Abstract:
Chlorine is used worldwide to assure the
microbiological safety of drinking water in
transport and distribution systems. There, its
concentration is usually kept within the
range of 0.2 mg L-1 to 1 mg L-1, in order to
protect public health (WHO, 2011).
However, chlorine concentration decays as
the water travels through the transport and
distribution systems. Such decay is mainly
due to chemical reactions of chlorine with
the water natural organic matter (NOM) and,
generally to a minor extent, with the pipes´
wall material. The former, the so-called bulk
decay (kb), is a key parameter in the
modelling of chlorine behaviour in drinking
water systems.
In addition to water NOM contents and
reactivity (Hua et al., 1999), kb is mainly
affected by the water temperature (Powell et
al., 2000). Powell et al. (2000) found that
10ºC raises in water temperature may lead to
2.5 fold increases in kb values. However,
increments as small as 5ºC may double the
rates of bulk chlorine decay (Kastl et al.,
1999).
Such phenomenon is particularly important
in Continental countries where the water
temperature spans from close to freezing to
very high. Ongoing climate changes,
including global warming and higher
frequency and severity of extremes, such as heat and cold waves, are likely to aggravate
such conditions and to extend them to other
areas including the Mediterranean regions
like Algarve (Portugal). There the
distribution systems water temperature may
range from 13ºC in winter to ca. 21ºC in
summer (Pina et al., 2010).
In this study the effect of temperature on kb
was investigated for raw and clarified waters
of surface origin. The latter had undergone
ozonation and
coagulation/flocculation/sedimentation. The
waters were from Alcantarilha and Tavira
drinking water treatment plants (DWTP),
located in Algarve.
