Cost and Sustainability Optimization of Desalinated Water Supply Chains

Abstract

The increasing demand for freshwater along with the diminishing conventional water resources are the major reasons why the demand for desalinated water has been escalating. Given that the desalinated Water Supply Chain (WSC) involves elevated levels of greenhouse gases emissions along with disposal of brine, it is imperative to develop a plan that safeguards the rights of future generations of sustainable production of freshwater. This thesis presents a mathematical model that minimizes the total cost and environmental impact associated with a set of strategic and tactical decisions taken over the planning horizon within the desalinated WSC. In order to validate the model, a case study was conducted in the Emirate of Sharjah, where forecasted water demand, operational data, and costs associated with WSC related decisions were collected from Sharjah Electricity and Water Authority (SEWA) and literature. The mathematical model was coded using GAMS and solved using CPLEX. Results collectively provided the optimal values of strategic and operational decisions over the entire planning horizon. These decisions include replacement of retiring units, installation of new desalination plants, utilized desalination technology, as well as location and expansion of new plants, pipelines, and storage facilities. Moreover, the results included the yearly production level in each plant, allocation of water to the different demand zones, and water levels in storage tanks. The minimum total cost of the model was found to be AED17.637 billion, and it was concluded that operational cost components of desalination, transportation pipelines, and storage facilities are more significant than their capital cost components. In addition, all replaced and new units employed Reverse Osmosis (RO) technology, which is in line with the trend worldwide. Finally, the effect of increasing the capacity of new units and varying the carbon emissions tax on the relevant decisions as well as the overall cost was studied as part of the sensitivity analysis.