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Research on sustainable aviation fuels investigates how urban waste, sewage, and landfill gases can enter industrial routes capable of reducing emissions and expanding alternatives to fossil kerosene.
Researchers evaluate the use of urban waste as a raw material to produce sustainable aviation fuel, in an attempt to expand alternatives to fossil kerosene.
A study linked to Tsinghua University and the Harvard-China Project analyzed the conversion of municipal solid waste into fuel through gasification and Fischer-Tropsch synthesis, with an estimated 80% to 90% reduction in greenhouse gas intensity compared to conventional fuel, according to the research authors.
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Aviation is considered one of the most difficult transport sectors to decarbonize because commercial airplanes rely on high energy density fuels, especially on medium and long routes.
In 2023, the sector accounted for about 2.5% of global energy-related CO₂ emissions, according to the International Energy Agency.
Sustainable aviation fuel from urban waste
The study analyzed an industrial route that combines gasification and Fischer-Tropsch synthesis.
In this process, urban waste is subjected to high temperatures to form a synthesis gas.
Then, this gas undergoes a chemical conversion that can generate liquid hydrocarbons used in the formulation of aviation fuel.
The proposal falls under the group of so-called sustainable aviation fuels, known by the acronym SAF.
These fuels can be mixed with conventional kerosene and used in existing aircraft, as long as they follow technical standards and certification limits.
According to the European Commission, currently certified SAFs are compatible with aviation technology in blends of up to 50%.
The raw material analyzed in the research includes municipal solid waste, such as food scraps, paper, plastics, and other materials discarded in cities.
In traditional waste management systems, part of this volume is sent to landfills or incinerators.
In the studied route, a fraction of the waste would supply a liquid fuel production chain.
Why aviation still seeks alternatives to kerosene
Electrification has advanced in land transport, but still faces technical limitations in commercial aviation.
Batteries add weight to aircraft and have restrictions for longer-range flights.
Hydrogen, in turn, requires changes in aircraft, storage, refueling, and airport infrastructure.
In this scenario, SAF appears as one of the alternatives studied to reduce emissions without immediately replacing the current fleet.
Production can use different raw materials, including residual oils, fats, agricultural residues, biomass, urban waste, and recycled gases.
Viability, however, depends on sufficient supply, competitive cost, and proof of emission reduction throughout the life cycle.
The scale is still limited.
The International Air Transport Association estimated that SAF production in 2025 would represent about 0.7% of the total aviation fuel requirement.
The percentage indicates that, despite ongoing projects, the available volume remains below 1% of the sector’s global demand.
How urban waste can reach airplane tanks
In the scenario considered most practical by the authors, global urban waste could generate about 50 million tons of aviation fuel per year, equivalent to approximately 62 billion liters.
Production would have the potential to reduce around 16% of aviation greenhouse gas emissions, according to the study.
Another simulation included green hydrogen in the process.
With this addition, annual production could reach 80 million tons, a volume sufficient to meet up to 28% of global aviation fuel demand.
The authors also estimate that this route could avoid up to 270 million tons of CO₂ per year.
Conversion, however, still presents technical limitations.
The research indicates that about 33% of the input carbon is converted into fuel, partly due to differences in the composition of gases generated during the process.
For the researchers, CO₂ capture and the use of green hydrogen can increase yield, provided the necessary infrastructure and renewable energy are available.
Sewage and landfill gas enter parallel studies
In addition to urban waste, researchers are investigating other residual sources for the production of synthetic fuels.
Among them are sludge from sewage and gases released by landfills, such as methane and carbon dioxide.
These routes appear in scientific studies and experimental projects aimed at recycling carbon already present in urban and industrial chains.
The difference between these sources lies in the composition of the residue and the technology required to convert it into fuel.
In the case of sewage sludge, the organic matter can undergo thermal or chemical processes to generate energy compounds.
Meanwhile, landfill gas needs to be captured, purified, and transformed into molecules suitable for fuel production.
The Tsinghua-Harvard study primarily focused on municipal solid waste.
The mention of sewage and landfill gas relates to a broader field of research, which seeks to use urban waste as an energy input without resorting to new fossil carbon sources.
Goals to Expand the Supply of Sustainable Aviation Fuel
The adoption of sustainable aviation fuels also depends on regulatory targets and incentives.
In the United States, the Sustainable Aviation Fuel Grand Challenge sets the production of 3 billion gallons per year by 2030 and 35 billion gallons per year by 2050, a volume expected to meet 100% of the projected domestic demand.
In the European Union, the ReFuelEU Aviation rule mandates a gradual increase in the share of SAF in the fuel supplied at the bloc’s airports.
The requirement starts at 2% in 2025 and reaches 70% in 2050.
The regulation also foresees an increasing share of synthetic fuels in air supply.
In Brazil, the Future Fuel Law created the National Sustainable Aviation Fuel Program, ProBioQAV.
The policy sets emission reduction targets for air operators on domestic flights starting in 2027, beginning at 1% and reaching 10% in 2037, according to federal government information.
Scale Production Still Limits the Technology
The transformation of waste into aviation fuel depends on an integrated chain.
Cities need to separate, collect, and prepare waste to an adequate standard.
The plants, in turn, must operate gasification systems on an industrial scale.
In the final stage, producers need to meet safety standards and technical specifications required by the aviation sector.
Jingran Zhang, the first author of the study, stated that transforming everyday waste into aviation fuel could represent “an innovative and important step in the short term” to reduce emissions in the sector.
According to him, the possibility of using the fuel in current engines would allow cuts without waiting for a new generation of aircraft.
The economic assessment cited by the research indicates that fuels produced from municipal waste can become more competitive in carbon pricing systems, especially when there are public incentives.
Even in this scenario, the authors identify large-scale gasification as the main technical challenge to expanding production.
Michael B. McElroy, the principal author of the study and a professor of Environmental Studies at Harvard, said that the research presents a “roadmap” for converting urban waste into sustainable aviation fuel.
He also stated that the expansion of production will depend on collaboration between governments, fuel producers, airlines, and aircraft manufacturers.
With global SAF production still far from the sector’s demand, the research places urban waste, sewage, and landfill gases among the routes studied to reduce dependence on fossil kerosene.
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