The UK's Sustainable Aviation Fuel Act became law in March 2026. Sewage sludge — a waste product water companies currently pay to dispose of — is now a legally mandated commercial feedstock worth billions of pounds. Here is what every water company, bioresources specialist and supply chain company needs to understand.
For most of the history of the UK water industry, sewage sludge has been a problem to be managed. Water companies have spent significant sums treating, transporting and disposing of biosolids — spreading them on agricultural land, incinerating them, or paying for increasingly expensive alternatives as environmental standards tighten.
That framing is about to change fundamentally. The Sustainable Aviation Fuel Act 2026, which received Royal Assent on 5 March 2026, establishes a mandatory UK blending obligation for sustainable aviation fuel. It creates, for the first time, a legally guaranteed commercial market for SAF — including SAF produced from sewage sludge and biosolids. For UK water companies, that is not an abstract policy development. It is a potential transformation of their biggest waste disposal challenge into a significant revenue stream.
Firefly Green Fuels is a Bristol-based startup founded by James Hygate OBE — a serial biofuels entrepreneur who also founded Green Fuels Limited in 2003, the company that holds a Royal Warrant of Appointment from HM King Charles III for the supply of sustainable fuel. Firefly was spun out of Green Fuels Research and has spent the better part of a decade developing and proving its sewage-to-SAF pathway.
The company's approach is not incremental. While other SAF pathways use agricultural waste, used cooking oil or purpose-grown energy crops as feedstock, Firefly uses processed human sewage — the biosolids produced by every wastewater treatment works in the country. The feedstock is abundant, continuous, geographically distributed and, critically, already being produced whether or not anyone uses it. That last point matters enormously for SAF economics: Firefly does not need to grow, harvest or collect its feedstock. Water companies are producing it around the clock, 365 days a year.
Most SAF feedstocks compete with other uses — agricultural land, food production, vehicle fuel markets. Sewage sludge competes with nothing. It is the only globally scalable SAF feedstock that is simultaneously a waste disposal problem for the entity that produces it. That makes the economics of sewage-derived SAF fundamentally different from any other pathway.
Understanding how sewage becomes jet fuel matters for anyone in the water sector supply chain. The process has six distinct stages, each involving different technologies and companies.
Wastewater arrives at water recycling centres via the sewer network. Solids are separated from the treated liquid, which is returned to the environment. The separated solids — biosolids — are the feedstock for the entire process. In the UK, roughly 53 million tonnes of wet sewage sludge is produced annually.
At most large treatment works, biosolids already pass through anaerobic digestion — breaking down organic matter to produce biogas and a stabilised digestate. The digestate is the input for the next stage. Water companies with existing AD infrastructure are already producing the right feedstock without any process changes.
This is Firefly's proprietary step. Biosolids are subjected to extreme heat (300–350°C) and pressure (200+ bar) in a continuous-flow reactor — essentially replicating the geological processes that created fossil crude oil, but in hours rather than millions of years. The output is bio-crude oil and biochar. The bio-crude is chemically analogous to fossil crude and can be processed through conventional refinery infrastructure.
The bio-crude is upgraded and refined using hydroprocessing — a well-established refinery process that removes impurities, saturates double bonds and adjusts the molecular weight distribution to produce aviation-grade fuel. Chevron Lummus Global (CLG) will license its hydroprocessing technology for Firefly's commercial plant. Haltermann Carless hosts the refinery site in Harwich, Essex — one of the UK's specialist hydrocarbon processing facilities.
The physical facility — HTL reactors, heat exchangers, hydroprocessing unit, utilities, pipework — is engineered and built by Petrofac, one of the world's leading energy EPC contractors. The pilot plant in Harwich will produce biocrude at scale for the qualification process, followed by a first-of-a-kind commercial-scale plant at the same site.
Before sewage-derived SAF can be used in commercial aircraft it must be qualified to ASTM D7566 international standards. Sewage biosolids (SBtJ — Sewage Biosolids to Jet) is not currently an approved ASTM pathway. Firefly is working through the qualification process — a multi-year undertaking that involves producing fuel at demonstration scale and demonstrating consistent quality and performance characteristics.
Wizz Air signed a 15-year, $1 billion offtake agreement for 527,861+ tonnes of Firefly SAF — the airline's first equity investment in SAF. Boeing and Clear Sky jointly announced support for testing and advancing Firefly's technology in July 2024. The Department for Transport provided a £2m Green Fuels, Green Skies research grant. The SAF Act 2026 now provides the mandatory blending framework that makes commercial-scale economics work.
| Stage | Company | Role |
|---|---|---|
| Feedstock | Anglian Water (pilot); all UK water operators (scale) | Biosolids supply |
| AD Infrastructure | Cambi, Monsal, STORTEC, BioteCH4 | Digestion pre-treatment |
| HTL Technology | Firefly Green Fuels | Bio-crude production |
| Parent & IP | Green Fuels Ltd | Technology origin & Royal Warrant |
| Hydroprocessing | Chevron Lummus Global | Technology licensing |
| Refinery Site | Haltermann Carless, Harwich | Host site for pilot & commercial plant |
| EPC Contractor | Petrofac | Plant design & construction |
| Independent Analysis | Cranfield University | Life cycle analysis & research |
| Offtake | Wizz Air | $1bn, 15-year SAF purchase agreement |
| Investment | Wizz Air, Boeing/Clear Sky, Builders Vision, DfT | Equity, grants, partnerships |
| Regulation | Department for Transport, CAA | SAF Act 2026, certification |
The Sustainable Aviation Fuel Act 2026, which received Royal Assent on 5 March 2026, is the commercial foundation that makes the entire Firefly model viable at scale. Before it existed, the economics of SAF were precarious — production costs far exceed those of fossil jet fuel, and airlines had limited incentive to pay a premium voluntarily.
The Act establishes a mandatory SAF blending obligation on UK jet fuel suppliers — requiring increasing percentages of sustainable aviation fuel to be blended into jet fuel sold in the UK year on year through to 2050. This creates a guaranteed minimum demand for SAF, underwriting the economics of capital-intensive production facilities. It is the same mechanism that made offshore wind commercially viable — a policy-backed demand floor that allows long-term investment decisions to be made with confidence.
The SAF Act does not just help Firefly. It creates a market for any organisation that can supply certified SAF feedstock. UK water companies collectively produce 53 million tonnes of sewage sludge per year. If even a fraction of that is directed to SAF production rather than agricultural spreading or incineration, the financial implications are material. The question is not whether this will happen — it is when, at what scale, and which water companies move first.
AMP8 (2025–2030) contains the largest investment in UK water infrastructure since privatisation. AMP9 (2030–2035) will be the first price review conducted under the new single water regulator established by the Water White Paper 2026. It will also be the first price review in which the commercial value of biosolids as a SAF feedstock is a real, quantifiable number rather than a speculative future possibility.
Water companies that have invested in advanced digestion — thermal hydrolysis, high-solids digestion, optimised dewatering — will be better positioned to supply the consistent, high-quality biosolids feedstock that SAF production requires. The investment case for upgrading sludge treatment infrastructure, which has historically been framed purely around cost reduction, now has a revenue upside attached to it.
Equally, water companies' bioresources strategies — currently focused primarily on biogas, biomethane and agricultural land application — will need to account for SAF as a third major outlet. The landbank pressures that are already tightening (as Germany's biosolids land application ban demonstrates) make diversification of biosolids outlets not just commercially attractive but strategically necessary.
Germany has already banned the land application of sewage biosolids in many circumstances, requiring incineration instead — a costly disposal route. The UK is under similar regulatory pressure. Water companies that develop SAF supply relationships now are building an alternative outlet before regulatory change makes the current primary outlet unavailable.
1. What is the quality profile of our biosolids output? SAF production via HTL requires consistent feedstock composition — solids content, organic loading, contaminant levels. Water companies should be characterising their biosolids outputs against SAF feedstock specifications now, not when the first commercial plant comes online.
2. Do we have the AD infrastructure to produce the right feedstock? Advanced digestion produces a more stable, better-characterised digestate than primary sludge. Investment in thermal hydrolysis and high-rate digestion has a direct SAF feedstock quality benefit — another reason to prioritise these technologies in AMP8 bioresources capital programmes.
3. How does SAF compare to our current biosolids disposal costs? Agricultural spreading, incineration and transport to third-party digesters all have cost profiles. Even at early commercial-scale SAF gate prices, the comparison may be compelling — particularly as landbank availability tightens and disposal costs rise.
4. Which water companies is Firefly talking to beyond Anglian Water? Anglian is the pilot feedstock supplier. The commercial plant will need significantly more feedstock. Water companies with large bioresources operations — Severn Trent, United Utilities, Thames Water, Southern Water — should be engaging with Firefly's commercial development team now rather than after the technology is ASTM-certified and demand is established.
5. What is our AMP9 bioresources strategy? The AMP9 price review will be set in a world where the SAF Act is in force, ASTM certification of the SBtJ pathway is likely complete or imminent, and at least one commercial-scale sewage-to-SAF plant is operating. Business plans that do not account for SAF as a bioresources outlet will be missing a material revenue line.
It is worth noting that this is not a speculative cleantech story. The Royal Warrant of Appointment held by Green Fuels Ltd — the parent company of Firefly — was granted when HM King Charles III was Prince of Wales, in recognition of Green Fuels' supply of sustainable fuel. King Charles has been one of the most consistent long-term advocates for exactly this kind of waste-to-resource circular economy thinking. The project has progressed from a research concept to a commercially backed, legislatively supported, Boeing-partnered venture with a billion-dollar offtake agreement. The question is no longer whether sewage sludge will become jet fuel. It is which water companies will be supplying it.
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