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Podcast: Here’s what happens when wastewater treatment facilities fail

Stereo Chemistry visits two struggling wastewater treatment plants in Baltimore to examine the impact on surrounding ecosystems and explore the future of wastewater chemistry

by Craig Bettenhausen , Ariana Remmel
June 6, 2023

A wide shot of a group of signs next to a road. Viewed from a diagonal angle, the large signs are posted in a shady, green space off the road. The nearest says "Neighborhoods First: Santiary contract No. 1025 Emergency Rehabilitation of Back River outfall" alongside the seal of the City of Baltimore.
Credit: Craig Bettenhausen
Credit: Craig Bettenhausen

When two wastewater treatment facilities in Baltimore, Maryland, broke down in early 2021, the surrounding waterways began filling up with sewage. In this episode of Stereo Chemistry, C&EN business reporter Craig Bettenhausen takes the pod to visit both the Back River Wastewater Treatment Plant and Patapsco Wastewater Treatment Plant in the Chesapeake Bay watershed to demystify how these facilities treat wastewater and take a deep dive into the chemistry behind enhanced nutrient-removal systems. Chemical engineers, environmental advocates, and infrastructure experts explore what happens to aquatic ecosystems when wastewater treatment systems fail—and share their perspectives on reimagining wastewater as a chemical treasure trove in the future. Subscribe to Stereo Chemistry now on Apple Podcasts, Spotify, or wherever you listen to podcasts.

And upward-looking view of two large, domed buildings connected by a T-shaped black structure. The tops of the domes are golden and geodesic.
Credit: Craig Bettenhausen
Golden eggs: The unofficial symbol of Baltimore's Back River Wastewater Treatment Plant, these twin anaerobic digesters use microbial action to convert organic waste into water and methane, the latter of which powers the plant and is also piped into the regional natural gas grid.

Listen to our bonus episode with Kerri Jansen here:

The following is a transcript of the episode. Interviews have been edited for length and clarity.

Craig Bettenhausen (field audio): So what are we coming up on here? Is this the outflow?

Desiree Greaver: Yep, this is the outflow pipe, and it comes right out at the end.

Craig: And I’m colorblind; what colors are we looking at here?

Desiree: Um, not water you want to get in. That would be . . .

Craig: Dark brown, green?

Desiree: Yeah, like this is all brown and just gross, yeah . . . Eww, what’s that? It looks like poop, doesn’t it?

Craig: A little bit.

Chris Kvech: Oh, there’s a dead fish there.

Desiree: Oh, that’s wonderful.

Ariana Remmel: That was Desiree Greaver, the project manager at the Back River Restoration Committee, and her colleague, talking with C&EN business reporter Craig Bettenhausen about what happens to aquatic ecosystems when they get flooded with sewage.

You’re listening to Stereo Chemistry and this is the next installment in our season about water and the ways it intersects with society, the environment, and chemistry. I’m your host, Ariana Remmel.

Before I bring in Craig, I want to do a bit of housekeeping. I know that to any long-time listeners of the pod, it is pretty obvious that I am not Kerri Jansen. Since 2018, Kerri has worked tirelessly to bring you top notch stories from across the chemical enterprise and I’m happy to share that Kerri is continuing that work as part of the production team at the American Chemical Society, which publishes Chemical & Engineering News. We at C&EN are certainly sad to see her go, but we’re also excited for her to take this next step. To wish her farewell, we recorded a bonus episode of the pod where Kerri talks about some of her favorite stories from the Stereo Chemistry archive. You’ll find a link in the show notes.

So without further ado, let’s get back to our water episode: Hello, Craig!

Craig: Hi, Ari. Good to be here.

Ariana: Over the past year, Craig, you’ve been looking into problems at two wastewater treatment facilities in Baltimore, Maryland—the Back River plant and Patapsco plant—that both drain into the Chesapeake Bay. Now, coming into this episode, I’m not sure that I’d ever spent a lot of time thinking about wastewater, like where it goes or how it’s handled. But when we started talking about this episode, I believe you went so far as to call yourself a . . . wastewater nerd?

Craig: Yeah, that is definitely true. Baltimore, where I live, has historically been a leader on the stormwater and wastewater infrastructure front. After the great fire of 1904, the city completely rebuilt its sewer system with cutting-edge infrastructure, at least by the standards of that time. When the Back River and Patapsco plants opened in the first half of the 20th century, they were supposed to set a new standard for what wastewater infrastructure could do. Over the last few decades, Baltimore has continued to invest billions of dollars into wastewater treatment facilities that handle huge volumes of water to remove biological and chemical contaminants before the treated effluent goes back into the environment. Both plants added enhanced nutrient removal in recent years to further improve the quality of the water they discharge into the Chesapeake Bay.

Ariana: Based on that conversation with Desiree, it doesn’t sound like that’s what’s happening.

Craig: Yeah. That’s exactly what I want to talk about today on the pod. The heart of the problem is that Baltimore’s wastewater treatment facilities have been plagued with maintenance and technical breakdowns in some of the basic equipment to separate the different components of the sewage and move them around the plant. And because that upstream stuff isn’t working well, the more chemically and biologically advanced systems intended to polish the water right before discharge—like those state-of-the-art nutrient-removal systems—get flooded with . . . materials they aren’t designed to handle, let’s say.

Baltimore’s wastewater system works similarly to what you find in any other large metropolitan areas, and the problems that are tripping it up could happen anywhere. So I want to show you what happens when these systems fail, what communities are trying to do to fix it, and how scientists are reimaging wastewater as a source of nutrients and other useful materials, rather than just waste.

Ariana: Okay, so how about we take a step back because I’m not entirely sure how wastewater treatment works. What are the key steps?

Craig: So, wastewater is a sort of a smorgasbord of fecal matter, food scraps, chemical runoff, basically all of the stuff that we put down the drain. Leaks between Baltimore’s sewage and storm drain systems—a common problem—mean that stormwater is in the mix too. In order to get that water safe enough to return to the environment, most wastewater plants use two main treatment stages.

After some basic filtration, the primary stage uses settling tanks to skim fats, oils, and grease off the top while microbial action starts to break down the solids. Next, the water—called the effluent—enters a secondary stage that removes most of the remaining organic material. It does this by harnessing the metabolisms of bacteria that live in the treatment plant that digest the organic matter and convert it to CO2, methane, and fertilizer. After a final disinfection to kill any remaining bacteria from the tertiary stage, usually using chlorine, that water is ready to go back into the watershed.

Ariana: Okay, so standard wastewater treatment plants remove the grease, break down dissolved organics, and sanitize the effluent, which is the aqueous portion of the wastewater that moves between treatment stages. Then the plant pumps the effluent back into the environment. But you said that the two plants in Baltimore, the Back River and Patapsco plants, were supposed to go above and beyond regular treatment facilities because of new technology.

Craig: You’re right. And that’s because these plants had the added capability of enhanced nutrient removal, called ENR systems. That cuts down on the amount of nitrogen and phosphorus that goes into aquatic ecosystems with the treated effluent. Those elements get in the water from bodily waste as well as fertilizer runoff and rotting garbage.

Alice: Yeah, so I think it was back in like early 2020, I think. They had like a ribbon cutting ceremony. They had a whole tour. And for a few months there it actually was functioning at ENR levels. And so you can look back at the data and you can see, yeah, it was working. And then something went terribly wrong.

Craig: That is Alice Volpitta, the Baltimore Harbor Waterkeeper, part of the environmental nonprofit Blue Water Baltimore. She’s talking about the Patapsco wastewater treatment plant. In April of 2021, her team began detecting really high bacteria levels in the water just outside the plant. This water had previously been some of the cleanest her team routinely tested, so it was alarming when those bacteria readings steadily got worse.

Craig: Tests from that time also showed high levels in the effluent of nitrogen and phosphorus, the main elements that water quality folks refer to as “nutrient loads.” In March of 2022, monitoring reports for the Patapsco plant were showing a nitrogen concentration above 22 mg/L.

Alice: And just for, like, some context there, what you would expect to see from a wastewater treatment plant with enhanced nitrogen removal systems is around 3 and raw sewage is about 30. And so this plant was discharging 22. So we’re not saying that what is being discharged is raw sewage. We know that it’s partially treated, but it’s closer, at least from the nitrogen perspective, to raw sewage than it is to truly treated effluent.

Ariana: Yikes.

Craig: This triggered investigations into the Patapsco plant, as well as the Back River plant. Both sites were blowing past their limits on nutrients and pathogens in the water they discharge into the rivers, which are themselves part of the Chesapeake Bay watershed.

Alice: And what we’re seeing here is two state-of-the-art, world-class facilities with a billion dollars of taxpayer money invested into these facilities that are now discharging way beyond their permitted limitations for pollution.

Ariana: I can pretty easily understand why a wastewater plant blowing past its pathogen limits is a health hazard. But can you tell me more about the consequences of exceeding the nutrient load limit?

Craig: Yeah. So, nitrogen and phosphorus tend to be limiting nutrients in aquatic ecosystems, which means that the growth of algae, plankton, and microbes at the bottom of the food chain is limited by the availability of those nutrients.

Ariana: Oh, sure. Those are the main ingredients in the fancy fertilizer I get for my very sad house plants.

Craig: Yep!

Alice: And so if you put a bunch of that into an aquatic ecosystem, with naturally occurring algae, you’re gonna get an explosion of growth. And so nitrogen and phosphorus in heavy amounts like this, it’s liquid fertilizer, it’s sewage, you’re gonna get an algae bloom.

Craig: Algae blooms are a big problem, often producing toxins that can harm fish and other wildlife, and they can continue wreaking havoc in aquatic ecosystems as they start to die off.

Alice: If you have an algae bloom, eventually, it can’t sustain that amount of growth. And so it begins to die off over time. And as bacteria come in and decompose that dying algae, those bacteria suck out all the oxygen in the water column, which then leads to a fish kill.

Ariana: Is that what’s happening in the ecosystems surrounding Baltimore’s wastewater treatment facilities?

Craig: That’s what I wanted to find out, which is how I ended up tagging along with Desiree and her colleagues at the Back River Restoration Committee. They let me join them on a visit to some of the areas along the Back River where they collect samples, and this was on June 13, 2022.

Craig: The group’s boat is a rough, unadorned pontoon, little more than a large sheet of plywood strapped to two empty tanks and a motor. We rode from their launch out through a series of floating booms that the group has placed across the Back River where it crosses Baltimore’s beltway to catch litter.

The outflow pipe from the wastewater plant is just around the bend. The pipe itself is underwater, and over it on the surface is a long steel and concrete pier under which, that day, was a thick, grimy-looking off-white foam. Desiree, and her colleague Chris Kvech, showed me where pollution appeared to have damaged the local ecosystem.

Desiree: There’s these weird pockets of bubbles popping out? Look, right there, what is . . . that must be . . . I don’t know what that is.

Chris: Yeah but these bubbles, It’s normal.

Desiree: It’s normal?

Chris: Well, normal now.

Desiree: Well, yeah. Which is very sad.

Chris: It’s all the methane bubbles.

Desiree: And before, before all of this, you would see birds galore. Like there was a feeding frenzy of fish here. And there’s . . . nothing.


Chris: Oh, yeah, there used to be, I mean, people used to fish all up under the pier there, and it would be, you could hear the fishes swarming around. Now there’s nothing in there. . . . I mean, I personally wouldn’t eat any fish in here anymore.

Desiree: Yeah, oh God, no.

Ariana: It may just be that I am very into birds, but I imagine it’s really hard for folks who have such a close relationship with this landscape to watch it take such a turn for the worse.

Craig: Yeah, that’s exactly how Desiree explained it to me. She says the Back River Restoration Committee was originally founded by a group of local residents who cared about the river and wanted to make it better. Since the Committee started keeping records of their clean-up efforts back in 2011, which I’ll note is before the enhanced nutrient-removal systems opened, Desiree estimates the group has removed more than six and a half million tons of trash and debris from the Back River. Now the wastewater pollution is making the problem even worse.

Desiree: And if we’re cleaning out all the debris and the trash, and they’re just dumping crap, you know, it’s like a kick in the face. I don’t think anybody expected it to get this bad or for it to be this bad. We were under the impression that things are going really well there.

Ariana: Wow, that sounds devastating. So if the Back River plant is equipped with these enhanced nutrient-removal systems, why are these die offs still happening?

Craig: The problem is that the primary and secondary treatment stages that I described before, the processes that remove the fats and organic waste, aren’t working properly at either the Back River plant or the Patapsco plant. ENR systems are at the leading edge of wastewater treatment, but as Alice puts it:

Alice: These processes that are high level and high tech cannot function properly, because the lower level processes are just breaking down.

Ariana: So who is going to fix the infrastructure problems at these plants? And how?

Craig: Desiree says that it could take months to get the plant back into compliance and years to make it resilient and reliable. That’s what she was told by Maryland Environmental Services, the quasi-governmental state agency that took over control of the plant after all these failed performance tests. They’re also involved over at the Patapsco plant. It took some time, but I was eventually able to arrange a visit to see the plant for myself and take photographs.

Ariana: What did you learn on that visit?

Craig: It was still tense there. Though the photos are on the record, the visit was under the condition that I didn’t have permission to interview anyone. What I saw was major overhauls being conducted on the primary stage settling tanks, which is, again, where fats, oils, and grease float to the top to get skimmed off. It’s also one of the places where suspended solids and nutrients get eaten by microbes, microbes that then settle to the bottom of the tank. Clean-ish water, kind of from the middle, flows out to further processing downstream. It’s a crucial step, and crews were working hard to get these tanks back online.

When those tanks haven’t been working properly though, the plant workers have had to resort to manually scooping off the floating fats with pool skimmers. And instead of the continuous mechanical systems to remove finished solids and grit from the bottom, they’ve had to drain the tanks and then lower backhoes and dumpsters in and out with a crane to shovel it out by the bucket, according to inspection reports.

Ariana: Whoa, okay. So, what I’m hearing is that enhanced nutrient-removal systems can be really fantastic at protecting aquatic ecosystems from nutrient overloads if they’re allowed to do what they were designed to do and not if they’re stopped up with . . .

Craig: Poop.

Ariana: Again, yikes. Well, on that note, let’s take a quick break. When we come back, Craig and I will dive into the chemistry behind wastewater nitrification, learn about the scientists trying to turn this liquid fertilizer into liquid gold, and check back in on how the Back River looks today.

Mark Feuer DiTusa: Hi, I’m Mark Feuer DiTusa, C&EN’s podcast producer! Do you want to make sure you never miss an episode of Stereo Chemistry, C&EN Uncovered, or Bonding Time? How about staying up to date on the latest C&EN news and content, including feature packages like the Talented 12, 10 Startups to Watch, and 50 Top Global Chemical Companies? Then sign up for the C&EN weekly newsletter. Get the latest and most comprehensive overview of the world of chemistry, distilled to your inbox every week. Subscribe now at That’s c-e-n-m-dot-a-g-slash-c-h-e-m-n-e-w-s. Okay, back to the show!

Ariana: And we’re back! So Craig, you’ve toured several wastewater treatment facilities, which is several more than I have, what else can you tell us about how these processes are supposed to work?

Craig: I do know a fair amount about wastewater treatment, but to get real expert insight, I visited Upal Ghosh, an environmental engineering professor at the University of Maryland, Baltimore County. Upal teaches courses on wastewater chemical engineering, and his research looks at small-molecule pollutants of human origin in natural waterways. He explained what, from a chemistry standpoint, is happening at a wastewater treatment plant.

Upal Ghosh: So basically, the idea is that all the complex organics that’s in there, they can get oxidized to CO2 and water. And that’s what the standard heterotrophic oxidation process does in the biological wastewater treatment plant, a big part of it is oxidized to CO2 and water. The other part is transformed into the . . . well, because the cells grow as they oxidize, and they produce more biomass. And that’s the biosolids. So we kind of split it two ways. We call it energy pathway and cell synthesis pathway.

Craig: In most treatment plants, the process for addressing the nutrient load of the effluent is a biochemical one that uses bacteria to oxidize ammonia to nitrites and nitrates, and eventually to nitrogen gas.

Ariana: Sure, those are the basic steps in the nitrogen cycle. Like you learn about when taking care of a home aquarium, right?

Craig: Pretty much, yeah. The problem, Upal says, is that this nitrification-denitrification process is really slow and prone to disruption. The bacteria doing this chemistry have to fix their own carbon along the way and that takes a lot of energy on their part. So all the residual junk left behind in the effluent from the broken primary and secondary stage equipment—that causes a pretty big disruption for those bacteria, and that swamps out their nitrogen removal capabilities.

Ariana: So what’s the solution here? Did Upal say anything about what needs to happen for Baltimore’s wastewater management strategy to move forward?

Craig: He did, but it’s not an easy fix.

Upal: A lot of these issues with nutrients, small molecules, wastewater treatment, some of the challenges that we are facing is related to infrastructure: in the US, we were the innovators of cutting edge infrastructure. And the problem with being innovators is that we went in early, building systems 100 years ago. But they come with a lifetime. And we are getting to the stage where we are seeing those cracks in the infrastructure.

Ariana: Okay, so, infrastructure funding is not exactly a sexy topic, though it does sound like some progress is being made towards repairing the treatment facilities in Baltimore already. But looking ahead, can you tell me more about what innovations could await us on the other side of fixing the pipes?

Craig: There’s lots of fascinating developments coming out of wastewater treatment research but I want to focus on some of the ways that scientists are rethinking the “waste” part of wastewater. I spoke with Katie Bell. She’s a water and wastewater expert at Brown and Caldwell Consulting. She’s involved in some interesting work to make use of all that energy-rich sewage instead of just disposing of it.

Kati Bell: Really, the emphasis is shifted away from looking at wastewater treatment plants as producing a discharge to producing a viable, marketable product that has value. Do you know there’s 9.3 times the amount of energy in wastewater as carbon as it takes to actually treat it? What if we could harness that other 8.3 times—the energy that’s embedded in that wastewater?

Craig: Kati told me this is just the start in terms of recovering carbon from wastewater that might have higher value in the marketplace.

Kati Bell: If we reframe how we think about wastewater treatment plants, we can think of them as chemical production facilities. So, we’ve actually done some research recently that shows that if we take a digester, and we do something called arrested anaerobic digestion, we can produce different types of carbon. So volatile fatty acids are one of the things that we can produce. And we can use that as a substitute for methanol in that denitrification process.


Craig: Going back to the discussion I had with Upal earlier, the big reason denitrification is slow and sensitive is that the microbes have to fix their own carbon from the air. Some plants give it a boost by adding methanol as a carbon source, which is expensive and hazardous. Here instead, they’re making these volatile fatty acids during the digestion phase of the plant, then using them to replace a relatively costly petrochemical input to that third stage, that’s called the polishing step. Those fatty acids could also become feedstocks for other biobased chemicals and fuels.

Kati: And the thing that I’m kind of excited about right now is a product called biochar. We actually can use that biochar to amend soils that have been contaminated with firefighting foams to help remediate PFAS, for example.

Ariana: And biochar is organic material that’s been treated with pyrolysis to be kind of a charcoal material. And PFAS are per- and polyfluoroalkyl substances commonly known as “forever chemicals.” Right?

Craig: Yeah, that’s right. And you can make biochar from all sorts of different things, including from some of the biosolids in a wastewater treatment plant. And Upal at UMBC is working on a project using biochar made from the Baltimore plants to help treat river sediments, sludges, and other wet solids for small-molecule pollution that can cause fish die offs. Upal hopes that using biochar to treat these wastewater materials could also make them safe to use as supplemental nutrients in agriculture. That could bring us one step closer to a circular economy.

Ariana: Sure, that makes a lot of sense.

Craig: And those are all examples of things that firms like Brown and Caldwell, where Bell works, are commercializing, these aren’t just theoretical. There are even more ideas that are still at the academic research phase, like extracting valuable phosphorus minerals directly from wastewater using magnets.

Ariana: Talk about turning trash into treasure.

Craig: Yeah, Kati even went so far as to call it “mining liquid gold.”

Ariana: But for that to happen, wastewater facilities have to perform their basic functions, like. . . treating wastewater. So where do things stand with Baltimore’s plants and the river ecosystems you visited before?

Craig: Unfortunately, the failure to do fundamental pathogen and nutrient removal is still sucking all the oxygen out of the room.

Ariana: Was that, uh, was that a bacterial decomposition pun?

Craig: A little bit, yeah.

Ariana: What is the way forward for Baltimore?

Craig: So really, at the core, these are engineering problems that the city is facing. And that means that they’re fixable if federal, state, and local governments put in the money and the time. Earlier this year, I checked back in with Alice to learn if she’s seeing the actual function of the plant improving. And here’s what she said.

Alice: So especially at the Back River plant, we’re seeing the effluent that’s discharged into the Back River is in much better shape now than it previously was. There’s still problems at both of these facilities. And so, neither of these plants are fully in compliance with the terms of their permits at this point. So, it’s one thing to be able to achieve a certain limit with your effluent. It’s another thing to be able to stay there long term.

Craig: But Alice also let me know that she’s optimistic about the prognosis, especially because there’s a new Secretary of the Environment in charge of this project at the state level.

Alice: I am feeling positive that we’re going to come to a strong agreement that is legally enforceable. We can all agree to anything under the sun in a consent decree. The trick is to be able to hold each other accountable to what we’ve agreed to. This is too important to let fail.

Craig: The Back River plant has been back in the news in recent weeks, and not for good reasons. First was an explosion on March 15 at the biosolids drying facility there, basically the last step of converting that new microbial biomass into fertilizer for sale to farmers. That didn’t affect the main water-cleaning functions or the total throughput of the plant, and, thankfully, there were no injuries. Still, it’s another concerning consequence of what can happen to neglected infrastructure.

And then there was a political dust-up that connects with another major chemical industry story C&EN has been following, the train derailment in East Palestine, Ohio.

Ariana: That was a major accident that spilled 11 tank-cars of hazardous chemicals like vinyl chloride. We’ve covered that in C&EN, but what does it have to do with Baltimore?

Craig: Well, the EPA wanted to give a company called Clean Harbors the contract to deal with 675,000 gallons of wastewater from that cleanup at their plant in the south end of Baltimore, near the Orioles stadium. Which would have meant that after Clean Harbors did their thing, the treated water would have been sent to the Back River plant.

Ariana: Right after an accident and while the plant is still struggling to operate at spec?

Craig: Exactly. I mean, honestly, it probably would have been fine. That’s a normal workflow for Clean Harbors’ Baltimore facility. And pre-treated industrial wastewater like that is part of the 132 million gallons the Back River plant handles every day. But politically, it was dead on arrival, and Baltimore’s elected leaders issued a statement saying the plant is not ready to take on that load right now. So now, Clean Harbors will still treat the derailment water in Baltimore, but then they’ll ship it back to Ohio, to Cleveland where it’ll presumably go through the wastewater system there. If that plan sounds a little bonkers to you, that’s because it is.

Ariana: Huh. I think I’m starting to see just how broad of an impact wastewater treatment facilities can have on our society even beyond their specific watersheds.

Craig: Exactly, wastewater treatment plays a big role in our lives.

Ariana: So you took that trip with Desiree back in June of 2022. Have you gotten a chance to see the Back River in person since then?

Craig: Yeah, so in late April of this year, I roped my dad into all this.

Ariana: Aw, I wasn’t expecting a classic father-son outdoor adventure to finish out the episode.

Craig: We took his boat and revisited the outflow pipe on the Back River where we started the episode. The water was still greenish brown, which is pretty normal for the Chesapeake Bay, but I didn’t see any of the white globs that I remember Desiree pointing out. There was a slight smell of chloramine, that pool-water smell that people often think is straight chlorine. The plant uses chlorine as a final disinfectant, but it’s supposed to be neutralized before the water is released. There, again, too much gunk left in the water can interfere. So, that smell suggested that maybe there were still some problems in that treatment stage. But I did see some wildlife that I think you might like, Ari.

Ariana: Oh yeah?

Craig (field audio): So here’s what I’m actually seeing here is I’ve got a medium-sized flock of seagulls stalking the boat I’m on as we exit the Back River. We didn’t see as much bird activity as we were heading up river, but as we came back down river, it was actually pretty heavy. There were ducks, cormorants, seagulls, and right now yeah, there’s 10 seagulls following us and as they follow us, they’re diving into the water for fish at a pretty high rate. I don’t know why they’re following us. But they’re catching fish. That’s for sure.

Ariana: This episode of Stereo Chemistry was written by Craig Bettenhausen with editing by Kerri Jansen and me, Ariana Remmel. Mark Feuer DiTusa is our audio editor. Full credits for this episode are in the show notes.

Stereo Chemistry is the official podcast of Chemical & Engineering News. C&EN is an independent news outlet published by the American Chemical Society. Thanks for listening.


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