Multiple
Media
Filters
These are down flow filters. The filter bed is composed of several different materials which are placed coarse-to-fine in the direction of flow. A simple type of multiplemedia filter, the dual-media filter, make use of two different materials.
Commonly a sand layer of about 0.3 to 0.5m thickness with an effective size of 0.4 to 0.7mm is used as a bottom layer, above which is a layer of anthracite or crushed coconut husks of 0.5 to 0.7m thickness with an effective size of 1.0 to 1.6mm. Multiple-layer filters are effective as final treatment filters
