Nonionic surfactant-enhanced solubilization and recovery of organic contaminants from within cationic surfactant-enhanced sorbent zones .2. Numerical simulations

A mathematical model is developed to investigate the simultaneous aqueous phase transport and partitioning behavior of a nonionic surfactant and a representative hydrophobic organic contaminant (HOC) in flow-through aquifer material-water systems. Unmodified aquifer material and aquifer material treated with a cationic surfactant are considered. Nonionic surfactant sorption is represented using the equilibrium, nonlinear two-term Langmuir equation and the kinetic, nonlinear Langmuir equation. HOC sorption and solubilization is represented by an expression relating HOC partitioning between the bulk solid phase and the bulk aqueous phase containing monomer and micellar pseudophases. The model is implemented in a one-dimensional finite difference numerical model that utilizes Picard iteration to accommodate nonlinearities. Column effluent breakthrough data are used to evaluate the modeling approach. Experimentally determined batch data provided most of the model input parameters. Model simulations show good agreement with measured results when mass transfer limitations for the nonionic surfactant are considered. The model is employed to examine the potential effects of influent nonionic surfactant concentration and flushing rate on the removal of HOCs from within a cationic surfactant-enhanced sorbent zone. The analysis revealed that increasing nonionic surfactant influent concentrations decreased the volume of nonionic surfactant required to recover an HOC pulse and that HOC removal increased with increasing nonionic surfactant Rushing rate. It is likely, however, that a maximum flow rate exists above which mass transfer limitations in HOC aqueous-solid phase partitioning will occur.