Filtration: sand

Sand filtration is one of the oldest methods of water treatment. A sand filter consists of a bed of sand of appropriate quality, through which the water runs relatively slowly.

Sand filters purify water in three different ways:

1. Filtration, during which particles are separated from the water being treated.
2. Flocculation, during which contaminants adhere to the surface of the sand, increasing its size.
3. Assimilation by micro-organisms that consume the water pollutants.