SORPTION NONEQUILIBRIUM EFFECTS ON COLLOID-ENHANCED TRANSPORT OF HYDROPHOBIC ORGANIC-COMPOUNDS IN POROUS-MEDIA

This paper presents the results of modelling and experimental investig ations of factors affecting enhanced transport of hydrophobic organic compounds (HOCs) on colloids in porous media, especially effects of no nequilibrium sorption/desorption. Simulations were performed with a mo del that considers equilibrium and rate-limited exchange of contaminan t between the true dissolved phase, the suspended and attached colloid s, and the fixed solid phase as well as the advection, dispersion, dep osition, and release of colloidal particles from the porous medium. Th e model was also applied to laboratory column data for colloid-facilit ated transport of a common HOC, phenanthrene. Simulations of colloid-e nhanced transport and fitting of experimental data indicated that coll oid-enhancement of hydrophobic organic contaminant transport can be si gnifi cant for sufficiently high colloid concentrations, a high partit ion coefficient of contaminant on colloids with respect to the fixed p orous medium, a low deposition efficiency of the colloids on the fixed porous medium surfaces, and a slow desorption rate of contaminant fro m the colloids. The last of these conditions was identified as probabl y the most important in enhancing transport distances of contaminants in natural systems with mobile colloids which usually occur at concent rations not exceeding a few mg/l. (C) 1998 Elsevier Science B.V.