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Polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) are found on fly ash and in flue gas of municipal waste incinerators. Municipal waste incinerators seem to be the most important source for PCDDs and PCDFs emitted into the air during the last decades. PCDD/F formation takes place in the cooler zones (250 °C-450 °C) of a municipal waste incinerator, at the electrostatic precipitator. Copper is an important component of the fly ash that can catalyse the formation of PCDDs and PCDFs. Inhibition of the formation can be done by complexation of the metals (Cu) with EDTA or NTA.

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Role of oxygen in formation of polychlorinated dibenzo-p-dioxins/dibenzofurans from carbon and fly ash. Addink, R.; Olie, K. Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Under an oxygen-deficient flow, no PCDD/F is formed from a carbon/fly ash mixture, but with a mixture of 1% 02 in N2 de novo synthesis of PCDD/F sets in. The 02 concentration was varied 0-lo%, formation was highest at 5-10% 02. Isomer distributions do not change with increased reaction times. Formation rates under conditions without a gas flow are higher than with a gas flow present, suggesting that 02 diffusion into the fly ash bed is more efficient than the supply of 02 through a gas flow.

Polychlorinated dibenzo-p-dioxins (PCDD) and dibenzofurans (PCDF) emitted from municipal waste incinerators appear to have a chlorination pattern that is quite constant across various samples and conditions. This suggested that these patterns may be controlled by thermodynamic properties of the individual PCDD/F congeners, such as the free Gibbs energy of formation (∆G°f ,T ). This would make prediction of the isomer composition of a particular sample (and hence its TEQ value) possible, based on values of ∆G°f ,T . A laboratory scale study was carried out with activated carbon on fly ash as the source of PCDD/F formation. Although it was found that the isomer distributions within homologues were independent of the reaction time (proof of thermodynamic control), other observations (lack of equilibrium/isomerization between isomers and lack of similarity between isomer distributions measured and predicted by ∆G°f ,T ) contradicted the possibility of thermodynamic control. Hence, this study could not confirm that de novo formation of PCDD/F could explain thermodynamically controlled isomer distributions in incinerators. Some recommendations for further workstime-based studies with precursors, isomerization studies with single congeners, and more data on ∆G°f ,T values of PCDD/ Fswere made.