Incineration pattern, PCDD

The relative ratio of regioisomers of PCDD/F and other chlorinated compounds formed in incinerators is called the incineration pattern. The pattern can be derived from statistical analysis of a large number of measurements of the same plants, and can be used for elucidation of thermal formation mechanisms in plants. In principle regioisomers can be formed either by stereospecific chlorination or dechlorination processes. The pattern has also been used as a part for explaining of the formation mechanism of PCDD/F and other chlorinated compounds formed in incinerations (see Figure 8.4). 

Dioxins are mainly by-products of industrial processes, but can also result from natural processes, such as volcanic eruptions and forest fires. Besides the anthropogenic (man-made) sources of PCDD/F discussed earher, biogenic and geogenic sources for dioxins also have been discovered recently. In natural clays of the kaohnite-type found in German mines in Westerwald, considerable levels of PCDD / F have been detected the same findings were obtained in special ball clays in the Mississippi area of the United States. The pattern (isomeric ratios) of this natural type of dioxins is different from the pattern obtained from incineration plants. 

Most of the analyses of samples from incinerators have been done using non-validated and non-isomer specific sampling and analytical methods. Recent studies show the presence of a multitude of PCDD and PCDF congeners, in fact all isomers seem to be present k) Moreover, a striking similarity in the isomeric pattern of PCDDs and PCDFs was found between samples from different incinerators... 

Hazardous waste incinerators. Hazardous waste incinerators have also been the object of public concern. However, available data indicate the emissions from such incinerators operating under good conditions are of the same magnitude as emissions from MSW incinerators. The isomeric patterns of PCDDs and PCDFs are similar to those reported from MSW incinerators... 

Recent studies using pre-spiked ( C) air samples and isomer specific analytical methods ( ) indicate that sub pg/m levels of a variety of PCDDs and PCDFs can be found in air sampled in an industrialized area. The isomeric patterns found in these samples were very similar to those found in samples from MSW and industrial incinerators, car exhausts and also in new sediments ( ). 

Wastes containing PAHs may be effectively destroyed by various incineration processes as mentioned briefly in the above section. Weber et al. (2001) have studied the mechanisms of formation of polychlorinated diben-zofurans (PCDF), polychlorinated biphenyls (PCB), polychlorinated naphthalenes (PCN) and polychlorinated benzenes (PCBz) from the degradation of PAHs in two types of incinerators, the stoker type- and the fluidized bed incinerators. Their studies have revealed the occurrence of a sequence of steps, such as the cleavage of C-C bond in the PAHs, chlorination at these cleaved positions, further chlorination or oxygen insertion at the ortho positions to the chlorine atoms in the intermediate chlorinated species. A perylene structure in soot is proposed as the basis for the observed PCDF pattern in the fluidized bed incinerators. Polychlorinated dibenzo-dioxins (PCDD) and the polychlorinated... 

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