(728e) Property-Based Optimization of Direct-Recycle Networks and Wastewater Treatment Processes

This paper presents a mathematical programming model to simultaneously optimize a recycle-reuse network together with a wastewater treatment process. Property-based constraints are used to characterize process and environmental requirements. The model is based on disjunctive programming, and considers the technologies that are commonly used to treat wastewater streams so that they meet environmental regulations. In addition to standard mass balance and composition constraints, the model incorporates environmental constraint properties such as toxicity, theoretical oxygen demand, pH, color, and odor. The problem results in a MINLP model, and is used to minimize the total annual cost of the system, which includes the cost for the fresh sources, the piping cost for the mass integration and the wastewater treatment cost. The model is formulated with linear relationships in the disjunctions to avoid numerical complications. The solution of the proposed model shows that the simultaneous consideration of the mass integration and wastewater treatment sections yields important economic savings with respect to the solution that considers the mass integration first and then takes into account the wastewater treatment facilities. Also, the simultaneous optimization can yield solutions that require more consumption of the cleaner fresh sources than the one provided with the optimization of the direct-recycle network alone, and the overall integration results in a lower total annual cost. The model did not show any numerical problems, and the CPU time required for the solution of the numerical examples was relatively small.