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55 ash is processed to recycle the ferrous and nonferrous metals and the remainder is graded and used in road and other construction. The biological processes produce residues as well. These are of two types: (1) inert residues that are landfilled and (2) organic residues that can be cured to be a soil amendment or compost. Biological WPT are mass reduction technologies so that contaminants such as heavy metals are concentrated in the residue. Tests for these contaminants need to be conducted during operations and appropriate measures taken. For all but the high- temperature thermal options and the anaerobic digestion system, an ash will be generated. Bottom ash will be discharged from the bottom of the furnace chamber, and fly ash will be collected by the air pollution control system. In accordance with applicable law, WTE ash must be tested to ensure it is non- hazardous. The test is called the Toxicity Characteristic Leaching Procedure (TCLP). Generally, the bottom ash has not been classified as a hazardous material, subject to ash testing and analysis. Fly ash, however, will have a higher concentration of heavy metals and may also contain residual organics. As such, it would likely be classified as a hazardous material if it fails toxicity testing, unless it is combined with bottom ash, as is the current U.S. practice. It should be noted that communities with aggressive, comprehensive recycling programs and programs focused on removing toxics from the MSW stream, such as those to divert used electronics (e- waste), household hazardous waste (HHW), mercury thermometers, fluorescent light fixtures, batteries, various metals and white goods, and the like, could be expected to have a post- diversion MSW stream for combustion containing less toxic materials and thus the ash from combustion to have a lower potential to exhibit hazardous characteristics upon TCLP testing. The solids residual from high temperature systems, such as plasma -arc or pyrolysis, may have a better opportunity for end -use applications and marketing. These glassy -type granules may be classified as non - hazardous and used in construction materials or as a fill. Vendors claim the substrate after digestion is beneficially processed and recovered, with the residue from anaerobic digestion is nothing more than stones, glass or similar items, which is normally directed to a solid waste landfill. However, digestion, like combustion, is a concentrating process. This is the result of the organic matter being converted to gas and utilized or released into the atmosphere. As a result toxic materials in the waste will be part of the residue but in a higher concentration than in the original feedstock. These claims are unproven in plants operating using MSW as feedstock. 5.3 Environmental Issues of Waste Processing Technologies 5.3.1 Air Quality 5.3.1.1 Applicable Regulations Solid waste incinerators, which the U.S. EPA refers to as Municipal Waste Combustors, are regulated under the federal Clean Air Act, originally passed by Congress in 1963 and updated in 1967, 1970, 1977,1990 and 1995 and 1998. Numerous city and local governments have enacted similar legislation, either GBB/C08027 -01 26 August 15, 2008