In the latest installment of "How New York City Works," NY1's Roger Clark takes a look at the city's wastewater treatment system to find out what happens to all of the dirty water we send down the drain.
New Yorkers use a lot of water. An average of 1.2 billion gallons goes down the drain every day. Plus, there's everything that falls on the city when it rains or snows. All of that water, and everything else that flows down with it, has to go somewhere. So where does it all go? The only place it can. Into the waterways that surround us.
Before it reaches the waterways, it passes through a complex wastewater treatment system run by the city's Department of Environmental Protection to clean and disinfect it so we don't get sick and wildlife can survive. Let's find out how it works.
Most of the city runs on what's known as a combined sewer system, meaning everything we send down the drain or toilet, and all the rain, snowmelt and other runoff that flows into any of our 140,000 street catch basins, all wind up in the same 6,000 miles of pipes. The "combined sewage" then travels, mostly by gravity, to one of 14 wastewater treatment plants. Sometimes, it needs a little push to get there, and that's where 96 pump stations come in. We went underground to check out one station in Manhattan.
The screen room is about 30 feet below street level, and that's where the raw sewage comes in. The room is the first place that it's going to be screened.
"The sewage comes through a series of metal bars that are spaced about an inch apart, and those bars remove things like sticks, leaves, plastic bottles, rags, anything that may find its way into the sewer system," says Vincent Sapienza, a DEP Deputy Commissioner in the bureau of wastewater treatment.
That material gets a lift upstairs to be loaded into containers and taken to a landfill. Every now and then, DEP workers come across some pretty interesting finds.
The whole thing about alligators living in the sewer system is an urban legend, but there is another type of reptile that somehow made its way into this pumping station: turtles. The workers are taking good care of them.
For the remaining sewage, it's on to the next step.
"The sewage that you see here, Roger, is now getting pumped up several stories into a surge tower, and then, by gravity, that can then flow to the next station in the treatment process, which is the Newtown Creek Plant in Brooklyn," Sapienza says.
With the sewage making its way under the East River, we drove to Newtown Creek, the city's largest treatment plant. Here, it heads through another bar screen to capture materials that may have made it through. Some materials in sewage can't be physically removed, so there is a biological process called aeration.
"In these tanks that are covered are colonies of microorganisms that we cultivate here at the plant, giving them the right conditions, and they actually consume other organic materials that are in the sewage," Sapienza says.
Sapienza: This is under the covers, and show you what aeration looks like, and so you can see because we're feeding air into this sewage with the microorganisms in there, it's bubbling.
Clark: And they eat the bad stuff, basically?
Sapienza: They eat all the organic material.
After three to six hours, the sewage moves into settling tanks, where things like cooking grease and lotions float to the top. That's slowly pushed to one end and removed to landfills. The microorganisms, now plump from the organic material they've eaten, sink to the bottom, creating sludge. More on that later. The water in between needs to be disinfected before it's released.
"We add sodium hypochlorite," Sapienza says. "It's a strong bleach, but it's the same chemical as Clorox, and that kills any type of microorganisms that may still be alive that are in this wastewater."
Once the water has been treated and tested, it heads out to the East River. Samples are tested at a lab to make sure it meets federal and state standards for release.
So what about the sludge from the settling tanks? It goes inside one of Newtown Creek's digester eggs.
"Those digesters are more of less like a human stomach, and what they do is, they take the organic material, carbohydrates, proteins, fats, and they further break it down into more basic components like water, carbon dioxide and methane gas," Sapienza says.
It takes about 15 to 30 days for that to happen. DEP Commissioner Emily Lloyd explained that the gas gets put to good use.
"What we are doing here is, we are reusing some of the digester gas, about 40 percent of it, to actually operate this facility," Lloyd says.
After the digestion process, there is still plenty of liquid sludge left. That liquid sludge needs to become solid sludge so it can be transported to a landfill, but that process can't be done at Newtown Creek. It has to go to another facility. That's where a boat comes in. The sludge travels underground from Newtown Creek, through a pipe, into a hose, and is loaded right onto a boat, where it takes a ride to Queens."
It's not the Circle Line, but it's still a great view of the city. The DEP has four of these vessels, which holds more than 500,000 gallons of sludge and makes two trips a day. When we arrive at the Bowery Bay dewatering facility, the sludge is unloaded.
Here's something you don't see every day: a fountain of sludge. That's the sludge that we traveled over on the boat with from Brooklyn.
It's spun through centrifuges to separate out the water. The leftover dirt-like substance, affectionately known as "cake," is taken to landfills or used in more inventive ways, like filling decommissioned mines down south. That's how the system works most days, but things get tricky during heavy rains. When the city gets soaked, the extra volume can quickly flood out the system.
You may have seen one of the signs at left in your travels around the five boroughs. This is one of more than 400 points where rainwater combined with untreated sewage can be released into the water that surrounds us, in this case, Jamaica Bay.
"It has to go somewhere. It can't go back into people's houses," Lloyd says. "And so it spills over into the harbor, into the rivers, as what are called combined sewer overflows. It's stormwater that has some sewage mixed in with it."
The DEP is taking steps to manage stormwater before it can overwhelm the system, like green infrastructure. A rooftop farm at the Brooklyn Navy Yard absorbs more than 1 million gallons of stormwater a year. The city is also building thousands of structures called bioswales. One in East New York stores up to 2,800 gallons per storm.
As part of this massive system of trying to keep the waterways around New York City clean, the DEP is constantly monitoring the water. One of the ways they do that is aboard a vessel.
During a voyage on Jamaica Bay, marine biologists send a computer underwater to collect samples. Some tests are done on board. Others are sent to a lab.
"We're out here to monitor the general health of the whole harbor and see the long-term trends and sort of keep up on how our infrastructure projects are doing," says Beau Ranheim, the DEP's Marine Sciences Section Chief.
It appears to be working. The DEP says the harbor is the cleanest it's been in more than 100 years.
So that's how the city's wastewater treatment system helps to protect the water that surrounds us, and that's how New York City Works.