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One of the points to be highlighted with relation to chlorine dioxide is the
fact that this is a gas that has to be generated at the point of use and then injected
in the water flow that is being treated. However, chlorine dioxide does not
react with organic compounds to form tryhalomethanes; it does not react with
ammonia to formnitrogenated compounds, and it is less aggressive than chlorine
to copper and steel (AWT, 2003). Lin
et al
. (2011) indicate yet that this compound
needs to be used for a long interval of time to present significant reductions in the
population of
Legionella
. Zhang
et al
. (2007) observe that a period of 18 months
is required to verify a significant reduction of
Legionella
in the samples of water.
When the temperature of the water is raised, a higher concentration of chlorine
dioxide must be injected to ensure the desired concentration. For example, to
ensure a concentration of chlorine dioxide in the hot water flow between 0.25
and 0.5 mg∙L
-1
the initial concentration must be between 3 and 5 mg∙L
-1
; parallel
reactions with existing rust andmagnetite in the galvanized pipes can also reduce
the concentration of chlorine dioxide (Zhang
et al
.,2007). The main challenge in
the use of chlorine dioxide is to ensure a residual concentration between 0.3 and
0.5 mg∙L-1 throughout the entire network of distribution of water.
Despite the high oxidizing power of the chlorine dioxide, contradictory
results have been reported by several authors. For example, Housein
et al
. (2005)
verified that a hospital using for two years a chlorine dioxide concentration of
0.5 mg∙L
-1
was not able to eradicate the presence of
Legionella
from the water
distribution system. Lin
et al
. (2011) citing multiple authors, verified that by
ensuring a chlorine dioxide residual between 0.25 and 0.5 mg∙L
-1
, after three
years of use, the presence of
Legionella
was not detected in the water distribution
system. But when there was a failure in the dosing systemof chlorine dioxide and
the concentration went below 0.25 mg∙L
-1
,
Legionella
could be detected in the
system after 4 days.
