A new study offers biodiesel producers a clearer framework for choosing feedstocks by weighing climate impact and air pollution together. Researchers at Chonnam National University in South Korea conducted a life-cycle assessment comparing five biodiesel feedstocks. The study, led by Professor Boreum Lee and Mr. Sanghyuk Koh, was published in Applied Energy.
Biodiesel is seen as a bridge technology for decarbonizing transport while renewable energy infrastructure scales up. But not all biodiesel is equally sustainable. Its environmental impact depends heavily on the feedstock used and how it is produced. Earlier assessments mostly focused on total emissions across a limited set of feedstocks and rarely examined air pollution.
The new study used a GREET-based framework covering three plant-based feedstocks and two waste-derived feedstocks. The plant-based group included soy oil, carinata oil and palm oil. The waste-derived group included used cooking oil and beef tallow.
Waste-derived feedstocks consistently showed lower emissions than plant-based oils, largely because they skip emissions tied to farming and land use. Among plant-based options, carinata oil had the lowest emissions, since it avoids land-use change impacts. Farming was the biggest emissions contributor for plant-based feedstocks, while production and refining mattered most for waste-derived ones.
Waste-derived pathways can reach net-negative emissions when paired with renewable energy in processing, removing more carbon than they emit, Professor Lee noted.
Lower emissions did not always mean cleaner air. Carinata oil, despite low emissions, had the highest volatile organic compound and carbon monoxide levels of all pathways tested. That suggests air pollution deserves separate consideration alongside carbon accounting.
Best-case scenarios showed reduction potential ranging from 66 percent to 352 percent, with waste-derived feedstocks offering the strongest results.
Professor Lee said the findings argue against one-size-fits-all biofuel mandates. Regions with strong waste-collection infrastructure should prioritize used-oil-based biodiesel, while agricultural regions may benefit more from dedicated energy crops.
