Circulation indices: new tools for analyzing the structure of material cascades

An improved understanding of the cascading structure of recycling is import ant for increasing resource productivity. The cascading theory,:developed t o analyze resource cascading, has two major dimensions; resource quality an d resource lifetime. The latter is the only dimension for which a quantitat ive evaluation has been carried our in the previous research. In this study , we propose new tools to quantify both dimensions. These tools enable stat istical estimation of the times of utilization of the material cascaded. Th e pre-circulation index (pre-CI) counts how many times the material has bee n utilized before consumption. For material in which quality deterioration is measurable largely on the basis of the number of utilization times, pre- CI can be an index of resource quality. The post-circulation index (post-CI ) counts how many times the material will be utilized after consumption. Th e higher the number of utilization times, the longer the lifetime of the ma terial. Thus, post-CI can be an index of resource lifetime. Total-circulati on index (TCI) is the sum of pre- and post-CIs. This can be an overall inde x of resource productivity. We apply the method presented herein to an anal ysis of the paper recycling system in Japan. Some important features of the CIs are demonstrated by the results; certain potential remains for further improvements in paper recycling in Japan. In the case that two products ha ve the same utilization rates, their pre-CIs can still differ according to the positions they occupy in the cascade. In the case that two recycling po licies achieve the same size of primary raw material reduction, they can st ill differ in their impact to the whole cascade. By the method described he rein, the CIs can represent the structure of a material cascade quantitativ ely and offer important knowledge by which to increase resource productivit y. (C) 2000 Elsevier Science B.V. All rights reserved.