Mobilization of soil-bound polycyclic aromatic hydrocarbons using surfactants

Batch experiments were performed to estimate the effectiveness of surfactant in mobilizing soil-bound PAHs. The desorption of naphthalene and phenanthrene from soils of varying f_oc was determined using two nonionic alcohol ethoxylate surfactants. A dramatic enhancement of desorption (80 - 95%) was obtained after one day of washing with surfactants, but relatively high surfactant doses (2 or 3 orders magnitude greater than CMC) were required. Kinetics of surfactant-enhanced desorption was also investigated using soils contaminated for different periods of time. The efficiency of surfactant washing was found to be significantly affected by the kinetics of both PAH adsorption and desorption; long contamination periods and short surfactant-washing periods resulted in decreased desorption of PAH. Both an equilibrium partitioning model and a radial diffusion model were used to analyze the results of PAH adsorption/desorption obtained in this study. The desorption data for soils of relatively long contamination age (22 days) were well described by the radial diffusion model while those from soils of short contamination age (1 day) were described better by the equilibrium model. From a practical standpoint, the radial diffusion model appears to be appropriate for use in the field because of the long contamination history of most hazardous waste sites.