MADDIE SOFIA, HOST:
You're listening to SHORT WAVE from NPR.
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SOFIA: Hello, and happy world toilet day - yes, that's a thing, and here on SHORT WAVE, we are taking it very literally and bringing you some toilet-based science.
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TAK-SING WONG: Imagine a toilet that can always keep itself clean, without leaving streak of human waste, that just makes it more appealing for people to use it - for example, in the case of public bathroom.
SOFIA: I mean, I've definitely gone into a public bathroom and been like, I'm going no further.
WONG: (Laughter) Yes. Yeah.
SOFIA: That's Tak-Sing Wong. He's a biomedical engineer at Penn State University, and he's trying to solve what he has called a universal problem, a problem as old as time.
WONG: Poop is sticky to the surfaces.
SOFIA: (Laughter) So basically you're saying, like, that poop sticks to a toilet bowl, is what you're saying.
WONG: Yeah. When a poop sees this surface, it just sticks on it.
SOFIA: Here's the thing - Tak-Sing isn't focused on this because he's an advocate for streak-free toilets; it's that getting all this sticky poop off the sides of the toilet takes water, and in areas of the world that use flushable toilets, it's a lot of water.
WONG: Everyone flush multiple times every day, and each flush takes about a couple liters of water. And if you multiply this to global population who have access to this flush toilet, it's tremendous amount of water. It is estimated that there's over 140 billion liters of fresh water just flushed down the drain every day.
SOFIA: Today on the show, we learn about a super slippery coating that could make toilets more efficient, plus a recipe for making synthetic poop - you know, in case you need that.
All right, you ready to talk about some toilet science?
WONG: Yes, I'm ready.
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SOFIA: We're talking with researcher Tak-Sing Wong today on the holiday of all holidays - world toilet day. Tak-Sing has spent years developing a nonstick coating that can be used in toilet bowls, and his inspiration came from kind of an awesome place.
WONG: The original inspiration is from this carnivorous plant called a pitcher plant.
SOFIA: Ooh, the pitcher plant, the, like...
WONG: The pitcher plant, yeah.
SOFIA: ...The one that eats bugs.
WONG: Exactly, yes.
SOFIA: As their name suggests, pitcher plants kind of look like water pitchers - think the Kool-Aid Man but without the creepy little face. There's an opening at the top of the plant the shape of a teardrop. And on the rim of that opening, some pitcher plants have these microscopic little scales that can trap water or plant nectar, and that trapped layer of liquid acts as a slippery little lubricant.
WONG: So this pitcher plant has evolved this really slippery coating that, when bugs like ants walk on this surface, they just slide off from the slippery surface and get digested by the plant. It's like a waterslide.
SOFIA: Tak-Sing borrowed the idea of this lubricant-infused surface to create a slippery coating called LESS. It's a spray that keeps poop and pee moving once they hit the toilet bowl. Can you just define what LESS stands for? Like...
WONG: Yeah. LESS is an acronym - stands for Liquid-Entrenched Smooth Surface.
SOFIA: Liquid-Entrenched Smooth Surface.
WONG: That's correct. And by having this LESS coating, you use less water. You use less cleaning chemical...
SOFIA: Oh, I see what you did there.
WONG: ...To clean the surface. Yeah (laughter).
SOFIA: I see - that's very clever there.
The coating comes with two parts. The first layer is made up of microscopic little hair-like material.
WONG: It's kind of like a hair or grass structure. You can imagine it's like a grass structure. But the size of this is about nanometer thick.
SOFIA: Oh, so very small.
The second layer is a lubricant made out of silicone that attaches to the tiny little hairs in the first layer.
WONG: And in combination of these two materials, then it becomes super slippery. Even poop doesn't stick on it.
SOFIA: Tak-Sing says it takes about five minutes to apply the whole shebang. And in order to test out the coating, they had to do some poop-based experiments.
So in one test that I saw, you were kind of trying to look at how artificial feces stuck to a toilet with your new coating versus stuck to a commercially available toilet.
WONG: (Laughter) That's right, yeah. So after we designed this coating, we needed to find some way to test it, right? And of course, the best thing is we test with the real human waste.
WONG: But in the lab setting, if I asked my graduate students to do it, they probably wouldn't want to do it for a long time.
SOFIA: Yeah, yeah.
WONG: So that's why we asked our collaborators from Cranfield University to see if there's a synthetic version of this human waste, that we can emulate its property. And then they sent us this recipe, and this, what I call the synthetic poop, is seven component materials that compose of peanut oil, miso, yeast and other materials. You mix them together, and we can control the property such that it can simulate the actual physical property of real human waste.
SOFIA: Tak-Sing, when you were younger, were you like, one day I'm going to make artificial poop in the name of science?
WONG: Yeah, I - yes, in the name of science. That's right.
SOFIA: So you - this wasn't a surprising turn in your career for you at all?
WONG: I wasn't expecting that at one point in my career we are making synthetic poop, but this is a very big problem. And as you mention, in the name of science and global health, we're happy to do that.
SOFIA: Tak-Sing sent me some videos of these experiments, and unfortunately - or very fortunately for you, dear listener - the videos do not have sound.
So I'm looking at two toilets. I'm watching somebody, I assume a graduate student, some poor graduate student, has flicked some of this artificial poop...
WONG: Mmm hmm. Right.
SOFIA: ...Onto the commercially available toilet. And it's kind of (laughter) - it kind of sticks, and it's, like, sliding down towards the little toilet hole. But it's making its way slowly. And then...
SOFIA: ...When they flick the poop onto your toilet, it just slams down to the bottom. Like, it's very impressive. It just, like, literally just goes right down there, immediately.
WONG: Thank you, yeah.
WONG: It takes us some time to create such a powerful poop-repellant coating.
SOFIA: After they went through the fake poop trials, it was time for the real thing.
But you also did experiments with actual, like, human feces, right?
WONG: That's correct.
SOFIA: And you - tell me if I'm wrong. Basically, you compared it to a service with your LESS coating on it - ceramic, which is common toilet material; Teflon, which is, you know, historically not sticky; and silicone. Tell me about the results of that experiment.
WONG: So after we test with the synthetic poop, we are very confident that this will work on the real human feces. In this test, they collect this human feces from three volunteers. They mix it. And then in the test, they have - they assign a setup where they put our coating surface - ceramic, Teflon and silicone - and what they do is they drop the human feces - which they put it in a pancake shape - onto each of these surfaces.
So what happens is that except our coated surfaces, which the human feces doesn't stick on it, all the other surfaces, the human feces just sticks to it and cannot be removed easily.
SOFIA: Yeah. How do you calculate how - like, how much less stickier your coating is?
WONG: So this goes back to our laboratory. We use an instrument that can measure the adhesion between the synthetic poop and the surface. And we compare this adhesion force with coated and uncoated surfaces. In our laboratory test, we find that the surfaces that is coated with our LESS coating is 90% less adhesive than the one that's just without a coating.
SOFIA: So in the U.S., an average toilet uses about 1.6 gallons per flush, and about half of that is used to get your waste off the sides of the bowl after you flush, and the other half is used to propel the poop through the pipes. Tak-Sing says his coating saves you the 50% you would normally need to clean the bowl.
So you can save 50% of that flush water because you're saving the water that is sticking or, like, helping get all the poop off the toilet bowl?
WONG: That's correct.
SOFIA: All right. But you still need water to shoot it down the pipe.
WONG: You still need that, yes...
SOFIA: Yeah (laughter).
WONG: ...To transport the waste. Yeah, that's right.
SOFIA: The main downside of the coating is it doesn't last forever. The top layer needs to be reapplied fairly frequently, and for high-traffic toilets, like public restrooms, that's a problem.
WONG: The second layer requires replenishment overuse, and if we can make it last longer, particularly for high-traffic toilet, I think that will be good. But again, like, reapplying this coating is very simple and straightforward; everyone can do that. And we hope the benefit will be way exceeding the downside, definitely.
SOFIA: Right now the coating is about $20 per kit. Tak-Sing says that would last you a few months, depending on how much you use your toilet. The technology is impressive, but before it can make a global impact, it'll probably have to last longer and cost less. Tak-Sing's results were published yesterday in the journal Nature Sustainability, and that's not all that was published there.
WONG: We do have the formula, the recipe, to create a synthetic poop in the paper published in Nature Sustainability.
WONG: If people are interested to make it at home, they're welcome to. I don't know why. But yeah (laughter), we do have the recipe there.
SOFIA: It's really a public service you're doing there.
SOFIA: OK. Tak-Sing, this was really fun. I really appreciate you.
WONG: Yeah. Thank you, Maddie. Yeah, nice talking to you.
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SOFIA: Today's episode was produced by Brit Hanson and edited by Viet Le. I'm Maddie Sofia. Thanks for listening to SHORT WAVE from NPR.
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