Measuring material cycling in industrial systems

Abstract

As the negative environmental implications of a modern industrial economy have begun to be recognized, a growing comprehension of the key role of material flows in industrial systems has developed. To this end, several indices characterizing material cycling have been developed. Current indices of material cycling for industrial systems, however, do not effectively measure cycling due to the lack of consideration of both direct and indirect flows in a system. A physical flow modeling approach from ecology, input–output flow analysis, is used in this study to develop cycling indices to address the limited scope of existing measures. The input–output cycling metrics measure the percent of both direct and indirect flows in a system or in a particular process that are cycled. Including the effects of indirect flows is particularly important because their role (relative to direct flows) grows as cycling increases. The input–output cycling indices are compared to traditional industrial cycling metrics in this paper with a set of hypothetical cases. From these comparisons, the input–output cycling metrics are shown to measure cycling of both direct and indirect flows in complex systems while traditional metrics are shown to only account for direct flows.