KINETIC ASPECTS OF SURFACTANT SOLUBILIZATION OF SOIL-BOUND POLYCYCLICAROMATIC-HYDROCARBONS

The effect of nonionic polyoxyethylene (POE) surfactants on the solubi lization rate of individual polycyclic aromatic hydrocarbons (PAHs) fr om a weathered, coal tar-contaminated soil obtained from a manufacture d gas plant (MGP) site was studied. The release of PAHs upon surfactan t washing were measured with time. Time-varying adsorption of PAHs to Tenax resin was also studied. Because of its large sorption coefficien ts for organic solutes, Tenax maintained near-zero concentrations of a queous PAHs, thereby maximizing transfer of PAHs at the soil-water int erface. The release of PAHs from the MGP soil exhibited a nonequilibri um behavior,typical of such soils. Surfactants significantly enhanced the rate of PAH solubilization, the amount solubilized being dependent upon the structure of the surfactant. It is postulated that the enhan cement of PAH release by surfactants occurs by two mechanisms: (1) mic ellar solubilization by increased concentration gradient at the soil/t ar-water interface and (2) sorption and penetration of surfactant mole cules, causing intrasorbent swelling of the soil-tar matrix and increa sed matrix diffusivity of PAHs. A modified radial diffusion model was used to evaluate the relative importance of these mechanisms in surfac tant washing of contaminated soils. It was concluded that surfactants enhanced PAH release from the test soil mainly by increasing matrix di ffusivities, while increase in solubility by partitioning of PAHs into the micellar pseudophase played a secondary role.