Norwalk sewage treatment plant pumps it out

Bob Sardaro of OMI shows off the Norwalk sewage treatment plant.

NORWALK, Conn. – These days when the Department of Public Works has an open house at its Smith Street facility most visitors watch Norwalk firefighters demonstrate techniques, but there is another attraction, more suited toward the older set.

The Norwalk sewage treatment plant handles all the sewage from Norwalk and Wilton in a process that turns bacteria-laced filthy fluids into relatively clean effluent suitable for dumping safely into the Norwalk River in about 10 hours, Bob Sardaro said to about 10 people during a tour in last Saturday’s open house.

Of course, if it’s raining and the plant is at maximum capacity – 94 million gallons – the effluent will contain chlorine, but it will still be up to state standards, he said.

In the 1930’s, the sewage and rain water arrived at the plant together. The city has worked to change that, with 85 percent of the rain water bypassing the treatment process and going straight into the river, he said.

On a dry day there are 14 million gallons of sewage to deal with, and the plant can fully treat up to 30 million gallons, he said. If it’s more than that, like in a heavy rain storm, the sewage is partially treated, chlorinated and sent into the river.

“That’s better than lot of other towns and we have been doing this since 1980. If we didn’t have that ‘anything above 30 million gallons,’ all raw sewage would go into the river to protect the plant,” Sardaro said. “But now we pull 30 million through, we can pump up to 94, at least we pre-chlorinate it, chlorinate it and get some solids out. Prior to 1980 it used to all go into the river after the 30 million gallon,s so Norwalk has been on the edge of all that technology since 1980.”

Sardaro said there are six stages of sewage treatment:

• Pre treatment

• Primary treatment

• Secondary treatment

• Chlorination

• Dechlorination

• Sludge disposal

“When a drop of sewage comes into the head of the plant it takes about 10 hours. All depends on how much flow we have coming in. If it’s a rainy day it’s going to speed it up because there’s more coming in. But our tanks are sized so it will get good treatment even how fast it is,” Sardaro said.


The story in photos:


Filtering out the big stuff


Norwalk sewage treatment plant 009-2014-09-27
A conveyor belt lifts rags and thing up to the main level.

First the sewage enters the new headworks, which took over the work from the 1980s-era headworks in 2012.  It’s filtered through screens on a lower level; whatever gets caught on the screens is carried upstairs on a conveyer belt.

Usually it’s rags, but sometimes it’s something weird – a bowling ball once stopped up the works, Sardaro said.


Norwalk sewage treatment plant 014-2014-09-27
The collected rags enter a hopper.

The collected rags and things go into a hopper and then through stainless steel tubes to squeeze the water out because the city disposes of them in a landfill and is charged by the weight of the materials, he said.


True grit


Norwalk sewage treatment plant 018-2014-09-27
The grit is collected.

Next, there’s an aerated grit tank, where the organic material is in suspension and the grit – dirt from the roads – settles to the bottom.

“We don’t get much grit down here anymore because the city does not put sand on the roads in the wintertime. They salt,” Sardaro said. “… You can see obviously why we have to remove this stuff. It’s nasty stuff.”

Norwalk sewage treatment plant 020-2014-09-27
Grit flows out of a hopper.

Controlling the aroma


Sardaro next took his tour by the original sewage treatment plant building, built in 1929 and added onto several times since then, he said. The tower is used for odor control, he said.

The original
The original Norwalk Department of Public Works sewage treatment building.


Grease is the word


Norwalk sewage treatment plant 028-2014-09-27
A grease collection tank.

The next step in the process is to remove grease. The sewage moves through tanks and the grease rises to the top. Collectors skim the top, moving slowly to one end as they are mechanically pulled by chains. A worker empties the grease into a pit, he said. It’s not discarded; it’s used as auxiliary fuel for burning sludge, he said.


Feeding time for microorganisms


Norwalk sewage treatment plant 044-2014-09-27
Bob Sardaro shows off the aerated microorganism tanks.

In the 1960’s, that would have been the end of the process and the fluids would have been chlorinated and dumped into the river, Sardaro said. But the state changed that, leading to a lot of busy microorganisms in the middle of Norwalk, cleaning up after the humans, with human supervision.

“We have to keep them real happy,” Sardaro said, explaining that oxygen is pumped into the tanks at just the right level. The microorganisms remove the solids and reduce the nitrogen by about 80 percent, he said, which is important because algae love nitrogen.


Getting the bugs out


Norwalk sewage treatment plant 054-2014-09-27
Microorganisms settle to the bottom of this 15-feet deep, 110-feet wide tank.

It takes the microorganisms about six to eight hours to break down the solids in the sewage, he said. It’s pumped to a settling tank, where the microorganisms settle to the bottom and are then pumped back to the beginning of the process. “It’s a continuous loop. When we have too many microorganisms we squeeze some out,” he said.

The colony of beneficial little bugs has existed since 1975, because Norwalk doesn’t have much industry, he said. Even though industrial facilities are required to pre-treat their effluent, sometimes things get through that kill off organisms, he said.


The sludge shed


Norwalk sewage treatment plant 050-2014-09-27
Sludge is stored in the building at left.

Sardaro made a brief stop at the garage where the sludge is stored, thankfully not opening the doors. This was the only part of the tour that featured a strong odor. The sludge is trucked to New Haven, he said.


The bleach pits


Norwalk sewage treatment plant 060-2014-09-27
A chlorine contact tank.

The second to last process for the sewage is the chlorine contact chambers, which resemble a maze. If you’re thinking bleach you’re close, except this sodium hypochlorite is 15 percent of the mixture, stronger than what you have at home.

The tank looks like a maze. “We need a maze. We want the water to go around. It takes time there so the chlorine can react and kill off the microorganisms” that remain that could cause disease, Sardaro said.


Rolling to the river


Bob Sardaro pulls up effluent to show how clean it is.
Norwalk sewage treatment plant 066-2014-09-27
Water flows from the dechlorination tank out to the Norwalk River.

Last but not least is dechlorination with sodium bisulfite, which works in a couple of minutes, he said. “There’s not much chlorine left. We have a little bit of wiggle room with the state, but by the time it hits the water it’s all gone,” he said, meaning that it might leave the tank with some chlorine but, by the time it gets to the end of the outflow pipe, the chlorine is gone.

The resultant fluid is clear. Fish would definitely live in it, he said.

“You can’t drink it,” Sardaro said. “But there are some places in the country that this effluent is someone else’s drinking water, but it has to go through more extensive treatment.”

Norwalk sewage treatment plant 071-2014-09-27
Bob Sardaro shows off the resultant effluent.


9 responses to “Norwalk sewage treatment plant pumps it out”

  1. Mike Mushak

    Great article. Thanks for sharing. I took this tour two years ago and was blown away by the sophistication of this whole process. This plant is owned by every single taxpayer in Norwalk representing hundreds of millions in public investment, who all should know what happens to the stuff they flush or pour into their drains, and be concerned about the itegrity of its operation.
    What many people don’t know is that all the trash they see in the streets and clogging storm drains, and all the oil and fluids dripping from cars and trucks they see in parking lots and driveways all over the city, and bird droppings including from geese that are loaded with phosphorus that cause deadly algae blooms and fish die-offs, does NOT go to this plant for removal, but gets swept directly into our streams, rivers, and harbors, contributing to degradation of our precious harbor for many species including people, occasional closing of shellfish beds, and the trash buildup along the harbor edges and beaches of the beautiful Norwalk Islands. Sometimes you can’t even walk along these areas with the heaps of trash that build up with the repeated high tides, and oil slicks and floating dead fish are a common sight in the harbor.
    We have federal, state, and local regulations to prevent much of this, but our Director at the P and Z Department frequently ignores them, which is all on the record. That’s right, Norwalk often ignores state and federal laws when it comes to our land use decisions, and my many attempts to fix this ongoing problem were met with derision, bullying, and retaliation when I served on the zoning commission, as if all these laws to protect the environment were just considered a big nuisance.
    We can do much better at solving this problem but we need a renewed commitment from City Hall to enforce our stormwater and erosion control regulations, including updating them to meet new standards, and to consider long-overdue staff changes to restore integrity to our dysfunctional P and Z Department. Sure it costs more initially to follow the laws, but that is minor compared to the real costs of a polluted harbor to our multi-million dollar shellfish and recreational boating industries, not to mention the local and migrating wildlife that are so important to our local fragile ecology.

  2. Oldtimer

    There are commissions, both shellfish and Harbor, that review applications for projects that can affect the harbor water quality, but they have very little power except the ability to influence permit decisions made by the DEEP, a State agency. Only projects with an obvious affect on the harbor are required to apply for a DEEP permit. Most building permits are not required to get DEEP permits and only some of them ever come to the attention of the local conservation commission which has some regulatory power in the permit process, but no real enforcement teeth, and is frequently ignored. P & Z has more power and could require approval by conservation before any plan is approved and building permits issued. Protecting the harbor requires a team effort.

  3. Oldtimer

    Unfortunately, a certain amount of drainage work, directly into the harbor, is still done under the radar without any permits and very little penalty for violations.

  4. EveT

    Do schools bring science classes here on field trips? If not, I hope they will. Seems like an amazing learning opportunity for students.

  5. OhNoNorwalk

    Can you post a tour when your inefficient system is not work preperly and raw sewage is pouring into the river and poisoning the waters. How often did that happen in the last 5 years.
    Isn’t that like fishing / eating out of the toilet. If your going to post the good info you have to post the bad info. I wish it was a perfect world but the managers / mayor would like us to be so gullible. Peel back the layers of supluflage to get the truth. Is smells like the sewage plant on a bad day.

  6. Oyster

    Just this past Wednesday, East Norwalk’s air was once again filled with the odors that waft over from the WWTP.

    1. Mark Chapman


      I notice it more often than not when I am out with the car windows open, driving near the plant and approaching and coming across the drawbridge, too. And I promise you it is NOT low tide. I grew up near the water on Cape Cod and I know low tide. I also know sewer plant odor — Hyannis has a big one unfortunately located near the back entrance to the Cape Cod Mall, across the street from where we used to buy our used cars. Not pretty.

  7. Oyster

    Right on both counts. I, too, grew up near the water and in a place which had a sewage treatment plant. One does not resemble the other. However, if you are an administrator of a treatment plant in Norwalk, but live somewhere else, you don’t have to “experience” the consequences on a daily basis.

  8. Oldtimer

    Odor control cost money. The plant is run by a for-profit company. Alvord has tried for years to make us believe the odor is not a problem. What is going on with the police investigation ?

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