Simulation of soil washing with surfactants

Abstract

A mathematical model of soil washing that incorporates the surfactant enhanced mobilization and solubilization of organic compounds was implemented using a finite difference compositional reservoir simulator. The primary objective of the model was identification of the contributions of the various mechanisms—water displacement, surfactant mobilization and dissolution—on the removal of organic contaminants from soil. Mobilization of the organic phase was described by a reduction in the residual oil saturation caused by decreased interfacial tension. Increased aqueous solubility of organic compounds due to solubilization by surfactant micelles was modeled assuming local equilibrium. Parameters for the model were obtained from experimental measurements and literature sources. The model was implemented in a two-dimensional, two-phase system. Experimental data from surfactant flushing of columns contaminated with automatic transmission fluid and a mixture of chlorinated organics were used to evaluate the performance of the model. In most cases, the predicted organic recoveries were found to agree well with experimental results. For the surfactant sodium dodecyl sulfate, mobilization of organic contaminants was the main recovery mechanism for both waste liquids modeled. The results suggest that complete dissolution of a contaminant nonaqueous phase, rather than mobilization and subsequent vertical migration, may be difficult to achieve at the surfactant concentrations studied.