SURFACTANT-ENHANCED SOLUBILIZATION OF RESIDUAL DODECANE IN SOIL COLUMNS .1. EXPERIMENTAL INVESTIGATION

The solubilization of dodecane by polyoxyethylene (20) sorbitan monooleate, a nonionic surfactant, was investigated as a potential means of recovering nonaqueous-phase liquids from contaminated aquifers. Residual saturations of dodecane were established by injecting C-14-labeled dodecane into water-saturated soil columns and displacing the free product with water. Flushing with a 43 g/L surfactant solution increased the concentration of dodecane in the column effluent by 5 orders of magnitude. However, effluent dodecane concentrations were considerably less than the equilibrium value of 3500 mg/L measured in batch studies. Subsequent column experiments conducted at several flow velocities and with periods of flow interruption confirmed the existence of rate-limited, rather than instantaneous, solubilization of residual dodecane. The results of this study demonstrate the sizable capacity of surfactant solutions to enhance the recovery of residual dodecane, even under conditions of rate-limited solubilization.