Performance measures of industrial symbiosis with inventory

Industrial symbiosis is a production practice that can mitigate the environmental impacts of production processes while generating economic benefits. However, the produced and used waste flows are usually unsynchronized and unbalanced, and depend on the main output demands of the production processes involved in the industrial symbiotic exchanges. Waste inventory can increase the environmental and economic effectiveness of this industrial practice. In this paper, we analyze the role of inventory under purely stochastic waste flows, which are assumed to be the worst cases of synchronization. Technical and economic models for a simple industrial symbiotic relationship and network are proposed, viewing inventory as a M/M/1/K queueing system. Then, environmental and economic performance measures, expressed in the closed form, are obtained, which permit us to answer research questions regarding the environmental and economic benefits and the optimal size of inventory for both industrial symbiotic relationships and networks, as well as to determine the best inventory location option for the network. Results from numerical case examples based on the end-of-life tire case show that the environmental performance measures always improve when the inventory increases. On the contrary, the optimal size of the inventory is affected by the environment- and inventory-related costs. As the waste production and use rates become more balanced, the economic benefit and inventory effectiveness increase. In the network, the optimal inventory location is affected by how the waste flows are designed and balanced for each specific relationship in the network. The limitations of this work and further research areas are indicated.