Transforming Waste Into a Climate Service (TWICS): A Comparative Assessment of Energy-from-Waste with CCS and Waste-derived Sustainable Aviation Fuels (Flexible Funding 2024)

Professor Mathieu Lucquiaud, University of Sheffield, was awarded funding in the UKCCSRC’s Flexible Funding 2024 call to look at “Transforming Waste Into a Climate Service (TWICS): A Comparative Assessment of Energy-from-Waste with CCS and Waste-derived Sustainable Aviation Fuels”.

Executive Summary

Municipal solid waste (MSW) is emerging as a contested climate mitigation tool, subject to competing claims from sectors pursuing decarbonisation under resource constraints. In the UK, MSW is targeted both for carbon dioxide removal via energy-from-waste (EfW) with carbon capture and storage (CCS) and as a feedstock for producing sustainable aviation fuel (SAF). These pathways are not complementary, each tonne of waste directed to one excludes its use in the other, yet current policy frameworks incentivise them in isolation without internalising the opportunity cost of allocation.

This study compares the climate performance of EfW with CCS and MSW-to-SAF using a consequential life cycle assessment framework aligned with ISO 14044. The aim is to inform climate-optimal waste allocation by quantifying the system-level greenhouse gas (GHG) implications of each route. Both pathways deliver net-negative emissions under baseline assumptions, but the mechanisms and sensitivities differ. EfW with CCS derives its benefit primarily from permanent biogenic carbon removal, while the SAF route relies solely on upstream fossil fuel displacement and material recovery credits.

The analysis shows that EfW with CCS generally provides the greater GHG benefit per tonne of MSW, achieving up to −1215 kg CO2-eq. in the base case and remaining net-negative (−610 kg CO2-eq.) even under conservative assumptions that exclude all credits from avoided burdens. In contrast, SAF delivers a smaller but notable benefit of up to −700 kg CO2-eq.

A sensitivity analysis on the biogenic carbon fraction of waste reveals a break-even point at 5%, below which SAF would become the more climate-effective option, compared to 50-70% biogenic carbon fraction in most post-residual waste feedstock. The findings raise questions about the traditional waste hierarchy, which prioritises material recovery over energy recovery without accounting for the permanence of emissions removal. In a carbon-constrained future, recognising the distinct value of durable carbon dioxide removal (CDR) alongside circular material flows will be essential to coherent and climate-credible waste allocation strategies.

Introduction

The UK faces a strategic challenge in determining how best to utilise residual MSW in pursuit of net-zero climate goals. Historically destined for landfill or incineration, residual waste is now being re-evaluated as a potentially high-leverage resource for carbon mitigation. Its biogenic fraction, arising largely from paper, food, garden, and other organic waste, enables certifiable CDR if captured and permanently stored. This has brought EfW with CCS into sharper focus, particularly as the UK seeks to scale industrial decarbonisation and meet its climate commitments.

Yet EfW is not the only climate-oriented use of residual waste. UK Government policy is actively stimulating the production of waste-derived SAF through the Renewable Transport Fuel Obligation (RTFO). SAF displaces fossil derived aviation fuel, e.g. Jet-A the most common fuel for jet aircraft, in a hard-to-abate sector but emits its carbon at point of use.

Objectives of TWICS

The Transforming Waste Into a Climate Service (TWICS) project seeks to clarify the climate-optimal use of residual municipal solid waste in a policy landscape increasingly characterised by competition, trade-offs, and conflicting incentives. Specifically, the project addresses the unresolved question of whether the UK should prioritise CDR via EfW with CCS, or fossil fuel displacement via the production of waste-derived SAF.

The project objectives are:

• Quantify and compare the global warming potential (GWP), avoided emissions, and CDR potential of two divergent waste-to-energy pathways in the UK context: EfW with CCS and MSW-to-SAF.
• Model both systems using a harmonised approach in terms of: system boundary, LCA typology, and functional unit.
• Assess implications for key policy domains, including: CCUS cluster deployment strategy, SAF mandates and subsidies, and long-term waste resource governance
• Provide evidence to guide decisions on where to direct residual waste.

Research Questions

1. Which pathway delivers greater climate benefit per tonne of residual MSW in the UK context: EfW with CCS or waste-derived SAF?
2. How sensitive are the comparative outcomes to key system parameters and assumptions (e.g. biogenic carbon content)?
3. What could implications be for UK policy in terms of waste allocation, climate strategy, and alignment with the waste hierarchy?

Methodology

To address these questions, TWICS utilises the ISO 14040 and ISO 14044 standards for LCA. The methodology is designed to isolate the net climate implications of diverting waste to either pathway, accounting for both direct and system-level impacts. The study follows the principles and requirements set out in ISO 14040 and ISO 14044, adopting a cradle-to-gate consequential life cycle assessment (LCA) framework to compare two alternative uses of MSW in the UK:

• EfW with CCS
• SAF production via a waste-to-ethanol-to-jet pathway (MSW-to-EtOH-to-SAF)

A consequential LCA approach is necessary to estimate the environmental effects of diverting residual waste to energy-from-waste with CCS versus SAF production and model systemic changes and capturing knock-on impacts across systems such as avoided emissions.

Key Results

Figure 1 – Global Warming Potential of Energy from Waste with CCS, including avoided landfill

Figure 2: Global Warming Potential of Energy from Waste with CCS, excluding avoided landfill

Figure 3 – Global Warming Potential of Municipal Solid Waste-to-Sustainable Aviation Fuel, including avoided landfill

Figure 4 – Global Warming Potential of Municipal Solid Waste-to-Sustainable Aviation Fuel, excluding avoided landfill

Conclusion

A consequential life cycle assessment framework shows that both waste pathways deliver net-negative greenhouse gas emissions but differ substantially in the structure, durability, and sensitivity of their mitigation benefits.

EfW with CCS emerges as the stronger performer in absolute terms, delivering up to −1215 kg CO₂-eq. per tonne MSW with avoided landfill credited, and remaining net-negative (−610 kg CO₂-eq.) even under conservative assumptions excluding all avoided burden credits. Its climate benefit is dominated by permanent carbon dioxide removal from the biogenic fraction of waste. By contrast, the SAF pathway’s benefit is distributed across material and energy displacement, and is inherently more sensitive to system expansion assumptions and upstream burdens.

The TWICS framework highlights the importance of evaluating waste valorisation with careful consideration of climate potential. A coordinated approach is needed for residual MSW, as a strategic climate resource. This approach must evaluate allocation based on system-wide mitigation effectiveness and the permanence of climate benefit.

Read more on Mathieu’s Flexible Funding 2024 project page.