Thermal formation of PCDD/PCDF: A survey

Since polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/PCDF) were quantified in the emissions from the Amsterdam municipal solid waste incinerator (MSWI) in 1977, more than 20 years of intensive research gave many answers on how PCDD and PCDF can form in thermal processes. As a result, it can be concluded that PCDD/PCDF can be formed in all combustion processes where organic carbon, oxygen, and chlorine are present. Although there are still open questions, findings can be summarized as follows: PCDD/PCDF can be formed in the gas phase as well as in the heterogeneous phase. Geometry of the combustion chamber, time, temperature, feeding rate, input (chlorine), and so forth may have an influence on the formation of PCDD/PCDF. There may be different processes dominating to form PCDD or PCDF. The amount of PCDD and PCDF formed differs between types of thermal processes. Within the same process categories, e.g., MSWIs, hazardous waste incinerators, steel mills, etc., the PCDD/PCDF pattern is very similar. Formation of PCDD/PCDF can be prevented by addition of "inhibitors" such as sulfur- or nitrogen-containing agents. Results from field investigations, i.e., waste wood combustion and a new technology for thermal treatment of municipal solid waste, support these basic findings.