Surfactant-Enhanced Dissolution of Phenanthrene into Water for Laminar Flow Conditions

The effects of surfactant solutions on processes influencing subsurface remediation are of significant environmental concern. We previously investigated the dissolution of solid phenanthrene into aqueous solu tions containing nonionic surfactants in a well-mixed system and developed a mechanistic model to describe the dissolution process. In the present work, we challenged this model by collecting data from a flow-through system in which the hydrodynamics are well defined and provided independent measurements of all parameters in the model. The dissolution process is assumed to be governed by the diffusion of phenanthrene away from the hydrocarbon−water interface in both the aqueous phase and micelles, and transport is formulated in a three-dimensional advective−diffusive model. The trends in model predictions and experimental data compare favorably, lending further support to the proposed mechanistic model. In particular, effluent concentrations of phenanthrene from the experimental apparatus were both predicted and observed to be substantially lower than saturation (equilibrium) concentrations, and this difference increased at increasing surfactant concentration over the range of laminar flow rates tested. Better quantitative agreement between the model and experimental data may require a more accurate measurement of the micellar diffusion coef ficient or a more complex description of interfacial processes. However, the proposed dissolution model provides an important step toward understanding the influence of surfactants on hydrocarbon dissolu tion and transport.