Garnet or Garnet filter media
- Its high specific weight allows for a unique filtration design.
- In combination with other filter media, higher flow rates, higher loads and better filtration can be obtained.
- Its high hardness reduces frictional material loss, providing many years of reliable service.
- An excellent support bed for other high density media.
- Meets the requirements of AWWA Standard B100-96.
It is a non-metallic mineral that is inert to chemicals and commonly found in the natural environment. Garnet has a high specific gravity. Its chemical properties, hardness and durability make garnet an ideal water filtration media for use in deep bed or multimedia filters.
As for multimedia or mixed media filtration, the small grain size of high density garnet #30-40 makes fine filtration at the end of the deep bed filter. In a single media granular filter such as a sand filter, the material will hydraulically sort during backwashing according to granule size, with the smaller material rising to the top. As water flows down through the sand, the fine particles at the top of the bed do most of the sediment casting. The solids form an agglomerate on the surface, with filtration typically taking place within a few inches of the top.
As the agglomerate forms, the filtration becomes finer and the pressure drop increases exponentially with time. The ideal situation would be to have the large grains in the middle at the top to trap the large solids and a uniformly decreasing grain size in the direction of fluid flow, with the smaller grains remaining at the bottom to do the final polishing.
The penetration of solids throughout the bed allows for greater solids storage, longer filtration runs and higher filtration percentages. A properly designed multi-media system will maintain its unique particle size of large grains on top and small grains on the bottom and provide superior performance even after many backwashes.
This stable condition of large grains over finer grains is achieved by using materials of different sizes and specific weights. Garnet with its high specific gravity of 4.0 forms the lowest layer of fine grains and its effective size of 0.3 mm can filter down to a range of 10-20 microns. Sand 30-40 (effective size of 0.5 mm) and anthracite (effective size of 0.9 mm).
Multi-media filtration technology is applicable to both water treatment and sewage treatment. Custom filters can be designed with variable filter bed configurations to meet specific customer requirements. For most municipal and industrial water supply applications, a filter bed composed of 55% low density media, 30% medium density media and 15% high density media is recommended.
Garnet #8 at 140 lbs/ft is a good choice for support beds when using other high density filter media, such as high purity Corosex II, as well as the new manganese dioxide oxidation media such as Pyrolox or Filox and deep bed or multimedia filters.