Inside Mecklenburg County's composting operations

For decades, Mecklenburg County, North Carolina, has composted yard waste out of necessity due to the state’s landfill ban on these materials.

Prior to moving to a new compost facility two years ago, the county leased property from the city of Charlotte near the Charlotte Douglas International Airport to run its operation; however, when the lease expired and the airport wanted to expand its runway, the county was notified that it needed to find a new home for its composting operations.

After an eight-month search, the county found a suitable location. Purchasing the property for $2.4 million, Mecklenburg County now operates on a 60-acre site it calls Compost Central & Recycling Center. It was the perfect location because of its close proximity to customers yet appropriate distance from adjacent neighborhoods, says Jeffrey Smithberger, director of solid waste management in Mecklenburg County.

"We try to be very conscious of what we’re doing and how we’re doing it from an efficiency standpoint. We’re quality-oriented on the incoming material.” –Jeffrey Smithberger, director of solid waste management in Mecklenburg County.

“We’ve been the best-kept secret in composting,” Smithberger says. “I’m pretty sure we have one of the largest compost facilities on the East Coast.”

Leading up to the move to the new facility, county staff embarked on a door-to-door education and outreach campaign in the neighborhoods near Compost Central. The residents were concerned about odors coming from the facility and had one stipulation: no food waste.

“One of the things we promised the neighborhood is that we would not do food waste composting. We would only do grass, leaves and limbs, but no food materials,” says Smithberger, who has been the county’s solid waste director for five years. Prior to that, he served as the solid waste director in Fairfax County, Virginia.

Built for growth

In addition to owning and operating a material recovery facility (MRF), Mecklenburg County, the largest county in North Carolina, operates five compost facilities, including one at Foxhole Landfill in Charlotte, to serve the county’s 1 million residents. Compost Central, the largest of the sites, accepts and processes yard waste from six municipalities within the county, including the city of Charlotte, which is the facility’s largest customer.

Because Charlotte allows yard waste to be collected in bags, Mecklenburg operates a satellite facility to process bagged yard waste before taking it to Compost Central. The county invested $1 million in equipment, including a low-speed shredder and trommel screen to free the yard waste from the bags.

One of the benefits of moving to a new site was being able to design and build the facility from the ground up, Smithberger says. Compost Central includes mostly outdoor space for windrow composting as well as a 2.5-acre drop-off area for recyclables and construction and demolition materials. The site also features a full-service maintenance shop where staff can work on the solid waste department’s equipment out of the elements. Recyclables collected at the drop-off site are then taken to the county MRF for processing.

When operations first started at Compost Central, the county sped up the composting process by building higher piles of the material; however, residents started complaining about odor coming from the site, Smithberger says. As a result, Mecklenburg created an odor hotline and worked with Byers Scientific & Manufacturing, an industrial odor management company based in Bloomington, Indiana, to design an odor control system around the perimeter of the facility. The blower system delivers a deodorizer in a vapor state via an engineered pipe distribution system. Smithberger says staff helped with the implementation of the system by utilizing an existing fence that surrounded the property to secure the pipe used in Byers’ odor control system.

“It’s a small blower system,” Smithberger explains. “[The deodorizer is] not designed as a masking agent. It’s designed to interact with and neutralize some of the sulfur compounds leaving the site.”

While the system costs $70,000 per year to operate, Smithberger says he hasn’t received any odor complaints since it was installed.

“Having zero odor complaints is worth every dollar of it,” he says.

Most of the yard waste taken to Compost Central is used for composting, while some material is grinded and hauled to South Carolina to be used as fuel for boilers. The county has what it calls a mobile grinding crew, which uses Diamond Z and Vermeer tub grinders to break down larger pieces of wood and limbs into smaller pieces for composting or fuel applications.

“Some locations using the ground wood material to make energy are converting it to natural gas,” Smithberger says. “However, we estimate within the next five years, there may not be a boiler market. When we were doing the layout of the Compost Central facility, we built it bigger because we expect the material we send for fuel may have to stay on our lots for composting.”

Quality first

Mecklenburg County handles 150,000 tons of yard waste per year, with 100,000 tons of this material processed directly at Compost Central. When yard waste is delivered by the municipalities to the Compost Central facility, a staff of eight inspects the material for contaminants.

“As time has gone on, we’ve gotten more sophisticated in the industry about managing the technical aspects of composting,” Smithberger says. “I have a technician on staff that records the age of the piles and the temperature and moisture within the piles. It’s a more technical approach these days. It’s not just going out and turning the piles when you think you want to.”

Composting equipment has also advanced over time, Smithberger says. Some of the equipment used on-site includes a Komptech star screen and an Edge Mulch Master. The entire composting process, from when material arrives at the facility to when it is ready as finished product, takes about six months, Smithberger says.

After years of processing these materials, the county has developed a high standard when it comes to the quality of its compost.

“One of the big reasons we’ve been in the composting business for a long time is because legally you can’t throw it in the landfill,” Smithberger says. “There are a number of different items banned from landfill in North Carolina, including plastic bottles, aluminum cans, batteries and yard waste.”

He adds, “We try to be very conscious of what we’re doing and how we’re doing it from an efficiency standpoint. We’re quality-oriented on the incoming material. We grump at folks who bring in items they shouldn’t because it affects our quality.”

Mecklenburg County sells its compost, which is certified by the U.S. Composting Council Seal of Testing Assurance (STA), under the brand name Queen City Compost, referencing Charlotte’s long-time nickname, Smithberger says. The finished compost is sold within 100 miles of Charlotte and used in several commercial applications. For example, the county supplied about 30,000 yards of compost for a project carried out by South Carolina’s Department of Transportation last year, Smithberger says. Mecklenburg also sells compost by the bag.

“Most of our sales are bulk sales, but we do sell our finished compost by the bag for residents and businesses,” Smithberger says. “We have a saying, ‘If you don’t have a truck, you’re not out of luck,’ because we have compost for sale by the bag.”

The sale of the compost helps offset tipping fees at Compost Central, which are currently $27 per ton, Smithberger says.

While composting food waste isn’t an option at the facility, Mecklenburg’s solid waste department supports a pilot food waste composting program at 25 area schools. Smithberger says growing food waste collection programs in the public sector is a challenge because of the county’s low tipping fees.

“Part of the issue here is the cost of landfill tipping fees are fairly low,” Smithberger says. “Sometimes compost costs for organics exceed that, so it makes that a hard sell to move forward with organics processing.”

This article originally appeared in the Nov./Dec. Issue of Waste Today. The author is the digital editor for the Recycling Today Media Group and can be contacted at kmaile@gie.net