EFFECTS OF EMULSION VISCOSITY DURING SURFACTANT-ENHANCED SOIL FLUSHING IN POROUS-MEDIA

Surfactants can potentially improve the efficiency of pump-and-treat t echnology for remediation of aquifers contaminated by nonaqueous phase liquids (NAPLs). However, the formation of emulsions during the remov al process can increase the viscosity in the system. This can result i n pore clogging a,ld reduction of flow, which inhibits the contaminant removal process. Formation of viscous emulsions has been identified i n previous research as one of the probable causes for in situ field te st failures using surfactant-enhanced soil-flushing technology. Howeve r, the effects of in situ emulsification and viscosity increases have not been quantified previously. The purpose of this article is to inve stigate effects of in situ emulsification on the remediation process. Laboratory column studies examined the mobilization of m-xylene from p orous media using a 1% alcohol ethoxylate surfactant solution (Witcono l(R) SN90). Effects of in situ emulsification were determined. Glass c olumns (1.1 cm i.d. x 30 cm) were packed with 0.2-mm glass beads to mo del soil media. Viscosities of emulsion solutions prepared with 1% SN9 0 and various concentrations of m-xylene were measured and compared wi th effluent collected during column-flushing experiments. It was deter mined that as m-xylene concentration in the emulsion solution increase s, viscosity increases. Viscosity increases caused a decrease in relat ive permeability within the soil column. As a result, the hydraulic gr adient required to maintain a constant flowrate of 1.1 ml/min (using a syringe pump) through the soil column increased. Results show that a relatively small increase in viscosity could have a noticeable effect on the mobilization process. It is suggested that the surfactant/conta minant systems be screened to determine emulsion rheology and the pote ntial effects on the remediation process. The use of low-concentration alcohol cosurfactants to reduce system viscosity was evaluated and wa s shown to be ineffective.