HEALTH AND SANITATION
system for harvested rainwater for small-scale water
supply. SOCO-DIS was compared to SODIS with the aim
of overcoming the limitations of SODIS. They reported
that in the SOCO-DIS system, disinfection improved by
20–30% compared with the SODIS system and that
rainwater was fully disinfected even under average
weather conditions due to the effects of concentrated
sunlight radiation and the synergistic effects of thermal
and optical inactivation.
An advantage of using SODIS on low pH waters include
increased inactivation rates due to the depletion of
Adenosine triphosphate, the main energy storage and
transfer molecule in the cells (Amin and Han, 2009).
Dowbrosky et al. (2015b) investigated the efficiency
of a closed-coupled solar pasteurisation system in
reducing the microbiological load in harvested rainwater
and to determine the change in chemical components
after pasteurisation.
Cations analysed were within drinking water guidelines,
with the exception of iron, aluminium, lead, and nickel,
which were detected at levels above the respective
guidelines in the pasteurised tank water samples.
Indicator bacteria including, heterotrophic bacteria, E. coli
and total coliforms were reduced to below the detection
limit at pasteurisation temperatures of 72°C and
above. However, with the use of molecular techniques
Yersinia spp., legionella spp. and Pseudomonas spp.
were detected in tank water samples pasteurised at
temperatures greater than 72°C.
33
lack of disinfectant residual to protect the water from
recontamination or microbial regrowth after treatment,
(ii) turbidity and certain dissolved constituents can
interfere with or reduce its disinfection efficiency and (iii)
high electricity usage is required to power the UV lamps
(Kowalski et al., 2000).
CHLORINATION
Among common point-of-use interventions, household
chlorination is the most cost-effective when resources
are limited (Clasen et al., 2007). Chlorination requires
that the appropriate dosage be administered. Chlorination
is known to be effective against bacteria, viruses and
protozoa. Several studies reported on chlorination as
an effective intervention strategy to prevent diarrhoeal
diseases (Semenza et al., 1998; Quick et al., 1999 and
Quick et al., 2002).
Free chlorine inactivates more than 99.99% of
enteric pathogens except cryptosporidium and
mycobacterium species (WHO, 2002). One of the
disadvantages of water chlorination process is the
formation of disinfection by-products which may
pose a health risk to consumers (Baker et al., 2002).
However, when compared to the other disinfection
method, it has residual disinfection. Nath et al. (2006)
reported that chlorination is less effective in turbid
water of > 30 NTU and that microbial contaminants
may be protected by particulates in the water.
Water purification is essential.
ULTRAVIOLET LIGHT
Disinfection using UV radiation is defined as a physical
method where water is exposed to a lamp producing
light at a wavelength of nearly 250nm. The wavelength
is l ocated in the middle of the germicidal band and is
responsible for damaging the DNA of microorganisms
(Bolton and Colton, 2008). Ultraviolet light treatment
method often requires filtration as a pre-treatment step
since it is not effective on turbid water (Qualls et al.,
1983; Macomber, 2010). Several studies have reported
on the effectiveness of UV as a disinfection method for
harvested rainwater (Jordan et al., 2008; Ahmed et al.,
2012). Kim et al. (2005) reported that the number of total
coliform present in rainwater were reduced by 50% even
at low exposure to UV.
Advantages of using UV radiation in treating harvested
rainwater include its high efficiency in the removal
of microbes from water and the fact that it does not
introduce chemicals or produce harmful disinfection
by-products (Vilhunen et al., 2009). Despite its positive
attributes in the treatment of harvested rainwater,
UV treatment has disadvantages which include: (i)
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September 2018 Volume 24 I Number 7