Reusing Remediated CCA-Treated Wood

Abstract: Options for recycling and reusing chromated-copper-arsenate- (CCA) treated material include dimensional lumber and round wood size reduction, composites, and remediation. Size reduction by remilling, shaving, or resawing CCA-treated wood reduces the volume of landfilled waste material and provides many options for reusing used treated wood. Manufacturing composite products from CCA-treated wood combined with untreated wood, plastic, or cement has been explored. Remediation strategies are numerous; chemica l extraction, bioleaching, chelation, and liquefaction or a combination of these techniques has been successful at removing metals from treated wood to varying degrees. Bioremediation is a novel approach to recycling CCA-treated waste wood and provides an opportunity to reuse this abundant fiber source in value-added composite products. In this method, oxalic acid extraction and bioleaching with a metal-tolerant bacterium have successfully removed 70 % copper, 81 % arsenic, and 100 % chromium from chipped CCA-treated Southern Pine. The two-step sequence of acid extraction followed by bioleaching removed more metals than either acid extraction or bioleaching alone. Reversing the sequence and bioleaching prior to acid extraction was also not as effective at metal removal. Metals that are released from CCA-treated wood during biomediation are recoverable from a liquid medium and available for reuse or disposal. The “cleaned ” wood particles were reassembled into medium-density particleboard prepared with urea-formaldehyde resin and evaluated for physical properties, such as internal bond strength, modulus of elasticity, modulus of rupture, thickness swell, and water absorption. Bioremediation removes 80% to 100 % of the heavy metals from spent CCA-treated wood enabling the wood fiber to be reused in composite products. However, as long as CCA-treated wood can be disposed in landfills, economics will remain unfavorable for wide acceptance of alternative reuse and remediation options