Environmental Engineering Reference
In-Depth Information
more economical if power generation facilities are far away. In addition to co-firing or
co-generation facilities, improvements in thermochemical conversion efficiency and
establishment of small-scale conversion facilities using gasification and/or pyrolysis
may favor the use of forest residues for biofuel production (Polagye et al., 2007).
A third major category of immediately available second-generation biomass is
wood residues from secondary mill products and urban wood waste . Urban wood
waste provides a relatively cheap feedstock to supplement other biomass resources
(Wiltsee, 1998). Urban wood waste encompasses the biomass portion of commercial,
industrial, and municipal solid waste (MSW), while secondary mill residues include
sawdust, shavings, wood trims, and other byproducts generated from processing
lumber, engineered wood products, or wood particles. Both urban wood waste and
secondary mill residues have several primary uses and disposal methods. Urban
wood waste not used in captive markets (such as the pulpwood industry) could be
used as a biomass either to generate electricity or to produce cellulosic ethanol when
it becomes commercially viable.
The amount of urban wood wastes produced in the United States is significant
and their use as biomass could be economically viable, particularly in large urban
centers (Wiltsee, 1998). Several national availability estimates exist for various types
of urban wood wastes, but estimates vary depending on methodology, product cover-
age, and assumptions about alternative uses (McKeever, 2004; Wiltsee, 1998). One
of the challenges with regard to the potential availability of urban woody waste is to
sort out the portion that is available (not currently used) and determine alternative
uses, including those used by captive markets (not likely to be diverted to bioenergy).
One assessment of urban wood waste finds that 36% of total biomass generated is
currently sold to noncaptive markets, and 50% of the unused residues are not avail-
able due to contamination, quality, or recoverability.
One source of recurring and potentially available carbon feedstock is municipal
solid waste. The U.S. Environmental Protection Agency (USEPA) estimated that in
2005 245.7 million tons of MSW were generated in the United States, of which 79
million tons were recycled, 33.4 millions tons were diverted to energy recovery, and
133.3 million tons were disposed of in landfills. As such, landfilled material repre-
sents a potentially significant source of renewable carbon that could be used for fuel/
energy production or in support of biofuel production.
Attributes of the Perfect Energy Crop
The perfect energy crop has
High biomass
Improved composition and structure
Disease and pest resistance
Optimized architecture
Salt, pH, and aluminum tolerance
Rapid and cost-effective propagation
Stand establishment (cold germination and cold growth)
Perennial
Deep roots
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