FLOW OF GASOLINE-IN-WATER MICROEMULSION THROUGH WATER-SATURATED SOIL COLUMNS

Much consideration has been given to the use of surfactants to clean u p nonaqueous phase liquids (NAPLs) from contaminated soil and ground w ater, Although this emulsification technique has shown significant pot ential for application in environmental remediation practices, a major obstacle leading to low washing efficiency is the potential formation of macroemulsions with unfavorable flow characteristics in porous med ia. This study investigated influences of the flow of leaded-gasoline- in-water (LG/W) microemulsion upon the transport of gasoline and lead (Pb) species in water-saturated soil columns. Two experiments were per formed: (1) the immiscible displacement of leaded gasoline and (2) the miscible displacement of LG/W microemulsion through soil columns, fol lowed by sequentially flushing with NaCl solution and a water/surfacta nt/cosurfactant (W/S/CoS) mixture. Comparison of breakthrough curves ( BTC) for gasoline between the two experiments shows that about 90% of gasoline and total Pb were removed from the soil columns by NaCl solut ion in the LG/W microemulsion experiment as compared to 40% removal of gasoline and 10% removal of total Pb at the same process in the leade d gasoline experiment. Results indicate that gasoline and Pb species m oved much more effectively through soil during miscible flow of LG/W m icroemulsion than during immiscible flow of leaded gasoline. In contra st to the adverse effects of macroemulsion on the transport of NAPLs, microemulsion was found to enhance the transport of gasoline through w ater-saturated soil. Mass balance analysis shows that the W/S/CoS mixt ure had a high capacity for removing residual gasoline and Pb species from contaminated soil. Comparison of water-pressure differences acros s the soil columns for the two experiments indicates that pore cloggin g by gasoline droplets was greatly minimized in the LG/W microemulsion experiment.