Slow sand filtration
Slow sand filters are suitable for community or municipal level water treatment, and provide a very high quality output of water with relatively simple operation, and are used in wealthy nations as well as poor communities.
Slow sand filters work by allowing gravity to draw water through a filter media that composed of sand and gravel. This type of filtration is differs from gravity filtration in that gravity filtration systems are generally designed to be back washed, when the filter becomes clogged. In slow sand filtration the top layer of sand acts to trap devolved solids and so when the filter becomes clogged instead of backwashing the whole system only the top layer of sand is removed and discarded. This saves the operators of the water treatment system the expense of having to design a backwash system.
Its downsides are the large area used and occasional downtime after maintenance; however both of these can be reduced by changing the system of maintenance, and ploughing rather than scraping the surface.
The Biosand filter takes the water cleaning functionality of a Slow sand filter and concentrates it into a smaller point-of-use/household appliance.
- More Information can be found about Slow Sand Filtration by contacting the Office of Water Programs at CSU Sacramento
- Water Treatment Plant Operation, A field Study Training Program. California State University Sacramento Office of Water Programs 2008