Design water-using network with multiple contaminants by step by step linear programming

A rapid method for designing water-using network with multiple contaminants is developed. It first arranges all processes based on their maximum outlet concentration, that is, list the limiting outlet concentration of each contaminant for each process, and mark their serial number by Ni,s (i represents the water-using process, and s the contaminant), calculate the product of serial number of every contaminant in each process and list those processes by the product. For each process on the list, a linear programming model in GAMS (general algebraic modeling system) language is used to determine the minimum freshwater flowrate and reuse wastewater flowrate from its precursor set. Delete the process from the list after its requirement is satisfied and add its wastewater data to the available wastewater set. Repeat the process until the last process on the list has been taken care of. The new method has been tested in two cases. The obtained solutions are at least as good as reported ones. In general, global optimality is not guaranteed by the new method, but it is simple and can be used to rapidly find an optimal or suboptimal solution.