Environmental Engineering Reference
In-Depth Information
Figure 9.9
The general structure for PSDD, PCDF, and PCB are shown in
the first row. An example of a congener derived from each of these is shown
in the second row.
MSW incineration was estimated to be the leading source of PCDDs in air
(EuroChlor, 2003) in Europe as well as in the United States. There are
generated end up in the ash residue (at ppb and ppt levels) (Abad et al.,
2000; EEA, 2000), and their disposal requires caution. Ash also carries a
host of metal residues that can readily leach out, especially under low pH
conditions.
Thanks to stringent regulation in mid-1990s, however, pollution control
technologies used in WTE plants in the United States meet the strictest
emission standards in the world. In modern municipal incinerators, the flue
gas is subjected to a temperature above 850°C (1560°F) for few seconds
to ensure the thermal breakdown of dioxins. WTE was claimed to be the
process for generating electricity with the least environmental impact
(Millrath et al., 2004)! The emissions from US waste incineration plants
(see
Table 9.7
) have come down drastically from the 1990s values. Presently
the dioxin release attributed to MSW combustion is minimal (USEPA,
2005), amounting annually to only 0.5 oz of dioxin toxic equivalents from
combustion. Recent data suggest that modern WTE facilities are more
environmentally acceptable than a coal-fired power plant contributing to
dioxin emissions. But they emit about 33% more CO
2
per unit of electricity
generated compared to the power plant. There is no universal agreement
