Welcome back to Florida Wonders, a series where Tampa Bay Times journalists answer your questions.
If you’ve ever wondered what happens after you flush the toilet or pour water down the sink, you aren’t alone. Reader Shea Dunifon posed the question: Where does my used wastewater go?
Dunifon already knows the answer. She’s an education coordinator at the South Cross Bayou Advanced Water Reclamation Facility in St. Petersburg. She gives over 40 school tours a year and often introduces herself as Lady Caca.
Over and over again, she hears the same thing from students who have seen Finding Nemo.
"They really think we have a pipe that goes straight from their house to the ocean,” she said.
To set the record straight, Dunifon guided a Times reporter and photographer around South Cross. The tour included a stop at her office, which is decorated with poop-themed pillows, board games, ornaments and an antique chamber pot. Dunifon left her handmade toilet paper earrings at home.
It all starts with the flush of a toilet. After wastewater leaves your home — whirling down your sink or shower drain, or the commode — it travels through your home’s pipes before joining city or county pipes and heading to a facility like this one.
The 22 million gallons that flow through here on an average day won’t end up back in our faucets, but they will end up irrigating our lawns and parks. The solid waste will eventually be baked into fertilizer pellets — 6,000 dry tons each year.
Dunifon says she’s used to the smell here. The worst part, she insists, is not the feces-laced water, but the sour stench of rotting trash that comes with it. That’s where our tour begins.
Wastewater from south Pinellas County homes and buildings comes in through a pump station, where any trash is pulverized into small, soggy chunks. The slurry continues on to what Dunifon called the “headworks,” where screens trap that trash. Water continues along the pipes, and the grouped-up trash is flung down a long chute into a dumpster below, soon to be incinerated.
"At this point, the kids are all gagging and coughing,” Dunifon says.
A peek inside the dumpster reveals wet, grayish mush speckled with shredded condoms, pills and feminine hygiene items. Much of the goop consists of wipes. Dunifon says the common “flushable” label is a marketing tactic, and should be ignored because wipes easily clog pipes. Sometimes, she sees needles and syringes.
“We always tell people not to use their toilet like a trash can,” she said.
Occasionally, she spots pieces of former family pets.
“If somebody flushes their fish, chances are it would be dead before it got here,” she said. “I don't know if that’s a good thing or a bad thing.”
Next, wastewater pours into round machines called teacups. The teacups spin quickly, whirring like the Gravitron at the county fair, sending heavier particles — like sand, dirt and seeds — to the bottom.
Why is there so much sand in the first place? Think of all the tourists showering after the beach. Why all the seeds? Our bodies can’t digest them, so they pass through.
Once separated out, the gritty, dripping goop travels along a conveyor belt of a machine called a grit snail and falls into a dumpster. Like the sopping trash bits from the previous step, this too will be incinerated.
The water that’s left flows to what are called primary clarifiers, where some sludge (the technical term for wet poop) is removed from the liquid. Some of the sludge is left in, however, because it contains important carbon, needed to feed bacteria microbes later.
The goal would be different if this facility were treating water so people could drink it. In that case, microbes would need to be killed. But here, the idea is to treat the water so it can be used for irrigation. That’s where those microbes come in — they help wipe out nitrogen, found in urine, cleaning products, food particles and more, because too much of it is bad for the environment.
The wastewater continues on to the anoxic tanks, where a giant blade at the bottom slowly churns the cloudy brown water above. Those clouds are really blankets of “happy bacteria,” as Dunifon calls them. The bacteria need oxygen to live.
“The word anoxic means that we’re not adding oxygen to that tank, so the bacteria have to find the oxygen that’s in the water already,” she said.
As they pull the oxygen off, they release nitrogen into the atmosphere.
“It’s based on something that nature naturally does by itself,” Dunifon said. “We’ve just engineered it on a large scale.”
In the next tank, air is pumped into the mixture, creating a bubbling brown soup rich in nutrients and toxins. There are many places in a wastewater treatment plant where one would not enjoy falling in, but this is the most dangerous: The density shift caused by the furious stream of bubbles would instantly drag a body down to the bottom, a la Augustus Gloop in Willy Wonka’s chocolate river.
Some of the “activated sludge” from two steps ago is added into this tank to replenish the microbial life. The bacteria gobbles up ammonia found in the urine.
Some of this “beautiful batch of bacteria” will remain, kind of like how a sourdough starter is kept to make future batches of bread.
But much of it travels to the next phase: a broad, round tank of water covered in floating ducks and ibises. A long metal arm slowly skims the surface and pushes any remaining solids to the bottom. Meanwhile, a “vacuum arm” on the bottom scrapes the sludge up to become future fertilizer.
The water is finally clear, but not yet clean. Filters remove additional nitrogen compounds. Then, it’s time to disinfect the water.
There are two ways of doing that: Some of the water is treated with concentrated chlorine gas. Other water will flow through a network of U/V bulbs that destroy RNA or DNA in organisms so they can’t replicate (Dunifon calls this a “really bad sunburn.”) Both methods take 15 minutes.
Ideally, once the water is disinfected, it flows into one of three 6-million gallon tanks at the facility. Off it will go to water lawns, wash cars or trickle into decorative fountains. If water is processed faster than it can be used and the tanks fill, any excess water is dechlorinated and discharged into Joe’s Creek next door.
The sludge is sent to two massive domes called egg-shaped digesters, like giant windowless stomachs. There, the microbes in the sludge gorge themselves on carbon and die, then are eaten by other microbes that die — on and on for two weeks.
“This is essentially a giant fecal feast,” Dunifon said.
The gas that is produced will be used for energy and sold. As of 2016, this saved South Cross Bayou $140,000. Finally, the wet concoction is pressed to remove excess moisture and carted off to a county-owned fertilizer factory.
What about Hillsborough’s wastewater?
The City of Tampa has just one treatment plant: Howard F. Curren Advanced Wastewater Treatment Plant. It’s a lot larger, with a 96-million-gallon-a-day capacity (three times the size of South Cross). The treated wastewater is dumped into Tampa Bay.
The process is very similar to the South Cross Bayou’s method. To take a virtual tour, visit the City of Tampa’s website.
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