By: Lauren McDonnell
Two major sources of urban wood residue are the woody portion of municipal solid waste (MSW) and construction and demolition debris. Of the 62.1 million dry tons of urban wood residues generated annually, about 28.3 million dry tons are economically and physically recoverable (McKeever, 2004). Natural disasters also create a large amount of debris, that if not salvaged, is often burned or ends up in a landfill.
Municipal Solid Waste The portion of MSW that is wood includes items such as discarded furniture, pallets, packaging materials, processed lumber, and yard and tree trimmings. Of the 13 million dry tons of woody MSW generated annually, approximately 8 million dry tons are available for recovery (McKeever, 2004). This material is generally recycled as mulch or compost; sent to a landfill; or burned for heat, power, and electricity.
In recent years, small, portable wood chippers and bailing units that press yard debris into “logs” similar in appearance to that of traditional firewood have emerged. Some municipalities provide large yard debris carts, which are collected weekly. Other areas work with local businesses to ensure collection options such as drop-off bins and designated collection facilities.
Construction and Demolition Residential and commercial wood frame construction and demolition generates cut-offs, scraps, and waste that constitute a relatively clean and homogeneous waste stream that can make an excellent feedstock for biomass fuel and energy production. Moreover, this particular waste is relatively easy to access. Wood waste processors can coordinate with construction contractors to designate an area for discarded wood waste or set up drop boxes on site for scraps. Of the 39.3 million dry tons of construction and demolition debris generated annually, approximately 20.3 million dry tons are available for recovery (McKeever, 2004).
It is important to note that the end-use of the feedstock determines how clean and consistent it is. Sometimes, urban and construction wood waste can contain too many contaminants to be used for certain applications. For example, air quality regulations may prevent creosote-treated telephone poles from being burned for heat and power. Another example is wood waste from demolition activities. This material can contain contaminants such as paints, plastics, and known carcinogens and may not be suitable for some applications. In other cases, the wood material may be in such poor condition that the cost of cleaning limits the economic viability of processing and reusing the material.