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Inside A Sewer Plant

McDowellScumTrough.jpg
The "scum trough" is the primary clarifier where solids are separated from the wastewater.

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The "scum trough" is the primary clarifier where solids are separated from the wastewater. Photo: Julie Rose The Charlotte-Mecklenburg Utilities Department wants to build a new sewer plant on the Catawba River - just upstream from the US National Whitewater Center. That got us wondering if rafting tourists might one day need nose plugs to handle the stench. But wastewater plants have come a long way in recent years - and CMUD officials say bad smells and water pollution coming from the new plant will be minimal. They point to similar technology already in use at the nearby McDowell Creek Wastewater Plant in Huntersville. WFAE's Julie Rose went for a look - and a sniff. Everything people flush in Cornelius, Huntersville and parts of Davidson ends up at the McDowell Wastewater Treatment Plant. But if you stand atop the 52-inch pipe where the plant's treated water flows into McDowell creek, you'd never guess it was raw sewage a mere 29 hours ago. It's actually cleaner than what's in the creek and you can see, hundreds - thousands of little fish hanging out down around the pipe, because they like the warmth of the water and the oxygen that's been added. "It's very rare to have a wastewater plant upstream of where a major reservoir or city water intake is located," says Joseph Lockler, plant manager of the McDowell Creek Wastewater Treatment Plant. He's talking about the city of Charlotte: Just around the bend, McDowell Creek enters into Mountain Island Lake, where we get our drinking water. Because of that - and because McDowell Creek already suffers from significant pollution problems - Lockler has to meet some of the strictest water quality regulations in the state. The Catawba River suffers similar pollution problems, so the plant CMUD hopes to build near the Whitewater Center would probably treat wastewater in the same way. On the odor front, McDowell gets very few complaints from neighbors. It doesn't handle the stinkier industrial waste some of CMUD's other plants do - and there are no big, open pools of raw sewage. It's processed indoors with a "bar screen" All of the waste that comes into the plant initially - about 5 million gallons a day - passes through the screen. When the screen gets clogged with gunk, a rake scrapes it clean. In the olden days, unfortunate sewer workers had to rake off the screens by hand. Here's a funny side note: raking screens was Barry Gullet's first job in the industry. Now he's in charge of the entire Charlotte-Mecklenburg Utilities department - and those sewer rakes are all automated. Non-biological solids in the wastewater are captured using screens and rakes, pressed free of water and sent to the landfill. Photo: Julie Rose Lockler says you wouldn't believe what they pull out. "Money. Toys. People's pets - anything you can put in a manhole," says Lockler. He's found bowling balls, chain link fence, two by fours. All of that goes to the landfill and the murky water is pumped to the top of a hill where biological solids are strained out. "We have to do something with that poop," says Lockler. He points to a large concrete tank called an anaerobic digester. The poop basically cooks for a month in that tank to kill pathogens and reduce it to manure some farmers will use. The methane gas created in the anaerobic process is burned to warm the digester. The slightly cleaner water then goes into a series of deep concrete pools. The first one has a squeegee arm that captures more floating solids and puts them in the "scum trough." The scum trough feeds back into the anaerobic digester. "And now you've got this nice chocolate milk color," says Lockler proudly. That's precisely the color he's going for. "What gives the water this color is all of the bacteria we're growing in our system. We're basically a bacteria farm." McDowell Wastewater Treatment Plant manager Joseph Lockler shoots for a fizzy, "chocolate milk" appearance as the wastewater is treated. Photo: Julie Rose The bacteria eat up phosphorous and nitrogen in the wastewater. Those are called biological nutrients and they can cause algae blooms and other problems in McDowell Creek. To keep those bacteria healthy, Lockler feeds them sugar. He turns the handle on a spigot with a sly smile. Brown liquid that looks just like Coke pours out. Pepsi and Coke flow into the pool to feed bacteria that remove phosphorous and nitrogen in the wastewater. Photo: Julie Rose "That is exactly what it is," says Lockler. "That's Pepsi and a little bit of Coke." The bacteria also like Cheerwine. Lockler gets a cheap deal on out-of-date product from local soft drink bottlers. The McDowell plant is the only one in the county using soft drinks to feed its bacteria, because it's currently the only one required to pull out phosphorous and nitrogen from the water. Once the bacteria have done their job, the water is filtered through sand and gravel and then disinfected with ultraviolet light. The final step is aerating the water before it goes into McDowell Creek. Fish and plants in the creek need oxygen, so the wastewater is sent tumbling over a series of man-made underground waterfalls just before it leaves the plant. Technology developed by NASA monitors the quality of the water as it hits the creek and sends real-time reports to Lockler's cell phone. It's many times cleaner than the water in the creek. "I'm actually cleaning the creek," says Lockler. In fact, during periods of drought, the treated wastewater from the McDowell plant is the creek . . . and Charlotte's drinking water.