Biosurfactant-enhanced solubilization of NAPL mixtures

Remediation of nonaqueous phase liquids (NAPLs) by conventional pump-and-tr eat methods (i.e., water flushing) is generally considered to be ineffectiv e due to low watts solubilities of NAPLs and to mass-transfer constraints. Chemical flushing techniques, such as surfactant flushing, can greatly impr ove NAPL remediation primarily by increasing the apparent solubility of NAP L contaminants. NAPLs at hazardous waste sites are often complex mixtures. However, the equilibrium and nonequilibrium mass-transfer characteristics b etween NAPL mixtures and aqueous surfactant solutions are not weil understo od. This research investigates the equilibrium solubilization behavior of t wo- and three-component NAPL mixtures (containing akylbenzenes) in biosurfa ctant solutions. NAPL solubilization is found to be ideal in water (i.e., o beys Raoult's Law), while solubilization in biosurfactant solutions was obs erved to be nonideal. Specifically, the relatively hydrophobic compounds in the mixture experienced solubility enhancements that were greater than tho se predicted by ideal enhanced solubilization theory, while the solubility enhancements for the relatively hydrophilic compounds were less than predic ted. The degree of nonideality is shown to be a nonlinear function of the N APL-phase mole fraction. Empirical relationships based on the NAPL-phase mo le fraction and/or micelle-aqueous partition coefficients measured in singl e-component NAPL systems are developed to estimate values fur the multicomp onent partition coefficients. Empirical relationships that incorporate birt h thr NAPL-phase mole fraction and single-component partition coefficients yield much improved estimates for the multicomponent partition coefficient. (C) 2001 Elsevier Science B.V. All rights reserved.