Bacterial Biodegradation of CCA-Treated Waste Wood

As wood treated with chromated copper arsenate (CCA) is removed from service, methods for eliminating toxic metals from the wood are needed. CCA-tolerant bacteria were evaluated for their ability to modify CCA-treated wood. Aerobic bacteria were isolated from a 20-year-old test plot of CCA-treated stakes. Bacteria selected for their ability to grow on nutrient agar containing CCA components, were identified as Pseudomonas putida, Bacillus licheniformis, or Bacillus coagulans. X-ray analysis using scanning electron microscopy revealed intracellular uptake of copper, chromium, or arsenic from nutrient agar containing 0.12 percent CCA by one or more bacterial isolates. Atomic absorption analysis of the sawdust exposed to these bacteria for 3 weeks showed a reduction of 22 percent to 46 percent for copper, 0 percent to 9 percent for chromium, and 0 percent to 8 percent for arsenic by weight compared with the unexposed sawdust. Bacterial exposure of waste wood chips shows potential as an effective means of modifying CCA-treated wood, ideally for recycling into value-added products, such as wood fiber composites.