Here are some things I do when I get up in the morning: fill a kettle for coffee; use the toilet; take a shower; brush my teeth; rinse out the coffee cup and coffee pot. Before I even leave for work, I've already sent gallons of water rushing out and down through assorted pipes and away from my North Knoxville house. Except for rare times when I'm afraid one of the kids might have put something down the drain that they shouldn't have, I don't think much about what happens to all that water once it leaves my sight. Neither, probably, do most of the people in the 69,000 homes and businesses served by the Knoxville Utilities Board. The whole point of modern sewer systems is that we don't have to think about it. We turn on the tap, run the washing machine, or flush the handle, and it all just seems to vanish.
It doesn't, of course. All of that wastewater—and there's a lot of it, about 40 million gallons in the KUB system on an average day—has to go somewhere. It travels through pipes of varying diameters and ages, some made of clay, some concrete, the more modern sections of ductile iron, PVC, or high-density polyethylene. There's an old saying about, um, stuff rolling downhill, but in a city with Knoxville's undulating terrain, it doesn't work that way. It goes down, and then it needs to go up again, which is why KUB has 64 pumping stations spread out through its 1,300 miles of pipeline to keep it all moving. Eventually, everything that leaves my house, or any other KUB customer's, finds its way to one of the utility's treatment plants. And then the fun begins.
"We've got four treatment plants," says Ted Tyree, standing in the breakroom of the Kuwahee plant on Neyland Drive. "This is by far the biggest." Kuwahee can handle up to 44 million gallons a day, absorbing flows from the First, Second, and Third Creek watersheds. By comparison, the plant in Lakeshore Park at Lyons Bend is rated for about 8 million gallons, and the one along Loves Creek in East Knoxville is about half that. The smallest facility, at Eastbridge Business Park, can treat just 1.3 million gallons a day. Tyree, a friendly silver-haired guy who can inflect words like "scum" and "sludge" with varying degrees of affection, runs all four of them. But his office is here at Kuwahee, the 31-year-old plant where the majority of everything that goes down Knoxville's drains winds up.
It's a big place, spread out along a stretch of highway squeezed between University of Tennessee athletic fields and the Tennessee River. But as Tyree leads a walking tour, it becomes clear that the plant, in a way, acts as a single unit—an industrial-sized digestive system that methodically sorts, separates, and breaks down all the different things that make up Knoxville's sewage stream. It is not particularly pretty work. Although the smells and sights even at the front end are not as bad as you might think, there is no escaping the base-level yuckiness of the whole endeavor. In brief, here's what happens between when the brown water arrives and when it flows back out again, cleaned and restored, straight to the river:
• Screening. Mechanical rakes pull anything sizable and solid (or semi-solid) out of the water, depositing the detritus in large garbage bins. In the one nearest me, I see a Pepsi can, a condom wrapper, bits of rag, and a lot of ugly brownish clumpy stuff that Tyree assures me "isn't what it looks like"—it's not fecal matter or toilet paper (long since broken into tiny pieces on the journey here), but grease, which gloops together artlessly in sizes ranging from golf-ball to soft-ball. KUB really wishes people would not wash grease down the drain. This is also where those things my kids aren't supposed to flush down the toilet would wind up. I ask Tyree if he ever hears from people who have lost wedding rings and the like down a drain. "We do get calls sometimes," he says. "Sometimes the guys even find the things. Of course, people might not want them back..."
• Grit removal. The screened liquid flows into large bays in the next room, where a series of chain-driven mechanical buckets trawls for smaller solids. Tiny rocks and cinders make up the bulk, but two things stand out visibly from the dank gunk: cigarette butts, thousands and thousands of them, and a lot of pale tooth-shaped tablets that Tyree identifies as kernels of corn. "Corn never gets digested," he says with a slight smile. The grit and the stuff in the screening dumpsters can't be further processed, so it's loaded onto trucks and sent out to the landfill. (In a sort of trashman's barter, KUB accepts and processes leachate from the landfill in return.)
• Clarifying. Now we're down to just liquid, but there are still a lot of suspended solids in it. So it runs into yet another set of tanks with another set of chain-driven buckets, which basically settle out solids and funnel them one direction while funneling the water in another. A skimming arm moves across the surface, collecting "scum"—grease and oil, basically. The water here is mop-bucket gray, and doesn't look or smell like anything you'd want to tumble into.
• Bacteria. Here's where the biology comes in. The clarified liquid runs through pipes down the road to big open nitrification tanks. These are full of different kinds of aerobic bacteria, which Tyree just calls "bugs," the mix of which has to be kept carefully balanced so that there are enough of the right kinds to eat and break down the assorted pollutants remaining in the water. Meanwhile, the solid stream is sent through a big circular tank called a "gravity thickener," which spins it to further concentrate the "sludge" (that's a technical term). This machine has my favorite single piece of equipment in the whole plant, a collector on the surface of the water that catches any remaining scum swept in by a skimmer. It is called a "scum beach." Anyway, from there the solids go into their own set of tanks, these ones enclosed because they're full of anaerobic bugs, which go to work munching their way through the sludge and turning it into an inert black mass.
• Back to nature. From the open tanks, the water moves through another set of clarifiers, which again pull any remaining solids out and send them back through the system. The liquid that flows off the edge of these tanks already looks indistinguishable from regular river water. But it still has to go through one more step, the only real chemical process in the whole shebang, and the same one you know from your neighborhood pool: chlorination. After a good bleachy rinse, there's a quick dechlorination (via sodium bisulfite), and then the water comes tumbling down a chute, through a gate, and into a pipe that takes it underground and releases it straight into the Tennessee. Tyree says with pride that the water that leaves the plant is cleaner than the river water it joins.
• Down on the farm. Meanwhile, the broken-down solids are pumped from their treatment tanks, dried, and collected in bins. The result looks like black, powdery potting soil, and it is distributed, free of charge, to large local farms for use as a soil supplement. Inspecting one load of it, Tyree says with enthusiasm, "It's a fine product." And one that all Knoxvillians can maybe take a little pride in helping to create.
It takes just 58 KUB employees to operate all four treatment plants. Their work is constantly monitored via regular testing of the water at all stages of the process. And for whatever jokes you might make about working at a sewage plant, Tyree says his staff takes a lot of pride in what they do—even though they know that if they do it well, you'll never even notice. "I think they're really the unsung environmental heroes of the county," Tyree says.