PWTSA Media Filtration and Systems
Why PWTSA Media Filtration should be used?
PWTSA filtration methods are used for the physical, mechanical and biological separation of solids from treated water. Filtration takes place after the clarification stage as an additional treatment step to remove any remaining suspended particles and unsettled floc to ensure safe water.
Activated Alumina Filtration
Activated alumina (AA) is the only filter material specifically designed to remove fluoride and arsenic from water. For arsenic and fluoride treatment, low pH (5.5-6) is superior. Activated Alumina Filtration can be regenerated with sodium hydroxide.
Crushed anthracite coal has long been a favourite medium-weight filter for sediment reduction. It is often used with sand and other media in multi-media filters.
Birm is a manufactured medium consisting of plastic coated with magnesium oxide. Designed for iron and manganese reduction. It causes iron and manganese to change from a dissolved state to a particulate, as a result, it then it filters out the particulate. Birm can be used with or without an oxidizer. Its success without an oxidizer depends a great deal on the amount of dissolved oxygen in the water. (Testing for dissolved oxygen isn’t easy, so trial and error is often the best policy.)
Calcite (Crushed marble) Filtration
Calcite is crushed marble. It is a naturally occurring calcium carbonate. It is used to raise the pH of acidic water. Since it is dissolved only in acidic water, it is self-limiting. When acidic water reaches neutral pH, no more calcite is dissolved.
Garnet is a natural medium used most often in multi-media filters. It is very fine and filters down to the 10-20micron range.
Granular Activated Carbon (GAC) Filtration
Granular carbon is the standard media filtration for most chemical reduction situations, including Chlorine and Organic removal. Its high surface area gives it massive adsorptive capacity. It can be manufactured from animal bones, wood, and petroleum, but most carbon is produced from anthracite coal or coconut shells.
Manganese Greensand Filtration
Manganese greensand is a purple-black filtration medium, made from naturally occurring greensand coated with manganese. It serves as a catalyst to precipitate hydrogen sulphide, iron and manganese. It can be continuously regenerated with chlorine and/or a purple liquid called potassium permanganate, or it can be intermittently regenerated with potassium permanganate alone.
Multi-media (multi-layer) Filtration
Multi-media filters consist of several layers—usually three to five—of different media. The media are loaded by density—the densest in the bottom of the tank, the least dense on top. This produces a filter with an excellent flow rate and relatively easy backwash properties that will filter down to ten microns.
The most common media mix is (top to bottom): anthracite, filter sand, garnet 30 X 40, garnet 8 X 12, and gravel. This is a typical mix, although many others are common.
Filter sand is naturally occurring sand that is high in silica and low in calcium. It is graded and washed. It can be used independently or as part of a multi-media filter. Sand filters are believed to be the oldest man-made filters and they imitate a common natural filtration technique.