Water filters through sand primarily by flowing downwards through a layer of sand and gravel. This process physically traps particles within the sand bed and also involves particles adhering to the sand grains.
Sand filtration is a common method used to clean water by removing unwanted materials. As water passes through the sand layer, it encounters a dense network of small spaces between the sand grains.
The Sand Filtration Process
The filtering action happens as water moves vertically through a bed of sand and/or gravel. This bed acts like a natural sieve, but the process is more complex than just straining.
Here are the key ways particles are removed:
- Physical Encapsulation: Larger particles in the water are simply trapped or physically blocked by the spaces between the sand grains. As more particles accumulate, they can form a 'cake' on the surface or within the sand bed, which can further enhance filtration by making the pathways smaller.
- Absorption: Smaller particles that might pass through the physical gaps can stick to the surface of the sand grains. This is known as absorption (or more accurately, adsorption), where particles adhere to the filter material due to various forces. The reference specifically states that particles are removed by way of absorption or physical encapsulation.
What Sand Filters Remove
Sand filtration is effective for cleaning water containing suspended solids – materials that are floating or suspended in the water.
| Particle Type | How Removed |
|---|---|
| Suspended Matter | Physical Encapsulation & Absorption |
| Floating Particles | Trapped at the surface or within the bed |
| Sinkable Particles | Trapped within the bed |
By combining these mechanisms, sand beds efficiently remove solids, improving the clarity of the water. The depth of the sand bed, the size of the sand grains, and the speed at which water flows are all factors that influence how effectively filtration occurs.
Essentially, the sand bed creates a tortuous path that forces particles to collide with and stick to the sand grains or get trapped in the narrow passages as the water makes its way through.
