Evaluation of Sub-Micellar Synthetic Surfactants Versus Biosurfactants for Enhanced LNAPL Recovery

EPA Grant Number: R83-0633-010

Title: Evaluation of Sub-Micellar Synthetic Surfactants Versus Biosurfactants for Enhanced LNALP Recovery

Investigators: David Sabatini et al (sabatini@ou.edu)

Institution: University of Oklahoma

EPA Project Officer: Bala Krishnan

Project Period: 9-1-04 to 8-31-05

Project Amount: $94,518

Research Category: Petroleum Environmental Technology - Recovery of free-phase LNAPL

Description:

The release of light non-aqueous phase liquids (LNAPLs) into the subsurface is a well-documented environmental concern. Past practices have led to extensive LNAPL groundwater contamination, mostly in the

form of petroleum products. Potential for further contamination is also a concern when considering the presence of LNAPL sources in the subsurface (e.g. underground storage tanks and oil/gas pipelines).

Surfactant flushing in the subsurface has emerged as one of the most technically effective and cost-competitive technologies for remediation of LNAPL contamination. Recent field studies (Surbec-ART Environmental,

LLC) have demonstrated the technical and economic efficiency of surfactant-enhanced LNAPL mobilization. Surfactant flushing was used to remove over 5000 gallons of previously unrecovered gasoline from an

abandoned UST site in southeast Oklahoma. Currently, surfactant-flushing is being used to recover gasoline from the UST pit at one of Oklahoma's busiest gas stations, without interrupting business activities. Thus, this technology has applications to filling stations, refineries, and even active well sites.

While advances in surfactant chemistry have dramatically improved LNAPL removal efficiencies, the key to further improvements in the economic competitiveness of surfactant-based technologies is to reduce the mass

of surfactant needed to recover the free-phase LNAPL. Flaming (2002) conducted a series of soil column tests to determine the effects of synthetic surfactants on residual water and oil saturations in porous

media. The results of that study suggest that low concentration (i.e., sub-micellar) surfactant solutions may have the ability to release significant amounts of previously trapped LNAPL in the vadose zone and lower LNAPL saturations to levels more favorable for biodegradation. Interestingly, McInerney et al. (2002) found that biologically produced, surface active agents, biosurfactants, can remove a large percentage of residual hydrocarbon from sand-packed columns at biosurfactant concentrations about 10 to 100-fold lower than typically used for surfactant-enhanced LNAPL mobilization. The objective of this research is to assess the relative technical and economic efficiency of synthetic surfactants versus biosurfactants used to recover free-phase LNAPL.