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Chapter 33
Disposal Management of Preservative-Treated Wood Products 1
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Timothy Townsend , Brajesh Dubey , and Helena Solo-Gabriele
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Department of Environmental Engineering Sciences, University of Florida, P.O. Box 116450, Gainesville, F L 32611 Department of Civil, Architectural, and Environmental Engineering, University of Miami, Coral Gables, F L 33124
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When treated wood structures reach the end of their useful lifespan they must be disposed of. Proper management of the preservative-containing wood is necessary to minimize any potential risk to human health and the environment. Treated wood products enter the waste stream in small amounts as remnants during construction activities, and at a much larger magnitude as a result of demolition. The first step in discarded treated wood management is determination of appropriate regulatory status, i.e. is should the waste be managed as a hazardous waste. Testing finds that creosote and pentachlorophenol treated wood do not typically leach preservative concentrations at sufficient quantities to be characterized as a hazardous waste in the U S . Chromated copper arsenate (CCA) treated wood does often leach arsenic (As) and chromium (Cr) above hazardous waste thresholds, but in most of the U S , CCA-treated wood is excluded from being defined as a hazardous waste because of a specific exemption under resource conservation and recovery act (RCRA). Other national or state specific regulations may impact disposal-end management requirements. The primary management options for discarded treated wood include landfilling, combustion and recycling. Landfilling is typically the least expensive option, but this practice is accompanied by concerns such as placement and compaction difficulties and the potential for contamination of leachate and groundwater. © 2008 American Chemical Society Schultz et al.; Development of Commercial Wood Preservatives ACS Symposium Series; American Chemical Society: Washington, DC, 2008.
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546 Recent research suggests that As leaching may pose a risk to groundwater at unlined C & D debris landfills and leachate management problems at a lined facility. Combustion is commonly practiced to recover energy from creosote and pentachlorophenol treated wood. Arsenic from CCA-treated wood may volatilizes at typical combustion temperatures so combustion facilities should be equipped with appropriate air pollution control devices. Recycling practices and extraction technologies such as bioremediation, chemical extraction, electrodialytic extraction and liquefaction have been developed, but these systems are more costly than traditional disposal options and separation of treated wood from the mixed wood stream can be challenging. As alternative treated wood products are developed and used, manufacturers should consider disposal-end management.
Introduction Treated wood products are designed to resist decay in harsh environments for many years, but ultimately these products are removed from service and discarded. The preservative chemicals added to treated wood function through their toxicity to organisms that would otherwise attack and deteriorate the wood. The presence of the potentially toxic chemicals raises a natural concern over environmental and human health risks when these materials are disposed. Historically, research on preservative treatment of wood focused on development of alternative preservatives and the ability of treated wood products to perform over their lifespan. In recent years research focusing on environmental and disposal issues has become more prominent. In this chapter, an overview of treated wood disposal issues is presented. Much of the discussion focuses on CCA-treated wood as this preservative system has been investigated most heavily with regard to disposal. Where appropriate, however, the discussion is generalized to include all treated wood products.
Treated Wood Within the Wood Waste Stream Treated wood products enter the wood waste stream as remnants of new construction activities (a relatively small contribution) and from demolition and renovation of existing structures. Reasons for removal from service include: (1) the product has reached the end of its useful life and no longer possesses desired structural requirements, (2) a structure containing treated wood is demolished,
Schultz et al.; Development of Commercial Wood Preservatives ACS Symposium Series; American Chemical Society: Washington, DC, 2008.
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destroyed or otherwise damaged, and (3) the structure is removed because of aesthetic reasons. Cooper and Ung (/) estimated that the service life of an untreated southern yellow pine fence post in the environment is between one and three years, whereas a post treated with preservatives can last from twenty to thirty years. In studies focusing on residential decks, McQueen and Stevens (2) and Alderman (5) estimated a lifespan of 9 and 12.8 years, respectively. The reason for early removal, as determined from surveys, was aesthetics due to color changes and cracking of the wood product as a result of weathering. The amount of a particular treated wood product discarded in any given time period depends on the amount historically entering the marketplace and the product's lifespan. Records of how much treated wood enters the waste stream are not tracked, but estimates can be made using historical production data and estimate of product lifespan. This process has been applied to estimating the amount of CCA-treated wood discarded in Florida, U S . Solo-Gabriele and Townsend (4) estimated that approximately 140,000 m of CCA-treated wood products were disposed in Florida during the year 1996. This quantity is forecasted to increase to 900,000 m by 2015 This estimate was further refined in 2005 (5) to account for the different lifespans of different products and to factor in the withdrawal of C C A from most residential applications in January 2004 (Figure 1). Currently the newer treated wood products, those that replaced C C A for residential use, are entering the waste stream primarily as construction remnants (
