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Above
all else, when a water supply becomes contaminated,
correct the problem at once. It is a basic rule of water
sanitation to get to the source of the problem and
eliminate it. If a well, for example, becomes badly
contaminated, it is necessary to trace the contamination
to its source and, if possible, remedy the situation. It
may even be necessary to seek out a new source of
supply.
There
are a number of ways of chemically disinfecting waters.
Of these, chlorination is the most widely used. Each
method has its advantages. In evaluating them the
following points should be considered:
(a)
A disinfectant should be able to destroy all types of
pathogens and in whatever number present in the water.
(b)
A disinfectant should destroy the pathogens within the
time available for disinfections.
(c)
A disinfectant should function properly regardless of
any fluctuations in the composition or condition of the
water.
(d)
A disinfectant should function within the temperature
range of the water.
(e)
A disinfectant should not cause the water to become
toxic or unpalatable,
(f)
A disinfectant should be safe and easy to handle.
(g)
A disinfectant should be such that it is easy to
determine its concentration in the water
(h)
A disinfectant should provide residual protection
against recontamination
At
present, chlorination in one form or another is regarded
as the most effective disinfectant available for all
general purposes.
Chlorine
is normally fed into water with the aid of a chemical
feed pump. The first chlorine fed into the water is
likely to be consumed in the oxidation of any iron,
manganese, or hydrogen sulfide present in any supply,
including bacteria, if present.
When
the "chlorine demand" due to these materials
has been satisfied, what's left over - the chlorine that
has not been consumed - remains as a "chlorine
residual".
The
rate of feed is normally adjusted with a chemical feed
pump to provide a chlorine residual of 0.5 - 1.0ppm
after 20 minutes of contact time. This is enough to kill
coliform bacteria but may or may not kill viruses or
cysts.
A
super chlorination - dechlorination system consists of
two basic units. The chlorinator feeds a stepped up
chlorine dosage into the water to provide a residual of
3.0 to 5.0 ppm. The de-chlorinator (activated carbon
filter) then removes the excess chlorine from the water
before it reaches the household taps.
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