Waste-derived biodiesel shows up to 352% reduction potential

Five feedstocks are lined up in the same accounting system: soy oil, carinata oil, palm oil, used cooking oil and beef tallow. The comparison, led by Boreum Lee and Sanghyuk Koh at Chonnam National University in the Republic of Korea, finds that waste-derived biodiesel has the lowest greenhouse gas emissions, with best-case reduction potential reaching 352% relative to conventional-input production.

The researchers used GREET, a life-cycle assessment framework, to follow emissions from production through the supply chain. Scope 1 covers direct emissions during biodiesel production; Scope 2 covers indirect emissions from energy use; and Scope 3 covers major upstream and downstream processes. For plant-based oils, that includes farming, oil extraction, refining, transport and indirect land-use change. Waste-derived routes instead involve rendering, extraction and refining, without the agricultural and land-use burden.

That difference explains the result. Among plant-based options, carinata oil had the lowest greenhouse gas emissions because it avoids indirect land-use change. But the climate ranking did not translate into a clean-air ranking: carinata oil recorded the highest volatile organic compound and carbon monoxide levels across all the pathways studied. The uncertainty analysis also found wider emission ranges for plant-based fuels than for waste-derived feedstocks.

So what changes in practice? Regions with strong waste-collection systems could prioritize biodiesel made from used cooking oil, while agricultural regions could look more closely at dedicated energy crops. The choice would depend on the local feedstock and supply chain, not on a one-size-fits-all biofuel mandate. Because biodiesel works with existing diesel infrastructure, the study frames these routes as options that could be deployed without extensive modifications while renewable energy capacity expands.

The most striking result remains conditional. Waste-derived pathways could reach net-negative emissions when renewable energy is used in rendering and refining, with reported reductions of 66% to 352% in best-case scenarios. Those numbers come from a GREET-based life-cycle analysis published in Applied Energy, not from an independent test of fuel in vehicles. The framework may also inform future assessments of biofuels for aviation and marine transport, but the study does not establish deployment there.