METHODS, TOOLS, AND SOFTWARE Industrial Waste Reuse and By-product Synergy Optimization Martin Maill´ e and Jean-Marc Frayret Summary By-product synergy is a growing practice worldwide. It consists in the maximization of resources utilization with the replacement of raw materials by by-products as inputs for industrial processes. In order to support decision making in such strategic projects, ap- propriate tools must be developed. This article presents the results of a research project, which includes the development of a multiobjective mathematical programming model for the optimization of by-product flows, synergy configurations, and investment decisions in eco-industrial networks. This model is evaluated using data related to the Kalundborg industrial symbiosis (IS) in order to illustrate its utilization, as well as to assess, in a retro- spective manner, the behavior of the companies involved with respect to both economic and environmental benefits of synergies. The experiments also illustrate the influence of the municipality on synergy implementation and how a scenario-based approach can be used to anticipate raw material price increase. The results are generally coherent with the actual timing of synergy initializations. Further, the considerable effect of water price on the length of investments’ payback period illustrates the impact of policies and regulations on IS. Keywords: by-product synergy eco-industrial park (EIP) industrial ecology industrial symbiosis (IS) Kalundborg, Denmark multiobjective decision making Supporting information is available on the JIE Web site Introduction Industrial symbiosis (IS) is a key concept of industrial ecol- ogy (IE) that aims to promote exchanges of by-product in the form of effluents, energy, and solid waste. ISs are by-product syn- ergy networks, which consist in business relationships between companies, in order to optimize resources utilization through in- dustrial waste utilization and resource sharing. Such networks can occur in a self-organized manner, although independent network facilitators can also play a critical role in the success of ISs (Kincaid and Overcash 2001). This article presents a multiperiod, multiobjective mathe- matical programming model, which can be used in different contexts. First, it aims to support the development of IS by identifying optimal industrial by-product and waste reuse in a network of potential partnerships. In particular, the proposed Address correspondence to: Jean-Marc Frayret, ´ Ecole Polytechnique de Montr´ eal, C.P. 6079, succ. Centre-ville, Montr´ eal, Qu´ ebec, Canada H3C 3A7. Email: jean- marc.frayret@polymtl.ca © 2016 by Yale University DOI: 10.1111/jiec.12403 Editor managing review: Olli Salmi Volume 00, Number 0 model takes into account synergy configuration, inventory lo- cation, as well as waste transformation and treatment technol- ogy. Consequently, it can be used either by a network facilita- tor to develop an efficient IS or by a single company to plan the strategic development and configuration of its symbiotic relationships. Next, because it is multiperiod, it can also take into account any trends of parameters (e.g., resource price increase) and analyze their impacts on synergy configuration. Similarly, its multiobjective version can also be used to analyze the trade-off between environmental and economic benefits of by-product synergies. Indeed, studies have shown that even if the first motivation behind eco-industrial projects seems to be the preservation of natural resources and the improvement of waste management strategies, economic feasibility is essential www.wileyonlinelibrary.com/journal/jie Journal of Industrial Ecology 1