Agriculture Reference
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Figure 3.12
De novo formation
of chlorinated dioxins and furans
after heating Mg-Al silicate, 4%
charcoal, 7% Cl, 1% CuCl
2
·
H
2
Oat
300
◦
C.
Adapted from L. Stieglitz, G. Zwick, J.
Beck, H. Bautz, and W. Roth,
Chemosphere
19, 283, 1989.
4.00E+04
Total chlorinated dioxins
3.00E+04
Total chlorinated furans
2.00E+04
1.00E+04
0.00E+00
1
2
3
4
5
6
Retention time (h)
migrate away from these sites and be transported in the atmosphere either as
aerosols (solid and liquid phase) or as gases (the portion of the compound that
volatilizes). Therefore, the engineer must take great care in removal and remedi-
ation efforts so as not to unwittingly cause releases from soil and sediments via
volatilization or via perturbations such as landfill and dredging operations.
Processes Other Than Incineration
Incineration is frequently used to decontaminate substrates with elevated concen-
trations of organic hazardous constituents. High-temperature incineration may
not, however, be needed to treat soils contaminated with most volatile organic
compounds. Also, in soils with heavy metals, high-temperature incineration will
probably increase the volatilization of some of these metals into the combustion
flue gas (see Tables 3.7 and 3.8). High concentrations of volatile trace metal com-
pounds in the flue gas pose increased challenges to air pollution control. Thus,
other thermal processes (i.e., thermal desorption and pyrolysis) can provide an
effective alternative to incineration.
When successful in decontaminating substrates, especially soils, to the neces-
sary treatment levels, thermally desorbing contaminants has the additional benefit
of lower fuel consumption, no formation of slag, less volatilization of metal com-
pounds, and less complicated air pollution control demands than other methods.
So beyond monetary costs and ease of operation, a less energy (heat)-intensive
system can be more advantageous in terms of actual pollutant removal efficiency.
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