REACTIVE SOLUTE TRANSPORT IN A HETEROGENEOUS COLUMN WITH MIXING EFFECT AND SCALE EFFECT

Physical, chemical, and biological transport processes in heterogeneous porous media are important for the quantitative evaluation of aquifer remediation, which are commonly reproduced in the laboratory column tests. Many observations demonstrated that non-Fickian effect, mixing effect and scale effect might exert profound impact on the data interpretation of the test, but were often grossly overlooked in previous models of the reactive solute transport. Mixing effect refers to the mixing processes of the injected solute with the original water in a pre-inlet reservoir or an after-outlet reservoir of the column. In this study, the new mathematic models and analytical solutions are developed by including all of these effects, where the non-Fickian effect is described by Mobile-immobile model (MIM), and the scale effect is described by the linear, exponential, and asymptotic functions, respectively. To test the robustness of the new model, three sets of the column experiments with various heterogeneous porous media were conducted under different flow conditions. Results show the new model of this study performed better than the previous ones in the interpretation of observed breakthrough curves (BTCs) in the different observing locations and different flow field, since the new model included non-Fickian effect, mixing effect and scale effect, implying that these three effect might not be ignored in the processes of reactive solute transport. The pre-inlet reservoir could cast influence on the transport process over the entire column, while the influence of the after-outlet reservoir on transport was usually limited to a finite region close to the outlet. The influence of the parameters in the scale-dependent dispersion models on mixing effect is obvious. The smaller values could increase the peak values of Error between the solutions with and without the mixing effect, and narrow the time interval of the non-zero Error.