electric) and the USEPA to specifically treat low permeable soils contaminated with chlorinated solvents. Terran Engineer, Chris Athmer was a member of the development team at Monsanto and participated as the field engineer and principal designer of the first Lasagna site at DOE's Paducah Gaseous Diffusion Plant (PGDP) for the in-situ treatment of TCE in clay using electroosmosis and zero valent iron treatment. Electroosmosis-induced pore water flow and elevated temperatures have been proven effective in the treatment of TCE in clay soils in a most cost efficient manner. At Paducah, the process reduced the soil concentrations from an average of 84 mg/kg (with a high of 1,500) to an average of 0.38 mg/kg (with a high of 4.5) in two years of operation. The project was highlighted in a recent "Technology News and Trends" newsletter (EPA, TIO). The Final RA Report for Paducah (DOE, 2002) shows the details of the installation and verification soil sampling.

EK-Overlays

EK-Overlays can be used as an add-on to existing extractive remediation systems like soil vapor extraction systems (VES) that have become “diffusion limited” due to areas of lower permeability but have not met the target clean up levels. A DC field that increases the soil temperature and flushes the lower permeable soils can be added at very a reasonable cost. Typically, the existing extraction wells are modified to be cathodes while a series of anodes are placed around the perimeter of the area needing additional treatment. The pore water (the soil need not be saturated) is drawn to the extraction wells (cathodes) as the heat helps mobile the VOCs. Terran installed and operated an EK-Overly site for about the cost of 1 year of O&M for the VES.

Rectifier for overlay system	SVE System	SVE plus overlay

Contact

Chris Athmer by phone at 937-320-3601 or email at cjathmer@terrancorp.com

News links

Technology News and Trends

Cooking Up Solutions, Cleaning Up With Lasagna^TM, United States Environmental Protection Agency, Solid Waste and Emergency Response, EPA505-F-99-004, April 1999. Cooking up Solutions.

Technical Articles

Record of Decision (ROD) for Paducah Site Specifying Lasagna

GWRTAC Technology Overview Report - Electrokinetics

Rapid Commercialization Initiative Verification Statement for Lasagna^TM, March 2, 1998.  This statement shows the agencies that recognize Lasagna as an acceptable remediation technology.

The Lasagna Technology for In Situ Soil Remediation. 1. Small Field Test, Sa V. Ho , Christopher Athmer, P. Wayne Sheridan, B. Mason Hughes, Robert Orth, David Mckenzie, Philip H. Brodsky, Andrew Shapiro, Roy Thornton, Josepy Salvo, Dale Schultz, Richard Landis, Ron Griffith and Steve Shoemaker, Environmental Science & Technology, 33, 7, 1086-1091, 1999.

Lasagna^TM/RTDF Technical Documents, Lasagna Remediation Technology, The Remediation Technologies Development Forum (RTDF).

Copyright © 2006 by Terran Corporation, Beavercreek, Ohio U.S.A.
Phone: 937-320-3601, Fax: 937-320-3620

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