From Waste to Fuel: Life Cycle Assessment of Utilising Used Railroad Ties through Carbonisation

Abstract

Creosote-treated railroad ties represent a hazardous biomass waste stream with significant environmental and disposal challenges. In the United States, these chemically treated wood products are commonly reused, landfilled, or combusted, practices with well-documented toxicological risks that persist due to regulatory gaps and economic convenience. This thesis investigates a sustainable alternative: converting these used railroad ties into biocoal through high-temperature carbonisation, aiming to substitute fossil coal in the Dutch steel industry. Using an attributional life cycle assessment, the study models a transatlantic supply chain from feedstock collection in South Carolina to fuel delivery in the Netherlands. Three scenarios addressing surplus electricity generation during carbonisation are evaluated: a baseline with no co-product credit, allocation based on energy content, and system expansion with local grid electricity substitution. Additionally, a qualitative analysis compares the environmental implications of carbonisation with conventional disposal methods in the United States. Results indicate that biocoal substantially outperforms fossil coal across key impact categories, including climate change, water consumption, and ecotoxicity, particularly when surplus energy is effectively utilised. Under the system expansion scenario, net-negative emissions are achievable, highlighting significant climate mitigation potential. Remaining environmental impacts predominantly arise from long-distance transport, suggesting opportunities for further improvements as transportation becomes decarbonised. Given the carbon-neutral end-use combustion of biocoal, the proposed supply chain offers potential for near-zero or negative emissions if integrated with carbon capture technologies. Despite these promising results, the study faced constraints from limited stakeholder input and data availability, restricting the quantification of toxicological impacts and detailed real-world variability in process operations. Nonetheless, the findings strongly support the environmental and circular economy benefits of converting creosote-treated wood into biocoal. Future research should prioritise empirical measurements of toxic flows, detailed techno-economic analyses,