Waste management approaches for net zero – Sustainability assessment of different thermochemical pathways in the UK

This thesis examines the environmental performance of advanced thermochemical technologies for plastic waste treatment through a comprehensive life cycle assessment framework. As the global plastic crisis intensifies amid rising consumption and inadequate disposal methods, there is a need to evaluate emerging solutions that can transform non-recyclable plastic waste into valuable resources whilst minimising environmental impacts. The research assesses three distinct thermochemical pathways: waste-to-energy with carbon capture and storage, waste gasification for hydrogen production, and small-scale pyrolysis with in-situ hydrogenation for naphtha production. Employing a comprehensive Life Cycle Assessment (LCA) methodology based on ISO 14040/14044 standards, this research explores various functional units, system boundaries, allocation methods, and datasets. This multifaceted approach unveils the complex narratives surrounding the potential deployment of these technologies and their environmental implications. Findings reveal that waste gasification for hydrogen production potentially offers the most substantial climate change mitigation benefits compared to conventional waste-to-energy, though these benefits are strongly predicated on the approach used to account for produced hydrogen and its market substitution. Furthermore, this pathway exhibits significant environmental trade-offs in other impact categories. Waste-to-energy with carbon capture demonstrated moderate but consistent improvements across impact categories, whilst chemical recycling via pyrolysis showed strength in resource conservation. Environmental performance for all technologies proved highly sensitive to feedstock composition, with biogenic carbon content (typically low in waste plastics) playing a decisive role in determining potential for negative emissions. As emerging technologies, all pathways face implementation challenges including technical optimisation, infrastructure integration, and scalability considerations. This thesis contributes to more informed decision-making regarding emerging waste treatment technologies by quantifying their environmental implications and illuminating performance trade-offs. These insights can guide technology developers, waste management stakeholders, and policymakers in optimising thermal treatment strategies for non-recyclable plastic waste within evolving waste and energy systems.