Potential trade-offs between eliminating plastics and mitigating climate change: An LCA perspective on Polyethylene Terephthalate (PET) bottles in Cornwall

Highlights

• New model to assess environmental impacts of PET bottles substitution from glass

• PET bottle substitution with glass could potentially increase carbon footprint case.

• Glass bottles need to be 3 times lighter to secure lower carbon footprint with PET.

Abstract

The aim of this study is to investigate whether eliminating plastics entirely under existing waste infrastructure and management practices could have an adverse effect on climate change, using a case study on the hypothetical substitution of Polyethylene Terephthalate (PET) with glass as the material for bottling liquids in the domestic sector in Cornwall, England. A life cycle environmental impacts-based model was created using high resolution local data on household waste and current management practices in combination with Life Cycle Assessment (LCA) datasets. The model allows users to define key system parameters such as masses of materials, transport options and end-of-life processes and produces results for 11 environmental impact categories including the Global Warming Potential (GWP). The results from the application of this model on the case study of Cornwall have shown that the substitution of PET with glass as the material for bottling under the current waste infrastructure and management practices could lead to significant increases in GWP and hinder efforts to tackle climate change. A sensitivity analysis of the glass/PET mass ratio suggests that in order to achieve equal GWP the glass bottles need to become approximately 38% of the weight they are now. Increasing the recycled content and decreasing losses during the recycling processes could also help lower the GWP by 18.9% and 14.5%, respectively. This model can be expanded further to include more types of plastics and other regions to evaluate designs of new regional circular economy with less plastics waste and pollution. Our study suggests that it is necessary and crucial to consider the specific waste infrastructure and management practices in place and use science-based models that incorporate life cycle thinking to evaluate any solutions to plastics pollution in order to avoid problem shifting.

Introduction

Plastic products play a major role in our modern society due to their many useful attributes such as durability, lightweight, flexibility, electrical and thermal insulation, water and air impermeability and low costs. It is projected that following the same use patterns, 12,000 million t of plastic waste will have been discarded in landfills or the natural environment by 2050, which is more than double the estimated 5800 million t of plastic waste ever generated from virgin sources up to 2015 (Geyer et al., 2017). Therefore, it is necessary to develop a circular economy approach to plastics that addresses the accumulation, impact and costs in the environment without compromising their use for multiple high value purposes.

In recent years, there are a growing number of local community-led “plastics free” initiatives in the UK, particularly the South West of England. One of the most obvious and practical options for these initiatives is to substitute plastics with other materials. However, whether efforts to eliminate plastics by material substitution can lead to negative impacts on other key environmental goals such as mitigating climate change needs to be carefully evaluated as it depends on a wide range of factors.

Polyethylene Terephthalate (PET) is a type of plastics widely used in packaging, particularly for non-alcoholic drinks, and can be easily eliminated and substituted by other established alternatives such as glass. However, several context specific factors can influence the climate impact of substituting PET with glass as a packaging material for drinks. On one hand, glass is much heavier than PET and higher energy consumption for transportation and production is expected. On the other hand, recycling rates for glass are usually higher than those for plastics, which are affected by consumer recycling behaviours as well as local waste infrastructure and management practices.

Studies comparing PET, glass and aluminium as bottling materials exist in the literature. For example, Romero-Hernández et al. (2009) have looked into this as part of their environmental implications and market analysis of soft drink packaging systems in Mexico using a waste management approach. However, their study was at a national level with little spatial granularity. In addition, the end of life options they considered included recycling and landfill but not incineration. Other studies investigated specific applications of glass containers including, e.g., a comparison between compared glass jars and plastic pots for baby food packaging (Humbert et al., 2009), an analysis of the impacts of glass and PET for extra virgin olive oil packaging (Accorsi et al., 2015) and a report on the carbon impact of bottling Australian wine in the UK using PET and glass bottles (Best Foot Forward Ltd for Wrap, 2008). The most recent and comprehensive study was carried out by Simon et al. (2016) who assessed the life cycle impacts of different beverage packaging materials and focused on the collection of post-consumer bottles. They examined five different packaging materials during their whole lifecycle and six bottle collection systems such as kerbside bin, kerbside bag, deposit-refund, combinations with thermal compression of plastic bottles and refill-bottles. However, their study was based on a generic hypothetical case study that did not reflect actual amounts of different types of waste generated and the actual amounts of waste treated in different ways. Overall, these existing studies tend to neglect local context in terms of volumes and types of waste, management practices and infrastructure and consumer recycling behaviour.

This study aims to assess the climate change impact resulting from the potential substitution of PET by glass as the packaging material for drinks using high resolution data on consumer waste disposal behaviour, waste infrastructure and current waste management practices. Life Cycle Assessment (LCA) is used to calculate a wide range of environmental impacts including Global Warming Potential (GWP), an indicator for climate change impact. The English county Cornwall is used as the case region given that it hosts many plastic-free initiatives (including the first plastic-free town in the UK) and mitigating climate change is a top priority in its environmental agenda (Cornwall Council, 2019). Our study will be crucial in informing sustainable material substitution in the rising plastic-free movements as consumer waste disposal behaviour and waste infrastructure and management can vary regionally and locally and waste contracts can last for many years or even decades.