Soil aquifer treatment (SAT) systems are used for reclamation of sewage effluent by groundwater recharge. Increasing demand on water supplies has stimulated the production or planning of many SAT systems that will use reclaimed wastewater for groundwater recharge. These systems are comprised of a series of infiltration basins. The design and operation of soil aquifer treatment systems presently relies primarily upon judgment and experience. This research effort is developing a methodology for determining the optimal operation of SAT systems that is based upon mathematically describing the problem as a discrete-time optimal control problem. The resulting mathematical problem is a large-scale nonlinear programming problem. Solution of the problem is being accomplished by interfacing a nonlinear programming optimizer, which is solved by a differential dynamic programming algorithm, with a simulator that describes the infiltration process, unsaturated flow, effects of surface clogging and biological clogging, biological removal of nitrogen and organics. Major efforts are devoted to numerical performance of the optimization model solution, and development of the simulator. Initial results of interfacing the optimizer with the simulator without water quality concern show high convergence rate. The operation pattern determined by this method is reasonable. This new methodology will be a tool for engineers to evaluate choices regarding the potential of the design and operation of SAT systems.

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