Incremental design of water symbiosis networks with prior knowledge: The case of an industrial park in Kenya

Abstract Industrial parks have a high potential for recycling and reusing resources such as water across companies by creating symbiosis networks. In this study, we introduce a mathematical optimization framework for the design of water network integration in industrial parks formulated as a large-scale standard mixed integer non-linear programing (MINLP) problem. The novelty of our approach relies on i) developing a multi-level incremental optimization framework for water network synthesis, ii) including prior knowledge of demand growth and projected water scarcity to evaluate the significance of water saving solutions, iii) incorporating a comprehensive formulation of water network synthesis problem including multiple pollutant and different treatment units and iv) performing a multi-objective optimization of the network including freshwater savings and relative cost of network. The significance of the proposed optimization framework is illustrated by applying it to an existing industrial park in a water scarce region in Kenya. Firstly, we illustrated the benefits of including prior knowledge to prevent an over-design of network at early stages. In the case study, a more flexible and expandable water network with 36% lower unit cost at the early stage and 15% lower unit cost at later stages for the overall maximum fresh water savings of 25%. Secondly, multi-objective analysis suggests an optimum freshwater savings of 14% to reduce the unit cost of network by half. Moreover, the significance of symbiosis networks are highlighted by showing that intra-company connections can only achieve a maximum freshwater savings of 17% with significantly higher unit cost (+45%). Finally, the values of symbiosis connectivity index in the Pareto front correspond to higher freshwater savings, indicating the significant role of symbiosis network in the industrial park under study. This is the first study, where all the above elements have been taken into account simultaneously for the design of a water reuse network.