Hydrothermal liquefaction of organic waste will remain the most environmentally friendly technology for aviation fuel production at least until mid-century. However, 50 years from now, it will be faced with challenges posed by gasification and vegetable oil recycling technologies. This is the conclusion reached by British scientists from the University of Sheffield, who compared 540 possible scenarios for sustainable aviation fuel (SAF) production up to 2075 for the United States, China, India, and Brazil.
Aviation remains one of the most challenging sectors to decarbonize. In 2023, aircraft accounted for about 2.5% of all anthropogenic carbon dioxide emissions, and when other factors are taken into account – including contrail formation and nitrogen oxide emissions – its contribution to climate change is roughly three times higher. Global air traffic volume is projected to double by 2045. At the same time, a complete transition away from liquid fuels is impossible in the coming decades, so the main focus today is on sustainable aviation fuel (SAF), which can be used in existing aircraft without engine replacement.
To determine which technologies will truly prove most environmentally friendly in the long term, the researchers examined five SAF production methods using six types of wastage, including used cooking oil, household solid waste, rice straw, wheat straw, corn stover, and sugarcane residues. The calculations covered four countries with different energy structures and waste management systems, specifically, the United States, China, India, and Brazil. For each option, the scientists assessed not only greenhouse gas emissions but also 17 other environmental impact indicators, including effects on soil, water resources, production toxicity, and mineral resource depletion.
It turned out that as the global energy system transitions to low-carbon sources, virtually all technologies become less carbon-intensive. In some cases, their emissions are projected to fall by more than 90% by 2075. At the same time, however, demand is growing for copper, platinum, and other metals needed for power grid construction, equipment manufacturing, and hydrogen production. Their extraction also has a significant environmental impact, so reducing CO₂ emissions does not always mean reducing overall environmental damage.
This is precisely why the composition of the most environmentally friendly technologies changes over time. According to the researchers’ calculations, if hydrothermal liquefaction of waste dominates the top ten solutions in terms of overall environmental performance until mid-century, then by 2075 waste gasification and used cooking oil processing technologies also join the leaders. The modeling results vary significantly by country: in most scenarios, the United States showed the best performance due to its cleaner energy system and modern waste management infrastructure, while India more frequently exhibited the highest environmental burden due to its widespread use of coal and open waste storage.
As a matter of fact, there is no universal technology for sustainable aviation fuel production whereas its effectiveness depends not only on the feedstock used but also on the specific characteristics of the energy system, waste management practices, and industrial infrastructure of each country.
