Online sorting of wood treated with chromated copper arsenate using laser induced breakdown spectroscopy

Abstract

The use of the CCA chemical as a wood treatment to protect against insect and fungal deterioration has had commercial application for the past twenty-five to thirty years. While CCA treated wood has several benefits, with perhaps the most important being the saving of an estimated 225 million trees annually due to its longer service life, there are growing concerns that the handling and disposal of CCA treated wood may have negative impacts on human health and the environment. Because CCA treated wood has a service life of nearly thirty years, the amount of CCA treated wood that will be disposed of is expected to dramatically rise in the near future. The disposal of the metals contained within CCA treated wood by incineration, land applications as landscape mulch or disposal in a landfill will all fail to meet leaching protocols established by the EPA. While there is an exemption in place for CCA treated wood to be disposed of in unlined construction and demolition landfills, there is a need to detect and sort CCA treated lumber from untreated lumber quickly and accurately with an online method. Sorting would allow the continued disposal of untreated wood as landscape mulch and in biomass combustors while easing the burden on landfills. This work details the design and evaluation efforts to develop an online detector using laser induced breakdown spectroscopy (LIBS) technology. By forming a plasma on the surface of the wood, the detector analyzed the spectral emission from the plasma to identify the metals present in the wood sample. This analytical process was performed twice per second with the demonstrated potential to increase to ten times per second. In addition to this rapid sampling and analysis, the results of this work demonstrated accuracies approaching 100%. With the cost effective development of an online LIBS detector for CCA treated wood, regulators and industry have a useful tool to meet the challenges of CCA treated wood disposal.