Paving the way
In Florida’s Highlands County, garbage is being repurposed to produce fuel for the county’s asphalt plant. By using landfill gas to power the production of its own paving material, the county is saving hundreds of thousands of dollars annually.
Before the project started, the county was burning the landfill’s 65 million standard cubic feet of methane per year in a flare to control odors. Solid waste managers considered several alternatives to use the energy, including generating electricity, cleaning and compressing the gas to make vehicle fuel, using the gas to dry sewage sludge and animal waste for fertilizer, and drying aggregate to make asphalt. Meanwhile, the county could not get the asphalt it needed from contractors in a timely manner to complete paving projects. So, the county applied to the state for a $1.65 million innovative grant to help fund construction of an asphalt plant that would use the landfill gas.
In 2007, the county’s solid waste consultant PBS&J began designing and constructing the project, which opened in October 2008 as the state’s only landfill-gas-powered asphalt plant. In its first fiscal year — from October 2008 through September 2009 — the plant produced 28,000 tons of asphalt, which was enough to pave about 48 miles of 24-foot-wide roadway with 1 inch of asphalt. The county’s bid price for asphalt last year was $85 per ton, but its production cost is $78 per ton, meaning last year the plant saved the county $196,000. The plant is permitted to produce 80,000 tons, so with a cost savings of $7 per ton, the annual savings are estimated at $560,000. “Now we have as much asphalt as we need to pave whenever we want to — and we’re saving money,” says Ken Wheeler, Highlands County’s solid waste director.
The asphalt is made from granite, limestone, coarse sand and asphalt binder purchased from outside vendors. Approximately 15 percent of the mix includes local sand from a county-owned site, and 400 to 500 tons of glass collected from residents is replacing much of the coarse sand in the mixture. Before the plant opened, the county had cut its recycling program because of a declining market for recycled glass. Now, all of the glass collected by the county for recycling, as well as some glass from other nearby communities, is used in the county’s asphalt.
Project: Landfill-gas-powered asphalt plant
Jurisdiction: Highlands County, Fla.
Agency: Department of Solid Waste Management
Vendor: Tampa, Fla.-based PBS&J
Date completed: October 2008
Cost: $3.3 million