| This work primarily concerns the issue of mass transfer. Specifically, laboratory scale measurements of mass transfer within an idealized porous medium are performed in a bed of packed uniform sand. The objective is to describe the effect a surfactant has on the mass transfer rate coefficient for dissolution of residual DNAPL from the sand pack.;The surfactant selected for this experiment was Triton X-102, a nonionic, commercial surfactant. The NAPL used in these experiments was PCE. This selection allowed reduced interfacial tensions without the formation of microemulsions, and the use of an ultraviolet spectrophotometer to measure effluent concentrations of both surfactant and dissolved PCE.;The experimental results indicate that dissolution of residual PCE using surfactant concentration below surfactant CMC shows almost no difference in mass transfer rate coefficient between experiments despite a 3 fold decline in surface tension. Above surfactant CMC the addition of surfactant reduces the mass transfer rate coefficient. The amount of the change in mass transfer rate coefficient is proportional to the normalized mass transfer rate coefficients found from batch systems. A method of calculating average diffusion length and interfacial area below residual NAPL saturation is developed. The down turn in the mass transfer rate coefficient is shown to be related to a diffusion length larger than expected during the initial stages of the experiment. Finally, though a decrease in mass transfer rate coefficient is found above CMC, there is an overall increase in mass transfer due to the higher solubility limit.;Surfactants are used to enhance mass transfer in many applications (dish soaps, laundry detergents). Previous research on surfactant enhanced solubilization of NAPLs in laboratory columns has focused on high concentrations of surfactant designed to remove the separate phase NAPL in just a few pore volumes. The choice of surfactant and surfactant concentration in such a system is governed solely by the surfactant's ability to increase the solubility limit for the NAPL. In this study surfactants were added in concentrations both above and below the critical micelle concentration (CMC), enabling examination of the effects of changing interfacial tension (below CMC) and solubility limit (above CMC) on the mass transfer rate coefficient. |
