Three kinds of filter media that may be used for rapid sand filters are which?

• A. Coal, Sand and Gamet
• B. Gravel, Sand and Garnet
• C. Coal, Garnet and Sand
• D. Gamet, Sand and Coal

Answer: (A)

In rapid sand filtration, a layered multi-media bed is used to remove particles of different sizes more effectively. The three media commonly chosen are coal (anthracite), silica sand, and garnet. Each layer serves a purpose: coal provides a rough surface that traps larger particles and helps keep the bed permeable; silica sand forms the main filtration layer with medium pore spaces; garnet is dense and fine, capturing smaller particles near the outlet. Gravel is typically used as a support layer beneath the filtration media rather than as part of the filtration trio. That’s why coal, sand, and garnet is the standard combination.