Water Network Optimization in a Paper Mill Based on a New Library of Mathematical Models I. Lizarralde*, F.Claeys**, R. Ordóñez***, M. de Gracia****, L. Sancho* and P. Grau* * Department of Environmental Engineering, CEIT, Paseo Manuel Lardizábal 15, 20018 Donostia, Spain (E-mail:ilizarralde@ceit.es; lsancho@ceit.es; pgrau@ceit.es) ** MOSTforWATER, Sint-Sebastiaanslaan 3a, B-8500 Kortrijk, Belgium (E-mail: fc@mostforwater.com) *** Department of Chemical Engineering, F. of Chemistry. University Complutense of Madrid. Av. Complutense s/n. Madrid 28040, Spain. (E-mail: rordonez@quim.ucm.es) **** ATM (Grupo Praxair), Epele Bailara, 29, 20120 Hernani, Spain. (E-mail: mdegracia@Praxair.com) Abstract The rising costs associated with the water supply and disposal of wastewater have motivated industries to seek more efficient water management approaches. Mathematical modelling and simulation of an industrial water network can be a very valuable tool for handling with the study of the multiple alternatives available and assessing optimum solutions for water management. This work introduces a new steady state model library able to reproduce industrial water circuits. It has been implemented in a novel software framework WQMT for the representation, simulation and optimization of industrial water networks. As an example of application, water circuit representing a paper mill has been modelled and simulated showing the capability of the models to reproduce real case studies. Different alternative scenarios of the water network have been also reproduced to assess the capability of the models to serve as additional tool for water circuits’ optimization in terms of minimizing water consumption and reducing the total exploitation cost. Keywords mathematical modelling; paper industry; water reuse INTRODUCTION In major water-consuming industries such as paper, food and textile it is often noted that water is used in a less than efficient manner. In recent years, the rising costs associated with the water supply and disposal of industrial wastewater have motivated industries to seek more efficient water management approaches. The availability of alternative water sources such as reclaimed municipal wastewater or recycled process water can encourage more efficient water use practices that translate into significant cost savings for many industries (P. Lens et al., 2002). Finding optimum solutions for reusing water in a water circuit is not a straightforward task since there is a high number of advanced wastewater treatment technologies present in the market and multiple choices for reusing water within a mill. Many alternatives can be assessed considering the specific water quality required at different points of the water circuit. In this context, mathematical modelling and simulation can be a very valuable tool for assessing optimum solutions taking into account economical costs and environmental impacts. Based on this, one of the goals of the AquaFitForUse project (www.aquafit4use.eu) is the development of mathematical models and simulation tools that allow the industrial users to explore different water reuse options in their mills. Those tools could be a valuable support to find optimum solutions for their water networks taking into account aspects such as the quantity and quality of water required at each point of the water circuit, operational costs related to water consumption, energetic requirements or environmental impact. Thus, on the scope of this project, a new software tool, named Water Quality Management Tool (WQMT), is currently being developed for the representation, simulation and optimization of water networks in paper, food, textile and chemical industrial sectors (Claeys et al., 2011).