How Sand Filters Work
Sand filters are used to remove suspended solids from water and wastewater. Because they have only one layer of filter media, sand filters remove only relatively large solids (normally in the range of 40-100 microns). The effective size of each granule of sand typically varies from 0.35mm to 1.2mm. Larger granules yield coarser filtration. Finer granules yield finer filtration. More about the operation of media sand water filters.
Removing suspended solids smaller than 40 microns requires filters with either two or three layers of filter media. These are referred to as dual-media filters or multi-media filters. When sized properly and with the correct configuration of filter media, these sand filters can remove suspended solids as small as 5 micron.
The size of each sand filter, the number of filters required, and the size of the sand granules themselves depend upon:
- how small a solid needs to be removed,
- how dirty the water is,
- and the source of backwash water needed to clean the filters.
Size of Solids to be Removed by Sand Filters
The smaller the solid to be removed, the slower the water must pass through the sand and the finer the granule of sand must be. Very often the end user doesn’t know how small a solid must be removed. In those situations, how the filtered water will be used will determine how small a solid should be removed.
Concentration of Suspended Solids
The higher the concentration of suspended solids, the larger the diameter of the filter needs to be.
Source of Backwash Water & Sand Filters
Backwash water is used to clean the sand filters and flush out the suspended solids that have been trapped in the media bed. Water for backwashing can come either from the sand filters themselves or from an external source of clean water (such as a domestic water line or a storage tank).
If backwash water comes from the filter system, during the backwash cycle, a portion of filtered water is used to clean the dirty sand filter. During these periods (which typically last for several minutes per filter), the amount of filtered effluent flowing downstream of the filter is reduced.
In cases where this temporary reduction in flow is acceptable, there will be two or more sand filters in the system and each one will have a filter area that requires less water than is flowing into the system.
If no decrease in the flow of filtered water can be accepted, then water for backwashing is supplied from an external source.
Call us at 1-800-360-8380 to learn more about our sand filters. An Everfilt applications engineer will discuss your application with you and will recommend the specific sand filter system that meets your requirements.
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