Investigation of Colloidal Transport in Saturated Porous Media: Experimental and Numerical Study

Field and laboratory scale observations conducted during last few decades provided ample evidences to prove colloid-facilitated transport of numerous contaminants in porous media including radionuclides, hydrophobic organic compounds (HOCs), heavy metals, pesticides, pathogens, etc. Therefore, it is vital to investigate colloid and colloid-facilitated contaminant transport in porous media and the soil physico-chemical parameters controlling their subsurface fate and transport processes. This study mainly focused on investigating the effect of flow rate (as a physical perturbation) and ionic strength (as a chemical perturbation) on mobilization and transport colloids in saturated porous media. A series of controlled-laboratory column experiments were conducted using a selected sand as the porous medium and colloids with the Stokes’ diameter <1 μm extracted from an agricultural soil. The ionic strength was controlled by changing the NaCl concentration in the influent colloidal solution while the flow rate changed by varying the hydraulic head of the column. The turbidity of the effluent solution was measured to estimate the colloid concentration and a series of breakthrough curves were obtained for different combinations of ionic strength and flow rates. The experimental results were numerically characterized based the advection–diffusion/dispersion modelling framework coupled with attachment, detachment and straining parameters which were inversely estimated using the HYDRUS 1D software. Estimated attachment coefficients of soil colloids were significantly higher in low flow rates and higher in high ionic strength. Also, the results of numerical analysis identified attachment as the key retention mechanism in saturated porous sand in an ionic solution.