Is sewage the future of green aviation?

Summary

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Podcast Summary: Short Wave — "Is Sewage the Future of Green Aviation?"

Date: June 17, 2026
Hosts: Emily Kwong & Regina Barber

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Episode Overview

This episode of Short Wave dives into the world of sustainable aviation fuels (SAF), specifically exploring wild new possibilities: could leftover cooking oil—or even human sewage—one day fuel your cross-country flight? Emily and Regina break down what it would take (chemically, technologically, economically, and politically) to decarbonize the aviation industry, spotlighting innovations, challenges, and the real numbers behind “greener” flying.

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Key Discussion Points & Insights

1. Current State of Sustainable Aviation Fuel (SAF)

• Virgin Atlantic's Milestone

  • In 2023, Virgin Atlantic operated a transatlantic flight powered entirely by a mix of biofuel and a synthetic alternative made from plant sugars.
    • Emily Kwong: “This flight was incredibly expensive, receiving up to 1 million British pounds from the UK government, all to prove a scientific point that a plane can fully run on something other than jet fuel...” (00:57)
  • The intent was to show that fossil fuels aren’t the only way—but scaling up is a huge challenge.

• Industry Pressures & Geopolitical Impact

  • Fuel prices surged due to the closure of the Strait of Hormuz from the Iran war, highlighting the need to break dependency on unstable foreign oil supplies.
    • Regina Barber: “Ticket prices have gone up. This has already affected my travel. This year, I've cut back.” (01:48)
    • Emily Kwong: “In a strange way, this global crisis has kicked down the door for a new kind of conversation about alternatives to jet fuel.” (02:00)
  • SAF is now seen as a national security issue as well as an environmental one.

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2. The Science of SAF: What Is It and How Does It Work?

• Chemistry & Types of SAF

  • Most SAF is made from cooking oils, fats, and greases. The key chemical process: hydroprocessed esters and fatty acids (HEFA).
    • Emily Kwong: “At a molecular level, they're similar to jet fuel. These long chains of hydrocarbons go through a chemical glow up to be something that airplanes can fly on.” (04:42)
  • Some SAF is created by converting ethanol from starches, like corn or cellulose, into jet fuel (alcohol-to-jet process).

• How Prevalent Is SAF?

  • It's already being blended in small amounts—especially at airports like LAX.
    • Joshua Hein: “So roughly 0.6% of the global jet fuel consumption is... used cooking oil and other fats, oils, greases.” (05:27)

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3. The Core Challenge: Scaling SAF

• Supply Limitations

  • There is nowhere near enough used oil or fat to meet global airline demands.
    • Joshua Hein: “What we need is a diverse portfolio... to enable the scale of SAF production globally to occur.” (05:58)

• Economic Hurdles

  • SAF remains much more expensive than conventional jet fuel, and supply chain limitations exacerbate costs.
    • Emily Kwong: “SAF is just extremely expensive to make.” (06:10)
    • Regina Barber: “De-risking this market is a big challenge for investors...” (06:23)

• Land Use Concerns

  • For crop-based biofuels, large-scale production could compete with food supplies and drive up food prices.
    • Emily Kwong: “We need land for crops. Do we also have enough to fuel cars and planes too?” (07:11)

• Alternative Pathways

  • Synthetic SAF can be produced using captured CO₂ and hydrogen—but it’s even more costly currently.
    • Emily Kwong: “It's just not practical right now to scale.” (07:59)

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4. Innovation Spotlight: Washington State’s Sewage-to-Jet-Fuel Program

• The Cascadia Sustainable Accelerator
  • A nonprofit alliance—including Alaska Airlines and Washington State University—dedicated to accelerating innovation in SAF production.
    • Emily Kwong: “The goal... is to make SAF for the Pacific Northwest... that portfolio Joshua was talking about, of all the different ways that SAF can be made in the future.” (08:51, 09:11)
  • Notable Quote (on sewage-to-fuel):
    • Joshua Hein: “We are working with companies that take post-anaerobic digested human sewage and turn that into jet fuel.” (09:30)
    • Regina Barber: “Sewage seems like the best fuel source... humans are always going to poop. Let's fly on it.” (09:40)

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5. Reality Check: Barriers to Mass Adoption

• Limited Commercial Scale

  • Out of 165 SAF projects announced, only 10 are producing commercial volumes.
    • Emily Kwong: “A recent Reuters investigation found... only 10 reported producing commercial volumes of SAF.” (10:01)
  • Barriers include high costs, supply chain issues, and the need for industry-wide collaboration.

• Ultimate Solution: Fly Less?

  • Both hosts acknowledge that reducing air travel itself is the most effective way to reduce aviation emissions.
    • Regina Barber: “The ultimate solution to all of this is just to, like, not fly, right? Cut back on flying.” (10:47)
    • Emily Kwong: “Driving emits much less carbon than flying.” (10:54)

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6. The Policy & Political Landscape

• Federal Policy Rollercoaster
  • SAF tax credits from the Biden administration were slashed by the Trump administration, reducing incentive for airlines.
    • Emily Kwong: “Last year, the Trump administration cut the SAF tax credit almost in half. Kind of took the heart out of the policy...” (11:01)
  • Despite federal cuts, some states—like Pennsylvania—are moving to support SAF production locally.

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7. Case Study: Pittsburgh International Airport’s Sustainability Strategy

• Microgrid Innovation
  • In 2021, Pittsburgh International Airport became the first major airport to run off its own microgrid (natural gas + solar)—providing resilience and setting a precedent for sustainability.
    • Christina Cassotis: “We can operate in any situation where the grid might go down.” (11:36)
    • Emily Kwong: “When the main grid that connects Pittsburgh goes down... the lights flickered for a couple of seconds and it kicked into gear.” (11:58)
• Pittsburgh’s SAF Ambitions
  • The airport aims to make its own SAF, relying on alcohol-to-jet and waste-to-fuel processes, including sewage.
    • Christina Cassotis: “There are live organs coming in, transplant teams coming in, and I feel like we have an obligation to make sure that no matter what, we don't close.” (13:20)

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Memorable Moments & Quotes

• The Power of Poop

  • Regina Barber (jokingly): “Sewage seems like the best fuel source... humans are always going to poop. Let's fly on it.” (09:40)

• Reality Check on Flying

  • Emily Kwong: “Driving emits much less carbon than flying.” (10:54)

• The Race to the Future

  • Emily Kwong: “Someone's got to do it. And maybe it'll be Washington, maybe Pennsylvania. Who knows?” (13:47)
  • Regina Barber: “We're in a race.” (13:51)

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Important Timestamps

• 00:57 — The first fully SAF-powered commercial transatlantic flight
• 05:27 — Current SAF use is only 0.6% of global jet fuel
• 06:44–07:08 — Critique and limitations of crop-based (bio) fuels for aviation
• 09:30 — Turning sewage into jet fuel: Innovation in motion
• 10:01 — Only 10 out of 165 SAF projects are at commercial scale
• 11:01 — Federal policy setback: SAF tax credits slashed
• 11:36 — Pittsburgh International Airport’s microgrid and resilience
• 12:45 — Plans for a local sustainable jet fuel plant
• 13:20 — The critical importance of airport resilience for medical needs

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Closing Thoughts

The episode ends on a mix of optimism and realism, highlighting both technological promise (from cooking oil to human sewage) and the massive economic, political, and logistical hurdles to decarbonizing flight. As the hosts quip about the “race” between states and institutions, listeners are reminded that every step counts on the path to climate action—but for now, flying green remains more aspirational than accessible.

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Transcript

[Angie]

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[Emily Kwong]

You're listening to Short Wave from NPR. Hey, shortwavers, Regina Barber here and Emily Kwong. And today we are taking to the skies on the wings of cooking oil. Well, today Flight 100 is flying from London to New York on sustainable fuel. Okay, that's.

[Regina Barber]

Richard Branson is the co founder of the Virgin Group. Was this the first flight run entirely on alternative jet fuel?

[Emily Kwong]

Yes.

[Regina Barber]

Wow.

[Emily Kwong]

Virgin Atlantic in 2023 operated a flight powered by biofuel and a synthetic alternative made from plant sugars. This flight was incredibly expensive, receiving up to 1 million British pounds from the UK government, all to prove a scientific point that a plane can fully run on something other than jet fuel, which, as you know, comes from fossil fuels.

[Regina Barber]

I love this. Because what's getting us into the air now? It's not great for a planet.

[Joshua Hein]

No.

[Emily Kwong]

And at any given moment, there are thousands of planes in the air, and jet fuel is the only thing energy dense enough and cheap enough to keep that industry aloft. But the war in Iran has put a damper on those economics. Ryan Spies, the managing director of sustainability for Alaska Airlines, is definitely feeling the pinch.

[Joshua Hein]

We were on track for a really, really great year. And fuel prices have, you know, put us back hundreds of millions of dollars.

[Regina Barber]

Right. The Strait of Hormuz has been effectively closed for months, so some airlines are running low on fue. Ticket prices have gone up. This has already affected my travel. This year, I've cut back.

[Emily Kwong]

Oh, really?

[Regina Barber]

Yeah.

[Emily Kwong]

Well, honestly, that is an airline company's worst nightmare. They need our butts in those seats to meet their bottom line. So in a strange way, this global crisis has kicked down the door for a new kind of conversation about alternatives to jet fuel. And someone who pointed this out to me is Annie Petsonk, the former assistant Secretary of Transportation for Aviation and International affairs under the Biden administration.

[Regina Barber]

Because of the Iran war fuel price shocks, a number of airlines and a number of policymakers are starting to see alternative fuel as a national security matter. We can produce our own fuel here in the United States and not be dependent on foreign oil producers. Today on the show Greener Flights, we explore a bunch of alternatives to jet

[Emily Kwong]

fuel, their chemistry, their cost, and what it would actually take to decarbonize the aviation industry for good. I'm Emily Kwong.

[Regina Barber]

And I'm Regina Barber. And you're listening to Shortwave, the science podcast from npr.

[Angie]

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[Regina Barber]

All right, Emily, let's start with basics. Okay, so the chemistry of alternatives to jet fuel. So some people call this fuel sustainable aviation fuel, or saf. So S a F saf. What's it made out of?

[Emily Kwong]

Yeah, so the most commonly used SAF is made from cooking oils, fats and greases.

[Regina Barber]

I love those.

[Emily Kwong]

Yeah, at a molecular level, they're similar to jet fuel. These long chains of hydrocarbons go through a chemical glow up to be something that airplanes can fly on.

[Regina Barber]

Cool.

[Emily Kwong]

This process is known as hefa, which stands for hydroprocessed esters and fatty acids. And by the way, that Virgin Atlantic flight we mentioned earlier was mostly powered by HEFA fuel. And this fuel is chemically similar to renewable diesels, which are already used in land and aquatic vehicles.

[Regina Barber]

And this fuel works for planes?

[Emily Kwong]

Yeah, it does. And the way it works is refineries will blend HEFA with regular jet fuel.

[Joshua Hein]

And Emily, I'm pretty confident you have Flown on a plane with some of this stuff on there.

[Regina Barber]

Wait, so they're already using this kind of jet fuel, this blend right now?

[Emily Kwong]

A very small amount, yes.

[Regina Barber]

Okay.

[Joshua Hein]

If you flew out of LAX within the last few years, it's likely been on a plane you've been on. So roughly 0.6% of the global jet fuel consumption is. Is this used cooking oil and other fats, oils, greases.

[Emily Kwong]

Joshua Hein is the director of the Bioproducts Sciences and Engineering Lab at Washington State University. And he explained to me that the main problem with SAF isn't the chemistry. It's not the science, it's the economics.

[Regina Barber]

Yeah. So what is the supply like for leftover cooking oil? I'm guessing there's not enough.

[Joshua Hein]

No, there. There's not enough. So what we need is a diverse portfolio of lots of different technologies that will enable the scale of SAF production globally to occur.

[Emily Kwong]

So the scale question is hard. And for Nafisa Lohualla, a fellow with the think tank Resources for the Future, the supply chain problem exists because of the underlying cost issues. SAF is just extremely expensive to make.

[Regina Barber]

Basically, de risking this market is a

[Christina Cassotis]

big challenge for investors, for private investors

[Regina Barber]

to feel comfortable, you know, spending their money here. Yeah. You said that the UK government granted 1 million British pounds to the Virgin Atlantic flight. So are there other ways to make SAF this sustainable aviation fuel besides cooking oil?

[Emily Kwong]

There are in fact, 11 conversion processes for SAF production have been approved by regulators. One of the most promising is the alcohol to jet process, where you convert starches like corn or cellulose biomass into ethanol, which then gets converted into jet fuel. It's technically possible, but scale it again. That scale question for airplanes would take a lot of financial investment and raw material.

[Regina Barber]

Right. Because all of this requires a lot of land.

[Emily Kwong]

Yes, yes. And that is a major critique of bio based fuels overall, their potential negative impact on land use and even food prices. I mean, we need land for crops. Do we also have enough to fuel cars and planes too?

[Regina Barber]

Yeah. I remember in the early 2000s, I was at Washington State University, a big agriculture school, and there was this huge push for biofuels made from things like corn. But then there were these environmental concerns. Like some people thought it could be better to use the land for other things, like solar panels, for instance, instead of crops. Although I should say, Emily, this debate was mostly about cars and the huge fuel demand that would create.

[Emily Kwong]

That's fascinating.

[Regina Barber]

Yeah. So is there a way to use something other than biofuels?

[Emily Kwong]

It's a Very good question. Yes, there is a way to make SAF out of thin air.

[Regina Barber]

What?

[Christina Cassotis]

Yeah.

[Emily Kwong]

The way you do this is you combine captured carbon dioxide, say from direct air capture, with hydrogen atoms found in water. And those liquid hydrocarbons can be converted into saf. However, this synthetic process is even more expensive than the bio based processes. So it's, it's just not practical right now to scale.

[Regina Barber]

Yeah, honestly em, all this sounds like a chicken and an egg problem. Like SAF is too expensive and resource intensive to make. So supply is low. So planes keep running on jet fuel

[Emily Kwong]

and the cycle just kind of repeats. Yeah, yeah, yeah, yeah. And I suppose that is where a new 20 million venture in Washington state is trying to break through.

[Regina Barber]

State and aviation leaders launched the Cascadia Sustainable Accelerator. It's a new nonprofit designed to help grow the region's clean fuel industry.

[Emily Kwong]

The goal of the Cascadia Accelerator in your home state of Washington is to make SAF for the Pacific Northwest. Alaska Airlines is a partner. Washington State University is a partner. They want to create a reference library. Basically that portfolio Joshua was talking about. Of all the different ways that SAF can be made in the future, being

[Joshua Hein]

able to source and find these reference materials, that's what we're hoping to really enable here in the next year.

[Emily Kwong]

Joshua is the technical lead for this project and a self described fuel nerd. His lab has already received SAF samples from 40 different institutions.

[Joshua Hein]

You know, we are working with companies that take post anaerobic digested human sewage and turn that into jet fuel.

[Emily Kwong]

It's a real twist on another man's trash.

[Regina Barber]

You know, this is so cool. Honestly, like sewage seems like the best fuel source. I mean I love it. Because humans are always going to poop. Let's fly on it.

[Emily Kwong]

You know, you make a good case.

[Regina Barber]

Thank you. But how much of this is like aspirational? Because planes only run on this tiny amount of stuff now.

[Emily Kwong]

Yeah, also true. I mean, exciting as this venture is, it has a lot to prove. A recent Reuters investigation found that of the 165 SAF projects that have been announced by airlines over the last few years, only 10 reported producing commercial volumes of SAF.

[Regina Barber]

Wow. Just 10.

[Emily Kwong]

Just 10. Because there's so many obstacles to doing this. There's high upfront costs, we have the raw materials question and also just the amount of cooperation needed between so many different groups, government, industry and research to truly make SAF at scale and reinvent flying as we know it. And that's kind of what I want to spend the rest of the episode talking about Gina. Just the sheer amount of collaboration and political will that would have to happen to decarbonize aviation.

[Regina Barber]

That would be amazing if it happened, though. The ultimate solution to all of this is just to, like, not fly, right? Cut back on flying.

[Christina Cassotis]

Yeah.

[Emily Kwong]

Climate experts would definitely back you up on this. Driving emits much less carbon than flying.

[Regina Barber]

So we should just road trip more, right?

[Emily Kwong]

Yeah, yeah. Short distances. Maybe drive instead of fly. This, of course, doesn't solve the problem, though, of decarbonizing aviation in the first place. That would take federal policy. Now, there were SAF credits put in place by the Biden administration in an effort to incentivize airlines to find alternative fuels. But last year, the Trump administration cut the SAF tax credit almost in half. Kind of took the heart out of the policy to make SAF desirable for U.S. airlines.

[Regina Barber]

So the political will is just not there anymore.

[Emily Kwong]

Not at the federal level right now, no. But at the state level, in the state of Pennsylvania, it's a slightly different story.

[Christina Cassotis]

The grid is our backup. We can operate in any situation where the grid might go down.

[Emily Kwong]

Christina Cassotis is the CEO of the Allegheny County Airport Authority, which operates Pittsburgh International Airport. Now, this airport's kind of interesting. Back in 2021, Pittsburgh became the first major airport in the world to be powered by its own micro grid.

[Regina Barber]

Oh.

[Emily Kwong]

Run on five natural gas turbines and eight acres of solar, which is super helpful when the main grid that connects Pittsburgh goes down like happened last year,

[Christina Cassotis]

the lights flickered for a couple of seconds and it kicked into gear. And we didn't even notice until a

[Emily Kwong]

few weeks later when London's Heathrow Airport had to shut down for a day for a similar reason.

[Christina Cassotis]

And somebody on my staff said, oh, you know, that just happened to us.

[Regina Barber]

And we were like, what?

[Christina Cassotis]

We didn't even know.

[Regina Barber]

They're just living off the grid. This airport is living off the grid.

[Emily Kwong]

They are, yeah. And this self sufficiency, this can do attitude has now inspired the airport to figure out how to make SAF to fuel they're planes. So last year, the airport announced it was teaming up with a company to build a plant to one day turn these starches into jet fuel.

[Regina Barber]

So they're going to use this alcohol to jet fuel process? Yes.

[Emily Kwong]

Though they are also exploring the waste to fuel pipeline, too. They just want to make SAF for Pittsburgh planes.

[Regina Barber]

It's the sewage, I'm telling you. I love it.

[Emily Kwong]

Yeah, we'll see what they come up with. By the way, Christina told me in an email that she doesn't anticipate any land use changes or impacts to existing commodities. For the sake of this SAF production plant, she wants to see that plant built near the Pittsburgh airport in the next two years. All of this to make the airport even more self sufficient. Because Pittsburgh is a health care town, people need to get reliably flown in. And organs too.

[Christina Cassotis]

Every day there are live organs coming in, transplant teams coming in, and I feel like we have an obligation to make sure that no matter what, we don't close. It's the same energy we bring to making sure that no matter how much snow is falling, those runways stay open. There's a real need for airports to be resilient. And I feel like let's, let's just go.

[Regina Barber]

I mean, they did make this micro grid happen, right? So maybe they could make a breakthrough with SAF too.

[Emily Kwong]

Someone's got to do it. And maybe it'll be Washington, maybe Pennsylvania. Who knows?

[Regina Barber]

We're in a race.

[Emily Kwong]

We probably should race for this. The planet may be counting on us.

[Regina Barber]

Emily Kwong, my shortwave co host, thank you so much for reporting.

[Emily Kwong]

Oh my gosh, thank you so much, Gina. This was really fun.

[Regina Barber]

This episode was produced by Hannah Chin. It was edited by Brent Baughman and our showrunner, Rebecca Ramirez.

[Emily Kwong]

Special thanks to Daniel Offman, Sarah Robbins and Julia Simon. Tyler Jones checked the facts. Kwesi Lee was the audio engineer. I'm Emily Kwong.

[Regina Barber]

And I'm Regina Barber. Thank you for listening to Short Wave from.

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