Original articleCombined effect of unsaturated soil condition and soil heterogeneity on methylene blue adsorption/desorption and transport in fixed bed column: Experimental and modeling analysis

Several series of batch and fixed bed column experiments have been carried out to study the methylene blue sorption and transport in sandy and clay soil under different experimental conditions. The non linear forms of the pseudo-second order kinetic model and the Freundlich and Langmuir isotherm models were used to quantify the maximum adsorption capacity of the used materials. The effects of several experimental factors (flow rate, initial concentration, saturation condition of soil and soil heterogeneity) on the breakthrough curves have been undertaken. Experimental data revealed that the breakthrough curves depend on flow rate, methylene blue inlet concentration, saturation condition of soil and soil heterogeneity. A two dimensional model based on Richards equation and advection-dispersion equation coupled with adsorption model was developed. A comparative analysis between this model and Thomas model showed the effectiveness of advection-dispersion model to describe the experimental breakthrough curves and particularly in an unsaturated heterogeneous medium. The advection dispersion model reproduces perfectly the transfer mechanisms in porous media and seems to be a useful tool to better understanding the physical processes and the effect of capillary barrier of methylene blue transport in unsaturated heterogeneous soil. The result shows also that the soil heterogeneity has a significant effect on methylene blue adsorption through unsaturated layered media. Furthermore, in the interface between two layers with different hydrodynamic proprieties, the adsorption capacity increases with a decrease in kinetic adsorption rate caused by the decrease in pore water velocity.