Slow sand filtration water treatment plants
Practical Action
The chlorine considered in this table is powdered HTH at 65%. If chlorine of another
percentage is used, then the necessary weight can be calculated with the following operation
(only the second column of the table will vary).
WEIGHT = WEIGHT (table) x _____65_____
% CHLORINE
• Calibration of the small-scale chlorinator: regulating the drip
Normal type of water is considered for the previous
data. However, some physical and chemical aspects
of the water could alter the chlorination. Consequently,
the drip must always be regulated when putting the
chlorinator into operation.
Measuring the residual chlorine in the tanks furthest
away from the network will demonstrate whether the
drip obtained in the table is correct.
If the necessary amount of residual chlorine is not
found (0.2 ppm – 1.0 ppm), the tap must be regulated
to increase the drip. Never increase the dose to more
than three times the amount calculated in the table.
• Operation of the small-scale chlorinator
The mother solution must be removed every two days –
because the chlorine tends to settle at the bottom of the chlorinator – and the number of
drips must be controlled to make sure they are adequate, otherwise the tap will need to be
regulated.
The drip control system, comprised of a flexible polyethylene pipe with a hole and a floater,
provides a constant drip. This system must be checked to make sure it is in good condition.
If for any reason the water stops flowing into the reservoir, the tap dripping the chlorine
solution must be closed immediately.
The chlorine loses its disinfecting power as the days go by, therefore the mother solution
must not remain in the chlorinator for more than seven days.
• Cleaning the chlorinator
Every time a new mother solution is prepared, the chlorinator must be cleaned to remove
previous particles and the remaining solution. To this end, remove the stopper of the
cleaning pipe and rinse with water.
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