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Rate-Limited Solubilization of Multicomponent Nonaqueous-Phase Liquids by Flushing with Cosolvents and Surfactants:  Modeling Data from Laboratory and Field Experiments

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journal contribution
posted on 03.04.2003, 00:00 by James W. Jawitz, Dongping Dai, P. Suresh C. Rao, Michael D. Annable, R. Dean Rhue
The impact of rate-limited mass transfer on in-situ cosolvent and single-phase microemulsion flushing for the solubilization of multicomponent nonaqueous-phase liquids (NAPLs) was investigated. Laboratory and field data from both cosolvent and microemulsion flushing studies were modeled using a one-dimensional flow, enhanced-dissolution code. Transport of the flushing agents was described with a one-dimensional advection−dispersion model; more complex heterogeneities encountered at the field scale were characterized using the superposition of two solute transport equations. Cosolvent and microemulsion flushing solubilize NAPLs by different mechanisms. The modeling results presented here show that nonequilibrium effects influence both of these processes differently. Solubilization of individual constituents by cosolvents was limited by the rate of diffusion or transport of the component through the organic phase, while the rate-limiting step for microemulsification was independent of the NAPL constituent and was likely external to the organic phase. These data indicate that by accounting for field-scale hydrodynamic variability, laboratory-measured nonequilibrium parameters may be used to accurately predict field-scale nonequilibrium NAPL solubilization. Finally, the effects of field-scale media heterogeneity are likely to dominate those of weakly rate-limited dissolution, and accurate characterization of the former may be sufficient for adequate prediction of field-scale NAPL solubilization.