Evaluation of ethoxylated nonionic surfactants for solubilization of chlorinated organic phases: Effects of partitioning loss and macroemulsion formation.

Selection of proper surfactants is critical for applying surfactant-enhanced remediation (SER) to sites contaminated with nonaqueous phase liquids (NAPLs). Here, ethoxylated nonionic surfactants (Tween 20, Tween 40, Tween 80, and Triton X-100) were evaluated for their applicability to remedy chlorinated organic phases, chloroform (CF), trichloroethylene (TCE), and tetrachloroethylene (PCE), on the basis of solubilization capacity, partitioning behavior, and macroemulsion formation. The most hydrophilic CF was not relevant for SER applications since excessive surfactant partitioning into CF rendered only few of them available for its solubilization. In contrast, the more hydrophobic TCE and PCE, having moderate surfactant partitioning, were effectively solubilized. Among Tween surfactants, a more hydrophobic surfactant showed a larger solubilization potential for both chloroethylenes, but it suffered from a greater partitioning loss. Depending on the type and extent of NAPL contaminations, thus, a prior consideration should be given to either solubilization capacity or partitioning loss when selecting the optimal Tween surfactant. Compared to Tween surfactants, the more hydrophobic Triton X-100 showed greater partitioning losses into all three NAPLs. Of particular, its partitioning into CF and TCE was nearly complete, making impractical its application to the remediation of both organic liquids. The formation of macroemulsions, characterized by a high turbidity, may significantly deteriorate SER applicability by producing undesirable flows in aquifers. Their formation became more problematic with the increasing surfactant hydrophilicity and the increasing NAPL hydrophobicity. When these combinations are applied, it is critical to keep such surfactant concentrations as to exploit the solubilization potential but not to cause the macroemulsion formation.