The use of surfactants for in situ extraction of organic pollutants from a contaminated aquifer

Abstract

Many common organic pollutants are characterized by low solubilities and high interfacial tensions; these characteristics combine to render pump-and-treat processes ineffective. Surfactants can dramatically increase the solubility of organic compounds in groundwater and lower their interfacial tensions; both effects theoretically can greatly increase the extraction efficiency of pump-and-treat systems. Lowering of interfacial tensions can result in movement of dense contaminants downward in an aquifer, potentially contaminating underlying layers. Increasing a pollutant's solubility increases the fraction of pollutant present as dissolved phase, increasing the efficiency of extraction using a modified pump-and-treat technique. Thus we propose that a surfactant solution intended for extraction of dense organic liquids should be optimized for solubilization, with a minimal reduction of interfacial tensions. The results of porous media experiments comparing the extraction efficiency of over 100 surfactants indicate that solubilization ability is the most important factor; although both the extent of reduction of interfacial tension and the tendency to form spontaneous emulsions must also be considered. Using a suitable surfactant mixture, a pool of tetrachloroethylene can be extracted from a lab-scale saturated porous media model in 7 to 14 pore volumes, depending upon the geometry of the contamination. Mass balance calculations indicate complete removal of the contaminant and analysis of sand samples at the conclusion of the experiment indicates less than 1 milligram of contaminant remains. In contrast, concentrations of the effluent average only 6 ppm when distilled water is used for flushing, producing no measurable reduction in the volume of the pool in 14 pore volumes. These experiments suggest that utilizing surfactants to increase the solubility of dense organic pollutants can be an effective and relatively inexpensive way of in situ remediation of contaminated aquifers.