Keeping Treated Wood Out of Landfills

Todd F. Shupe, Bogren, Richard C.  |  9/21/2005 1:06:29 AM

What to do with decommissioned, preservative-treated wood has become a burning issue. Well, not burning, actually. That’s one of the methods that can’t be used any longer, according to Todd Shupe, a forest products researcher in the LSU AgCenter’s School of Renewable Natural Resources. Shupe has been looking for answers for what to do with the products no longer serviceable.

“Disposal of decommissioned, preservative-treated wood has increasingly become a major concern because the popular disposal options – burning or land filling – are becoming more costly and impractical,” Shupe said. “Recycling – both of treated wood and of the preservatives – must be considered.”

Finding new uses for these products is important to Louisiana because nearly half of the southern yellow pine grown in the state ends up being treated with either creosote or chromated copper arsenate (CCA) for use in industrial applications ranging from utility poles to highway and bridge guardrails.

Although the wood processing industry has voluntarily withdrawn CCA-treated wood products from use in residential construction, the product is still widely used in industrial applications.

“Preservative-treated wood is often recommended to prevent decay and ensure structural integrity,” Shupe said. “Without treatment, exterior wood products are at a disadvantage against other materials, such as steel, concrete, plastic and aluminum.”

To keep the products as viable alternatives, users need to have a way to dispose of the used wood.

Shupe’s answer includes several types of recycling.

“The chemical method has the most potential for industrial adoption,” he said. “It’s quick, environmentally safe and benign.”

In a process Shupe calls liquefaction, treated wood is ground and liquefied with an organic solvent. “The process uses relatively low temperature, short reaction time and small amounts of organic reagents,” he said.

Shupe said the process is economically viable and environmentally friendly.

“This approach has the best opportunity for success,” he said. “There’s zero discharge, and it produces multiple products.”

The results can include the chemicals originally used to treat the wood as well as nontoxic liquefied wood that can be used for resins, molded wood products, foams and plastics.

A second process uses super critical water – water at high temperature under high pressure – to recover the preservatives and detoxify the wood for reuse. Shupe said research has shown that the process can remove creosote from wood and yield a mixture of industrially useful hydrocarbons and other chemical compounds along with toxic-free wood.

In addition to removing chemicals from treated wood, Shupe said, the LSU AgCenter has researched re-using the wood with the preservatives still in it.

“Decommissioned wood products often have residual preservatives that can be reconfigured and reused in industrial applications,” Shupe said.

Discarded utility poles can be cut lengthwise and glued together to be used again. And other obsolete or damaged wood products can be flaked and made into structural flakeboard, which research shows maintains acceptable mechanical and physical properties and adequate decay resistance with as much as 50 percent treated material in the panels.

Shupe and his colleagues in the Louisiana Forest Products Development Center are hopeful that they can find funding to develop the Louisiana Center for Treated Wood Recycling at the LSU AgCenter’s Calhoun Research Station.

“This would be the only center for recycling treated wood in the United States,” Shupe said.

(This article appeared in the summer 2005 issue of Louisiana Agriculture.)
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