Environmental and economic consequences of circular systems

Abstract

While economic growth is increasing at global level, there is a growing awareness that the current development is not sustainable and is in fact detrimental to the climate and the environment as a whole. In the last decade, the circular economy and recycling have been promoted as our best chance of decoupling economic growth from resource consumption and at the same time reducing environmental impacts: if resources were repeatedly recirculated throughout society, consumption might not be a problem. Plastic has become the symbol of anthropogenic impacts. This versatile, light and cheap material has succeeded in all industrial sectors but is still characterised by low collection and recycling rates. Widespread attention has fallen on this material especially, due to its low degradability and high durability in the environment. The goal of this PhD thesis was to quantify the environmental and eco-nomic consequences of increasing plastic circularity and to evaluate po-tential measures to support the transition from a linear to a circular so-ciety. Environmental and economic assessments were utilised to evaluate several different future alternatives for plastic: improvements in the waste management system, the implementation of different policies at national and European levels, a reduction in consumption, and the substi-tution with biodegradable and bio-based plastic materials produced from urban biowaste. Three case studies were performed, covering Italian plastic packaging waste, European PET packaging waste and the produc-tion of the biopolymer polyhydroxyalkanoates (PHA) from food waste and sewage sludge. Within this context, this PhD contributed with model-ling approaches for robust and quantitative assessments of impacts caused by either increased or decreased circularity on different regional scales. The results clearly demonstrated that the future of plastic circularity is paved with numerous challenges and several strategies were identified to improve the current situation. First of all, the extended producer respon-sibility (EPR) is a well-established tool to incentivize producers to take responsibility of the waste, i.e. by paying an environmental fee financial-ly supporting the source-separation. However, the first two case studies showed that the environmental and economic savings are solely propor-tional to the quantity of secondary material produced by recyclers and absorbed by manufacturers, and not to the mass of material separated by citizens. EPR systems need to better modulate the economic incentives to minimise the amount of material source-separated by citizens but lost in the different sorting steps (e.g. half of what is source-separated by Italian citizens was calculated to be sorted out in the material recovery facili-ties). Furthermore, the relationship between the environmental fee and product recyclability is also to be strengthen. Indeed, the design and the recyclability of the input products are key factors in the plastic circular economy, which needs to be specifically addressed, even if the growing use of multi-polymeric layers, additives, and adhesives in plastic appears to be going in the opposite direction. Finally, the market response, i.e. how markets react to the increased pro-duction of secondary material, is critical for quantifying current and po-tential market sizes and the risks of market saturation. The market analy-sis and economic results led to two outcomes. First, it identified materials (e.g. low-quality plastics) that may be exported to countries with lower operational costs but poorer plastic waste management, potentially lead-ing to pollution issues for surrounding areas. Second, it identified the weakest stakeholders in the value chain (e.g. soft plastic recyclers in the first case study) that could lead to the implementation of different strate-gies/policies to support them. However, despite the implementation of dramatic changes in product de-sign, recyclability and market conditions, increasing plastic consumption may outbalance these improvements at the societal level. The third case study demonstrated that the environmental impacts associ-ated with plastic cannot be eliminated simply by substituting fossil plastic with bio-based and biodegradable polymer from urban biowaste. The in-vestigated PHA was proven to have lower environmental and economic impacts compared to the fossil polyurethane traditionally used in adhe-sives and sealants, and currently not recycled, but the benefits were not as clear when compared to more common plastics as LDPE. Consequent-ly, investments supporting biorefineries involving urban biowaste should focus on optimising both the PHA extraction and the downstream pro-cesses (e.g. by upgrading biogas or minimising methane leakages), where the majority of environmental hotspots are found. However, the results strongly depended on the local conditions in which the analysis was per-formed. All in all, this PhD work highlights the critical need for a systematic quantification of large-scale changes in the society, reflecting the transi-tion to circular systems, including identifying how systems respond to different market dynamics and policies implementation.