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Rapid Sand Filtration
Rapid sand filtration is a purely physical drinking water purification method. Rapid sand filters provide rapid and efficient removal of suspended particles. A gravity sand filter was designed for Kyamagemule on the site conditions. The initial design foresaw building a filter from bricks and mortar with an interior width and length of 60 cm and 90 cm, respectively and height of 1.5 m
These dimensions were chosen for maintenance purposes, since the maintenance would be simple and mechanical. The maintainer would remove the top layer of sand for cleaning. The opening size makes it possible for a person to fit inside the filter and remove the clogged sand easily. 

Representation of designed filter

For the actual construction on site, any large sized container is suitable.  When using brick and mortar, thought should be given to providing an access hole for cleaning purposes.  For the work in Kyamagemule, a 1000 L poly water storage tank was used.  The lowest layer should be gravel or rock to protect the outlet pipe from clogging and preventing loss of sand.  A minimum of 60 cm of 0.3 to 0.8 mm sand is needed for the turbidity removal process.  The remaining 20 cm between layers was provided by coarse gravel.  The filter at Kyamagemule reduced the turbidity by 98%.

Rapid Sand Filter


Cross sectional view of RSF

Backwash was provided through the use of a small elevated tank connected to the bottom of the filter, providing the necessary pressure to backwash the fine sand particles, click here for more information on this process.
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