Pw. Cains et al., POLYCHLORINATED DIBENZO-P-DIOXINS AND DIBENZOFURANS FORMATION IN INCINERATION - EFFECTS OF FLY-ASH AND CARBON SOURCE, Environmental science & technology, 31(3), 1997, pp. 776-785
Research aimed at understanding polychlorinated dibenzo-p-dioxin (PCDD
) and dibenzofuran (PCDF) formation in combustion and incineration pro
cesses constitutes an important component in developing strategies for
controlling their emission. Incinerator ashes from six different proc
ess sources have been examined and characterized in terms of their beh
avior with respect to PCDD/F formation in laboratory experiments. The
effects of varying the carbon content of one ash has been investigated
by replacing the native carbon content with activated charcoals and p
yrocarbons from paper and PVC. Analysis of homologue totals and full i
somer profiles indicate that PCDDs tend to form in preferential isomer
groups, while PCDF isomers are distributed more broadly. PCDD formati
on is consistent with condensation of chloro phenols, together with st
epwise chlorination and dechlorination. Experiments with % pentachloro
phenol precursor show that fly ashes are more reactive dechlorinators
than model systems, probably due to the presence of alkali elements. P
CDF formation probably occurs via condensation of nonchlorinated pheno
l followed by chlorination of the dibenzofuran skeleton; this gives sc
hemes of formation for both PCDDs and PCDFs that start with phenol. De
monstration of the formation of phenols in ashes and simulates is not;
currently satisfactory, but aromatization of residual aliphatic oils
is believed to be the most probable source. A relationship was found b
etween the amounts of such oils present on the original carbons/ashes
and the quantities of PCDD and PCDF formed.