Technical ArticleSolute Transport Dynamics Where Highly Treated Effluent Is Applied to Soil at Varying Rates and Dosing FrequenciesHassan, Gaber M.1; Reneau, Ray B. Jr2; Hagedorn, Charles2Author Information 1Department of Soil and Water Sciences, College of Agriculture, Alexandria University, Alexandria, Egypt. Dr. Gaber M. Hassan is corresponding author. E-mail: [email protected] 2Department of Crop and Soil Environmental Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA. Received April 17, 2009. Accepted for publication May 10, 2010. Soil Science: June 2010 - Volume 175 - Issue 6 - p 278-292 doi: 10.1097/SS.0b013e3181e73be8 Buy Metrics Abstract The number of on-site wastewater systems in the United States continues to increase as the population increases, with subsequent increased potential for soil-water pollution. Properly functioning on-site wastewater systems are necessary to renovate wastewater before it reaches groundwater or surface water. One method to accomplish this is to use a highly treated effluent, such as recirculating media filter effluent and a subsurface drip irrigation system, where effluent dispersal and dosing frequency can be controlled. A series of soil columns were used to simulate a subsurface drip irrigation system dosed with recirculating media filter effluent at varying application rates (518, 1,036, and 2,071 cm3/d) and dosing frequencies (6, 12, and 24 doses/d). The two-dimensional code in HYDRUS-3D was used to simulate solute transport (Cl−, NO3−, and PO4−3) in this system. Results show that most of the Cl− was lost from the system in seepage (91% to 98%), whereas seepage (65%) and denitrification (31%) were the primary mechanisms for reducing NO3− concentrations in the soil. Most of the PO4−3 remained in the soil (between 94% and 98%), with seepage loss accounting for a relatively small percentage of the PO4−3 added (from >0.01% to 4% at the 518 and 2,071 cm3/d application rates, respectively). Agreement between the measured and simulated Cl−, NO3−, and PO4−3 concentrations indicated that HYDRUS adequately simulated transport of these solutes through the soil under a range of environmental and effluent application conditions. The simulated PO4−3 concentrations in the soil leachate tended to be slightly higher than measured concentrations and may indicate underestimation of P immobilization based on P sorption isotherms. © 2010 Lippincott Williams & Wilkins, Inc.