Optimal scheduling of pumping and chlorine injections under unsteady hydraulics

This paper describes the methodology and application of a genetic algorithm (GA) scheme, tailor-made to EPANET for simultaneously optimizing the scheduling of existing pumping and booster disinfection units, as well as the design of new disinfection booster chlorination stations, under unsteady hydraulics. The objective is to minimize the total cost of operating the pumping units and the chlorine booster's operation and design for a selected operational time horizon, while delivering the consumers' required water quantities, at acceptable pressures and chlorine residual concentrations. The decision variables, for each of the time steps that encompass the total operational time horizon, include: the scheduling of the pumping units, settings of the water distribution system control valves, and the mass injection rates at each of the booster chlorination stations. The constraints are domain heads and chlorine concentrations at the consumer nodes, maximum injection rates at the chlorine injection stations, maximum allowable amounts of water withdraws at the sources, and returning at the end of the operational time horizon to a prescribed total volume in the tanks. The model is demonstrated through an example application.