WEST LAFAYETTE, Ind. -- It's the environmental equivalent of turning a sow's ear into a silk purse -- Purdue University researchers have developed a process for making topsoil from coal ash, yard waste and industrial byproducts.
"There are many potential benefits to this project, including the long-term economical and environmental management of two so-called waste products -- coal ash and industrial byproducts," says Joseph Mikesell, director of utilities at Purdue and one of the participants in the soil-making project.
Jody Tishmack, ash management coordinator for Purdue Physical Facilities, says the combination of minerals from the coal ash and the nutrients in an organic-rich industrial byproduct makes a very effective soil additive.
"Mixing this material with poor-quality soil -- even sand and gravel -- creates a man-made topsoil that in preliminary laboratory tests outperformed local topsoil in terms of yield," she says.
The main ingredients in the soil all come from Purdue and the surrounding area. The coal ash comes from Purdue's Wade Utility Plant, which burns Indiana-mined coal in a clean coal combustion unit. The organic material, which also is used on farmland as a fertilizer, is a nontoxic byproduct left over from the manufacture of antibiotics at two Eli Lilly and Co. plants -- Tippecanoe and Clinton Laboratories. The yard waste, containing "friendly" bacteria that break down the organic material, is supplied by a local composting operation.
The main uses for the soil are for reclamation of Purdue's gravel pit and campus landscaping projects, but Tishmack says coal companies and other industries could use it to reclaim areas depleted of vegetation by industrial use.
"There are a number of sites, such as coal mines and gravel pits, where land has been depleted," she says. "To reclaim these sites quickly with vegetation requires nutrient-rich topsoil, and we can't afford to take that away from farms. In addition, if this process is effective on a large scale, waste management companies will have an opportunity to take waste and turn it into a 100 percent recycled commercial product.
"If this type of operation were set up at power plants, the soil could be sent back to the coal companies on their empty coal trucks, and they could use it to help reclaim the areas they mine."
In May, more than 600 tons of the Purdue-made soil were shipped to the Chinook Mines in Brazil, Ind., in cooperation with Indiana Department of Natural Resources. The topsoil was spread an inch-and-a-half thick on three one-acre test plots, tilled into the existing soil and seeded.
"We've incorporated this material into coal slurry ponds at the mines to determine if we can reclaim the acid-saturated land, which won't support vegetation," Mikesell says. "The goal is to show that this material will allow vegetation to take hold there."
Based on greenhouse and lab tests at Purdue, the material is environmentally safe, Tishmack says, noting that coal ash is used in the construction of roads and embankments and that the industrial byproduct is used as a fertilizer on farms. The Indiana Department of Environmental Management has granted Purdue a preliminary permit to use the soil on campus. The Department of Natural Resources also has a permit from IDEM to use the soil at the Chinook Mines. Field tests at the mines will determine whether the soil can be used for coal mine applications.
Tishmack says it probably would not be cost effective to use the soil on farms, noting that it can cost about $2,000 an acre to spread a 12-inch-thick layer.
To make the topsoil, the ingredients are mixed in piles on the ground. Wood chips are added to provide volume and allow air to circulate through the piles as they compost for at least three months.
"During the composting process, bacteria eat their way through these piles and digest the organic materials. The materials break down into smaller particles, combining with the minerals in the coal ash to form very nutrient-rich soil," Tishmack explains.
The "Soilermaker" project started in the lab in 1993, and the first large-scale mixing operation started in the fall of 1995, producing about 200 cubic yards of topsoil, or roughly 200 tons. The name Soilermaker is derived from "Boilermaker," the nickname for Purdue sports teams and students.
The latest phase of the project is a larger-scale pilot program, which has yielded about 1,000 tons of material in addition to the 600-plus tons now at the Chinook Mines. Purdue and Eli Lilly are developing a business plan to set up a full-scale composting facility on campus.
Indiana produces about three million tons of coal ash a year, and about 10 percent of that is used for beneficial purposes, according to statistics from the Indiana Electric Association. Nationwide, according to 1996 data from the American Coal Ash Association, more than 75 million tons of coal ash are produced annually, with about 25 percent used beneficially. The remaining ash usually is sent to a municipal or company-owned landfill, Tishmack says.
Purdue produces about 30,000 tons of coal ash a year, but not all of it is suitable for making the topsoil, Mikesell says. He estimates a cost-effective, full-scale operation at Purdue would use about half the coal ash to produce about 20,000 to 30,000 tons of soil a year.
The Purdue group is working with a laboratory in Maine to optimize the mix design of the topsoil.
"Different combinations of these materials can be used to produce soil for different applications," Mikesell explains. "For example, we might come up with four or five types of soil or soil additives, some suitable for plants used for reclamation, and some more suitable for landscaping vegetation."
The Soilermaker project is funded in part by the Indiana Department of Commerce.
Sources: Joseph Mikesell, (765) 494-7327
Jody Tishmack, (765) 494-0387; e-mail, solem@ce.ecn.purdue.edu
Writer: Amanda Siegfried, (765) 494-4709; e-mail, amanda_siegfried@uns.purdue.edu
Purdue News Service: (765) 494-2096; e-mail, purduenews@uns.purdue.edu