Aviation is one of the biggest polluting industries in terms of relative size. The Global Carbon Project estimates that airlines contribute around 2.5% of total CO₂ emissions.
However, its overall contribution to climate change could be significantly higher because plane emissions significantly impact the concentration of other atmospheric gases and pollutants. Some scientists estimate aviation could be responsible for as much as 4% of the global temperature rise since pre-industrial times alone.
Rather than being grounded by the negatives, the sector has turned to new technology, one of which is Firefly, to propel itself to a greener future.
Some people say they often do their best thinking on the toilet. But Firefly Green Fuels has found a way to make those most sacred moments on the porcelain throne even more productive — by turning poop into petrol.
It’s not quite a flight of fancy; the Bristol-based company plans to turn sewage sludge into sustainable aviation fuel (SAF) and, in doing so, reduce carbon emissions to over 90% lower than standard fossil jet fuel.
According to the IATA, Sustainable Aviation Fuel (SAF) refers to fuels used in aviation that are not derived from fossil fuels. These fuels are sometimes called sustainable alternative jet fuel, renewable jet fuel or bio-jet fuel.
Initially, the term ‘biofuels’ was used for fuels made from biological materials such as plants or animals. However, technological advancements make it possible to produce fuel from non-biological and alternative sources. As a result, the terminology has evolved to emphasise the sustainability aspect of these fuels.
For SAF to be considered sustainable, it must meet strict criteria, including reducing lifecycle carbon emissions, not competing with food production, avoiding deforestation, and ensuring its production is environmentally responsible.
The heart of Firefly’s project is a process known as hydrothermal liquefaction. Think of it as a pressure cooker for excrement.
Simon Black, head of circular economy at Anglian Water (which will supply the sewage, or ‘biosolids feedstock’), explains that the journey begins with wastewater from households and various businesses. “It then goes through the collection network, miles and miles of pipework and pumping stations, to bring it to water recycling centres.
“They then separate the solids from the water to effectively clean the water and put it back into the environment.” The separated solids, rich in organic matter, will eventually be converted into fuel.
The separated solids undergo anaerobic digestion, a biological process in large tanks maintained at around 37°C.
Unlike chemical processes, this stage relies on the activity of microbes to break down the organic matter.
The result of this digestion is the production of biogas, which can be harvested for energy, and a by-product known as bio-sludge or biosolids. This material, comparable to manure, has traditionally been used as a fertiliser in agriculture.
Firefly’s innovative approach utilises hydrothermal liquefaction to emulate the natural geological processes that produce crude oil but at a much faster rate.
Applying high temperature and pressure converts the bio-sludge into bio-crude oil, transforming the solid waste into a liquid form that can then be refined into SAF.
Black explains that this process’s ability to guarantee the consistency of the sludge is crucial for any subsequent conversion processes, like turning the sludge into SAF.
“The benefit of using sewage sludge is that it has been through a very advanced form of anaerobic digestion and leaves the final material very consistent because it’s so highly treated, unlike livestock waste,” he says.
One of the main problems with producing SAF using conventional feedstocks, such as cooking oil and animal fats, is that they are costly and limited in availability.
While plant by-products can also be an alternative, the excessive use of agricultural land and forests to obtain large amounts of biomass can negatively impact ecosystems and biodiversity.
Paul Hilditch, co-founder of Firefly, explains that Firefly’s SAF technique is more affordable and scalable: “There’s enough biosolids in the UK to produce more than 200,000 tonnes of SAF. That’s enough to satisfy about half of the mandated SAF demand in 2030.
“We need the other routes to SAF, too,” Hilditch adds. “However, this new route has the potential to move the needle and make a significant contribution to UK SAF production. And not just the UK. Anywhere in the world where there are people, there is poo.”
According to Hilditch, scientists estimate the average human produces 30kg of dry-weight waste per year, which could produce over 14 billion litres of SAF.
Another by-product of this process is Biochar, a charcoal-like substance that can be used for carbon sequestration and could be used in construction or agriculture.
Firefly’s venture facilitates a circular economy where waste is not simply discarded but becomes a valuable resource. They say this model promotes efficient resource use, minimises waste, and stimulates economic growth by creating new industries and job opportunities related to SAF production.
By converting sewage sludge, a by-product of human activity that poses a disposal challenge, into clean fuel, they claim to address aviation’s carbon emissions and contribute to a broader sustainability agenda.
The first facility, set to break ground at the Harwich (Essex), UK site, will use existing infrastructure previously used for traditional crude oil and gas refining, saving production time, costs, and emissions.
It is poised to produce 100,000 tonnes of sustainable fuel per year. It’s backed by significant investments from key industry players, including Wizz Air, which recently committed to fuelling 10% of its flights with sustainable fuel by 2030.
Yvonne Moynihan, corporate & ESG officer at Wizz Air, described the partnership with Firefly as “a marriage of low costs.” This refers to how Firefly’s SAF, “the cheapest and most abundant feedstock,” is a perfect match for an airline focused on low costs and fares.
The Hungarian airline has ordered up to 525,000 tonnes of Firefly’s fuel over the next 15 years, potentially worth hundreds of millions of pounds.
Other partners include Petrofac, which will construct the SAF production facility; Haltermann Carless, which owns the site in Essex; Chevron Lummus Global, which will license its hydro-processing technology to Firefly; and Anglian Water.
Indeed, aviation is a notoriously tricky sector to address concerning carbon emissions, so Firefly’s innovative approach couldn’t come at a better time.
In 2022, the International Civil Aviation Organization (ICAO), a UN agency overseeing civil aviation worldwide, set the target of achieving net-zero CO2 emissions from international aviation by 2050.
This ambitious goal underscores the urgent need for innovation and investment, estimated at up to $5 trillion in clean aircraft and fuels.
The International Council on Clean Transportation (ICCT) Aviation Vision 2050 report outlines the technologies and policies essential for reaching net zero within that timeframe.
It highlights sustainable aviation fuels (SAF), zero-emission planes (ZEPs) powered by hydrogen or electricity, and efficiency measures as critical levers.
Europe is leading the charge with legally binding SAF requirements, setting a precedent for 2% global SAF uptake by 2030.
However, electric aircraft development has encountered obstacles, and Airbus’s decision to “start small” with its deployment of hydrogen-powered aircraft signals a recalibration of expectations.
Wizz Air, named Europe’s most sustainable airline, has pivoted its efforts from hydrogen power to SAF: “We see things progressing very slowly [with hydrogen] — there’s a lot of investment in infrastructure and regulatory framework to be put in place. So, we’ve really shifted our focus to sustainable aviation fuel as the future,” said Moynihan.
The post-COVID rebound in traffic, forecasted to exceed 2019 levels in the first quarter of 2024, adds another layer of complexity to reducing the industry’s carbon footprint.
Meanwhile, the EU Emissions Trading System (ETS) stands as a lone but critical mechanism for carbon pricing, covering a significant portion of passenger aviation CO2 emissions and supporting SAF deployment.
Wizz Air has noted that more needs to be done for them to reach their targets: “We call on policymakers to address barriers to SAF deployment at scale by incentivising production, providing price support, and embracing additional sustainable feedstocks for biofuel production,” said Moynihan.
In this context, Firefly’s initiative represents a beacon of hope and innovation.
By turning sewage sludge into SAF, Firefly contributes to the diversification of sustainable fuel sources and displays the creative thinking needed to overcome aviation’s environmental challenges.
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