How building wetlands could allow the world to recycle water

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Intro: This is Berkeley Voices. I’m Anne Brice.

Narration: In the second half of the 20th century, California’s population exploded.

[Music: "Stucco Grey” by Blue Dot Sessions ]

To keep all these people going, the state needed a source of water. Most of the water supply that was then built for cities came from snowmelt and rainfall collected in the mountains.

But now, California’s cities can’t rely so heavily on that water supply anymore.

David Sedlak: That water infrastructure that our grandparents and great-grandparents built for us is no longer able to deliver what we expect.

Narration: David Sedlak is a professor in the Department of Civil and Environmental Engineering and director of the Berkeley Water Center at UC Berkeley.

David Sedlak: And some of that is because over the past few decades, the population in the state has continued to grow. But a lot of it is due to the fact that the climate is changing. So, less rain and snow is falling in the mountains. And, almost as importantly, at higher temperatures and with drier weather, more of that water evaporates before it gets into the reservoirs.

So, we’re seeing shortages of water in places where we never saw it before. And the idea of doubling down and just building more reservoirs and imported water systems is not going to work this time.

Narration: Sedlak says that we need to figure out new ways to generate an ongoing, stable water supply in our cities that isn’t as reliant on the weather. In addition to being more efficient and conserving our water, he says it’s important that we invest in water recycling.

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David Sedlak: Californians are leaders worldwide in the recycling of water. And the big change that has happened in the last two or three decades is that, instead of sending our treated wastewater to golf courses and farms and power plants, we’re increasingly taking treated wastewater and putting it back into our drinking water supply.

David Sedlak is a professor in the Department of Civil and Environmental Engineering and director of the UC Berkeley Water Center. His research focuses on how we get water to our cities, how we treat our water and then, what we do with it after we’re done with it. (UC Berkeley photo by Elena Zukhova)

Narration: Instead of discharging conventionally treated wastewater - called wastewater effluent - into local waterways, like oceans, bays and rivers, advanced wastewater treatment facilities take this treated wastewater and they use an advanced purification process that removes salt, viruses, bacteria and almost all of the chemicals that might be in the water. And this ultra-treated wastewater is potable, or clean enough for us to drink.

There are already several advanced water treatment plants in the state - the oldest and best-known project is in Orange County.

In the Bay Area, the Valley Water District is pursuing a large water recycling project, working to build partnerships with Palo Alto, Mountain View and, perhaps in the future, with San Jose.

David Sedlak: And the reason that that water recycling plant is interesting to me is that it will be the first major water recycling plant in the Bay Area, and it has a challenging problem that needs to be solved that the projects in Southern California have not yet dealt with.

[Music: "Coulis Coulis” by Blue Dot Sessions ]

And I think if it can be solved, it may open up water recycling opportunities in many parts of the world.

Narration: OK, here’s the problem: During the treatment process for water recycling, which uses reverse osmosis, what’s left over is a concentrate - a super-salty substance packed with nutrients and chemicals. And this concentrate has to go somewhere.

In Southern California, they’ve been putting it into a pipe that discharges deep in the ocean, where it’s diluted. But if there were a big water recycling plant in the South Bay, that concentrate would be discharged in part of the bay south of the Dumbarton Bridge, where there’s not a lot of mixing with open ocean water.

David Sedlak: And so, you could build up high levels of salts and nutrients and metals and organic chemicals, and there are concerns that could create an ecological problem.

So, the solution to that is to treat the water after it has gone through this process, that is to take the concentrate and subject it to some form of treatment. But those treatments have proven to be elusive because this stuff is pretty rough to treat and anything that you do that requires a lot of energy or a lot of intense treatment gets to be very expensive.

[Music fades]

Narration: But Sedlak and a team of researchers have found a potential solution - one that is human-built, low-cost and low-maintenance that relies on nature and mitigates the effects of climate change.

[Natural sound: Walking, ground crunching, birds singing]

Angela Stiegler: Yeah, so here we are at the Oro Loma Sanitary District in San Lorenzo, California. I am at the demonstration scale horizontal levee treatment wetland site.

Angela Stiegler is a sixth-year Ph.D. candidate in the Department of Civil and Environmental Engineering. She studies how horizontal levees work to break down certain pharmaceuticals found in wastewater effluent. (Photo courtesy of Angela Stiegler)

Narration: Angela Stiegler is a sixth-year Ph.D. candidate in civil and environmental engineering at Berkeley. She’s one of the researchers who works with Sedlak.

Angela Stiegler: When we look out on the landscape here, the horizontal levee project is about the size of an American football field.

Narration: In 2015, UC Berkeley partnered with the Oro Loma Sanitary District to build a series of test horizontal levees. A horizontal levee, also called a living levee, is a natural treatment system - a kind of constructed wetland.

Angela Stiegler: And it gradually slopes downhill at a 30 to one slope. It’s planted with a lot of different types of plants, but right now, the plants are kind of sleeping. It’s winter time and there’s less sunlight for them to grow, so it looks a little bit more brown than it would look if we were here in the summertime when things are still growing. But the birds are still here. You can kind of hear the birds singing. They really like the willow trees and also hanging out in some of our taller plants.

[Music: "Littl Jon” by Blue Dot Sessions ]

Narration: A horizontal levee works a lot like a natural wetland: It filters out contaminants, protects against storm surges and flooding, while providing habitat for wildlife. They’re called horizontal levees because they’re built next to conventional storm control levees, so they’re also useful in mitigating sea level rise, another effect of climate change.

[Music fades]

Stiegler studies how horizontal levees work to break down certain pharmaceuticals, like antibiotics, beta blockers and antivirals, that are found in wastewater effluent.

Angela Stiegler: When we take medication every day, or whatever we take, you’d think it kind of just goes to the wastewater treatment plant and is removed, and it doesn’t end up in the environment. Or perhaps you never thought about the fact that these chemicals can go into the environment, but they do.

But they’re at pretty low concentrations, so, like, part per trillion, part per billion levels, if that kind of gives you a sense of how concentrated they are. But these chemicals are designed to work on our bodies at pretty low concentrations. They’re biologically active molecules.

But the effects that they have in the environment, it varies by compound and species. Usually, when we’re concerned about these chemicals in the environment and the ecological effect, we’re thinking about fish or insects that are kind of living their lives in the water. It’s like the air we breathe around us - if you had to breathe in these chemicals all the time, it would be kind of difficult, as opposed to something that would eat something that ate something else.

Narration: Researchers are studying what direct effects these kinds of chemicals might be having on fish and insects that live in the water. But because it’s tricky to study animals in the wild, and because funding is limited, it’s not clear yet what the risks are.

Angela Stiegler: But in terms of human health, there are parts of the country where a wastewater treatment plant discharges to a river, and then that river serves as the drinking water source for downstream communities. So, there are parts of the country outside of the San Francisco Bay, for example, where we’d be concerned about these chemicals ending up in the water supply for drinking water purposes in humans.

[Music: "Caprese” by Blue Dot Sessions ]

Narration: In her research, Stiegler discovered that when wastewater effluent from the Oro Loma treatment plant was put into the horizontal levees, the pharmaceuticals she studies were mostly degraded - eaten up by microorganisms living in the soil.

Angela Stiegler: There are lots of surfaces and, like, little microorganism homes in the soil. And they kind of coincidentally also break down these organic chemicals because they might look similar to something that it would normally eat.

[Music fades]

Narration: So, let’s get back to that concentrate that Sedlak was talking about - that thick brine packed with nutrients and chemicals left over from the advanced purification process at a water recycling facility.

David Sedlak: A few years into the project, we realized that this same approach could be used for concentrate. So, we convinced Valley Water to send us concentrate. So, every month or so, they send us a great big tanker truck full of reverse osmosis concentrate, and we feed those to the wetlands to see what happens. And thus far, the wetlands have performed very well and have removed the nutrients and chemicals that we’ve been monitoring.

Anne Brice: Wow, that’s incredible. Are there moves to create more of these wetlands?

David Sedlak: Yeah. This project, which we call the horizontal levees, has picked up a lot of steam and support in the Bay Area from the local regulators and many of the utilities and non-governmental organizations. It’s just really challenging building something on the edge of the bay, especially if there’s potential that it could affect the natural wetlands. So, it’s a slow process.

But there are other communities interested in building similar systems. For example, Richmond is interested in it. Palo Alto is interested in it. There are a few more communities a little farther north around the corner on the delta who are looking at these ideas. So, we think it could take off because there’s going to be major investments in the flood control infrastructure on the bay shoreline to prepare for sea level rise.

[Music: "Greylock” by Blue Dot Sessions ]

And so, there’s this feeling that if you could have a multiple-benefit project, that is a project where you’re addressing sea level rise and water quality at the same time, it’s a win-win and allows those public investments to go further.

Narration: The Build America Act of 2021 will provide $3.5 billion over the next five years to improve water infrastructure across the state and to ensure that clean, safe drinking water is a right in all communities. Sedlak says that while this funding will be helpful in moving some of the state’s water projects along, California was already committed to making them happen.

David Sedlak: I’m so happy to be here in California because, despite what the popular perception is, there’s not a water zombie apocalypse going on now. It’s really not as dire - and that can be chalked up to the energy and creativity and efforts of people who work in the water field.

Narration: And horizontal levees, he says, could be one of the many solutions that will help California - and, perhaps, many parts of the world - to recycle our water and become less reliant on our changing climate for our cities’ water supply.

Outro: I’m Anne Brice, and this is Berkeley Voices. Illustrations for this episode are by Neil Freese. Music by Blue Dot Sessions.

You can follow us on Spotify, Apple Podcasts, Acast or wherever you listen. If you like what we do, please leave us a rating and a review. New episodes come out every other Friday. You can find all of our podcast episodes with transcripts and photos on Berkeley News at

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By Anne Brice

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