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In the race for alternative, sustainable jet fuels, some companies are getting creative. We’ve heard of airplanes powered by cooking oil, but what about jet fuel made entirely from human excrement? Firefly Green Fuels, an aviation company based in Gloucestershire, UK, has created just that and, unsurprisingly, the prospect of excrement-powered aircraft is attracting attention.
While sustainable aviation fuel (SAF) is not new, the idea of using wastewater (an abundant and inevitable waste) is a novelty. So could it really be the future of air travel?
Commercial aviation produces about 2.5% of global carbon emissions, contributing to climate change. Efforts are being made to reduce the impact of the sector, with the development of electric and hydrogen-powered aircraft. But the technology is still a long way from powering long-haul passenger flights. Instead, the industry is looking to use SAF, and the International Air Transport Association (IATA) estimates 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 while a plane flies, but it has a smaller carbon footprint throughout its production cycle because it is typically made from plants that have absorbed carbon dioxide. (CO2) from the atmosphere when they were alive. Or, in the case of wastewater, it is made from plants and other foods that have been ingested by humans and passed through the digestive system. That absorbed CO2 is released into the atmosphere when SAF is burned, while burning jet fuel made from fossil fuels emits locked-in carbon.
Until now, wastewater has been an untapped resource as far as SAF is concerned, but James Hygate, CEO of Firefly, believes it is a missed opportunity. “There’s so much of it, it’s everywhere in the world and there’s really no good use for it right now, which makes it a very low-value material,” he tells CNN.
That’s why the company, a spin-off of Green Fuels, which has been developing low-carbon fuels since the early 2000s, including biodiesel made from rapeseed oil for cars and trucks, turned to jet fuel. .. and the poop.
Processing poop
To convert human waste into usable fuel, Firefly uses a method called hydrothermal liquefaction, which is good for wet waste. By combining high pressure and heat, it converts wastewater into carbon-rich biochar (a powder that can be used as fertilizer for crops) and crude oil.
Until now, production has been done on a small scale in a laboratory. But early results have been promising: An independent analysis by international aviation regulators found it nearly identical to standard fossil jet fuel. According to a life cycle analysis by Cranfield University in the UK, it also has a 90% smaller carbon footprint than standard jet fuel.
Firefly is looking to increase production in the coming years. It is currently undergoing a fuel qualification process with standards body ASTM International, which Hygate expects to last up to two years. It will then begin building a processing facility in the UK, which Hygate expects to be operational before 2030 and capable of processing 100,000 tonnes of biocrude oil a year, or producing around 40 million liters of SAF. To put this into perspective, according to Hygate, that’s enough for 800 flights from London to New York. He adds that it would be more expensive than conventional kerosene used in airplanes, but cheaper to produce than other biofuels.
Getting the wastewater should be simple, he says, adding that Firefly is already in talks with several UK water utilities. But he admits that financing the processing facilities could be a challenge. “These are big infrastructure projects that need money behind them to come to fruition,” she says. So far, the company has 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 wastewater is something that cannot be increased. Hygate estimates that if all of the UK’s usable wastewater waste were used to manufacture aviation fuel, only 5% of the UK’s SAF demand would be met. Therefore, it would have to be used together with other SAF raw materials, such as rapeseed oil.
A 2023 Royal Society report on net-zero aviation solutions found that “scale and feedstock availability” is a constraint for biofuels, and that producing enough to sustain UK aviation demand would require more than half of the country’s agricultural land.
He also noted that there is some debate about whether agricultural waste is actually “waste,” since it is often used as bedding or animal feed. Cait Hewitt, policy director at the Aviation Environment Federation, a UK nonprofit that monitors the environmental impact of aviation, raises the same question about wastewater.
“One of the important questions to ask about any form of feedstock for alternative fuels, including waste, is what would have happened to this material otherwise?” she says. In the UK, farmers currently use a lot of wastewater as fertilizer, she adds. If it is instead used to produce SAF, that fertilizer would need to be replaced.
Hygate says farmers could use the biochar byproduct as an alternative, although potentially not on the same scale. He adds that there is a possibility that the UK will follow other countries such as the Netherlands in banning the spread of wastewater on fields. If this happens, the other most common disposal route is incineration, an energy-intensive process.
Not to be sniffed
Despite their limitations, biofuels are likely to play an important role in the future of aviation. The first commercial transatlantic flight powered by 100% SAF, made from used cooking oils and animal fats, took off from London to New York in November.
Wastewater is an interesting potential solution and should not be overlooked, says Hewitt. But he warns that, as with all SAFs, it will still produce the same amount of carbon emissions when the plane is flying, and it does not solve the problem of contrails, which also contribute significantly to the warming created by aviation.
“To have a chance of getting from where we are today to net-zero aviation by 2050, we need to really focus on genuine, scalable, zero-emission solutions,” he says.
“Some of these alternative fuels may have a limited role in the short and medium term,” adds Hewitt. “But the big danger is that when you hear something like this, it intuitively sounds like a good idea, and people say, ‘That’s great, we’re on the path to sustainable flying, we don’t have to worry about how much to fly.'”
Jacopo Prisco contributed to this report.
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