Technical and environmental performances of alternative treatments for challenging plastics waste

Abstract

The recovery of resources from streams of mixed plastics waste is a technological and economic challenge since they contain various (and generally non-compatible) polymers, different (and often hazardous) additives, as well as multilayer structures and fiber-reinforced composites. Only a too limited part of these plastics - such as those coming from waste of electric and electronic equipment (WEEE), end-of-life vehicles (ELV) and construction and demolition waste (C&DW) - can be treated by mechanical techniques in the conventional recycling facilities, and a still smaller part is reintroduced into the market. Some innovative treatments have been recently proposed and appear suitable for these challenging waste streams. The paper describes technical characteristics of some of them, and compares their environmental performances with those of currently adopted management options. An environmental life cycle assessment was developed by taking into account the substitutability factor of obtained products and technological readiness level of the analyzed resource recovery processes. The focus is on new treatments of dissolution/precipitation, supercritical fluid extraction, catalytic pyrolysis, and waste-to-energy (WtE) equipped with carbon capture and storage unit (CCS). The results highlight the promising performances of some of these new options, quantify their potential environmental advantages, and suggest to take them into account in the definition of sustainable management schemes for the examined challenging plastics wastes. In particular, physical recycling by dissolution/precipitation process applied to one tonne of WEEE plastics, not treatable by mechanical recycling, can save up to about 2 tCO2,eq. with respect to landfill disposal and WtE with CCS, and more than 3 tCO2,eq. with respect to WtE without CCS. The performances of WtE with CCS appear of interest, particularly for WEEE and ELV mixed plastics, allowing to save up to 0.5 tCO2,eq. and 1.7 tCO2,eq., with respect to pyrolysis and WtE without CCS, respectively.