Profit-based grassroots design and retrofit of water networks in process plants

In this paper, we present a methodology for the grassroots design and/or retrofit of water utilization systems using mathematical optimization to maximize net present value (NPV) and/or return of investment (ROI) instead of minimizing freshwater consumption. The examples show that the solutions where savings and/or profit are maximized can be different from those where freshwater is minimized. They also differ from each other when ROI or NPV are used. In addition, when the NPV objective is used, the optimum solutions also vary depending on the interest rate used to calculate the discount factor.