Effects of Operating and Media Conditions on the Change of Reclaimed Water Quality in Soil Aquifer Treatment (SAT) System: Experimental and Simulation Study

In order to select efficient media and find the optimum operation conditions for contaminant removal in soil aquifer treatment (SAT), column experiments with three different media were carried out under two different dry-wet ratio conditions. Phreeqc and Hydrus-1D were used to simulate the hydrogeochemical interactions. The results based on dissolution kinetics and cation exchange showed that the water-rock interaction in the columns led to the increase of Ca2+ and decrease of K+ in reclaimed water. The transfers of Ca2+ by cation exchange and calcite dissolution were 0.16-0.24 mmol/L and 0.13-0.22 mmol/L, respectively. The adsorption distribution coefficients (K-d) of NH4-N in columns ranged from 0.02 to 4 cm(3)/g. Higher K-d values were obtained in the columns of finer particle size or with the addition of biochar. The nitrification rates of NH4-N ranged from 0.08 to 0.4 day(-1), but the denitrification rates of NO3-N were low (0-0.005 day(-1)). This indicated that NO3-N removal in the columns was insignificant. The increase of the drying period from 1 to 3 days promoted the microbial-mediated nitrification that transforms NH4-N to NO3-N. Our results indicated that the sand with a 15-cm biochar layer on the top reduced saturated hydraulic conductivity and was suitable for NH4-N removal. A low dry-wet ratio (i.e., 2:2 days) could be selected to prevent the transformation of NH4-N to NO3-N. The findings are helpful to assess hydrochemical characteristic change in SAT and provide a basis for the selection of a reasonable dry-wet ratio.