Competitive Effects of Nondisplaceable Organic Compounds on Trichloroethylene Uptake by Activated Carbon. I. Thermodynamic Predictions and Model Sensitivity Analyses

Abstract

Theoretical analyses were performed to investigate potential mechanisms affecting observed reductions in uptake of trichloroethylene from the aqueous phase by activated carbon loaded with nondisplaceable organic molecules. Isotherm sensitivity analysis and thermodynamically based competitive adsorption model predictions give a clear and consistent mechanistic interpretation. At low loadings of nondisplaceable organics, the most significant effect is to reduce the number of high-energy sites available to subsequently adsorbed TCE. The loss of high-energy sites causes a significant reduction in site-energy heterogeneity and reduces TCE uptake in low-equilibrium concentration regions (parts per billion) of the isotherm. As the loading of nondisplaceable compounds increases, further reductions in TCE uptake occur; however, further changes in the site-energy heterogeneity are distributed across a wide spectrum of site energies. This suggests a lowering of the average site energy, a reduction in the total number of sites, or both. In terms of TCE isotherms, this corresponds to a roughly constantpercentagereduction in uptake over a wide range of equilibrium concentrations, displacing the isotherm downward relative to the uptake axis.