Environmental Engineering Reference
In-Depth Information
drinking water treatment companies commonly use Ozone for drinking water dis-
infection, while chlorine or chlorine dioxide is used only if it is required. An
engineer from a drinking water treatment company in Hamburg, Germany said that
they have not used chlorine to disinfect their distribution system since the beginning
of the 1950s and there is no chlorine residual at all in their 10 waterworks and the
distribution system.
3
In Denmark there has been a policy of gradual elimination of all chlorine from
their water treatment plants. In fact, according to the online edition of Copenhagen
Post (
2009
, June 3), Copenhagen became the last municipality to rely completely
on underground aquifers and completely stopped using all chlorine after using it for
the past 37 years. They have no need to worry about THMs, as there are none in
their drinking water.
In the Netherlands, they have gone considerably further in that as of 2005, no
chlorine is used at all (Smeets et al.
2009
). From 1976 onward, the use of chlorine
has been steadily reduced until 2005, when the last use of chlorine was replaced by
UV. Moreover, according to Smeets et al. (
2009
, p. 3),
UV inactivates a wider
spectrum of pathogens than chemical disinfection, and microbial safety is easily
warranted by process monitoring and control.
“
”
Note also that no chlorine is used in
“
”
the distribution system; the approach is to
starve
regrowth of pathogens rather
than rely on disinfection. To quote again:
There was no more need for a disinfectant residual during distribution to prevent regrowth.
The level of post-disinfection at surface water treatment plants was lowered to such an
extent that, in 2008, no chlorine is being applied at all, and the few locations where
chemical disinfection is applied (chlorine dioxide) no residual disinfectant can be measured
in the distributed water.
”
Thus, the Netherlands has more or less completely eliminated
THMs and HAAs.
9.4 Conclusion
Recently epidemiological studies have con
rmed associations between human
health effects and exposure to chlorinated DBPs. The evidence for carcinogenicity
of DBPs is strongest for bladder cancer, while some but not all
findings have
reported positive associations between colon and rectal cancer and DBP exposure.
In addition, some epidemiological studies also reported associations between
consumption of chlorinated water and adverse reproductive outcomes, including
preterm births and defects in the unborn child. The regulation of DBPs has played
an important role for safe drinking water and public health; however, more than
50 percent of the toxic halides formed during disinfection have not been de
ned. In
some developed countries, particularly in EU countries, alternative methods of
disinfection of drinking water such as Ozone and UV and cartridge
filtration are
3
Personal communication by E-mail, from Dr M. Scheemann, Hamburg.
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