The quantity of waste materials generated and disposed in the United States is staggering. The U.S. Environmental Protection Agency estimates that we generate annually approximately 250 million tons of municipal solid waste, 7.6 billion tons of industrial solid waste (including wastewater) and over 34 million tons of hazardous waste. Most of that waste is disposed in landfills or streams (following wastewater treatment) or incinerated. The costs to the waste generators and the environmental impacts on communities are among the significant drawbacks of this practice.
Many of the wastes are secondary materials such as spent materials, byproducts or sludges produced by the manufacturing process. A spent material is a used material that as a result of contamination can no longer serve the purpose for which it was produced without processing. Sludge is material generated from a wastewater treatment plant (other than treated effluent) or from an air pollution control facility. A byproduct is a material that is not one of the primary products of, nor separately produced by, the manufacturing process. (See 40 C.F.R. §261.1(c).)
