Using Sludge Waste to Produce SAF

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September 29, 2023

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(Biofuels International) ... (U)sing human waste from sewage systems to produce SAF would provide an ideal, circular solution. Sustainability for aviation. A way to limit feedstock costs. A means of limiting the need for human waste to be disposed of into rivers and seas. An additional revenue stream for water companies. And a real opportunity for biofuel enterprises. The work at Cranfield with Green Fuels Research and energy services company Petrofac is proving the viability of the approach.

SAF boom ahead

There have been a range of technological advances around sustainable aviation, but none have led to short-term solutions. Electric aircraft have been demonstrated as having the potential to take on shorthaul and regional flights, but are unlikely to have the ability to take on long-haul.

Hydrogen-powered flight has the greatest potential generally as a zero-carbon option, but its adoption involves a root-and-branch transformation of aircraft engines, fuel supplies and storage. Meanwhile, levels of interest in SAF is growing exponentially. Last year saw the first commercial flight with a full load of passengers using 100% SAF for one of its two engines.

Rolls-Royce has confirmed that all of its engines will be SAF-ready this year. The US government has taken a lead on incentivising the use of SAF through its Inflation Reduction Act (IRA) 2022 and has a goal of enabling the production of 3 billion gallons of SAF by 2030, with a trajectory of growing production facilities in order to deliver 35 billion gallons a year by 2050.

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There are alternatives in the form of waste products, which would provide more of a sustainable option.
Food waste, the types collected through municipal collections from households, have potential as an ongoing supply.

However, this would need a strong intervention from local authorities across the country to ensure food waste was collected separately in order to deliver the kind of consistency and quality of waste that is needed for conversion into a biofuel. The technology and processes for converting the world’s mass of waste plastics into SAF is currently being trialled across a number of schemes.

Virgin Atlantic has a deal with Norwegian chemicals firm Agilyx to turn plastic waste into a crude synthetic oil that will, in turn, be converted into SAF at a US facility.

In the UK, the Clean Planet Energy start-up has a production facility capable of converting 60 tonnes of plastic waste a day into SAF that is expected to deliver a 75% reduction in carbon emissions.

The bigger question here though is over the use of plastics for burning as fuel at all. It should not be regarded as a ‘sustainable’ process, not when it involves the use of a finite resource – hydrocarbons that have been created over millions of years are a critical element to the chemical engineering industries and in so many different polymers and plasticbased products and materials, which are not re-used or recycled, but destroyed.

Flying on sewage

Using human sewage sludge to produce SAF will be a genuinely sustainable foundation, addressing both waste management and lowcarbon energy demand.

As a feedstock, the scale of supply more than works.

It is estimated that around 53 million tonnes of untreated sewage sludge are collected in the UK from about 8,500 wastewater treatment works each year. The UK’s wastewater system is heavily over capacity, meaning storm events (or even, in some locations, just rain) regularly lead to raw sewage ending up in rivers and seas.

According to Environment Agency figures, there has been a 37% increase year-oyear in incidents – meaning 9 million hours of sewage being pumped into rivers and seas since 2016. Finding alternative uses for sewage sludge will be a huge benefit to businesses, to the environment and society as a whole.

The FIREFLY project, funded by Department for Transport as part of its Green Fuels, Green Skies competition, has shown how this can work, proved that the quality of the resulting biofuel will meet strict industry standards, and led to the engineering design and construction of a demonstrator plant for production.

With further industry investment, the project is due to lead to a first-of-a-kind commercial refinery and the development of a network of UK sites close to airports, pipeline terminals and wastewater treatment works. The integrated processes involved will also reduce the processing costs involved and help keep unit costs low.

Alongside other development pathways, the FIREFLY technology is expected to become a strategic asset for the UK as part of the broader national SAF portfolio. Costs for SAF will remain relatively high, at least for the short-term. This is why the huge potential for SAF – and the opportunity for a circular economy approach to their production – will only be realised with a clear mandate from government, stimulating mass uptake of SAF, more investment from finance institutions and a rolling cycle of lower costs for every stakeholder involved.

For more information: Visit: cranfield.ac.uk READ MORE

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Firm develops jet fuel made entirely from human poo (BBC)
Utilising sludge waste in the production of SAF (Biofuels International)

Excerpt from BBC: A new aviation company has developed a type of jet fuel made entirely from human sewage.

Chemists at a lab in Gloucestershire have turned the waste into kerosene.

James Hygate, Firefly Green Fuels CEO, said: "We wanted to find a really low-value feedstock that was highly abundant. And of course poo is abundant."

Independent tests by international aviation regulators found it was nearly identical to standard fossil jet fuel.

Firefly's team worked with Cranfield University to examine the fuel's life cycle carbon impact. It concluded that Firefly's fuel has a 90% lower carbon footprint than standard jet fuel.

Mr Hygate, who has been developing low-carbon fuels in Gloucestershire for 20 years, said although the new fuel was chemically just like fossil-based kerosene, it "has no fossil carbon, it's a fossil-free fuel".

"Of course energy would be used (in production), but when looking at the fuel's life cycle, a 90% saving is mind-blowing, so yes, we have to use energy but it is much lower compared to the production of fossil fuels," he added.

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On a small farm in Gloucestershire, Mr Hygate began turning rapeseed oil into 'bio-diesel' for cars and trucks 20 years ago.

His company, Green Fuels, now sells equipment to turn cooking oil into biodiesel, and has clients all over the world.

Then he started looking for ways to make green jet fuel. They tried waste oils, waste food, even agricultural scraps.

Then they experimented on human waste.

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He teamed up with a chemist from Imperial College, London, Dr Sergio Lima.

Together, they developed a process which transforms poo into power.

First, they create what they call "bio-crude".

It looks like oil: thick, black, gloopy. Most importantly, it behaves like crude oil chemically.

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The bio-kerosene is now being tested independently at the DLR Institute of Combustion Technology at the German Aerospace Center, working with Washington State University.

Further future testing will also be carried out by the UK SAF (Sustainable Aviation Fuels) clearing House, based at University of Sheffield.

First results have confirmed the fuel has near-identical chemical composition to A1 fossil jet fuel.

The UK Department of Transport has awarded the team a £2m research grant.

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Put another way, the UK's total sewage supply would meet about 5% of the country's total aviation fuel demand.

It may sound small, but he insists: "That's pretty exciting."

"There's a 10% sustainable aviation fuel requirement, that's a legal mandate. And we could meet half of that with poo."

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They are more supportive of the sewage-based fuel, because "human waste is perhaps the one form of rubbish that society really can't avoid producing", as Cait Hewitt, policy director of the Aviation Environment Federation put it. READ MORE