Slow sand filtration water treatment plants
Practical Action
The filtration speed is selected depending on the quality of the water: It increases in
accordance with the quality at a rate of 1 to 1.5 m/h.
The speed ratio in the secondary and main pipes that distribute the water in
the bottom of the unit should be Vp/Vs < 0.462 for an even distribution. The
diameter of the secondary pipes is thus obtained.
The loss of volume in the bed during the normal pre-filtration operation is
approximately 20cm.
The pre-filtration-filtration system has a limited capacity for assimilating
sudden differences in the quality of raw water.
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