Environ. Sci. Technol. 2000, 34, 1985-1990
Screening Commercial Surfactants Suitable for Remediating DNAPL Source Zones by Solubilization† MEIFANG ZHOU AND R. DEAN RHUE* Soil and Water Science Department, University of Florida, IFAS, Gainesville, Florida 32611
Surfactants can enhance the removal of nonaqueousphase-liquids (NAPLs) from porous media by two very different mechanisms: (1) increased solubilization 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. Since dense-NAPLs, like PCE, pose the greatest risk of migration, there is a need for more information on surfactants that are capable of solubilizing DNAPLs 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 experiments. 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 ∼40 000 mg/L, macroemulsion stability became a problem. Addition of IPA did not affect the amount of PCE solubilized but decreased macroemulsion stability, resulting in more rapid formation of Winsor Type I microemulsions. The most efficient surfactants were Brij 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 column 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 ∼9.5 pore volumes, but about 30% of the PCE was mobilized. Removal of PCE was rate-limited with Brij 97/IPA, suggesting that flow interruption may be an effective remediation strategy.
Introduction Two very different technologies have been proposed that utilize surfactants to remove dense nonaqueous-phaseliquids (DNAPLs) from porous media. One is based on the increased solubilization that occurs in the presence of surfactant micelles and the other one mobilization of residual liquids trapped in porous media by capillary forces (1). Mobilization technologies are limited to sites where the flow of mobilized liquid can be controlled and the potential for migration through layers that previously acted as capillary barriers is extremely small. Solubilization technologies * Corresponding author phone: (352)392-1951; fax: (352)392-3902; e-mail:
[email protected]. † Florida Agricultural Experiment Station, Journal Series No. R-07155. 10.1021/es9811546 CCC: $19.00 Published on Web 04/07/2000
2000 American Chemical Society
generally pose less risk with regard to uncontrolled migration and are less complex to design. Thus there is a need for more information on surfactants that are capable of solubilizing DNAPLs and removing them as single phase microemulsions without mobilization. Addition of medium chain length alcohols to surfactant solutions often enhances solubilization and aids in the formation of microemulsions. A microemulsion is an optically transparent dispersion of liquid droplets (
