Solar Disinfection of Drinking Water and Oral Rehydration Solutions
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Disinfection Guidelines for Household Application in Developing
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Foreword
Oral Rehydration Therapy: The Revolution for Children
Oral Rehydration Therapy: The Four Simple Technologies
Global Rehydration Therapy: Global Diarrhoeal Diseases Control Programmes
Oral Rehydration Therapy: Causes, Transmission, and Control of Childhood Diarrhoea
Oral Rehydration Solutions: The Practical Issues
Oral Rehydration Solutions: Domestic Formulations
Oral Rehydration Solutions: Disinfection by Boiling
Solar Energy: Fundamental Considerations
Solar Energy: From Sun to Earth
Solar Energy: World Distribution
Solar Energy: A Competitor
Solar Energy: Some Practical Hints
Solar Disinfection Studies: Drinking Water
Solar Disinfection Studies: Oral Rehydration Solutions
Appendix: Source of Information on Diarrhoeal Diseases
Solar Disinfection Studies
Oral Rehydration Solutions
One of the practical problems in preparing oral rehydration solutions
with unclean water in villages not provided with safe drinking water
supplies is the potential risk to consumers. Decontamination by an
appropriate and simple method that can be performed by a housewife in
rural areas in developing countries is therefore indicated.
As previously discussed in the section "Disinfection by
Boiling," neither boiling nor the use of chemical agents are
suitable for the disinfection of oral rehydration solutions because of
the inherent handicaps that preclude their use. One possible way to
overcome this problem is to take advantage of the germicidal
properties of sunlight. We have found that exposure to sunlight in
transparent containers renders these solutions bacteriologically safe,
without deterioration of the ingredients.
In the course of our study on the small-scale disinfection of drinking
water for home use, we experimented with standard ORS solution
prepared with chlorine-free tap water deliberately contaminated with
fresh sewage. The contaminated ORS solution was distributed in
portions of one litre into sterile polyethylene bags, some of which
were placed in direct sunlight, some kept indoors under natural and
artificial light, and some in the dark inside a cabinet. The initial
coliform counts, typical for heavily contaminated water from village
sources, ranged from 7,100 to 16,500 per 100 millilitres.
The results, reported in a letter to The Lancet (2:1257, 1980)
and reproduced in Table 2, indicate that zero coliform and
Streptococcus faecalis counts were obtained in one and two
hours respectively, in samples kept in direct sunlight. That the
action of sunlight is irreversibly lethal was demonstrated by the
inability of the coliforms to regrow when the exposed solutions were
kept in the dark for 24 hours. Coliform reductions of around 80% took
place in two hours at room conditions and in the dark, but heavy
regrowth occurred upon further storage for one day.
The temperature of the test ORS solution did not rise much beyond
30°C after two hours of exposure to sunlight, thus supporting the
hypothesis that heat was not a factor involved in the destruction of
microorganisms. As was shown in the case of solar disinfection of
water, the germicidal action seems to be due mostly to solar radiation
in the near UV region (A) of the spectrum (315 nm to 400 nm). The fact
that the sodium bicarbonate concentration and the pH of 8.33 did not
change indicates that there was no detectable decomposition of the
constituents.
These experiments clearly demonstrate that ORS solutions in
transparent containers will lead to the complete destruction of such
enteric bacteria as coliforms and Streptococcus faecalis, as well as
90% reduction in the total bacterial count, within a period of two
hours.
| Experiment A |
Exposure
(min) |
Dark | Room | Sunlight |
Dark | Room | Sunlight |
| Coliforms/ml |
Total Bacteria/ml |
0
30
60
120
|
71
24
16
14 |
71
24
16
15 |
71
1
0
0 |
1550
1075
1380
2240 |
1550
2070
1735
1625 |
1550
610
165
155 |
| Experiment B |
| Coliforms/ml |
Strep. faecalis/ml |
0
30
60
120
24h |
163
46
37
26
1290 |
165
52
51
31
1620 |
165
6
0
0
0 |
75
42
52
27
-- |
75
49
42
26
-- |
75
24
4
0
-- |
These results are substantially supported by those obtained for plain
water as described previously. This is expected because in both cases
the procedure and experimental conditions applied were similar in
every respect. A salient difference, however, pertains to the
additional constituents present in ORS solutions, as well as a
slightly higher pH. The differences in composition of the two media
have apparently not altered significantly the ultimate lethal action
of sunlight, which in both cases was irreversible. It can be
concluded, moreover, that even the presence of a carbohydrate, salts,
and some nitrogenous substances from the added sewage would not hinder
the solar germicidal action. This is in sharp contrast to the
legitimate expectation that ORS solutions, being a more appropriate
medium for the support of microorganisms, might somehow inhibit the
action of sunlight.
The lack of regrowth of the affected bacteria suggests the
practicality of storage of both drinking water and ORS solutions for
use when needed provided these commodities are protected from
recontamination. When storage is desired, it would be wise to keep
them in the same containers used in the disinfection process to
eliminate the possibility of postcontamination from other vessels, or
through handling. Along the same vein, it appears feasible for health
care centres and dispensaries involved in oral rehydration therapy to
prepare stock, concentrated solutions of ORS, disinfect them by
exposure to sunlight, and appropriately dilute them with
decontaminated water just before distribution to villagers. Such a
system will facilitate matters, reduce efforts and costs, and take the
burden off the shoulders of housewives. Wherever such an arrangement
is not possible, then housewives need to be instructed on the proper
method for the preparation and decontamination of home- made oral
rehydration solutions.
Our experimental work was designed merely to demonstrate the
feasibility of decontamination of an ORS solution freshly prepared
according to the WHO-UNICEF standard formula, using available plastic
bags with screw caps. No attempt was made to expand and diversify the
work as all the essential experimental information had already been
derived from the much more extensive study on decontamination of
water. Accordingly, it would be logical to assume that the specific
conditions pertaining to containers, fluids, and exposure would be
applicable in the two cases. It would be possible, for instance, to
use any other type of container which is available and meets the
requirements.
In highly endemic rural areas, it would be useful for families to
practice routinely solar disinfection of drinking water, in which case
the decontaminated water would be available for the preparation at
home of ORS solutions when needed. If this procedure is adopted, at
least in emergencies, then the time required for disinfection of the
ORS solutions after their preparation would be saved in favour of an
early start of oral rehydration therapy. In such an event, the only
disadvantage is the potential risk of contamination of the ORS
solutions from the ingredients or containers.
Indeed, this technology provides a good deal of flexibility which
allows for the possibility of adaptation to suit local conditions and
needs.
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