Water reuse planning models: Extensions and applications

A water reuse planning model has been developed for determining the optimum allocation of water and reuse of wastewater on a regional basis for multiperiod planning that minimizes the overall cost of water supply. Both water quantity and water quality parameters of various sources of flows are considered. Wastewater from all use sectors, along with freshwater, can be considered as candidate sources or origins of water. The model considers the capacity expansion of treatment facilities and allows for economies of scale in treatment and transportation through the use of nonlinear objective functions. Either the large-scale generalized reduced gradient or the successive linear programing methods can be used to obtain solutions to the models. Both single-period and multiperiod models are applied to a region including San Antonio, Texas. The single-period model was applied to planning scenarios for the years 1980, 2000, and 2030. The multiperiod model was applied using a planning horizon consisting of three periods, 1980–2000, 2000–2030, and 2030–2060. Comparisons were made of the single-period model applications and the multiperiod applications. The solution of a sequence of single-period problems does not correctly represent the dynamic nature of the systems.