The Effect of Concentrated Electron Donors on the Solubility of Trichloroethene

Abstract

AbstractThe use of enhanced in situ bioremediation to remove chlorinated ethenes in sources areas is an emerging application of this remediation technology. Contaminant mass removal likely involves a number of different physicochemical processes; however, recent vendor claims suggest that the addition of highly concentrated electron donor solutions to increase the aqueous solubility of trichloroethene (TCE) is a significant mechanism of contaminant mass removal. To assess the validity of these claims, experimental measurements of the solubility of TCE in aqueous solution with eight typical electron donors at concentrations ranging from 0.5% to 25% are presented. The results of these measurements, in accordance with the theoretical understanding of solubility, indicate that the salts of carboxylic acids, including common electron donors (e.g., sodium lactate), depress the solubility of TCE in accordance with the theoretical predictions of the Setschenow equation. Three of the electron donors tested (ethanol, acetic acid, and lactic acid) increased the solubility of TCE. The largest increase in solubility resulted from ethanol addition, with only a fourfold increase at an ethanol concentration of 25%. These results suggest that salting‐out effects are yet another consideration, along with stoichiometric electron donor requirements, adverse geochemical impacts, utilization by dechlorinating organisms, and electron donor longevity, for electron donor selection.