In 2021, NREL fermented food waste into volatile fatty acids and catalytically upgraded them to jet fuel; the SAF was estimated to cut net carbon emissions by up to 165% when landfill disposal was assumed

For years, airlines have been looking for an alternative fuel that could replace kerosene without requiring airports to overhaul their infrastructure. In a 2022 study titled 'Toward Net-Zero Sustainable Aviation Fuel with Wet Waste-Derived Volatile Fatty Acids,' published in the journal Proceedings of the National Academy of Sciences (PNAS), a group of scientists led by the National Renewable Energy Laboratory (NREL) gave an unexpected answer: garbage. By fermenting food waste and then converting the resulting molecules into jet fuel through catalysis, the researchers produced a fuel that, under certain assumptions, was estimated to cut life-cycle carbon emissions by as much as 165% compared with conventional jet fuel.

Why wet waste is hard to turn into fuel

Decarbonization is particularly difficult for aviation, as long-haul aircraft would require a high-energy-density fuel that is liquid in nature, making battery-powered propulsion impractical for the majority of the routes. In addition, the industry uses enormous volumes of fuel: U.S.- based airlines alone consumed about 18.3 billion gallons of jet fuel in 2019, according to Department of Energy analyses, and the U.S. Energy Information Administration projects that global commercial jet fuel demand will more than double by 2050 under baseline scenarios.


Food waste has long been an underused feedstock. It is inexpensive and ubiquitous, and even accounting only for its energy content, it could theoretically displace more than 20% of the jet fuel consumed by U.S. based airlines. The challenge is that wet, mixed organic waste is difficult to process efficiently; most of it is simply landfilled rather than converted into methane at all, let alone into fuel.

Interrupting fermentation before it reaches methane

The paper details how the fermentation step was deliberately halted partway through, arresting microbial methane formation before it could run to completion. Researchers managed to get the intermediate products in the form of volatile fatty acids (VFAs), which consisted of hydrocarbons with chain lengths of two to eight carbons.

Zirconia-based catalysts have demonstrated stable performance over about 100 hours in fuel-reforming tests, according to a 2023 study in 'Catalysts' on doped ceria–zirconia reforming catalysts. The reaction produced two types of products: straight-chain (normal) paraffins, which qualify under ASTM International's 'Fast Track' pathway for jet fuel blends of up to 10%, and branched isoparaffins, which could raise the renewable blend limit even further. Together, the two products help address blend-limiting properties such as flash point and viscosity; the normal paraffins support near-term certification at the 10% blend level, while the isoparaffins are aimed at eventually supporting a much higher blend limit, up to 70%, pending further certification. In one study, a 70% blend of wet waste-derived volatile fatty acid SAF showed 34% lower sooting than fossil jet fuel, as reported in a 2022 paper in Proceedings of the National Academy of Sciences (PNAS).

Why the 165% figure depends on where the waste would have gone

The number is not inherent to the chemical composition of the fuel itself. A peer‑reviewed life‑cycle assessment in 'Environmental Science & Technology' used a conventional jet fuel reference of 88.9 g CO₂‑eq/MJ and reported SAF pathways in the low‑double‑digit g CO₂‑eq/MJ range. It is the difference that leads to 165%, but this is true only if the food waste used for the fermentation would otherwise be disposed of by means of a landfill.

This greenhouse gas is responsible for a much stronger heat-trapping effect compared to carbon dioxide and food waste is especially efficient in creating this gas after being disposed of under anaerobic conditions. In particular, an independent study by the EPA called ‘Quantifying Methane Emissions from Landfilled Food Waste’ shows that while food waste accounts for about 24% of all material delivered to U.S. municipal landfills, it is estimated to generate almost 58% of all fugitive methane escaping to the atmosphere. Redirecting such waste to a fermenting tank instead of a landfill saves such emissions and that is why, combined with just fuel displacement from petroleum jet fuel, it results in over 100% savings.

What NREL says this means for getting to the runway

According to NREL's project materials, the SAF produced through this pathway is compatible with existing aircraft engines, avoiding the years of redesign a wholly novel fuel would require. The short-term, 10%-blend version was engineered for ASTM's Fast Track certification process, while the higher-blend isoparaffin version is intended for the longer certification pathway that could eventually support up to a 70% blend. The two blends are thus meant to accomplish different things: the 10% blend is aimed at near-term deployment, while the higher-blend isoparaffin pathway is aimed at maximizing long-term emissions reduction.

Where the approach still has to prove itself

None of this proves the issue of wet-waste SAF is easy to solve. Engineering challenges involved in scaling up a fermentation and catalytic upgrading process, which uses laboratory reactors, to a production process that will process millions of tons of mixed and regionally scattered food waste is a completely different thing from working with a flow reactor over several days. The question of collection infrastructure, consistency of the feedstocks and costs of building a special facility for VFA upgrading remains unclear.

One should add to it the fact that 165% is more of a ceiling than a guarantee, because it presupposes that the food waste would have generated its full methane potential in a landfill; in reality, the amount of methane that actually escapes varies by region and by site, depending on how much landfill gas is captured and used for energy or flared. However, in its essence, the main conclusion of the 2022 paper is valid by itself: waste that has long been harmful to the environment by sitting in landfills can, with the help of fermentation and catalytic chemistry, be turned into aviation fuel with lower carbon dioxide emissions.