Filter Media Sand By Shri Sai Enterprises

MIXED MEDIA FILTER BEDS

The terms "multilayer," "in-depth," and "mixed media" apply to a type of filter bed which is graded by size and density. Coarse, less dense particles are at the top of the filter bed, and fine, more dense particles are at the bottom. Downflow filtration allows deep, uniform penetration by particulate matter and permits high filtration rates and long service runs. Because small particles at the bottom are also more dense (less space between particles), they remain at the bottom. Even after high-rate backwashing, the layers remain in their proper location in the mixed media filter bed.

Table 6-1 lists four media that are used in multilayer filtration. Several other mixed media combinations have also been tested and used effectively. The use of too many different media layers can cause severe backwashing difficulties. For example, if all four materials listed in Table 6-1 were used in the same filter, a wash rate high enough to expand the magnetite layer might wash the anthracite from the filter. High wash water requirements would also result.