Potential Role of Chlorination Pathways in PCDD/F Formation in a Municipal Waste Incinerator

The role of chlorination reactions in the formation of
polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans
(PCDFs) in a municipal waste incinerator was assessed
by comparing predicted chlorination isomer patterns with
incinerator flue gas measurements. Complete distributions
of PCDD and PCDF congeners were obtained from a stoker-type municipal waste incinerator operated under 13 test
conditions. Samples were collected from the flue gas prior
to the gas cleaning system. While total PCDD/F yields
varied by a factor of 5 to 6, the distributions of congeners
were similar. A conditional probability model, dependent
only on the observed distribution of monochlorinated isomers,
was developed to predict the distributions of polychlorinated
isomers formed by chlorination of dibenzo-p-dioxin (DD)
and dibenzofuran (DF). Agreement between predicted and
measured PCDF isomer distributions was high for all
homologues, supporting the hypothesis that DF chlorination
can play an important role in the formation of PCDF
byproducts. The PCDD isomer distributions, on the other
hand, did not agree well with model predictions, suggesting
that DD chlorination was not a dominant PCDD formation
mechanism at this incinerator. This work demonstrates
the use of PCDD/F isomer patterns for testing formation
mechanism hypotheses, and the findings are consistent with
those from other municipal waste combustion studies.