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According to theWorldHealthOrganization (WHO), the concentrations
of
Legionella
can be reduced in the different phases of the production of
drinking water, that is, during the phases of coagulation, flocculation and
sedimentation (WHO, 2002). However, the production of drinking water can
also cause an increase in the population of this microorganism at the interior
of the activated charcoal filters, in case there was previous colonization by
other microorganisms, or because of the presence of protozoan. However,
this problem can be controlled by reducing the temperature in this phase to
values below to 20 °C.
Besides the cautions with the production and the control of the
temperature during the production, storage and distribution of the water, the
use of disinfection processes that employ chemical biocides, the heating or the
use of ultraviolet radiation can also be employed to the control of
Legionella
.
However, the water disinfection processes often present efficacy just for short
periods of time, after which, it is possible to isolate again this microorganism.
Consequently, controlling
Legionella
in a storage or distribution system of
water requires the constant use of proven effective disinfection processes.
The WHO demonstrates that the thermal inactivation of Legionellae
starts at 50 °C (WHO, 2002). According to several authors, the decimal
reduction times (D values) – necessary time to cause a reduction of 90% in
the population of a determined microorganism in a constant temperature –
vary from 2500 minutes at 45 °C to 0.45 minutes at 66 °C (Schulze-Röbbecke
and Buchholtz, 1992, Sanden
et al
., 1989, Stout
et al
., 1986 and Dennis
et al
.,
1984). From these data we can define another important parameter – the
z value – that is, the variation of temperature that is required to have the
decimal reduction time reduced in 90%. Figure 1 shows the relation between
the decimal reduction time and the temperature for
Legionella pneumophila
.
