An innovative scheme of groundwater recharge for wastewater effluent reuse has been practiced on a large scale in the Dan Region Project in Israel since 1977. The system, referred to as SAT (for Soil Aquifer Treatment), provides advanced treatment prior to effluent reuse for unrestricted irrigation. A major study recently carried out consisted of a comprehensive analysis of the water quality data available in the recharged effluent (before SAT), as well as in observation wells and recovery wells (after SAT). The results obtained with respect to suspended solids, organics and nutrients (nitrogen compounds and phosphorus) are presented and discussed. The main processes occurring in the soil-aquifer system, which are responsible for the removal of the above contaminants are filtration through the upper soil layer, organic matter biodegradation and adsorption, ammonia adsorption and biological nitirification-denitrification, and chemical precipitation and adsorption of phosphorus. The findings of the study have provided valuable information on the above processes and their interaction, and have demonstrated that the SAT system should be considered an attractive method for effluent reuse in areas where hydrogeological conditions are suitable for groundwater recharge via spreading basins.

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