How does the bio-sand filter work? The bio-sand filter works the same way as traditional slow sand filters, which have been used for centuries. The difference is that the bio-sand filter is smaller, and water does not need to flow through it constantly. The filter can be built anywhere worldwide because it uses locally available materials. The filter is simply a concrete or plastic container with layers of sand and gravel inside. The sand and gravel remove sediment, pathogens, and other impurities from the water.
Contaminated water is poured into the top of the filter whenever needed. A diffuser plate placed just above the sand bed absorbs the falling water's shock so it does not disturb the sand. The water slowly passes through the biolayer, sand and gravel. Filtered water flows out of the tube and is collected by the user in a storage container. The storage container is placed on a block or stand, so the opening is under the spout.
How does it remove contaminants? As with all slow sand filters, a physical layer (often called a biolayer) of sediment and microorganisms develops at the sand surface. Pathogens and suspended material are removed from contaminated water through biological and physical processes in the biolayer and sand bed. These processes include:
Mechanical trapping Sediment and pathogens are physically trapped in the spaces created between sand grains.
Predation Other microorganisms consume pathogens in the standing water and biolayer.
Adsorption/Attraction Pathogens become attached to sediment and sand grains.