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In the race for alternative, sustainable jet fuels, some companies are starting to get creative. We’ve heard of planes running on cooking oil, but what about jet fuel made entirely from human feces? Firefly Green Fuels, an aviation company based in Gloucestershire, United Kingdom, has created just that, and unsurprisingly, the prospect of poop-powered planes is attracting attention.
While sustainable aviation fuel (SAF) is not new, the idea of using sewage, an abundant and unavoidable waste, is an innovation. So could this really be the future of air travel?
Commercial aviation contributes to climate change by producing approximately 2.5% of global carbon emissions. Efforts to reduce the impact of the industry continue with the development of electric and hydrogen-powered aircraft. But the technology is still a long way from powering long-haul passenger flights. The industry is considering using SAF instead, with the International Air Transport Association (IATA) estimating it could contribute up to 65% of the emissions reductions needed for aviation to reach net zero by 2050.
SAF burns like regular jet fuel and produces the same amount of emissions as an airplane flies, but it has a lower carbon footprint over the entire production cycle because it is generally made from plants that absorb carbon dioxide (CO2) from the atmosphere. they were alive. Or, in the case of sewage, it is made from plants and other foods eaten by humans and passed through their digestive system. The CO2 absorbed when SAF is burned is released back into the atmosphere, while burning jet fuel made from fossil fuels releases locked-up carbon.
So far, sewage has been an untapped resource when it comes to SAF, but Firefly CEO James Hygate thinks this is a missed opportunity. “There’s so much of it, it’s all over the world, and there’s no really good use for it right now, making it a very low-value material,” he told CNN.
So the company, a spinoff of Green Fuels that has been developing low-carbon fuels for cars and trucks since the early 2000s, including biodiesel produced from rapeseed oil, has turned its hand to jet fuel and fecal matter.
poop being processed
Firefly uses a method called hydrothermal liquefaction, which is good for wet waste, to turn human waste into a usable fuel. By combining high pressure and heat, it turns sewage into carbon-rich biochar (a powder that can be used as crop fertilizer) and crude oil.
Until now, production was done on a small scale in the laboratory. But initial results have been promising, with independent analysis by international aviation regulators finding it was nearly identical to standard fossil jet fuel. According to a life cycle analysis conducted by Cranfield University in England, it has a 90% lower carbon footprint than standard jet fuel.
Firefly plans to increase production in the coming years. It is currently going through a fuel qualification process with standards organization ASTM International, which Hygate expects to take up to two years. It will then begin building a processing plant in the UK, which Hygate hopes will be operational before 2030 and have the capacity to process 100,000 tonnes of biocrude per year, or produce around 40 million liters of SAF. According to Hygate, this is enough perspective for 800 flights from London to New York. He adds that it will be more expensive than traditional kerosene used in airplanes, but cheaper to produce than other biofuels.
Sewerage should be easy to access, he said, adding that Firefly was already in talks with some water utilities in the UK. But he admits that financing processing facilities can be difficult. “These are big infrastructure projects that need money behind them to come to fruition,” he says. The company has so far received a £2 million ($2.5 million) research grant from the UK Government and a £5 million ($6.3 million) investment from European airline Wizz Air.
However, the amount of sewage is something that cannot be exaggerated. Hygate estimates that if all of the UK’s usable sewage was used to make aviation fuel, it would still only meet 5% of the UK’s SAF demand. It will therefore need to be used in combination with other PURE raw materials such as rapeseed oil.
A 2023 report from the Royal Society on net-zero aviation solutions found that “scale and availability of feedstock” was a constraint for biofuels and that producing enough to sustain the UK’s aviation demand would require more than half the country’s farmland.
It was also noted that there is some debate about whether agricultural waste is truly “waste” since it is often used as animal bedding or feed. Cait Hewitt, policy director at the Aviation Environmental Federation, a UK non-profit organization that monitors the environmental impacts of aviation, asks the same question about sewage.
“One of the important questions you need to ask about any feedstock for alternative fuels, including waste, is what would happen to them otherwise?” says. He adds that large amounts of sewage in the UK are currently used as fertilizer by farmers. If used to make SAF instead, the fertilizer will need to be replaced.
Hygate says the biochar byproduct could potentially be used by farmers as an alternative, although not at the same scale. He adds that the UK is likely to follow other countries, such as the Netherlands, in banning the spread of sewage on fields. In such a case, the other most common means of disposal is incineration, which is an energy-intensive process.
To avoid being smelled
Despite their limitations, biofuels are likely to play a major role in the future of aviation. The first commercial transatlantic flight powered by 100% SAF, made from waste cooking oils and animal fats, took off from London to New York in November.
Hewitt says sewers are an interesting potential solution and not one to be underestimated. But he warns that, like all SAFs, the aircraft will produce the same amount of carbon emissions while flying and does not solve the contrail problem, which contributes significantly to aviation warming.
“To have a chance of getting from where we are today to net zero aviation by 2050, we need to focus on truly original, scalable, zero-emission solutions,” he says.
“Some of these alternative fuels may have a limited role in the short to medium term,” Hewitt adds. “But the biggest danger is that when you hear something like this, it intuitively sounds like such a good idea and people say, ‘We’re on this great, sustainable flight path, we don’t need to worry about how successful we are at flying.'”
Jacopo Prisco contributed to this report.
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