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multiplication. Cells of
Legionella
at the interior of cysts of protozoan of
Acanthamoebae can also survive to concentrations of free chlorine of
approximately 50mg∙L
-1
. Using this concentration of free chlorine (50mg∙L
-1
), by
twelve hours, Saby
et al
. (2005) demonstrated the survival of
Legionella
in a water
distribution system.
Sout and Yu (2003) observe that the most recommended disinfection
processes for the control of
Legionella
are still the rinsing with hot water and the
hyperchlorination. However both processes can not bemaintained for long period
due to the facts pointedout previously: the rinsingwithhotwater takesmanyhours
and requires a lot ofmanpower to become effective, and the hyperchlorination can
cause serious risks of corrosion to the pipes, mainly those made of carbon steel.
They also point out that the control of
Legionella
using these two processes ends
when the temperature or the concentration of free chlorine are reduced. Saby
et
al
. (2005) observe also that due to the difficulty tomaintain the water temperature
elevated for long intervals of time at the interior of the distribution system, the best
alternative to avoid themultiplication of
Legionella
seems to be the application of a
shocktreatment (thermalorhyperchlorination,dependingonthebuildingmaterial
of the pipe) followed by a process of continuous chlorination.
Another chlorinated compound that is being employed for the disinfection
of water distribution systems is the
chlorine dioxide (ClO
2
)
. This chemical
compound is used in the water treatment in Europe since the 1940s in the last
century. Several studies indicate chlorine dioxide as beingmore effective than the
other chlorinated compounds that generate HOCl due to its superior oxidative
power and its ability to act on biofilms (WHO, 2002, AWT, 2003, Lin
et al
., 2011).
Other important characteristics related to chlorine dioxide are: the biocidal
action is maintained in a wide range of pH and the corrosivity of this compound
is much lower than that of chlorine.
