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Reductive Dechlorination of Perchloroethylene with a Direct Current, Different Salts, and Vitamin B12

Abstract

Initial tests to reductively dechlorinate perchloroethylene (PCE) by using vitamin B12 dissolved in water and a small direct current were successful; however, the transformation process was inefficient (less than 30 percent transformation). If the process is to be utilized in the field, the efficiency must be improved. The objective of this study was to identify environmental conditions that increase PCE transformation into trichloroethylene (TCE) by electrokinesis and vitamin B12. Tests were conducted using 12-inch glass tubes filled with 3.5 milliliters of aqueous solutions containing 10 to 50 milligrams per liter (mg/L) vitamin B12, 0.1 to 25.0 mg/L PCE, and a variety of salts. The ends of the tubes were sealed with silicone gel with a platinum electrode extending through the silicone. A direct current was applied to each test chamber using the platinum electrodes and a constant power supply. Preliminary results show that the salt type and concentration had an effect on PCE-transformation efficiency. For example, test solutions containing 25 mg/L vitamin B12 and 100 mg/L of CaCl2 had an 85-percent greater transformation of PCE to TCE than distilled water only containing vitamin B12. Solutions containing NaCl and CaCl2 were twice as effective as solutions with FeCl3 and Fe(NH4)2(SO4)2 at enhancing transformation of PCE to TCE. Addition of the salts NH4Cl and FeSO4 produced the lowest remaining concentrations of PCE but produced no significant amount of TCE in the test chamber. Whether PCE volatilized or was completely dechlorinated in those tests is not known. Also, a steady low voltage (200 mV) was more effective than higher voltages (greater than 400 mV) at inducing reductive dechlorination. The efficiency of the dechlorination reaction appeared to be unaffected by PCE concentration when PCE concentrations ranged from 0.1 to 25.0 mg/L. This information will be useful for adapting the method from the laboratory to the field.

This abstract can be cited as follows:

Alam, Majharul, and Byl, T.D., 2001, Reductive dechlorination of perchloroethylene with a direct current, different salts, and vitamin B12 [abs.], in Tennessee Water Resources Symposium, 11th, Burns, Tenn., 2001, Proceedings: Tennessee Section of the American Water Resources Association, p. P-1.


U.S. Department of the Interior, U.S. Geological Survey
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Last update: Tuesday, 08-Jan-2013 14:46:39 EST
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