Abstract
The syntheses of water network systems are usually performed by minimizing the total annual cost. In this contribution, Mixed Integer Nonlinear Programming (MINLP) syntheses of water networks are performed by using various economic objectives, in order to investigate their effects on the structural, environmental, and economic characteristics of optimal water networks. Batch-semicontinuous and isothermal continuous water networks were analyzed during this study. Significant differences between optimal networks were obtained when using different economic objectives. Minimization of freshwater costs produced highly integrated designs with high levels of water reuse, regeneration reuse or recycling, but low profitability. In contrast, maximization of the internal rate of return resulted in highly profitable designs with low investment and a low level of water integration. Either minimization of the total annual cost, maximization of the net present value, or maximization of the annual profit produced designs with intermediate or high levels of integration between water using operations, and modest profitability. These criteria produced compromise solutions with proper trade-offs between the profitabilities and sustainabilities of water network designs.
