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258 Waste Management Practices: Municipal, Hazardous, and Industrial
9 1
O
8 2
7 3
O
6 4
Cl x Cl y
(a)

6 4
O
7 3
8 2
9 1
Cl Cl
x y
(b)

Cl O Cl

Cl O Cl
FIGURE 9.5 Structure of (a) a generic PCDD molecule, (b) a generic
(c) PDCF molecule, and (c) 2,3,7,8 - tetrachlorodibenzodioxin.

TABLE 9.3
Concentrations of Tetrachloro through Octachloro Group Isomers of
PCDD and PCDF in Fly Ashes from Five North American MSW Incinerators
Incinerator Cl 4 Cl 5 Cl 6 Cl 7 Cl 8
PCDD (ng/g)
1 85 213 354 184 97
2 a
3 2.7 6.6 11.6 5.7 3.5
4 12.9 37.5 75.6 41.9 35.2
5 2.4 7.9 9.7 9.1 2.1
PCDF (ng/g)
1 209 549 1082 499 24
2 a
3 7.0 17.8 32.1 10.9 0.7
4 8.2 19.8 38.7 20.6 4.0
5 4.4 21.0 21.6 16.6
a < 0.5 ng/g
Source: Lisk, D.J., Sci. Total Environ., 74, 39–66, 1988. Reproduced with kind permission from
Elsevier, Oxford, UK.

PCDDs form in incinerators at temperatures of approximately 500ºC and are destroyed at a
minimum of 900ºC. PCDD and PCDF formation and persistence are favored by low combustion
temperature, wet MSW, insufficient or excess oxygen, and inadequate residence time (Lisk, 1988).
High temperatures and well-oxygenated multistage combustion zones are incorporated in modern