Integrated Optimization of a Dual Quality Water and Wastewater System

When addressing urban water problems, it is no longer adequate to consider issues of water supply, demand, disposal, and reuse independently. Innovative water management strategies and opportunities for water reuse can only be properly evaluated in the context of their interactions with the broader water system. An integrated linear deterministic optimization model is applied to Beirut, Lebanon, to determine the minimum cost configuration of future water supply, wastewater disposal, and reuse options for a semiarid coastal city. Previous urban water system optimization models considered only a single quality of potable water and were thus unable to demonstrate the cost-effectiveness of reclaimed water among all viable options for water supply. Two innovations of our work include incorporation of the entire anthropogenic water cycle including interconnections between supply, demand, disposal, and reuse and modeling of the suitability of nonpotable and potable qualities of water for each demand sector. The optimization model yields surprising insights. For example, after full use of inexpensive conventional sources, nonpotable direct reuse appears to be Beirut's most cost- effective option for supply of its urban nonpotable and irrigation demands. Our work highlights the importance of modeling the utility of multiple qualities of water in modern water supply planning.