Surfactant-enhanced dissolution under conditions of surfactant partitioning between water and NAPL: Micromodel experiments and modeling implications

摘要

The effect of surfactant partitioning between the NAPL and aqueous phases on NAPL dissolution is investigated. Dissolution experiments are conducted in a 2D transparent glass micromodel using aqueous solutions of a non-ionic surfactant (Triton X-100) to dissolve residual perchloroethylene (PCE), trapped in the form of ganglia. The dissolution experiments are conducted at different flow rates of the flushing solution and contrasted to experiments using clean water. The concentration of dissolved PCE in the effluent is measured and the evolution of PCE ganglia size distribution directly observed. Solubility and interfacial tension measurements complement these experiments. Surfactant partitioning into the NAPL is observed to drastically retard the dissolution of PCE during the initial stages. Numerical simulations confirm that the kinetics of surfactant transfer from the aqueous phase into the NAPL must be taken into account to predict the dissolution behavior.