ESTIMATION METHODS FOR PRIMARY MILL RESIDUES

The forestry residue data included in this book are the same as that used in the DOE/USDA publication entitled “Biomass as Feedstock for a Bioenergy and Bioproducts Industry: The Technical Feasibility of a Billion Ton Annual Supply. The resource estimates contained in the following tables have been disaggregated to states.

Primary Mill Residues
Primary mill residues include bark, coarse residues (chunks and slabs), and fine residues (shavings and sawdust) generated at sawmills that process harvested wood. The mill residue data were downloaded by state and county from the U.S. Forest Service’s Timber Product Output database (http://www.fia.fs.fed.us/tools-data/tools/). Because primary mill residues tend to be clean, uniform, concentrated, and of a low moisture content, most of these materials are already used for products or boiler fuel at the mills. The U.S Forest Service estimates current usage by type as follows:

•    Bark – 80% used as fuel and 13% used in products
•    Coarse residues – 85% used in products and 13% used as fuel
•    Fine residues – 55% used as fuel and 42% used in products

This leaves a very small amount (~2%) of unused primary mill material available for energy. Residues are also generated at secondary processing mills (e.g., millwork, furniture, flooring, containers, etc.). Secondary mill residue data are not collected by the U.S. Forest Service.

ESTIMATION METHODS FOR URBAN WOOD RESIDUES

The state-level estimates provided for urban wood residues are consistent with the estimates found in the DOE/USDA publication entitled “Biomass as Feedstock for a Bioenergy and Bioproducts Industry: The Technical Feasibility of a Billion Ton Annual Supply."

Residues for MSW Landfills
MSW consists of a variety of items ranging from organic food scraps to discarded furniture and appliances. Wood and yard and tree trimmings are the two sources within this residue stream that are potentially recoverable for energy use. The wood component includes discarded furniture, pallets, containers, packaging materials, lumber scraps (other than new construction and demolition), and wood residuals from manufacturing. McKeever (2004) estimates the total wood component of the MSW stream at slightly more than 13 million dry tons. About 55% of this material is either recycled as compost, burned for power production, or unavailable for recovery because of excessive contamination. In total about 6 million dry tons of MSW wood is potentially available for energy. The other component of the MSW stream — yard and tree trimmings — is estimated at 9.8 million dry tons. However, only 1.5 million dry tons is considered potentially available for recovery after accounting for what is currently used and what is unusable.

Residues from Construction and Demolition Debris Landfills

The amount of available construction and demolition residue is correlated with economic activity (e.g., housing starts), population, demolition activity, and the extent of recycling and reuse programs. McKeever (2004) estimates annual generation of construction and demolition debris at 11.6 and 27.7 million dry tons, respectively. About 8.6 million dry tons of construction debris and 11.7 million dry tons of demolition debris are considered potentially available for energy. Unlike construction residue, which tends to be relatively clean and can be more easily source-separated, demolition debris is often contaminated, making recovery much more difficult and expensive.

Reference: McKeever, D. 2004. “Inventories of Woody Residues and Solid Wood Waste in the United States, 2002.” Ninth International Conference, Inorganic-Bonded Composite Materials. Vancouver, British Columbia. October 10-13.