Effects of Surfactant Sorption on the Equilibrium Distribution of Organic Pollutants in Contaminated Subsurface Environments

Abstract

Abstract:Partitioning of two hydrophobic organic contaminants (HOCs), phenanthrene and naphthalene, to surfactant micelles, kaolinite and sorbed surfactants was studied to provide further insight on (1) the effectiveness of using sorbed surfactants to remove HOCs from water and (2) the feasibility of using surfactant-enhanced aquifer remediation (SEAR) for contaminated subsurface systems. Sorbed surfactant partition coefficients (K ss ) showed a strong dependence on the surfactant sorption isotherms. K ss values for sodium dodecyl sulfate (SDS) were always larger than the corresponding micellar partition coefficient (K mic ) values. For Tween 80, however, K ss values were higher than K mic values only at the lower sorbed surfactant concentrations. HOC distributions between immobile and mobile compartments varied with surfactant dose and solution chemistry, and were primarily dependent on the competition between sorbed and micellar surfactants for HOC partitioning. Overall results of this study demonstrate that surfactant sorption to the solid phase can lead to increases in HOC retardation, a desirable effect when the treatment objective is to immobilize HOCs by removing them from water but an undesirable effect in SEAR applications. Therefore, appropriate consideration must be given to surfactant sorption and HOC partitioning to immobile versus mobile phases when using surfactants to remediate contaminated subsurface systems.