224
2005, AWT, 2003, Stout and Yu, 2003, Franzin
et al
., 2002, Sabria and Yu, 2002,
WHO, 2002andLin,
et al
., 1998).However, Lin
et al
. highlight that suchprocesses
are shown effective only for short terms, given the limitation associated to each of
these disinfection processes.
For example, Lin
et al
. (1998) declare that the employment of ultraviolet
radiation and even the process of heating water at elevated temperatures must
be applied only as local solutions, due the fact that they are not effective when
the distribution system is highly contaminated by
Legionella pneumophila
. In
these cases, when the disinfection of the entire distribution system is required,
the recommendation is to use hyperchlorination or the ionization of copper
and silver, continuously. However, both methods can have inconveniences,
such as corrosion in the case of hyperchlorination, or the presence of elevated
concentrations of heavy metals (copper and silver ionization).
Among the chemical disinfection processes of the water, chlorination is the
most widely used (Kim
et al
., 2002). Chlorine can be added to the water by using
chlorine gas or sodium or calcium hypochlorite. In water, the chlorine or the
hypochlorites generate hypochlorous acid (HOCl), a molecule that effectively
presents bactericidal action, but in alkaline water, the hypochlorous acid is
dissociated and generates hypochlorite ion (OCl
-
). Both, HOCl and OCl
-
are
called free chlorine, but HOCl presents higher biocidal activity than OCl
-
(Kim
et al
., 2002). Also, according to these authors, and as demonstrated below, there
are three aspects thatmust be consideredwith relation to chlorination: long-term
effectiveness; corrosivity; and formation of by-products as well as the toxicity
itself of chlorine.
Themain factors affecting the efficiency of chlorine-basedbiocides (chlorine
gas, sodium or calcium hypochlorite and chloramines) in the destruction of
Legionella
, as demonstrated by Kuchta
et al
. (1983) are: concentration of free
