Experimental and simulation study on ammonium transport and turbidity changes in a strong leakage zone during surface-water recharge in the Yufu River Basin, China.

Managed aquifer recharge is an effective technology for replenishing groundwater. This study investigated ammonium transport and turbidity changes in alluvial aquifers during surface-water recharge in the Yufu River Basin, China. Batch experiments were conducted to study ammonium adsorption to aquifer materials, while sand column experiments were used to represent ammonium transport and turbidity variation during groundwater/surface-water interaction. A coupled model of ammonia convection, dispersion, and adsorption processes was established in PHREEQC based on the parameters quantified through laboratory experiments. The results showed that the pseudo-second-order adsorption kinetic model best described the adsorption kinetic behavior of ammonium in sand samples from the Yufu River Basin, subjected to the combined effect of membrane diffusion and intraparticle diffusion. The distribution coefficients obtained by linear fitting of adsorption were 0.66 L kg−1 for coarse sand, 1.05 L kg−1 for medium sand and 2.61 L kg−1 for fine sand. The turbidity and ammonium concentration at the outlet in sand column experiments were influenced by the hydraulic head and turbidity of the recharge water and the particle size of porous media. Ammonium concentration increased with the increasing hydraulic head of surface water above the sand column. The decrease in the average particle size of the porous media led to a slow increase in the concentration of ammonium and high turbidity at the outlet. These findings provide a critical insight of predicting the transport of ammonium and turbidity changes in aquifers during recharge. [ABSTRACT FROM AUTHOR]