ON THE SIMULTANEOUS DETERMINATION OF DISPERSION AND NONLINEAR ADSORPTION PARAMETERS FROM DISPLACEMENT TESTS BY USING NUMERICAL-MODELS AND OPTIMIZATION TECHNIQUES

The determination of the dispersion and adsorption parameters (either for the Freundlich or Langmuir adsorption isotherm models) can be dete rmined by optimising the matching of the numerical solution of the ads orption-convection dispersion equation with the experimental effluent curves measured on displacement tests in core material using multivari able optimisation techniques. The numerical solutions are obtained by solving the convection-dispersion-nonlinear adsorption equation by fin ite differences using the Crank-Nicolson method with iterations to acc ount for nonlinearities. The optimisation routines are used to find th e parameters that give the global minimum error between predicted and measured effluent curves. The results show that whenever the three par ameters (the dispersion coefficient and two adsorption parameters) are simultaneously determined, the solution is not unique and depends on the adsorption model used. The nonuniqueness can be removed by perform ing an independent test such as a static adsorption test.