A sand filter consists of a tank filled with specially graded sand. Water flows through the sand bed, and the particles in the water get trapped in the spaces between the sand grains. Clean water then exits from the bottom of the tank.

Key Components

• Tank: Usually made of metal, fiberglass, or concrete.

• Sand media: Filter sand, typically silica, is the primary filtration medium.

• Underdrain system: Collects filtered water and supports the sand bed.

• Control valves: Used to direct flow during filtration and backwashing.

How It Works

• Filtration mode:

  • Water enters from the top.

  • Suspended particles are trapped in the sand bed.

  • Clean water exits from the bottom.

• Backwash mode (cleaning):

  • Flow is reversed.

  • Water enters from the bottom, lifting and flushing the sand.

  • Dirty water is discharged to waste.

Types of Sand Filters

• Slow sand filters:

  • Use biological processes for purification.

  • Low maintenance, but slow flow rates.

  • Used in drinking water treatment.

• Rapid sand filters:

  • High flow rate, mechanical filtration.

  • Requires regular backwashing.

  • Common in water treatment plants and pools.

Advantages

• Simple design and operation

• Effective for removing turbidity and suspended solids

• Low operational cost

Disadvantages

• Not effective for removing dissolved contaminants or bacteria (unless slow sand filter)

• Needs periodic backwashing

• Requires a relatively large space for installation