Modeling colloid-associated atrazine transport in sand column based on managed aquifer recharge

The Yellow River with high silt concentration is the main source of domestic water supply for downstream cities. After desilting, 85% silt is removed but fine suspended particles remain in the water, which may cause health and environmental risks, and the traditional water treatment technology by a water plant is ineffective in removing fine suspended particles. Atrazine is one of eight priority-controlled trace organic pollutants in Yellow River water. As one of the effective measures, managed aquifer recharge (MAR) is adopted to improve the Yellow River water quality. The model of colloid-associated atrazine transport is simulated at laboratory scale. The migration experiment of atrazine in heterogeneous porous medium (non-uniformity coefficient of 25.2) with saturated and steady flow is conducted under sand washing condition. The observed data of breakthrough curves are numerically simulated using convection-dispersion equation and CXTFIT 2.1 software. Results show that in the absence of montmorillonite, atrazine reaches a peak at approximately 100min, and the peak is 82% of the initial value; whereas in the presence of montmorillonite, atrazine reaches a peak at approximately 55min. Thus, atrazine can be absorbed on colloidal particles and spread in the area, and the remaining atrazine aggravates the risk of pollution for groundwater environment. Therefore, preventive measures should be considered in the MAR system to reduce the exogenous colloid into the aquifer, it is significant for sustainable MAR operations. Equilibrium and non-equilibrium models can better fit the experimental data and can be utilized to analyze the colloid-assisted atrazine transport in saturated heterogeneous porous media under a steady state.