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Biodiesel’s environmental impact depends on what it is made from and how it is produced. A 2026 study in Applied Energy modeled five feedstock pathways and found baseline greenhouse-gas (GHG) emissions of 11.90–32.15 g-CO₂eq per megajoule of biodiesel. Waste-derived feedstocks had the lowest modeled GHG emissions; among the plant-based options, carinata was lowest. But the study also found that a lower climate impact does not necessarily mean lower emissions of every air pollutant.
How sustainable is biodiesel?
There is no single sustainability result for biodiesel. In the study, the ranking depended on feedstock and production pathway, and the answer also changed depending on whether the measure was GHG emissions alone or a wider set of air pollutants. The authors compared soy oil, carinata oil, palm oil, used cooking oil (UCO), and beef tallow using a harmonized, GREET-based Well-to-Tank life-cycle assessment. The publisher describes the study’s methods and baseline range in its Applied Energy abstract.
Well-to-Tank means the analysis assessed stages involved in producing and supplying the fuel, rather than directly measuring emissions from commercial vehicles using it. The results are therefore model-based comparisons under the study’s assumptions—not universal values for every plant, sourcing region, or use case.
Which feedstocks had lower modeled life-cycle GHG emissions?
Across the five pathways, the study reported baseline emissions of 11.90–32.15 g-CO₂eq/MJ-biodiesel. The university’s summary says waste-derived UCO and beef-tallow pathways had the lowest modeled GHG emissions. Among plant-based pathways, carinata had the lowest result, which the summary attributes to avoiding indirect land-use change emissions.
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The assessment accounted for Scope 1, 2, and 3 emissions. In the university’s account, farming in Scope 3 was the largest GHG contributor for plant-based pathways. For waste-derived pathways, Scope 1 production emissions together with Scope 3 refining emissions dominated. These stage contributions help explain why feedstock choice alone does not determine the outcome: processing and upstream inputs matter too. See Chonnam National University’s study summary.
What did the assessment include—and leave outside its boundary?
For plant-based pathways, the university summary lists farming, extraction, refining, transportation, and indirect land-use change. For waste-derived pathways, it lists rendering, extraction, and refining. The summary also says overseas imports and long-distance international transport were excluded for waste feedstocks. That qualification matters when applying these results to imported UCO or tallow: the modeled waste pathways do not establish the full impact of every international supply chain.
The study compares five selected pathways under a harmonized framework; it does not represent every biodiesel feedstock, production configuration, geography, or end-use condition. Its results should be read within those boundaries.
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No—not across all pollutants measured. The study included volatile organic compounds (VOC), carbon monoxide (CO), nitrogen oxides (NOx), fine particulate matter (PM2.5), black carbon (BC), and primary organic carbon (POC). Its abstract concludes that lower GHG intensity does not imply lower emissions for every air pollutant.
One example in the university summary is carinata: although it had the lowest GHG emissions among the plant-based pathways, it also had the highest VOC and CO levels among the pathways compared. Climate impact and air-pollutant emissions are distinct assessment axes, so a favorable result on one should not be treated as a blanket environmental ranking.
How certain are the pathway rankings?
The authors used Monte Carlo uncertainty analysis to test how results changed when model inputs varied. The university summary reports wider emissions ranges for plant-based pathways and narrower ranges for waste-derived ones. The publisher abstract says the analysis supported the robustness of the feedstock emission hierarchy across perturbation levels.
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That finding concerns the input ranges and assumptions used in this model; it does not remove uncertainty for other regions, sourcing practices, or production systems.
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What do the best-case mitigation percentages mean?
The abstract reports approximately 66–352% GHG reductions in best-case mitigation scenarios. The university summary describes waste-derived pathways paired with renewable energy inputs in processing as capable of modeled net-negative outcomes. Professor Boreum Lee’s quoted upper figure is a reduction of up to 346–352% relative to those pathways’ own conventional-input baseline.
A reduction above 100% is a comparison against that baseline in the modeled scenario. It is not evidence that ordinary commercial biodiesel production removes carbon from the atmosphere. The renewable-processing assumptions and the baseline comparison are essential to interpreting the percentage.
When was the paper published?
The paper, “Decarbonizing biodiesel supply chains: a GREET-based life cycle assessment with Scope 1–3 emissions and best-case mitigation,” by Sanghyuk Koh, Seonhwa Choe, Seokju Kim, Dohyeon Kim, and Boreum Lee, is listed in Applied Energy, Volume 422, article 128326, DOI 10.1016/j.apenergy.2026.128326. Chonnam National University said it became available online on July 1, 2026. The journal record lists an issue date of November 1, 2026, which is still in the future as of October 11, 2026. See the university announcement and the journal record.
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