What is the minimum thickness of filter sand in a filter bed installation?

What is the minimum thickness of filter sand in a filter bed installation?

• A. 60 cm
• B. 75 cm
• C. 90 cm
• D. 100 cm

Answer: (B)

In a filter bed, the sand layer acts as the main filtration medium, providing surface area for physical trapping of solids and room for biological treatment as wastewater percolates through. The thickness of this layer is chosen to balance effective filtration with practical bed size. A minimum of 75 cm gives enough depth for solids to be captured, for flow to spread evenly across the bed, and for microbial activity to reduce contaminants without rapid clogging. If the sand layer were thinner, clogging and under-treatment would occur sooner; if it were much thicker, the extra depth would increase cost and construction without a proportional gain in performance. Therefore, the minimum thickness is 75 cm.

In a filter bed, the sand layer acts as the main filtration medium, providing surface area for physical trapping of solids and room for biological treatment as wastewater percolates through. The thickness of this layer is chosen to balance effective filtration with practical bed size. A minimum of 75 cm gives enough depth for solids to be captured, for flow to spread evenly across the bed, and for microbial activity to reduce contaminants without rapid clogging. If the sand layer were thinner, clogging and under-treatment would occur sooner; if it were much thicker, the extra depth would increase cost and construction without a proportional gain in performance. Therefore, the minimum thickness is 75 cm.