Evaluation of methods for sorting CCA-treated wood.

Area of Science:

• Environmental Science
• Materials Science
• Waste Management

Background:

• Construction and demolition (C&D) wood often contains preservative-treated wood, such as chromated copper arsenate (CCA).
• Recycling C&D wood requires removal of preservative chemicals to meet product specifications.
• Effective sorting methods are needed to identify and separate treated wood from the waste stream.

Purpose of the Study:

• To characterize the C&D wood waste stream regarding treated wood content.
• To evaluate the efficacy of different sorting techniques for identifying treated wood.
• To assess the cost-effectiveness of various sorting methods.

Main Methods:

• Documenting C&D wood waste stream characteristics.
• Evaluating visual sorting, visual sorting with PAN indicator stain, and visual sorting with hand-held X-ray fluorescence (XRF) units.
• Conducting experiments on source-separated and commingled C&D wood loads.

Main Results:

• Seventy-seven percent of treated wood identified was CCA-treated.
• Visual sorting effectively removed treated wood from uncontaminated source-separated C&D wood (<1% treated).
• PAN indicator stain augmented visual sorting for contaminated source-separated wood (approx. 50% treated).
• Hand-held XRF units proved effective for sorting commingled C&D wood due to dirt interference with PAN stain.
• Sorting costs ranged from US$21-US$96/ton for visual sorting and US$113/ton for visual sorting with XRF, primarily driven by labor.

Conclusions:

• The effectiveness of sorting methods for treated C&D wood depends on contamination levels and wood source.
• Augmented sorting techniques (PAN stain, XRF) are necessary for higher contamination levels or commingled waste.
• Future research should focus on automating XRF sorting to reduce labor costs and improve efficiency.