Flying on Feces: Can Sewage-derived Jet Fuel Really Soar?
Revolutionizing aviation, a UK company pioneers jet fuel derived solely from human waste, offering a sustainable and eco-friendly alternative for air travel
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In the pursuit of alternative and sustainable jet fuels, some companies are thinking outside the box. While we have heard about planes powered by cooking oil, what about jet fuel derived from human waste? Firefly Green Fuels, an aviation company based in Gloucestershire, UK, has achieved exactly that - and understandably, the concept of waste-powered planes is capturing attention.
While sustainable aviation fuel (SAF) is not a new concept, the idea of using sewage as a source is a recent development. This has led to questions about whether this innovative approach could be the future of air travel.
Commercial aviation is responsible for approximately 2.5% of global carbon emissions, which has a significant impact on climate change. In response to this, efforts are being made to reduce the sector's environmental footprint, including the development of electric and hydrogen-powered planes. However, these technologies are not yet capable of powering long-haul passenger flights. As a result, the industry is turning to SAF, with the International Air Transport Association (IATA) estimating that it could potentially contribute up to 65% of the emissions reduction necessary for aviation to achieve net-zero status by 2050.
SAF burns like regular jet fuel and produces the same amount of emissions while a plane is flying. However, it has a lower carbon footprint during its entire production cycle because it is typically made from plants that absorbed carbon dioxide (CO2) from the atmosphere when they were alive. In the case of sewage, it is made from plants and other food that have been eaten by humans and passed through the digestive system. This absorbed CO2 is released back into the atmosphere when the SAF burns, while burning jet fuel made from fossil fuels emits locked-away carbon.
Sewage has been an untapped resource for SAF so far, but James Hygate, CEO of Firefly, believes this is a missed opportunity. "There's plenty of it, it's everywhere in the world, and there's not really any good use for it at the moment, which makes it a very low-value material," he tells CNN.
That's why the company, a spin-off from Green Fuels, which has been developing low-carbon fuels since the early 2000s, including biodiesel made from rapeseed oil for cars and trucks, turned its attention to producing jet fuel - and even poop.
The sewage is processed and converted into crude oil through a process called hydrothermal liquefaction.
Firefly Green Fuels Ltd.
Processing poop
Firefly utilizes a process known as hydrothermal liquefaction to transform human waste into a viable fuel source, particularly suitable for wet waste. By employing a combination of intense pressure and heat, this method converts sewage into carbon-rich biochar, a powdery substance that can be utilized as a fertilizer for crops, as well as crude oil.
Production has been limited to a laboratory on a small scale. Initial findings have been positive, with independent analysis from international aviation authorities deeming it nearly indistinguishable from traditional fossil jet fuel. Furthermore, a life cycle analysis from Cranfield University in the UK revealed that it has a 90% lower carbon footprint than standard jet fuel.
Firefly is seeking to increase production in the upcoming years. Currently, it is undergoing a fuel qualification process with the standards body ASTM International, which Hygate anticipates will take up to two years. Following this, the company will construct a processing facility in the UK, with the goal of having it operational before 2030 and capable of processing 100,000 tons of biocrude oil annually - resulting in around 40 million liters of SAF. To put this into perspective, this would be enough for 800 flights from London to New York, according to Hygate. He notes that while it may be more expensive than traditional kerosene used by planes, it is cheaper to produce than other biofuels.
Obtaining the necessary sewage should be manageable, and Firefly is already in discussions with several UK water utility companies. However, financing the processing facilities may present a challenge. "These are large infrastructure projects that require substantial financial backing to become a reality," he remarks. To date, 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 the European airline Wizz Air.
James Hygate founded Firefly Green Fuels with the goal of developing low carbon biofuels.
Firefly Green Fuels Ltd. acknowledges that the sewage quantity is not scalable, according to Hygate estimates. Even if all usable UK sewage waste was utilized for aviation fuel production, it would only fulfill 5% of the UK's demand for Sustainable Aviation Fuel (SAF). Consequently, it would need to be combined with other SAF feedstocks such as rapeseed oil.
In a 2023 report, the Royal Society identified "the scale and availability of feedstock" as a limiting factor for biofuels in achieving net zero aviation solutions. It highlighted that meeting the UK's aviation demand would necessitate using over half of the country's agricultural land for biofuel production.
The report also raised debate on whether agricultural waste is truly "waste" as it is often repurposed for animal bedding or feed. Cait Hewitt, policy director at the Aviation Environment Federation, a UK non-profit that monitors aviation's environmental impact, similarly questions the classification of sewage waste.
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When considering any type of feedstock for alternative fuels, such as waste, it's crucial to question what would have been done with it otherwise," she explains. In the UK, farmers currently utilize a significant amount of sewage as fertilizer. If this sewage is diverted to produce sustainable aviation fuel (SAF), an alternative for the fertilizer would need to be sought out.
Not to be sniffed at
According to Hygate, farmers could potentially use the biochar by-product as an alternative, although perhaps not on the same scale. He also suggests that the UK might consider following countries like the Netherlands in prohibiting the spreading of sewage on fields. In the event of such a ban, incineration, an energy intensive process, would become the most common disposal route.
Despite their limitations, biofuels are anticipated to have a significant role in the future of aviation. In November, the first commercial transatlantic flight powered by 100% SAF, derived from waste cooking oils and animal fat, departed from London to New York.
"Sewage is an intriguing potential solution and should not be overlooked," says Hewitt. However, she warns that, like all SAF, it will still generate the same level of carbon emissions during flight and does not address the issue of contrails, which also make a significant contribution to aviation-induced warming.
Airbus unveils blueprint for hydrogen fuel cell-powered aircraft. "In order to achieve net zero emissions in aviation by 2050, we must concentrate on developing authentic, scalable, zero-emission solutions," she states.
Hewitt adds that there could be a limited role for some alternative fuels in the short to medium term. However, he warns about the danger of people quickly embracing the idea of sustainable flying without considering the impact of their flying habits. This report includes contributions from Jacopo Prisco.
