(515g) The Use of Life Cycle Assessment to Identify Sustainability Characteristics of Plastic Recycling Systems: A Review

The extensive use of plastics in a “take, make and dispose” order is putting a strain on our environment. Conventional end-of-life treatments of plastics diminishes the potential of waste plastics to extract the maximum value from it through recycle or upcycle. Life cycle assessment (LCA) is an established tool to evaluate technologies of their environmental footprints. A standardized LCA framework enables comparison between technologies and guide the path forward. We have critically reviewed 33 research articles and scientific reports of published LCAs with a view to present an extensive state of the art of the current chemical recycling processes involved in the plastics circular economy system along with their economic and environmental impacts. The overarching goal is to compare environmental implications of technologies for waste to fuel/monomer pathways (such as pyrolysis, and/or gasification) with that of the conventional waste plastic conversion technologies such as incineration and/or landfilling. An array of different waste feedstocks (e.g., both high- and low-density polyethylene, polystyrene, and polyethylene terephthalate) with or without contaminants were analyzed. In the process, the results obtained imply large uncertainties, for example, one study showed mixed plastic incineration was a better option than gasification-pyrolysis due to lower greenhouse gas (GHG) emissions whereas a large number of other studies favored gasification and pyrolysis over incineration due to lower emissions. This work also aims to develop systematic guidance for researchers and practitioners to use LCA to inform decision-making, design, and optimization of recycling pathways and infrastructure, and to support the development of new technologies to advance the plastics circular economy.

Currently, the availability of life cycle inventory (LCI) data remains a major problem. Previous studies usually apply static data inputs (such as using Ecoinvent inventory which is mostly for European data when conducting LCA for US based scenarios), despite the large variations stemming from assumptions of capacity, process design decisions, unit operation performance, etc. To address this gap, lab-scale results coupled with systems design and scale-up must be integrated with LCA. There’s also a clear need to provide transparent characterization of uncertainty and the sensitivity of results in modeling environmental impacts of plastic recycling systems, but this is yet to become standard practice in the field, only 15% of the total papers include both sensitivity and uncertainty analysis. Furthermore, use of different impact assessment (IA) methods may present variability in the result due to differences in characterization factors across IA methods under the same impact category. For co-products handling, System expansion is most used in the reviewed papers, with the need to examine how different co-product allocation methods can impact environmental implications. Finally, while addition of TEA strengthens the feasibility of newer technologies in plastic upcycling, very few studies have incorporated both techno-economic analysis (TEA) and LCA together. To elucidate the sustainability implications of technologies via comparative systems analysis, a unified LCA framework is required along with quantifying the technical and economic implications of the system via TEA. Addressing these gaps will help practitioners to make informed and justified methodological decisions on the current upcycling technologies.