Session 6

Statistical entropy quantifies resource efficiency: Case study on phosphorus use in Austria
Helmut Rechberger, David Laner, Ottavia Zoboli
Technische Universität Wien, Austria

The turnover of materials of an economy has been described as the consumption of raw materials (low-entropy) that are used and transformed into products and wastes (high entropy). Thus, the economy can be viewed as an entropy-producing process. In a circular economy, entropy generation must be kept low. Generated wastes should be transformed into low-entropy recycled products that can reduce the use of primary resources. Entropy reduction is achieved by the concentration of materials or by avoiding dissipation/dilution. Hence, efficient resource use aims at minimizing dissipation/dilution of a substance during its use. The ability of a material flow system to concentrate or dilute a substance can be assessed by statistical entropy analysis (SEA).
The goal of the presented study was to use SEA to evaluate the resource efficiency of a complex system exemplified by phosphorus (P) use in Austria. The efficiency of P use in Austria is evaluated from two perspectives: Firstly, P utilization is assessed for two different years (2000 and 2010) to explore the ability of SEA to reflect temporal changes. Secondly, optimized P management on the national level is assessed by applying SEA to a desired state of the system (=target system), which could be achieved by implementing specific measures aimed at reducing consumption, increasing recycling, and lowering emissions.
The results show, that the entropy approach improves our understanding of industrial metabolism and is a useful decision support and design tool, since the resource efficiency of complex systems is thereby characterized by a single metric per substance. In all the cases, the entropy of P use increases from crop farming to the end-of-life phase. However, the target system exhibits a nearly horizontal entropy trend, which indicates that P dissipation is minimized and P is substantially recovered from various residues in the system.