Recharging Aquifers in Saudi Arabia with Secondary Effluents through Amended Sand

In the Kingdom of Saudi Arabia, artificial recharge of aquifers with treated wastewater has proven to be one of the most promising techniques for its reuse. The addition of clay to the sands is believed to improve the performance of the Soil Aquifer Treatment process. Thus, a laboratory study was conducted to investigate the effect of clay amendment on the removal efficiency of sand. Six identical sand columns, with five sampling ports in each, were fabricated and were filled with 0%, 5%, 7.5%. 10%, 12.5%, and 15% clay amended sand. The experiments were run simultaneously for a period of 14 days using chlorinated secondary effluent. Samples were collected from all the ports in the columns and were analyzed for pH, Turbidity, Electrical Conductivity, Nitrogen, Phosphorus, BOD, TOC, and Total Coliform. Results of this study show that the infiltration rate was relatively small for columns having high clay content. However, the rate of decrease in infiltration increased with a decrease in clay content. The headloss buildup was rapid in columns with low clay content and mostly occurred in the top 15 cm of the columns, thus, resulting in unsaturated flow in these columns. High clay content columns showed no significant headloss buildup. The clogging layer formed at the surface was found to control the hydraulic characteristics of the soils, excepting in those having significant clay content. Clay amendment positively affected the Turbidity removal. The presence of clay caused an increase in the electrical conductivity of the effluent after infiltration. Nitrate-N was not affected by the presence of clay. However, the phosphate-P concentrations decreased significantly in columns with high clay content and at greater depths. BOD removals improved significantly in columns with more clay content. The TOC removals were strongly affected by the depth of infiltration. Greater Total Coliform reductions were achieved in columns with high clay content.