A mixed media sand filter typically contains which materials?

A mixed media sand filter is specifically designed to enhance filtration efficiency by utilizing various materials that possess different physical characteristics, which allows for improved removal of a broader range of particles from water.

The inclusion of gravel, sand, and anthracite is significant for this type of filter. Gravel serves as a support layer and helps in preventing the finer media from clogging. Sand is crucial for trapping smaller particles and impurities in the water. Anthracite, a type of coal that is denser and larger than sand, is often placed as the top layer in mixed media filters. Its larger size allows for better water flow while capturing finer particles that may pass through the sand layer. This combination maximizes filtration effectiveness and ensures clearer water output.

While options mentioning gravel and sand only or sand only do not account for the enhanced filtration that anthracite provides, and the choice of carbon with gravel does not align with the common composition used in mixed media filters, the combination of all three materials—gravel, sand, and anthracite—supports the principle of multi-layered filtration that is key to the function of a mixed media sand filter.