Screening commercial surfactants suitable for remediating DNAPL source zones by solubilization

Surfactants can enhance the removal of nonaqueous-phase-liquids (NAPLs) fro m porous media by two very different mechanisms: (1) increased solubilizati on that occurs in the presence of surfactant micelles and (2) mobilization of NAPL ganglia held by capillary forces. Solubilization technologies pose less risk of uncontrolled NAPL migration and are less complex to design. Si nce dense-NAPLs, like PCE, pose the greatest risk of migration, there is a need for more information on surfactants that are capable of solubilizing D NAPLs and removing them as water continuous, low viscosity, microemulsions without mobilization. Forty-two commercial, water-soluble surfactants were screened for PCE solubilization in batch experiments and one nonionic (Brij 97) and one anionic (SDS) surfactant were further evaluated in column expe riments. Of the 42 surfactants that were screened, 12 nonionic surfactants with HLB values between 10.8 and 13.2 solubilized the most PCE. However, as PCE solubilization exceeded similar to 40 000 mg/L, macroemulsion stabilit y became a problem. Addition of IPA did not affect the amount of PCE solubi lized but decreased macroemulsion stability, resulting in more rapid format ion of Winsor Type 1 microemulsions. The most efficient surfactants were Br ij 97 and Ritoleth 10, both being ethoxylated oleyl alcohol ethers. At 3 wt % IPA and surfactant, these surfactants solubilized >70 000 mg PCE/L. In c olumn experiments, Brij 97/IPA removed >92% of the residual PCE in 11 pore volumes without mobilizing the PCE. An SDS/pentanol/IPA system removed 98% in similar to 9.5 pore volumes, but about 30% of the PCE was mobilized. Rem oval of PCE was rate-limited with Brij 97/IPA, suggesting that flow interru ption may be an effective remediation strategy.