Every other Friday, the Outside/In team answers one listener question about the natural world.
This week, Jeannie from Burlington, Vt., asked us about wastewater treatment plants. She said she's "curious more about how they work in general," but she also asked how many "are at risk of becoming inundated during extreme flooding events as those become more frequent."
Outside/In’s Felix Poon and Nate Hegyi looked into it.
Transcript
This has been edited for length and clarity.
Felix Poon: To understand how waste treatment plants work, I spoke with Sri Vedachalam, a water and climate policy specialist. And, you know a lot of cities and towns combine wastewater (from our toilets and sinks) and stormwater (from street gutters, sewers, and open drainage canals). So Sri says the first step is to filter out all of the stuff that shouldn’t go into the plant.
Sri Vedachalam: Imagine a big screen that simply blocks out big pieces, maybe some boulders some rocks, plastics. These pipes are huge. Sometimes there are shopping carts, I mean, literally.
Nate Hegyi: I always see the ubiquitous shopping cart in a river or a ditch. So these filters stop them and other unseemly things.
Felix Poon: The second step, Sri says, is to add a whole bunch of bacteria into the water, which eat the poop, transforming it into a kind of nutrient-rich sludge that falls to the bottom of the water. And some facilities actually sell or give this stuff away to farmers as fertilizer.
Nate Hegyi: That seems like actually a pretty climate-friendly solution.
Felix Poon: Yeah, and the water is 99% clean at this point. So the third and final step is to disinfect it with ultraviolet ozone or chlorine to kill off bad bacteria, viruses and parasites. After that, they discharge the water, usually into a river. And as gross as it sounds, this water is tested and generally clean and safe to drink. Like, cities downstream from water treatment plants do end up using this water for their own drinking supply.
Nate Hegyi: Las Vegas uses that water pretty much in this full almost closed-circle recycling program that allows them to be able to have drinkable waters coming out of the taps in the middle of the desert.
Felix Poon: I mean, you know, Las Vegas right? What happens in Vegas stays in Vegas. Quite literally.
Nate Hegyi: Quite literally.
Felix Poon: But you know, it’s not just Vegas. This is how it’s always worked, across the planet, like water on this planet is billions of years old.
Sri Vedachalam: Maybe millions of years ago, it came out of a dinosaur, you know, maybe that's the pee of a dinosaur. Who knows. That's the process. It's all old and recycled in some way or the other.
Nate Hegyi: Okay so we know how these wastewater treatment plants work. But going back to that question, are they threatened by climate change?
Felix Poon: Yeah, so there are a few ways in which they’re vulnerable to climate change. One of them is because of their very design.
Sri Vedachalam: They rely a lot on gravity. So because of that, they end up being located in the lowest spot in the city topography.
Felix Poon: So this means they’re vulnerable to flood damage and even power outages. Worst case scenario they’d have to stop treatment temporarily, which means untreated wastewater ends up in our waterways.
Nate Hegyi: Oh, not good.
Felix Poon: There’s not much we can do about this besides build barriers around the treatment plant, or build new plants on higher ground. And then the other thing is because a lot of our systems have combined wastewater and stormwater, every time there’s a superstorm it super multiplies the volume of our waste, and treatment plants can’t keep up, so wastewater will go untreated into our waterways. And obviously because of climate change, there’s more superstorms. And in fact, one-third of all wastewater systems in the U.S. are at risk of flooding if a big storm hits, according to an AP report.
Nate Hegyi: Wow.
Felix Poon: So agencies and utilities are trying to separate wastewater systems from stormwater systems.
Nate Hegyi: I hope that we figure this out soon because if we don’t, we’re gonna be in one stinky pickle.
If you’d like to submit a question to the Outside/In team, you can record it as a voice memo on your smartphone and send it to outsidein@nhpr.org. You can also leave a message on our hotline, 1-844-GO-OTTER.
