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SORPTION OF NONIONIC SURFACTANT OLIGOMERS TO SEDIMENT AND PCE DNAPL: EFFECTS ON PCE DISTRIBUTION BETWEEN WATER AND SEDIMENT. (R826650)
Citation:
John, W. W., B. Bao, W. P. Johnson, AND T. B. Stauffer. SORPTION OF NONIONIC SURFACTANT OLIGOMERS TO SEDIMENT AND PCE DNAPL: EFFECTS ON PCE DISTRIBUTION BETWEEN WATER AND SEDIMENT. (R826650). ENVIRONMENTAL SCIENCE & TECHNOLOGY. American Chemical Society, Washington, DC, 34(4):672-679, (2000).
Description:
Introduction of surfactant mixtures to the subsurface for the purpose of
surfactant-enhanced aquifer remediation requires consideration of the effects of
surfactant sorption to sediment and nonaqueous phase liquids. These effects
include alteration of the solubilizing properties of the surfactant mixture and
alteration of the sorption properties of the stationary phase. Sorption of
octylphenol ethoxylate (EO) surfactant oligomers to a low organic carbon content
(foc) aquifer sediment and to dense nonaqueous phase liquid
(DNAPL) consisting of tetrachloroethene (PCE) was examined in batch experiments.
At aqueous surfactant concentrations far below the critical micelle
concentration (CMC) of the mixture, sorption to sediment was characterized by an
initial steep isotherm for both high and low EO content oligomers, with somewhat
greater uptake of high EO content oligomers. This stage of sorption resulted in
mild increases in the equilibrium constant, Kd,PCE, for
distribution of PCE between solution (including surfactant) and sediment
(including sorbed surfactant). As the aqueous surfactant concentration
increased, surface aggregation of low EO content oligomers on the sediment
commenced, and a dramatic increase in Kd,PCE was observed. At
aqueous surfactant concentrations increasing above the CMC, the formation of
solution micelles caused the sorbed surfactant concentrations to plateau and
then decrease. This decrease in sorbed surfactant, along with competition by
micelles for contaminant, likely contributed to the observed rapid decrease in
Kd,PCE toward zero. Surfactant sorption to PCE DNAPL was
greater relative to sediment by 1-2 orders of magnitude, with much greater
uptake of the low EO content oligomers. Sorption of all but the lowest EO
content oligomers to the PCE DNAPL was terminated by micellization.