Fundamentals of surfactant-enhanced remediation technology

Surfactant-enhanced subsurface remediation is a promising technology for expediting source-zone treatment of the sparingly soluble hydrophobic organics (HOCs).; This research focuses on the fundamentals related to the application of this technology: the molecular interactions of the PAHs with multiple phases in the sandy soil matrices. Three PAHs (pyrene, phenanthrene and naphthalene) and benzene were chosen as the target source-zone HOCs. Sodium dodecylsulfate, (SDS) and sandy soil of 0.16% natural organic matter were selected as representative of an anionic surfactant and a geo-sorbent. The columnar experiment is the major investigation methodology.; A prediction model for the distribution coefficient of PAH between the micellar-water pseudo-phases is developed using the surface tension reductions and molecular surface areas of the PAH compounds. In the dilute range of five surfactant micellar solutions involving anionic, nonionic and cationic surfactant, this prediction model is generalized for 14 chemicals that include 11 homo or hetero PAH compounds and 3 liquid polyhalogenated chemicals. The accuracies of model prediction are less than the scatter between the experimental data reported by other researchers.; A two-term model, which is the sum of the sorbed SDS phase-related partition coefficient of PAH and the organic matter-related partition coefficient of PAH, is developed to predict the SDS-related solid-liquid partition coefficients of PAH. Using the developed model to predict the SDS-related solid-liquid partition coefficients of four PAHs in three different soil matrices, the sandy soil, the clay soil and the mixture of soil and sediments, over 86% accuracy is achieved.; The diffusion coefficients of PAH-containing SDS micelles in the flushing liquid are measured by dynamic light scattering. From it, together with the diffusion coefficient of the PAH molecules in water, the effective diffusion coefficients of PAH in the real world of a surfactant-enhanced soil flushing process are obtained.; A linear log-log relation is established between the first-order desorption rate coefficients and the SDS-related solid-liquid partition coefficients for PAHs. This relation indicates that the mechanism of surfactant-related intra-organic matter diffusion predominantly accounts for the nonequilibrium SDS-enhanced desorption of the PAHs sorbed on the organic matrix of the soil.