Synthesis and optimisation of an integrated water and membrane network framework with multiple electrodialysis regenerators

• A water-regeneration network is modelled for synthesis and optimisation purposes.
• Detailed model allows for design of the multi-regenerator subnetwork.
• Recycles, series and parallel regenerator links important for optimal synthesis.
• Setting the removal ratio as a decision variable guarantees better solutions.
• Pulp and paper case study shows a potential 12% reduction in freshwater intake.

The shrinking supplies of freshwater globally, coupled with strict environmental regulations, have driven the manufacturing industry towards sustainable water management for the minimisation of freshwater intake and wastewater generation. By using process integration and its enabling tools, this work considers the synthesis of an optimal water network with multiple regeneration capabilities. Development of the proposed framework is achieved by embedding a subnetwork of detailed electrodialysis models within a water network. Based on a superstructure and fixed flowrate, the optimisation problem is formulated as an MINLP model and solved in GAMS/DICOPT. To demonstrate the applicability of the proposed mathematical model a literature case study on a pulp and paper plant is presented and the results indicate a potential of 12% savings in freshwater intake, 16% reduction in wastewater generated and a 14% saving in the total annualised cost for the entire network.