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Superfund Innovative Technology Evaluation
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EPA/540/R-97/509

Innovative Technology Evaluation Report (ITER)
Sandia National Laboratories In Situ Electokinetic Extraction Technology
Full Report (PDF, Size 620kb, 69 pp) May 1999
Technology Capsule Report (PDF, Size 620k, 12pp) December 1998

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Abstract:

This report evaluates an in situ electrokinetic extraction system's ability to remove hexavalent chromium in the form of chromate ions from soil under unsaturated conditions. Specifically, this report discusses performance and economic data from a Superfund Innovative Technology Evaluation (SITE) demonstration of an In Situ Electrokinetic Extraction (ISEE) system developed by Sandia National Laboratories (SNL). The ISEE system demonstrated combines electrokinetic and lysimeter technologies. The lysimeter technology hydraulically and electrically creates a continuum between fluid in the anode casings (anolyte) and soil pore water, thereby enabling extraction of the chromate ions in the anolyte while the anolyte is held in the electrode casing through application of a vacuum. This feature allowed removal of chromate from unsaturated soil during the demonstration without significantly altering the soil moisture content. The ISEE system developed by SNL was demonstrated at the U.S. Department of Energy SNL Chemical Waste Landfill (CWL) site's Unlined Chromic Acid Pit (UCAP) in Albuquerque, New Mexico, from May 15 to November 24, 1996. The system was housed in two buildings: a control trailer and a temporary structure. The electrode system of the ISEE system consisted of an anode row oriented east to west and four rows of cathodes parallel to the anode row, two rows to the north and two rows to the south of the anode row. The entire system was operated for a total of 2,727 hours during 13 tests performed in six phases. The first 12 tests were performed to determine the preferred operating conditions for Test 13, which consisted of system performance testing under SNL's preferred operating conditions for the SITE demonstration. Approximately 520 grams (g) of hexavalent chromium was removed during the demonstration. Overall hexavalent chromium removal rates varied from 0.074 gram per hour (g/hour) during Test 1 to 0.338 g/hour during Test 5. Overall hexavalent chromium removal efficiencies varied from 0.0359 gram per kilowatt-hour (g/kW-h) during Test 7 to 0.136 g/kW-h during Test 13. More than 50 percent of the postdemonstration soil samples exceeded the toxicity characteristic leaching procedure (TCLP) limit of 5 milligrams per liter (mg/L) for total chromium. The soil TCLP leachate concentrations that were above the TCLP limit ranged from 6 to 67 mg/L. Downtime during system operation ranged from 0 percent during Test 11 to 66 percent during Test 1. Over the entire demonstration, the ISEE system was on line 64 percent of the time. Economic data indicate that the costs for treating 16 cubic yards (yd 3 ) of hexavalent chromium-contaminated soil with the ISEE system configuration used during Test 13 are about $1,400 per yd 3 for 200 g of hexavalent chromium removed. The ISEE technology developed by SNL is applicable for treating unsaturated soil contaminated with hexavalent chromium. According to SNL, this technology can be modified to treat saturated contaminated soil and to remove contaminants dissolved in pore water other than chromate. A full-scale, commercial system has not yet been developed. SNL maintains that a full-scale system would be significantly be improved over the system tested during the demonstration. Therefore, further performance and cost analyses should be performed on a full-scale system.

Contact:

William Frietsch
frietsch.william@epa.gov

 

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