Bi-objective optimization of a water network via benchmarking

This paper presents an approach to water system retrofitting by estimating both the economic and environmental impacts of a water network structure, using bi-objective optimization. The environmental impact is evaluated via benchmarking. By using benchmarking, the decision maker can have an insight, not only into the environmental impacts of certain designs belonging to Pareto optimal solutions, but also into the competitiveness of the design within a particular production sector. The economic criterion used is the total cost of the water network involving the freshwater cost, wastewater treatment cost, and the annual investment costs of storage tank, piping, and local treatment unit installation. A mixed-integer nonlinear programming (MINLP) model is used for water re-use and regeneration re-use within batch and semi-continuous processes. The Pareto fronts are generated using the classic and adaptive weighted-sum methods. The proposed approach was applied to an industrial case study within a brewery. The results obtained show that the benchmark could not be reached by process integration within the packaging area, therefore investment is needed regarding new technologies that lower freshwater consumption. Within the production area, however, the freshwater consumption could be reduced below the benchmark by water re-use and regeneration re-use, meaning that the brewery could achieve better performance than its competitors.