Which filter component is critical for supporting percolation in a sand filter?

• A. Gravel layer
• B. Sludge layer
• C. Activated carbon
• D. Coagulation agent

Answer: (A)

The gravel layer is essential for supporting percolation in a sand filter because it serves multiple key functions. Primarily, it provides a stable base for the sand, ensuring that the filter maintains its structure and does not collapse under the weight of the sand above it. Additionally, the gravel layer allows for efficient water flow through the filter. It facilitates the smooth transfer of water from the sand layer down into the underlying components of the filtration system, helping to maintain a consistent and effective filtration process.

Furthermore, the larger particle size of gravel compared to sand aids in preventing the clogging of the sand layer, which can inhibit water movement and reduce filtration effectiveness. This layer also plays a role in distributing the incoming water evenly across the sand filter surface, promoting uniform percolation and preventing uneven flow paths that could lead to inadequate treatment of the water.

In contrast, the other options do not serve the same primary structural supportive role that is crucial for effective percolation in a sand filter.