BRUNSWICK COUNTY — What happens after you flush, shower, do the laundry, or wash the dishes?
If you don’t have a septic system, your wastewater joins an interconnected network — most often managed by a municipality — and is later treated before being returned back to the environment.
At Brunswick Regional Water and Sewer H2GO’s extended aeration wastewater treatment plant, no chemicals are used to bring wastewater to a state that meets permit standards.
Brian Griffith, the plant’s superintendent, has worked for H2GO since 2004. Though he’s shown the inner-workings of the plant to professional groups in the area, he said children visiting on recent elementary school tours got the most out of the tour.
“They loved it,” he said. “The kids just loved it for the smell.”
Here’s an elementary take on how wastewater gets treated:
How it starts
Waste is delivered to a manifold that feeds the Chappell Loop Road plant. Eight pipes send flow to the manifold from all over the system, including waste stemming from Highway 17 and N.C. 133.
First step: the wastewater gets filtered through a static screen. The screen has no moving parts, which Griffith said is good for maintenance. Wastewater cascades down through a screen mesh. The mesh catches solids like corn, hardened grease, feminine products, pulped paper products, and plastic wrappers.
“This screen is a really valuable asset out here. it stops a lot of stuff,” Griffith said. “The more we can remove at the screen the less we have to remove from the water.”
Fats, oils, and grease sent down the drain can cause issues at home and in the regional collection system. These materials can harden inside pipes (the same thing can happen inside the pipes in your body). H2GO has a program, the Cooking Oil Recycling Effort aka “C.O.R.E.” that invites customers to collect cooking oils. Customers can drop off collected oils at three collection sites.
When collected, these oils are turned into biofuel.
Humans can’t digest the skin of corn kernels. Wastewater treatment systems can’t process flushable wipes. These lessons, among others, are clear from observing the waste produced from this initial screening process.
A pulpy, corn-filled pile of waste builds up over a period of about one-and-half months before being removed from the troph. This gives enough time for tomato, squash, cucumber, and other plant seedlings to sprout.
“Usually out here, there’s a tomato somewhere,” Griffith said.
Next comes the equalization basin.
“This stops us from storm surging,” Griffith said. “This keeps us from overloading the plant.”
As flows fluctuate, this basin helps operators not worry about hydraulically overloading the plant. Wastewater has never overflowed or reached the brim, Griffith said, but it has gotten close. During Hurricane Florence, he estimated the plant reached a peak pumping rate of treating about 500 gallons a minute (this pumping rate, if kept constant, equals 720,000 gallons per day (gpd) — the plant is permitted to operate at a maximum capacity of 400,000 gpd.
“It definitely got high,” Griffith said. “There were times we worried. But during a hurricane, there isn’t much you can do.”
In an emergency, Griffith said his team can “surge” the plant — meaning push partially-treated wastewater through the system — to prevent an overflow. But this move would reduce treatment quality and has not yet been necessary.
“Skimmers” catch anything floating on the surface. These devices pick up fine particles and solids before wastewater moves on to the next treatment process.
Mixing with sludge
After the equalization basin, wastewater moves on to the “reactor” tank.
The reactor mixes filtered wastewater from the equalization basin with settled sludge and raw sewage. Over time, sludge settles down and is eventually pumped from the bottom of two clarifying tanks back through the plant.
“It will circulate over and over. It’s a continuous process,” Griffith said. “We build it up and we’ll do the same thing. We’ll let it settle down, take the clear water off the top until we can’t no more.”
Extended aeration involves long retention times. Through a process called endogenous respiration, bacteria begin to break themselves down after they run out of food.
“They’ve been here long enough, they start eating each other,” Griffith said. “They break down the solids so there’s less solids to be disposed of.”
“It’s what nature does, but it’s on steroids. we can control it,” he said. “What it takes the river seven miles to do, we do in a little area like this.”
Between May 2018 and May 2019, the plant treated approximately 121.42 million gallons of wastewater, according to H2GO’s recent annual treatment report. During that time, plant operators emptied just one 130,000-gallon tank full of sludge — about 0.1% of its total treated wastewater.
H2GO pays a company to pick up this sludge, but Griffith said some larger systems have the ability to sell the material. Sludge has value. Depending on what entity produces it, sludge can have agricultural benefits. These benefits also have associated risks, like containing high concentrations of cancerous, unregulated chemicals.
“We have to get rid of some solids,” Griffith said. “If you let too many solids build you don’t have enough to settle.”
Too much sludge in the tank can cause biological issues, he said, which reduces the efficiency of the endogenous respiration process that breaks down solids.
With the exception of bleach occasionally used to scrub algae off the side of tanks, no chemicals are used at the plant.
Wastewater moves through sand and anthracite filters, which get washed every few days, before heading to the clearwell. At this stage, the wastewater is almost in its final treatment process.
In the clearwell, the water moves through a troph into a UV system.
“It’s basically like a giant tanning bed. as the water passes through that UV, it messes up the cell walls and disinfects the water,” Griffith said.
From there, treated effluent is released at the plant’s outfall pipes into the Brunswick River.
Send tips and comments to Johanna Ferebee at firstname.lastname@example.org