The ultimate goal - to improve the overall sustainability of industrial processes from an economic, environmental and social point of view - cannot be achieved only through the classical scheme of competition. Indeed, the cooperating management of resources (including energy, waste and by-products) and the consequential integration of processing activities, by means of a nature-inspired industrial symbiosis, has to become a major driver in the transition to truly sustainable process industries. Many motivations exist for pursuing this type of industrial symbiosis, either directly or indirectly as a result of trying to meet other objectives.

Industrial clusters are groups of inter-related industries that drive wealth creation in a region, primarily through export of goods and services, while Industrial Symbiosis (IS) can be considered a way to handle activities among companies in the same Industrial cluster. Inside decisions are related to the single plant and they can be related to the single Production Units (PUs) within each plant. These decisions are optimized respect to own KPIs. We deny the PUs as the atomic decision units within an industrial cluster and we treat each of them as a single decision maker. Indeed, when dealing with a symbiotic cluster, the moment we have to take some decisions we have also to consider what is happening at cluster level. For this reason, we can introduce the concept of outside decisions. They are optimized respect to cluster-level KPIs, which in turn have a twofold purpose: from one side they have to increase the wealth related to a symbiotic approach at cluster level, on the other to maintain the single PU decision autonomy.

We introduce the concept of cluster coordinator, namely an organization that coordinates the cluster. This can be a physical organization or, more easily, a virtual platform, and this depends on the working context as well. At Company-level, each Industry performs its Supply Chain Optimization (SCO) to gain a high efficiency at operative level optimizing its short-term and long-term decisions. These decisions do not take into account any of the decisions of the other industries in the cluster or, in other words, are completely independent. To govern the whole cluster performance we introduce the Cluster-level optimization, whose aim is the increasing of the global cluster efficiency.