What specific property of anthracite makes it a preferred filter media component in multi-media filtration systems?

The specific property of anthracite that makes it a preferred filter media component in multi-media filtration systems is its low density. Multi-media filters typically consist of layers of different materials, such as anthracite, sand, and garnet, with the largest and least dense material on top and the smallest and most dense material on the bottom. Anthracite's low density, being less dense than sand, allows it to remain on top of the sand layer after backwashing. This arrangement enables the filter to remove larger particles in the upper anthracite layer and smaller particles in the lower sand layer, resulting in more efficient filtration and longer filter run times. Because the larger particles are removed in the upper layer, the sand layer below is not as quickly clogged, reducing the frequency of backwashing. Furthermore, anthracite has an irregular shape and a relatively high porosity, which provides a larger surface area for particle removal and reduces headloss compared to a single-media sand filter. These properties of anthracite, particularly its low density, contribute to its effectiveness as a key component in multi-media filtration systems.