Effects of Cosolvent Addition on Surfactant Enhanced Recovery of Tetrachloroethene (PCE) from a Heterogeneous Porous Medium

Abstract

The ability of surfactant formulations containing ethanol (EtOH) to enhance the recovery of a representative dense nonaqueous phase liquid (DNAPL), tetrachloroethene (PCE), was evaluated in batch, column, and heterogeneous, two-dimensional (2-D) systems. The experimental studies were designed to investigate the influence of EtOH addition, rate-limited mass transfer and subsurface layering on the micellar solubilization of PCE by aqueous solutions (4% wt.) of polyoxyethylene (20) sorbitan monooleate (Tween 80). In completely mixed batch reactors, the solubility of PCE in Tween 80 solutions (0.5 to 4% wt.) increased incrementally as the EtOH concentration was raised from 0% to 5% and 10%. Results of one-dimensional column studies demonstrated that solubilization of residual PCE was rate-limited regardless of the EtOH concentration. Effluent data were used to develop effective PCE mass transfer coefficients (K_e) as a function of EtOH concentration, Darcy velocity, and duration of flow interruption. For the heterogeneous 2-D system, solutions containing 4% Tween 80 or 4% Tween 80+5% EtOH were injected into rectangular boxes packed with 20–30 mesh Ottawa sand and three low permeability layers. Visual observation of surfactant fronts and effluent concentration data demonstrated that the addition of 5% EtOH resulted in density over ride of the injected solution, and failed to enhance PCE recovery compared to the 4% Tween 80 solution alone. The results of this work indicate that although relatively small additions of EtOH can improve the solubilization capacity of surfactant formulations, differences between flushing and resident solution density must be carefully accounted for when utilizing cosolvent-amended surfactant formulations for DNAPL remediation.