What happens after you flush the toilet?

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Aerial view of Wards Island Wastewater Treatment Plant in New York City.

What happens after you flush the toilet?

What happens after you flush the toilet?
September 26, 2017

New York City generates a lot of waste. Pam Elardo, the deputy commissioner for the Bureau of Wastewater Treatment at the New York City Department of Environmental Protection, oversees the treatment of more than a billion gallons of wastewater per day. New Yorkers don’t often think about waste treatment, but Elardo argues that it is a necessary topic of discussion. In an interview with City & State, she discussed the daily duties of wastewater treatment plants, the DEP’s partnership with National Grid and what happens after you flush the toilet.

C&S: As deputy commissioner for the Bureau of Wastewater Treatment, what are your daily job duties?

PE: Considering that we’re a 24/7 operation where we cannot stop what we do – which is treating all the wastewater from the millions and millions of people who live, work and play in New York City – it’s about making sure our operations are running smoothly, making sure they have the resources to get their work done, planning for near-term capital investments and long-term capital investments. Maintaining staff morale, visions for the future, setting goals for ourselves, creating a level of morale and pride in the work we do, applying strategy to our internal operations as well as going external to advocate for our needs in the context of the city and stakeholders.

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Pam ElardoC&S: Describe the partnership between the DEP and National Grid.

PE: Every treatment plant takes in all the wastewater comes through us, and we essentially make the water clean and take the solids – which are organic solids – and put it in what are called digesters. In those digesters, we use anaerobic bacteria to break down that waste and we create methane gas, (carbon dioxide) and water. The methane gas is a very important energy resource that we try to utilize at each of our treatment plants. At Newtown Creek, we actually have excess digester capacity, meaning for all the solids we put in the digesters from our process, we don’t use 100 percent of the space that we have in there. So, National Grid and Waste Management work with us to create a food waste to digesters program, where Waste Management collects food waste and they create a slurry and that goes directly into our digesters.

With that we’re creating more gas, about 10 percent more than we would otherwise. So, considering that we don’t necessarily use all our gas and we’re getting this extra gas, National Grid came along. We created a program where they’re going to build a scrubber, which is basically a method to clean the gas and strip out the water and other impurities from the gas. Then they’re going to put that gas directly into their regional pipeline, which then will be going to people’s homes so they can cook their dinner, and then use their toilets, and then put the waste in our system. Then we’ll create more gas from that and then it’s a full circle.

C&S: The state is investigating a recent spill of wastewater into the Niagara River. How do you prevent a similar crisis from occurring in New York City?

PE: I have 1,800 people in this bureau, and every single day they are putting out fires that could potentially cause a problem. We’ve got a lot of aging infrastructure, some of which is really challenged to keep operating. So, we avoid that by dealing with things that need to be adjusted or replaced or (have an) emergency contract to fix in the short term, but in the long term we avoid that by making the right kind of investments in our utilities so that we replace this aging infrastructure before anything bad happens.

C&S: What is a challenge that you face in treating wastewater?

PE: The problem we have is people do flush a lot of things that shouldn’t be in the toilet. Even if it says “flushable” on the box, if it's not toilet paper, it should not be flushed. So what happens is all those baby wipes, and facial wipes, and Clorox bleach wipes and whatever makeup stuff that people flush – tampons, condoms, everything – it comes to the plant. We have to screen out that debris before we put it into the treatment plant. We do our best to screen it out, and we spend over $7 million a year hauling off just stuff that gets stuck in our screen. Even with the screens, a lot of (those) rags, and baby wipes, and facial stuff gets through the screens and ends up clogging pipes.

When it clogs pipes it’s really bad, but you got raw sewage that can’t flow and you have to have people in there getting inside the pumping mechanism to retrieve the wipes and all the garbage people throw in there. If I didn’t have the staff or the expertise or the people that stay on top of it, we’d be backing up sewage into people’s homes all the time or overflowing sewage into the receiving waters so it’s something that we constantly have to put up with. I think we need to develop a stronger partnership just with everyday people so they know what not to put in their toilet. The more people understand that, the less they have to pay for it on our end, and the less risk that we have to put our utility under.

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C&S: What is the daily capacity for New York City’s wastewater treatment plants?

PE: New York City has 14 treatment plants. Every borough has at least one. We treat about 1.3 billion gallons a day of wastewater, and that’s on a dry day. Because a lot of our systems are combined, meaning they also take stormwater from the streets, that flow can easily be over 3 billion gallons in a given day.

C&S: What is the process for wastewater treatment?

PE: It comes to the treatment plant, it’s wastewater, which is obviously the organic loading coming from people. The first stop is to take out the rags and the wipes and all that stuff, and that’s the big screens that screen that out. Then it goes to a grit chamber usually, so stuff that will make it through the screen like small rocks or debris. If you lose a wedding ring, it’ll probably end up in the grit chamber. Then it goes into these very large, long sedimentation basins, which is just a long channel where it’ll take the solids and it’ll fall out of the top, and the grease will float at the top. So we take out the floaters and the sinkers, and that goes to solids handling. This water that’s got very high organics in it, and then that goes through a biological process that is aerated. What we do is we use biology. We set up conditions to bring a biological community to these treatment plants that actually consume the organic matter.

If you think about it this way, if a bear poops in the woods, their poop will eventually become soil because all this bacteria that lives in the environment will degrade that waste. So we’re taking something that takes weeks in the natural environment, and make it happen within a few hours within the treatment plant. Then we have the final settling tank where we settle the biological flock out, and then the water is very clean at that point. It gets disinfected just using a household bleach type, and then the clean water is discharged into the receiving water. But that whole thing about the biology and the solids that we pull off – we take a small portion of the active biological community, it’s called sludge, and we put that into the digesters.

We’ve still got a lot of organics in there that breaks down in an anaerobic environment and that’s where we create the methane gas. So we’re really a resource recovery utility. We’re taking waste and making clean water. We’re making usable biogas. We can take that biogas to heat. We can take that biogas to create electricity. We also produce the biosolids, which is the final product that is safe out of those digesters, so that’s another component that can be used for a beneficial use. 

Grace Segers
is City & State’s digital reporter. She writes daily content on New York City and New York state politics.