UF Researchers: Instrument Aids Sorting Of Treated Wood

November 14, 2001

GAINESVILLE, Fla. — University of Florida and University of Miami researchers have designed a new laser-based technique for sorting treated wood that they say will dramatically improve the safety of the products’ disposal.

Wood treated with chromated copper arsenate, or CCA, is used in everything from porches and picnic tables to playground equipment, but researchers say the chemicals in CCA pose environmental and health risks.

David Hahn, assistant professor of mechanical engineering at UF, said because of the risks, disposal of the wood naturally raises concerns.

“Everyone agrees — industry, consumers and environmentalists — that if you can recycle untreated lumber, either burn it or make mulch out of it, that’s wonderful,” he said. “Everyone also agrees you should not recycle, burn or mulch treated lumber. If you can sort lumber, you can’t go wrong.”

The sorting instrument was developed as a demonstration project for a recycling facility in Sarasota, Fla., in collaboration with the county government. It consists of a conveyor belt that carries pieces of wood past an online laser system, known as Laser Induced Breakdown Spectroscopy, or LIBS. A commercial instrument, X-ray fluorescence, or XRF, in which the emissions from X-rays of the wood identify the presence of chemicals, also was evaluated.

LIBS fires onto the wood and creates a laser-induced plasma. Within that plasma, a portion of the target is vaporized and the atoms from the vapor produce light. In less than a second, the distinct wavelengths of light from the chromium atoms identify the wood as treated with CCA. The wood then is manually sorted into treated and untreated piles, though the project team hopes to automate this process in the future.

The untreated wood sorted at the facility was sent to a landfill, burned or recycled for mulch, and the treated wood was sent to a lined landfill. However, depending on the facility housing the instrument, disposal policies may differ, Hahn said.

Timothy Townsend, assistant professor of environmental engineering at UF and project co-investigator, said that if the instrument were implemented at other recycling facilities, either LIBS or XRF would be used.

“All indications are that the laser method has a lot of advantages, both economically as well as in terms of speed,” he said.

Townsend, who has been researching CCA for five years, said current methods for sorting wood include stains that change color when applied to treated wood; visible sorting; which becomes difficult after wood is weathered or painted; and XRF. This is the first time LIBS has even been used for sorting wood.

Hahn said LIBS and XRF are the fastest and most accurate sorting technologies available. He also said the technologies are the most cost-effective. “It would cost more to put everything in a lined landfill than it would to sort it with this equipment,” he said.

John Schert, director of the Florida Center for Solid and Hazardous Waste Management in Gainesville, said treating wood with CCA started in the 1970s and as that wood comes out of use in the coming years, disposal amounts will dramatically increase. Currently, 10 percent of the country’s wood disposal comes from Florida, and an instrument such as this would greatly help in determining the proper disposal of treated wood, he said.

“This is a really great technology,” Schert said. “It’s the most exciting development in this area.”

Funding for the project was part of a 12-month grant awarded to Sarasota County in August 2000 by the Florida Department of Environmental Protection Innovative Recycling Program. Testing of the instrument was completed in August 2001.