When you think about progressive composting and recycling programs, big cities such as Seattle, San Francisco, and Los Angeles might come to mind—yet one of the most efficient composting facilities in the world is in Appalachian Tennessee.
Because of this plant, the majority of the county’s waste is composted or recycled.
Sevier County, Tennessee, is home to the twin tourist destinations of Gatlinburg and Pigeon Forge, and attracts more than 11 million visitors per year. Gatlinburg is a quaint mountain town packed with quirky stores, restaurants, moonshine shops, and an aquarium. Pigeon Forge is home to the Dollywood amusement park. These towns are poised at the edge of the Great Smoky Mountains National Park, which covers roughly a third of the county.
Perhaps it’s this proximity to the natural world that helped inspire Sevier County’s unique approach to waste disposal. When it opened in 1991, the Sevier Solid Waste Composting Facility was one of the first in the world to use rotating drums, or “digesters,” for breaking down compost. Because of this plant, the majority of the county’s waste is composted or recycled. Today, it’s still a rare breed.
“There’s about 12 or so [composting facilities] in the world like this,” explains Tom Leonard, general manager of Sevier Solid Waste. “Every one of them has gotten some design feature from here, because we’re one of the oldest.”
As we walk around the facility, Leonard points to a grassy rise in the distance. “That back there is our old Class 1 landfill, but we don’t use it anymore.”
Measures of success
About 100,000 tons of solid waste and treated sewage pass through this facility every year—and an astounding 70 percent is diverted from landfills by being composted or recycled. That’s compared to 34.5 percent of all U.S. waste that was diverted in 2012, according to data from the U.S. Environmental Protection Agency. San Francisco, declared the greenest city in America by the Siemens Green City Index, recycled 77 percent of its waste in 2010, but was the only North American city of the 27 listed in the index to recycle more than Sevier County.
The county’s waste diversion rate becomes even more impressive when Leonard explains that 99 percent of the county’s waste is diverted from its Class 1 landfill—the most environmentally harmful type, requiring heavy lining to prevent runoff, careful regulatory oversight, and decades of maintenance. Garbage in these landfills is eventually covered up, but it never really goes away, Leonard says.
“I just don’t like the word ‘forever,’ because that’s a long time. So what we’re doing is, we’re stabilizing the material back down to its form, and our ultimate goal is not to put anything from this plant into a landfill.”
"Our ultimate goal is not to put anything from this plant into a landfill.”
Another unique component to Sevier County’s approach: residents and businesses aren’t required to separate recyclables from their daily waste. There are no recycling bins for home pickup, and the only items people are required to separate are construction and demolition materials, electronics, and tires. The separation of recyclables happens on the back end, as a part of the composting process. (While cardboard can be composted, citizens are asked to separate it because it makes more money for the county as recycled cardboard than as compost.)
In the end, this facility is financially self-sustaining, thanks in part to the money saved by not sending waste to a Class 1 landfill, where most non-recyclable waste in the U.S. ends up. A great deal of money is also saved on transporting garbage to landfills, which are often far away from pickup locations because of the challenges of finding affordable, usable land.
The facility also ensures that waste management is relatively affordable for the county and its cities; the cost of handling waste is $40 per ton, lower than the national average. In Sevier County, these costs are covered in part through a $12-per-month fee for curbside pickup. The Waste Business Journal reported that the average cost to place a ton of municipal solid waste into a landfill in 2012 was $44.23.
Meanwhile, individuals get free compost, with the rest being used for city and county projects such as road maintenance.
The recipe for compost
The tourist industry posed a unique dilemma when Sevier County administrators began seeking new waste disposal options in the late 1980s: “Because so much of our waste stream comes from our millions of visitors that come to the county every year, it’s almost impossible to get them to recycle in the way that we’d need them to,” explains Larry Waters, who has been Sevier County mayor since 1978. The county is home to nearly 94,000 people, a population dwarfed by the huge volume of tourists.
County administrators visited other sites where composting strategies had been implemented and ultimately contracted with Bedminster Bio-Conversion to build the original facility and operate it for the first few years.
Waters says that the county was the first to install a facility of this type. “We were pretty nervous about that—whether or not it was going to meet our needs and do what we needed it to do.”
However, the Sevier County facility would soon become a model for other, similar composting plants throughout the world. What’s more, the tourist industry proved to be a key advantage, since the high volumes of restaurant food waste are great for compost.
“For us, [composting and recycling] is not only the right thing to do, it financially makes sense for us to do it, so it’s exciting.”
Today, the Sevier Solid Waste Composting Facility receives visitors from around the globe, seeking to gain insights from what Sevier County has learned through trial and error. More efficient processes and technologies have been developed over the lifetime of the facility, and even today operators are always on the lookout for better approaches, Leonard says.
Constant improvement is on Leonard’s mind as he guides me through the facility. We walk inside a huge structure covered with corrosion-resistant plastic, where broken-down materials are pulled from the ends of 185-foot-long cylindrical digesters that rotate slowly.
After three days, materials are pulled out of the digesters and placed onto a conveyor belt, which carries them into the next room. There, they’ll be sifted for glass and recyclables, then laid out into windrows for roughly 37 days. Windrows are narrow, long piles of material that are turned regularly to improve aeration and aid the breakdown into compost.
For all the streamlining this process has undergone, Leonard is today preoccupied with resolving two problems: First, he needs to reduce the moisture in these massive rooms of windrowed compost—not so much that the microorganisms breaking down the compost die, but enough to make it easier to separate glass from the moist compost. It’ll mean more glass recycling in the long run, and will increase the amount and quality of compost the facility can produce.
The second problem is how to make more efficient use of the plastics the facility collects. Many of them can be recycled, but there may be a more financially and environmentally efficient way to put them to use. Leonard believes this problem may soon be resolved with the type of innovative approach that has become the norm here. He hopes to sign a contract with the technology company PHG Energy soon, in the hopes of starting to convert used plastics into fuel within a year.
“We can produce about 6 megawatts of power from just our plastics,” Leonard says, enough to power about 2,400 homes per year.
“For us, [composting and recycling] is not only the right thing to do, it financially makes sense for us to do it, so it’s exciting,” Leonard says.
About 300 tons of garbage a day pass through the 188,000-square-foot Sevier Solid Waste Composting Facility in Pigeon Forge, Tenn., and this tipping floor is where that garbage is first collected. The floor is enclosed by a woven, corrosion-resistant plastic. Garbage is funneled through five pits in the tipping floor and into up to five “digesters,” which are long, cylindrical drums that rotate 24 hours a day.
“Paper, food waste, cardboard—anything that’s organic can be broken down in our system,” explains Tom Leonard, general manager of the facility. Biosolids from the local wastewater treatment plant are also mixed in, and help contribute to the microorganisms that will eventually break down waste into compost.
Leonard explains how the composting process gets started. The tipping floor is where municipal waste and biosolids from the wastewater treatment plant are first collected before they’re funneled into rotating “digester” drums, which start the composting process.
Leading from the tipping floor to another enclosed structure, digesters rotate 24 hours a day. It takes three days for garbage to travel 185 feet along these drums. The three larger digesters are 14 feet in diameter, and two more measure 12 feet in diameter; all are slightly tilted toward the building where compost will eventually be removed.
“Basically, it’s breaking up all those bags and allowing all that stuff to mix together, so now you can get all your organics, all your food waste and paper waste, all mixing together, and then the bugs can start working on that,” Leonard explains. Microorganisms are naturally occurring in the garbage and sewage that enter the digesters. The process is aerobic, so air is blown into the digesters to keep the microorganisms alive and well.
The process of breaking down the waste creates a lot of energy, increasing temperatures in the middle of the digesters to between 160 or 170 degrees.
“They turn 24 hours a day, seven days a week, so about one revolution a minute,” explains Leonard, showcasing the digesters that kick-start the composting process. The functionality of these digesters has been improved over the years through trial and error, and now they serve as models for composting plants around the world.
Leonard points out the ends of the digesters, where garbage is removed after three days of constant rotation. By this time, much of the garbage resembles compost, but large pieces of plastic, metal, and other items that can’t be broken down into compost remain. The material that comes out of the digesters is transported by conveyer belt into the next room, where it’s sifted to remove larger items.
Construction materials such as wire, carpet, hoses, and large pieces of plastic aren’t allowed in everyday trash, since they can clog up the digester.
After the garbage is sifted, “there’s no organics left,” Leonard says. “It’s inert material, so it goes into a Class 3 landfill, which takes construction, demolition, vinyl siding, plastic, glass windows.” Leachate—runoff that has passed through waste and often carries elements and chemicals from that waste as a result—is minimal in Class 3 and Class 4 landfills, meaning these landfills are less harmful to the environment.
Most organic materials have started to break down into compost after three days in the digesters, but recyclables such as the metal can that Leonard is pictured with here still need to be sifted out. The conveyer belt to Leonard’s right transports the materials to a primary trommel screen, which sifts the materials that come out of the digesters down to a 1-inch diameter. In this way, items like recyclable cans and plastics are separated.
After larger items are filtered out, remaining organics are laid out in windrows—long rows of compost pictured at left. Compost in the windrows will be turned twice a day over a period of about five weeks.
Leonard holds finely sifted compost after it’s passed through a final trommel screen, which sifts down the compost to particles not larger than a quarter-inch in diameter. The sifting process helps to separate glass from the organic material. That glass can be recycled later. One of the biggest challenges the Sevier Solid Waste Composting Facility faces today is managing the moisture in the area of the windrows: it needs to be moist enough to keep the compost breaking down, but dry enough so that glass can be better separated from the compost. The better it separates, the more can be recycled.
Though cardboard can break down into compost, Sevier Solid Waste asks customers to separate it, since it has more value when sold for recycling. It can be sold at about $100 to $125 per ton. Sevier County has plenty of cardboard waste, too, because of the many restaurants catering to the county’s large tourism industry.
After about 40 days, what was once considered trash has become finely sifted, nutrient-rich compost. “Sixty percent of everything that comes in goes out as compost … and is used on farms, goes back to the earth,” explains Leonard, who is pictured holding the final product here. An added bonus: individuals can come and pick up bags of compost for free.
“That’s one way the citizens can see that we can make something useful out of this waste,” says Larry Waters, Sevier County mayor.