Visually Identifying Common Wood Waste Contaminants

Material:  Wood Waste

Issue:  Various sources generate wood waste; this variability causes it to usually contain contaminants. These contaminants might not interfere with processing for particular end-products. For example, compost end-markets could be indifferent to the dirt and grit commonly found in wood waste, whereas composite panel-board markets could have trouble during manufacturing and with end-product performance. However, the end-uses that tolerate contaminants in recovered wood waste generally have the lowest-value markets. To successfully compete with virgin wood materials in higher-value markets, wood-waste processors must minimize the presence of contaminants in their end products.

Best Practice:  This Best Practice recommends that operators become aware of the common wood-waste contaminants that pose problems for end users. This awareness is among the first steps in achieving satisfactory quality control in wood-waste processing. Visually inspect all incoming loads of material to identify contamination. Following is a listing of the contaminants that frequently enter a processing facility along with recovered wood waste:

·   Dirt and grit	·   Rocks
·   Ferrous metals (nails, screws, staples, hardware, cans, etc.)	·   Non-ferrous metals (soda cans, etc.)
·   Plastic (packaging, wrappers, containers, etc.)	·   Rubber (gloves, etc.)
·   Drywall	·   Cardboard and paper
·   Glass	·   Styrofoam
·   Insulation materials	·   Asphalt shingles and tar paper
·   Painted wood	·   Laminated wood (melamine, foil, plastic, etc.)
·   Chemically treated wood (CCA, pentachlorophenol, and others)	·   Composite or engineered wood products (depending upon end-use application)
·   Bark	·   Caulking
·   Hazardous materials (asbestos, lead paint, etc.)	·   Miscellaneous garbage

 

Implementation:  Careful visual inspection of incoming loads of recovered wood waste reveals the wide varieties of non-wood contaminants they contain. Processing facilities should designate inspectors who inspect incoming loads before unloading them from trucks. Inspectors should verify that no prohibited contaminants are present. When inspectors find unacceptable material or excessive contamination, they should either downgrade or reject the load and document its contaminants to clearly communicate their facility requirements to delivering generators. Inspectors quickly become alert to individual generators that deliver certain types of wood-waste containing more contaminants than others. This awareness and subsequent feedback to problem generators can assist them in controlling contamination.

When inspectors have visually inspected loads, trucks dump the wood waste onto receiving decks. Then, processors segregate the wasste wood in the storage yard according to the degree of contamination. The wood waste is subsequently processed appropriately.

Plant operators should have some mechanism (manual or automated) for removing these contaminants from wood waste. Typically, mechanisms to remove contaminants include the following: manual picking, magnetic removal, air-density separation, screening, or chip washing.

Documentation of problem loads is necessary. Using a predetermined sampling method, sample and store key portions until the problem is fully resolved. Immediately contact the generator of the load to discuss and arbitrate the problem. Most importantly, to avoid future occurrences both the processor and the generator should quickly understand and agree on the problem’s source.

Benefits:  A working understanding of, and ability to manage, common wood-waste contaminants enables wood-waste processors to better address the challenge of meeting end-user quality specifications. This basic knowledge also leads to intelligent decisions concerning raw-material sourcing, wood-waste processing, and end-product marketing.

Application Site:  This Best Practice applies to wood-waste processing facilities.

Contact:    For more information about this Best Practice, contact CWC (206) 443-7746, e-mail info@cwc.org.

References: 

1.       Horne-Brine, Preston. Clean Washington Center, Seattle, WA.

2.       International Resources Unlimited, Inc. Eugene, OR.

3.       Portland Metropolitan Service District. Investigation of Alternative Markets for Recycled Wood. Prepared by International Resources Unlimited, Inc. 1992.

4.       Rosen, Howard. United States Department of Agriculture, Forest Service. Washington, DC.

5.       Steuteville, Robert. “Large Scale Wood Processing and Marketing.” BioCycle; January 1997.

6.       Walsh, Dan. Northwest Wood and Fiber Recovery. Portland, OR

Issue Date / Update:  March 1997