Media filter is a type of filter that uses a bed of sand, peat, shredded tires, foam, crushed glass, geo-textile fabric, crushed granite or other material to filter water for drinking, swimming pools, aquaculture, irrigation, water management and other applications.
The filter "media" start with fine sand on the top and then graduating coarser sand in a number of layers followed by gravel on the bottom, in gradually larger sizes. The top sand physically removes particles from the water. The job of the subsequent layers is to support the finer layer above and provide efficient drainage.
A Multi Grade Filter consists of vertical or horizontal pressure sand filters that contain multiple layers of coarse and fine sand (pebbles and gravels) in a fixed proportion.
It is a kind of a deep filter bed with adequate pore dimensions for retaining both large and small suspended solids and un-dissolved impurities like dust particles. As compared to conventional sand water filter, this multi-grade filtration system works on higher specific flow rates. It is also a low cost pre-treatment system for ion exchangers (deionizer and softener) and membrane systems such as reverse osmosis etc. With high throughputs, high dirt-holding capacity and capacity to reduce turbidity and TSS (< 5ppm) from water, it protects ion-exchange resins and membranes from physical fouling due to suspended impurities present in the water.
The contaminants in the water are captured in the media bed and filtered water passes into the discharge manifold at the bottom of the tanks. The next and last step is backwashing, a process of effectively removal of captured contaminants from the media bed. After back-washing the filter is rinsed with raw water and after the required quality of water is achieved the filter is put back into service. The working principle of a multi-grade filter is quite straight forward. In a multi-grade filter or pressure sand filter, water is passed through multi layers of filter media consisting graded sand, pebbles and gravels layers.
In some waste water applications, Media filters are also used for cleaning the effluent from septic tanks and primary settlement tanks. The materials commonly used are sand, peat and natural stone.