Garnet

Called multi-media or mixed mediafiltration, the high density, small grainsize of Clack #30-40 Garnet solves amajor filtration problem. In a singlemedia granular filter such as a sand filter,the material will hydraulically classifyduring backwash according to granulesize, the smallest rising to the top. Whenwater flows downward through the sand,the fine particles at the top of the bed domost of the straining of the sediment. Thesolids form a cake on the surface withfiltration typically taking place in the topfew inches. As the cake forms, thefiltration becomes finer and the head lossincreases exponentially with time.The ideal situation would be to have thelarge grains of media at the top to trap thelarge solids, and a uniformly decreasinggrain size in the direction of fluid flowwith the small grains at the bottom to dothe final polishing. The penetration of thesolids into the entire bed allows forincreased solids storage, longer filterruns, and higher filtration rates.A properly designed multi-mediasystem will maintain its unique grading oflarge grains on top and small grains on the bottom and provide superior performanceeven after many backwashings.This stable condition of large grainsabove finer ones is achieved by the use ofmaterials of different sizes and specificgravities. Garnet with its high specificgravity of 4.0 forms the lower fine grainlayer, its 0.3 mm effective size can filterdown to the 10-20 micron range. FilterSand, (effective size of 0.5 mm) andAnthracite, (effective size of 0.9 mm), orFilter-Ag can form the larger, less denselayers.Multi-media filtration technology isapplicable to both water and waste watertreatment. Custom designed filters withvarying filter bed configurations can bedesigned to meet specific needs. For themajority of municipal and industrialwater supply applications, a filter bedcomposed of 55% low density material,30% medium density material, and 15%high density material is recommended.#8 Garnet at 140 lb/ ft is a good choicefor support beds when using other highdensity filtration media such as high purityCorosex II or the new manganese dioxideoxidation medias such as Pyrolox.