Revolutionizing Space Water Systems: Dr. Paul Westerhoff on UV Light, Biofilms & the ISS

Susan Wise: Welcome to Stars Launch Pod: Space, Technology, and Research Sciences, brought to you by Starsciences.org, where we connect, collaborate, and accelerate. I’m your host, Susan Wise, and joining us on the podcast today is Dr. Paul Westerhoff, Regents Professor and Fulton Chair of Environmental Engineering at Arizona State University.
Welcome to the podcast, Paul.

Paul Westerhoff (ASU): Thanks, Susan. Nice to be here.

Susan Wise: We’d love to know a little more about you and what you’re doing to further the space industry.

Paul Westerhoff (ASU): Sure. I’m an environmental engineer, and I love water. I grew up on the East Coast, where there was plenty of water. Then I moved to Colorado—less water. Now I live in Arizona, and there’s even less. What I realized here in Arizona is that we rely on rivers that bring us water, but most of it eventually evaporates.
I haven’t historically done much with NASA, but I’ve worked extensively with other federal agencies like the National Science Foundation (NSF). There was an opportunity through NSF to collaborate with CASES to plan an interesting experiment for the International Space Station (ISS). I saw that as a really cool challenge: how is something we’re studying about water here in Arizona relevant on the space station? So I approached it as a science challenge, more than a pure technology challenge. Hopefully, we can get into that today.

Susan Wise: I’d love to hear more about that! So tell us—what did that entail regarding water on the International Space Station? I know it’s highly valued, hard to get, and hard to keep.

Paul Westerhoff (ASU): Right. The natural thing people think about is astronauts needing to drink water, go to the bathroom, or shower. But water is actually used in about 21 different systems on the ISS—not just for drinking, sanitation, and food.
It’s also used in radiation shielding and thermal insulation. You can’t bring up traditional radiator fluids because they’re toxic, so water’s unique thermal and radiation-protective properties make it invaluable.

The station is essentially like a giant submarine—it gets humid because you can’t just open a window for fresh air. So they condense that humidity back into liquid water and reuse it again and again. Water cycles through the system many times.

And whenever something stays wet, it grows what we call a biofilm—that slimy layer, like what forms on your teeth or inside a sink. That’s a biofilm. It grows on any moist surface, and it causes real problems on the space station. So that became our main focus: understanding biofilms from both a biological and technological point of view.

Susan Wise: Oh, interesting!

Paul Westerhoff (ASU): We reached out to researchers here at ASU and at Texas State University who had studied biofilms in space. They’d looked at how adding chemicals—like chlorine, iodine, silver, or hydrogen peroxide—affects biofilm growth. Those methods work, but they require storing and handling chemicals, which is tricky in space.

So I thought, here’s an opportunity. We have a chemical-free technology that controls biofilms using UV light. UV light breaks the DNA of bacteria and microorganisms, disinfecting surfaces effectively.

You’ve probably seen UV systems since COVID—like those airport escalator handrails that claim to be disinfected by UV light. It’s also used in soda machines to keep flowing water clean. But the challenge is that biofilms grow on surfaces, not just in the flowing water.

We’ve developed a technology using optical fibers—thin, flexible fibers, even thinner than a human hair—that emit UV-C germicidal light along their sides, like glow sticks. You power them at one end, and they “glow” UV light along their length. Everything within that glow zone gets disinfected.

We can place these fibers inside tubing or storage tanks to prevent biofilm growth. What we wanted to learn was: biofilms grow differently in space than on Earth—so how do they respond to UV light in microgravity?

Susan Wise: That’s fascinating. I can actually relate. We built our home with a well system, and over time, I noticed the water flow slowed down. I assume biofilms were building up in the pipes. And since we’re on a septic system, I can’t just pour bleach through—it would harm the ecosystem. So this is really interesting to me.

Paul Westerhoff (ASU): Exactly—that slimy stuff you clean out of the sink or even your dog’s water bowl. It’s slippery until you scrub it off—that’s biofilm.

We’re focused on how to deliver UV light to those surfaces. Light usually travels in straight lines, so it’s hard to shine inside curved pipes or tanks. But with our flexible fibers, we can bend them wherever needed to target biofilms directly.

Susan Wise: Was that your “aha” moment?

Paul Westerhoff (ASU): Kind of! It was a scientific “aha” moment that works for both the space station and right here on Earth. On Earth, biofilms cause about $4 trillion in economic damage every year.

They corrode metal surfaces—a process called biocorrosion—essentially, bacteria “eat away” at structures. On the ISS, that means bacteria can literally degrade parts of the station. Biofilms also grow on the hulls of ships, increasing drag and fuel use by around 10%.

Susan Wise: Wow. What about in medical settings—like tubing and catheters?

Paul Westerhoff (ASU): Exactly. In hospitals, biofilms grow in catheters—those tubes used for drainage. Every year, over 13,000 people in the U.S. die from infections caused by catheter-associated biofilms. The bacteria grow in the biofilm, enter the bloodstream, and cause deadly infections.

You also see biofilm as mold on surfaces after floods or leaks. People have to scrape it off and use toxic paints or chemicals to prevent regrowth. UV light can control mold, too, without chemicals. The big challenge has been figuring out how to deliver UV light effectively to those hidden, moist surfaces.

Susan Wise: So what’s been your biggest challenge so far?

Paul Westerhoff (ASU): Definitely the logistics of doing an experiment on the ISS. It’s not like walking down the hall to your lab and tweaking something. You get one shot.

In August and September this year, we had two launches—one carrying the biological samples (the bacteria that form the biofilms), and another carrying the hardware, including our light engines. We worked with a company called BioServe, which specializes in ISS experiments.

They helped us build small cassettes to grow bacteria, integrate our fiber system, and ensure everything met safety and performance standards. It’s a huge process—testing for vibration, vacuum conditions, and certification.

The astronauts will start the experiments in December, and they’ll run for about 30 days. We’ll get the results once the samples return. So yes—one chance, fingers crossed!

Susan Wise: One shot indeed! Having good partners must be critical.

Paul Westerhoff (ASU): Absolutely. The science itself isn’t the hardest part—it’s the execution in such a unique environment. Having experienced partners like Cheryl, Bob, and the BioServe team made all the difference.

Susan Wise: And if this succeeds, it could change everything—and save billions. Paul, what one piece of advice would you share with our listeners?

Paul Westerhoff (ASU): I’d say there’s tremendous opportunity to do exciting science in space—but it’s just as valuable to connect it back to challenges here on Earth.

In addition to NSF support, we’ve also worked with NASA funding through a startup company that developed these side-emitting UV fibers. Having that NASA connection adds credibility and opens doors.

Some might ask, “Why focus on something for just a handful of astronauts in space?” But space research pushes us to solve problems in creative, rigorous ways—and those lessons translate back to Earth. I’m really glad I spent the 100-plus hours writing the proposal and that NSF decided to fund it.

Susan Wise: I’m so excited for you! I can’t wait to hear how it goes. Before we wrap up, do you have a passion project—past or present—you’d like to share?

Paul Westerhoff (ASU): Sure. When you think about the ISS, remember—astronauts can’t open a window. Everything is recycled: air, water, humidity. Here in Arizona, it’s the opposite—very dry. We import water, and it evaporates.

My passion project is figuring out how to recapture that water vapor from the air and condense it back into usable water—a new kind of recycling. Instead of just recycling graywater or wastewater, we’d recycle water vapor back into liquid water.

When I was a kid in New Jersey, my job was emptying the basement dehumidifier every day. Inside it, I’d see slime growing on the coils—that same biofilm! My UV fibers can help solve that slimy problem.

So, everything connects—natural and engineered water cycles, space and Earth. I’m fascinated by how we can reuse water more efficiently, whether through nature or technology.

Susan Wise: I love what you’re doing, Paul. If it works in space, it can work here on Earth too. Thank you so much for sharing your story. We’ll definitely want an update after the first of the year—fingers crossed for December!

Paul Westerhoff (ASU): Thanks, Susan.

Susan Wise: And thank you all for joining us. Remember, at Stars Launch Pod, we connect, collaborate, and accelerate. Join us at Starsciences.org for a free one-year membership—just use promo code FRIENDS321.
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