225
chlorine, temperature and pH. According to these authors, in order to have
a reduction of 3 log cycles in the population of
Legionella
using 0.1 mg∙L
-1
and 0.5 mg∙L
-1
it was necessary 60 and 5 minutes, respectively, when water is
used at 21 °C. With relation to the pH, it was noted that at 21 °C and using a
concentration of free chlorine of 0.1mg∙L
-1
, to achieve a reduction of 3 log cycles,
it was necessary at least 60 minutes when the pH of the water was 7.6, and 5
minuteswhen the pHwas 6.0. Temperature alsohas a significant influence on the
efficiency of the disinfection process.The time to cause a reduction of 2 log cycles
in the population of
Legionella pneumophila
, using 0.1 mg∙L
-1
free chlorine was
reduced from 40 minutes at 21 °C to less than 30 minutes at 32 °C. At 4 °C, this
destruction was obtained at a time interval between 60 and 90 minutes. In their
work, Muraca
et al
. (1987) show that a concentration of free chlorine between 4
and 6 mg∙mL
-1
causes a reduction between 5 and 6 log cycles in the population
of
Legionella pneumophila
in six hours when the temperature of the water is at
25 °C. By increasing the temperature of the water to 43 °C, it was achieved a
reduction of 7 log cycles in the same time interval. However, Muraca
et al
. (1987)
observe that due to the decomposition of the hypochlorous acid, it was necessary
to add an amount of chlorine 120%higher at the temperature of 43 °C than at the
temperature of 25 °C inorder tomaintain the concentration in thewater between
4 and 6 mg∙L
-1
.
The WHO recommends the maintenance of the concentration of free
chlorineat 0.2mg∙L
-1
inwatercirculating inthe interiorof thepipes (WHO, 2002).
With this concentration it could not be observed a significant multiplication
of
Legionella
. However, in standing water, even with the maintenance of this
chlorine concentration in building reservoirs, it was not possible to interrupt the
multiplicationof theorganism. Incaseof reservoirswithstandingwater, theWHO
suggests the application of additional measures to prevent the multiplication of
