PARTITIONING OF HYDROPHOBIC ORGANIC-COMPOUNDS TO SORBED SURFACTANTS -1 - EXPERIMENTAL STUDIES

Partitioning of two hydrophobic organic compounds (HOCs), phenanthrene and naphthalene, to surfactant micelles, kaolinite, and sorbed surfac tants was studied to provide further insight on (1) the effectiveness of using sorbed surfactants to remove HOCs from water and (2) the feas ibility of surfactant-enhanced remediation (SER) for contaminated subs urface systems. Sorbed surfactant partition coefficients, K-SS, showed a strong dependence on the surfactant sorption isotherms: at low sorb ed surfactant levels K-SS values were at their highest and then decrea sed with increasing surfactant sorption densities. K-SS values for SDS were always larger than the corresponding micellar partition coeffici ent (K-mic) values; for Tween 80, however, K-SS values were higher tha n K-mic Values only at the lower sorbed surfactant densities. HOC dist ributions between the immobile and mobile phases varied with surfactan t dose be ca use of the competition between sorbed and micellar surfac tants for HOC partitioning: distribution coefficients increased initia lly with increasing surfactant concentrations before decreasing at hig her doses. Overall results of this study demonstrate that surfactant s orption to the solid phase can lead to increases in HOC retardation wh en equilibrium conditions are applicable (e.g., slow advection rates). This effect is desirable wh en the treatment objective is to immobili ze HOCs by removing them from water; however, the effect is undesirabl e in SER applications. Before any surfactant-enhanced mobilization/imm obilization process is selected, appropriate consideration of surfacta nt sorption and HOC partitioning to immobile versus mobile phases pert inent to a specific subsurface system must be contemplated.