OCR Text |
Show Introduction Recent discussions in the public press and scientific literature have focused on the potential harmful effects associated with certain possible emissions from incinerators and resource recovery plants. Emissions include substances produced by other common combustion devices such as acid gases, nitric oxides, particulates and metals, as well as trace amounts of organic compounds. Among the chemicals that have received the greatest attention are a class of organic compounds collectively referred to as the polychlorinated dibenzo-p-dioxins (PCDOs) and the polychlorinated dibenzofurans (PCOFs). It is evident that public acceptance of incineration as a means of disposing of MSW depends on the anticipated effects of PCDD and PCDF emissions. Exact formation and occurrence mechanisms of PCDDs and PCOFs are not thoroughly understood, however, three theories have been proposed to account for the presence of PCDDs/PCDFs in incineration effluents, as follows: · The compounds are trace components of refuse and undergo little or no thermal transformation, the remainder being volatized. · The compounds are produced from precursors such as polychlorinated biphenyls (PCBs), chlorophenols, and similar materials. · The compounds are formed de novo from materials that are unrelated to PCDF and PCOD compounds, such as polyvinyl chloride (PVC) and other plastics, petroleum products, chlorocarbons, and inorganic chloride ions. The first theory recognizes that materials containing PCDDs and PCOFs may be fed into a municipal incinerator with the raw refuse. In contrast to the significant quantities of dioxin emission data available, limited studies have focused on MSW PCDO/PCDF analysis. A recent Canadian study 1 (Environment Canada) conducted at Prince Edward Island analyzed the feedstock for both PCDDs and PCDFs. The results indicated PCODs in the MSW of approximately 3080 micrograms/ton while PCOD stack emissions were 395 micrograms/ton, an eight-fold reduction. On the other hand, PCOFs were essentially undetected in the MSW, while PCDF stack emissions averaged 470 micrograms/ ton. An earlier Canadian study by Envirocon 20n the SWARU (Solid waste and Reduction Unit) incinerator reported that total PCDD in the MSW was about 90 percent of total PCDO leaving the incinerator, while PCDF content in the raw refuse was only 4 percent of that leaving the stack. |