Intrinsic sustainability assessment at technosphere level by adapting entropy based ecologic indicators. A preliminary analysis for some main waste treatment processes

Abstract

The present study was developed on the following evidence: "what is considered to be environmentally sustainable in the technosphere has to be in compliance with the development tendency of the ecosphere". Starting from this hypothesis, two entropy-based indicators were proposed: the specific entropy per amount of exergy gained (SEEG); the specific entropy per amount of exergy exploitable in the technosphere (SEEE). These were retrieved from the specific entropy (SE) indicator largely exploited for assessing the health status and the development tendency of ecosystems. Entropy based indicators SEEG and SEEE were used for assessing the environmental sustainability of incineration, anaerobic digestion and composting of waste. The aim of these indicators was to support already available methodologies for environmental impact assessment for better understating the intrinsic sustainability of specific processes, since the only quantification of the emission appears not enough informative for this goal. Concerning the ecosphere, SE minimization follows the Darwinian principle "survival of the fittest", being the fittest ecosystems those able to make the most efficient and effective use and storage of energy and materials, at the lower relative entropy generation. Consequently, the lower are SEEG and SEEE the fittest is the analysed system (i.e. sustainable). Main findings indicate SEEG ranging from 2.471 to 3.705, for incinerator, from 0.007 to 0.106 for anaerobic digestion whereas resulted constant = 0.266 for composting. The SEEE ranged from 0.433 to 0.484 for incinerator, from <0.001 to 0.008 for anaerobic digestion and resulted constant = 0.014 for composting. These preliminary results indicates that processes and system able to return chemicals and materials exploitable at technosphere level were characterized by higher ability in returning exergy flows at the lower entropy increase compared to hose returning only energy.

Keywords: Anaerobic digestion; Composting; Entropy-based indicator; Environmental impact; Incineration; Intrinsic sustainability.