Constructing a 10000 LITER Filtration Tank for Rainwater Harvesting at VERC, AL Islam Garments

Engr. Aditya Dev

Rainwater harvesting has become a vital solution for sustainable water management. One of the key components in an effective rainwater harvesting system is a filtration tank, which ensures that the collected water is safe for drinking. In this guide, LET'S walk through the construction of a filtration tank I hand overed on ( 9 October 2024 at VERC, Al Islam Textile limited , Karna Para, Savar.

Filtration Tank Specifications:

  • Height: 9.17 feet
  • Diameter: 7.63 feet
  • Function: Rainwater enters from the bottom, passes through multiple filtration layers, and then is supplied as potable water.

Let’s break down the layers used in this filtration system and the role of each.

Layer-by-Layer Breakdown:

1. Support Layer: Healthy Blocks (3 ft)

The bottom layer of the tank is made of Healthy blocks, which are lightweight, reducing the need for air conditioning, precast building materials. Healthy blocks are more environmentally friendly compared to clay bricks, as their production requires less energy and produces less CO2. These blocks are used to support a 12 mm percolated PVC sheet, allowing water to pass upward through the filter. This layer provides a sturdy foundation for the filtration system and allows for smooth water movement.

  • Material Used: Healthy blocks, which are lightweight and easy to install.
  • Purpose: To support the PVC sheet and create a base for the filtration layers above.
HEALTHY BLOCK


Used as a Support

2. Percolated Pvc Board

25 mm PVC  board has been used as percolated layer and  support for upper layers. 







3.First Filtration Layer: 3/4- inch Down Stone

Above the Healthy blocks, the second layer consists of 3/4- inch down stone. This stone size is ideal for primary filtration, as it effectively captures larger debris while allowing water to flow freely.

  • Material Used: 3/4- inch down stone.
  • Purpose: To filter out larger particles and provide initial water cleaning.

4.Second Filtration Layer: 25- 45 mm Size Stone

The third layer includes 25-45 mm stones, which help with intermediate filtration. These stones trap medium-sized debris and offer better water clarity before the finer layers are engaged.

  • Material Used: 25-45 mm size stone.
  • Purpose: To filter out medium-sized particles and enhance water clarity.

5. Third Filtration Layer: Activated Carbon

The fourth layer uses activated carbon, a powerful material for water purification. Activated carbon is known for its ability to absorb impurities, chemicals, and odors, making the water much safer for drinking.

  • Material Used: Activated carbon.
  • Purpose: To purify water by absorbing chemicals, odors, and other contaminants.


6. Final Filtration Layer: Silica Sand (FM 2.5-3)

The fifth and final filtration layer is made of silica sand with a fineness modulus (FM) of 2.5-3. Silica sand is excellent for fine filtration, ensuring the removal of any remaining small particles. It also polishes the water, making it crystal clear.

  • Material Used: Silica sand FM 2.5-3.
  • Purpose: To provide fine filtration and ensure crystal-clear, safe drinking water.

Layer Separator: Fishnet

Between each layer, fishnet is used as a separator to ensure that the different materials don’t mix. This keeps the filtration process efficient and allows each layer to function independently.

  • Material Used: Fishnet.
  • Purpose: To separate filtration layers and prevent mixing of materials.

Filtration Process

The unique feature of this filtration tank is that the rainwater enters from the bottom and moves upward due to uplift pressure. As the water passes through each layer, it is progressively filtered:

  1. Bottom Entry: Rainwater enters from the bottom of the tank.
  2. Layer-by-Layer Filtration: The water is pushed upward by pressure, passing through the Healthy blocks, stone layers, activated carbon, and silica sand.
  3. Filtered Water Collection: After being filtered, the water rises to the top of the tank.
  4. Supply as Drinking Water: The clean, filtered water is then ready for use as potable water.

Key Advantages of this Filtration Tank Design:

  • Efficient Use of Lightweight Materials: The use of Healthy blocks and fishnet separators makes the tank lightweight yet durable.
  • Multilayer Filtration: A variety of filtration media ensures that different contaminants are captured at each stage.
  • Upward Filtration: The upward movement of water maximizes filtration efficiency by evenly distributing uplift pressure through the layers.
  • Sustainable Water Supply: This system effectively transforms rainwater into clean drinking water, contributing to sustainable living.

Conclusion

Constructing a filtration tank with a height of 9.17 feet and a diameter of 7.63 inches can provide an efficient, space-saving solution for rainwater filtration. By using a carefully designed combination of Healthy blocks, stones of varying sizes, activated carbon, and silica sand, this system ensures that the collected rainwater is filtered and safe for drinking. With the inclusion of a PVC sheet for structural integrity and fishnets as layer separators, the tank is designed for durability and efficiency, making it a great addition to any rainwater harvesting system.

This method not only supports water conservation but also ensures a reliable source of drinking water, which is crucial for sustainable urban living. 

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