The U.S. forestry industry, in the process of harvesting and converting wood into consumer products, generates a number of residue and waste materials that could be used for bioenergy and bioproducts. Primary mills (sawmills that produce lumber, paper and pulp mills, veneer mills) produced an estimated 86.7 million dry tons of residues in 2007, but because the residues are relatively clean and concentrated at the site of production, all but 1.3 million dry tons were used to produce energy or other products.
In addition to wood residues, pulp and paper mills also generate black liquor (about 52 million dry tons) as a by-product of the kraft pulping process. Black liquor is currently used by the mills to produce heat, steam, and electricity and is the single largest source of bioenergy produced today.