What if we told you the banana peel you threw away this morning could help power a transatlantic flight?
Welcome to FreeAstroScience — where we break down complex science so it feels like a conversation between friends. We're Gerd Dani and the Free Astroscience team, and today we're tackling something that sounds like science fiction but is already happening in labs and refineries around the world.
We're talking about SAF — Sustainable Aviation Fuel — a biofuel made from municipal solid waste. Yes, your everyday garbage. The same bags that pile up in landfills could soon help commercial planes fly with up to 90% fewer greenhouse gas emissions.
Sounds too good to be true? Stick with us to the end. By the time you finish this article, you'll understand exactly how it works, why it matters, and what stands between us and a cleaner sky. Let's get into it.
📑 Table of Contents
- 1. Why Can't Airplanes Just Go Electric?
- 2. What Exactly Is SAF — And Where Does It Come From?
- 3. How Do Scientists Turn Trash Into Jet Fuel?
- 4. The Numbers: How Much Can SAF Actually Do?
- 5. What Are Governments Doing About It?
- 6. If SAF Is So Great, Why Aren't We Using It Everywhere?
- 7. A Cleaner Sky Starts on the Ground
Why Can't Airplanes Just Go Electric?
Here's a number that should make you pause. Commercial aviation accounts for roughly 2.5% of all human-caused CO₂ emissions worldwide. That doesn't sound enormous — until you realize passenger flight demand is expected to double by 2040.
Cars and buses? They're steadily going electric. Trains? Many already run on clean power. But airplanes? They're a different beast entirely.
Long-haul flights demand incredible energy density. A transatlantic crossing needs fuel that packs a massive punch per kilogram. Batteries, for all their progress, simply can't match that energy-to-weight ratio — not yet, and likely not for decades on commercial scales. The engines, the infrastructure, the sheer physics of keeping hundreds of tonnes airborne for hours — all of it fights against easy electrification.
So the aviation industry is stuck. Growing fast, hard to electrify, and contributing more CO₂ every year. That's exactly why SAF has become the most promising path toward cutting aviation's carbon footprint at industrial scale.
What Exactly Is SAF — And Where Does It Come From?
SAF stands for Sustainable Aviation Fuel. It's a certified biofuel designed to replace conventional jet fuel — the kerosene-based stuff that powers every commercial flight you've ever taken.
What makes it "sustainable"? The feedstock. Instead of drilling petroleum from underground, SAF can be produced from municipal solid waste (MSW) — the ordinary mix of organic scraps, paper, cardboard, and plastics that cities collect every day.
Researchers at Tsinghua University, working alongside the Harvard China Project on Energy, Economy and Environment, recently demonstrated that this conversion is technically feasible. They proved you can take trash destined for a landfill or an incinerator and turn it into aviation-grade fuel.
And here's what makes it even more appealing: SAF is fully compatible with existing turbofan and turboprop engines. Airlines don't need new planes. Airports don't need new refueling systems. It's a drop-in replacement. The only thing that changes is where the fuel comes from — and how much carbon it releases.
On a full lifecycle basis, SAF cuts greenhouse gas emissions by 80 to 90% compared to conventional jet fuel. That's not a marginal improvement. That's a transformation.
How Do Scientists Turn Trash Into Jet Fuel?
This is where it gets fascinating. The process reads like an industrial recipe — step by step, raw garbage becomes something that can lift an Airbus off the ground. Let's walk through it.
Step 1 — Sorting the Waste
Mixed municipal waste arrives at the plant. It's a messy cocktail of organic matter, cardboard, paper, and plastics. Workers and machines separate out the usable material through a quality-based screening process.
Step 2 — Gasification
The selected waste enters a high-temperature thermo-chemical gasifier. Intense heat breaks it down into syngas — a gas mixture rich in hydrogen (H₂) and carbon monoxide (CO). Think of it as reducing solid junk to its chemical building blocks.
Step 3 — Cleaning the Syngas
Raw syngas contains impurities, tar, and contaminants. Before it can go any further, it passes through integrated purification and fine filtration systems. Clean syngas is essential — impurities would poison the next stage.
Step 4 — Fischer-Tropsch Synthesis
Here's where chemistry does its magic. The clean syngas enters a Fischer-Tropsch reactor, where catalysts convert hydrogen and carbon monoxide into long-chain hydrocarbons — specifically, linear paraffins. These are the molecular cousins of the compounds found in petroleum-based kerosene.
Step 5 — Upgrading
The crude liquid paraffins aren't quite ready for a jet engine. They undergo hydroisomerization and selective cracking — processes that reshape and refine the molecules into a kerosene fraction that meets strict aviation fuel specifications.
The final product? A certified, flight-ready biofuel.
| Stage | What Happens | Key Output |
|---|---|---|
| 1. Sorting | Municipal waste is screened and classified | Selected organic & carbon-rich material |
| 2. Gasification | High-temperature thermo-chemical breakdown | Syngas (H₂ + CO) |
| 3. Purification | Tar, impurities, and contaminants removed | Clean syngas |
| 4. Fischer-Tropsch | Catalytic synthesis of long-chain hydrocarbons | Crude liquid paraffins |
| 5. Upgrading | Hydroisomerization & selective cracking | Certified SAF kerosene |
The Numbers: How Much Can SAF Actually Do?
Let's talk scale — because a neat process means nothing if it can't operate at the size the world needs.
Right now, SAF represents less than 1% of global jet fuel consumption. That's tiny. But the growth potential is staggering.
According to the Tsinghua–Harvard research, if we scaled up waste-to-SAF conversion globally, municipal solid waste alone could produce around 50 million tonnes of SAF per year. That's roughly 62 billion liters of fuel, every single year.
What would that mean for the climate? It would reduce lifecycle CO₂-equivalent emissions from commercial aviation by approximately 16% worldwide.
Now, here's where it gets even more exciting. If we integrate green hydrogen — produced through electrolysis powered by renewable energy — into the Fischer-Tropsch stage and optimize plant efficiency, production could reach 80 million tonnes per year. That would cover 28% of global jet fuel demand and prevent up to 270 million tonnes of CO₂-equivalent emissions annually.
| Scenario | Annual SAF Output | Global Jet Fuel Coverage | CO₂-eq Avoided |
|---|---|---|---|
| Waste-to-SAF (baseline) | 50 million tonnes (62 billion L) | ~16% of lifecycle emissions cut | Significant reduction |
| With green H₂ integration | 80 million tonnes | 28% of global demand | Up to 270 million tonnes |
Those aren't just numbers on a page. Each tonne of avoided CO₂ is a tiny piece of a liveable future. And we get it from something we were throwing away anyway.
What Are Governments Doing About It?
The policy world isn't sitting still. Two regulatory frameworks are already pushing SAF adoption forward.
ReFuelEU Aviation
The European Union adopted Regulation 2023/2405, known as ReFuelEU Aviation. It requires fuel suppliers to provide EU airports with blends containing at least 3% SAF starting in 2026. That mandate scales up gradually — reaching 70% by 2050. It's one of the most ambitious clean-fuel mandates in aviation history.
CORSIA
At the international level, the ICAO (International Civil Aviation Organization) created CORSIA — the Carbon Offsetting and Reduction Scheme for International Aviation. The program aims to stabilize CO₂ emissions from international flights at 2020 levels. Airlines that exceed that threshold must purchase certified carbon credits to compensate.
Here's the practical connection: as SAF adoption grows, airlines using it can dramatically reduce their need to buy carbon offsets. That translates directly into financial savings for carriers — making SAF not just an environmental choice, but increasingly an economic one too.
If SAF Is So Great, Why Aren't We Using It Everywhere?
Honest question. And the honest answer? Money and scale.
SAF production costs remain 3 to 5 times higher than conventional fossil jet fuel. Building the industrial capacity to convert millions of tonnes of waste into fuel requires enormous investment. The technology works — but the factories, supply chains, and infrastructure to do it at global scale don't exist yet.
That gap is real, and we shouldn't pretend otherwise. The path from lab-proven to globally deployed is long and expensive.
But here's why optimism isn't naive. Decarbonization policies are tightening. Mandates like ReFuelEU create guaranteed demand. Technological improvements are steadily bringing costs down. And the feedstock — municipal waste — is one thing the world produces in abundance, with volumes growing every year in every city on Earth.
We've seen this pattern before. Solar panels were absurdly expensive in the 1990s. Today, they're among the cheapest energy sources on the planet. Scale, policy, and engineering have a way of bending cost curves. SAF is on that same trajectory.
A Cleaner Sky Starts on the Ground
Let's bring it home.
Aviation is growing. Electrification can't solve it — not with current physics and engineering. We need a fuel that works in today's engines, uses today's airports, and produces far less carbon. SAF checks every one of those boxes.
The idea that our discarded food scraps, cardboard, and plastics could fly us across continents with 80–90% fewer emissions isn't a dream. It's a demonstrated, certified, deployable technology. The challenge now is building enough plants, fast enough, to meet the scale of the problem.
We don't have to wait for a miracle. We just have to invest in what already works.
This article was written for you by FreeAstroScience.com — where we explain complex scientific ideas in plain language, because we believe knowledge belongs to everyone. At FreeAstroScience, we want to educate you to never turn off your mind and to keep it active at all times. Because, as Goya once reminded us, the sleep of reason breeds monsters.
Come back soon. There's always more to learn — and we'll be here, making sense of the science that shapes our world.
Sources
- Geopop — SAF, il carburante sostenibile per aerei: cos'è il biocombustibile prodotto dai rifiuti urbani, Davide Spinosa, 5 February 2026. Link
- EASA — European Union Aviation Safety Agency, SAF documentation.
- Interesting Engineering — SAF production processes reference.
- Tsinghua University / Harvard China Project on Energy, Economy and Environment — Research on MSW-to-SAF conversion feasibility.
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