Optimization of Integrated Water and Wastewater Systems: Case Study of Beirut, Lebanon

Abstract

The water problems of the Middle East and other similarly arid regions are not isolated within any given segment of the water cycle, nor is it efficient to consider the challenges of water supply, demand, disposal and reuse independently. This paper presents an integrated linear, deterministic optimization model developed to determine the minimum cost configuration of future water supply, wastewater disposal, and reuse options for Beirut, Lebanon. To the best of our knowledge, this is the first study to demonstrate an optimization model of the entire anthropogenic water cycle. The model includes interconnections between supply, demand, disposal and reuse, thereby minimizing the cost of both water supply and wastewater disposal simultaneously. By distinguishing between potable and nonpotable demands and permitting the supply of a lower grade of water to some demands, our results reveal new opportunities for cost- reductions in Beirut's water system. After use of inexpensive conventional sources, reclamation and reuse are shown to be more cost-effective than desalination to provide nonpotable water for toilet flushing, lawn watering and irrigation. Furthermore, if nonpotable aquifer recharge were permitted, reclaimed water from the centralized wastewater treatment plant could be used to augment Greater Beirut's coastal aquifer, which in turn could supply increased quantities of both potable and nonpotable water to the urban sectors. 1. Introduction Greater Beirut currently experiences water shortages in the dry season, and the next twenty-five years are expected to bring increases in population, economic development, tourism and the adverse effects of climate change, all of which are likely to further stress the water system. Beirut is actively seeking solutions to its escalating water supply and demand concerns. Among its most promising options are: 1) reduction of distribution system losses, 2) demand management, 3) acquisition of new water sources, and 4) adoption of alternative water-supply technologies such as desalination or water reuse. At the same time, it is striving to improve its wastewater management, which as of now is gravely inadequate. Beirut's plans to improve its water and wastewater infrastructure by repairing leaking pipes and repossessing illicit connections are outside of the scope of this study, and the anticipated improvements are included in the model framework as adjustable parameters (CDR, 2004).