Granular Activated filter
Granular activated carbon has a relatively larger particle size compared to powdered activated carbon and consequently, presents a smaller external surface. Diffusion of the adsorbate is thus an important factor. These carbons are therefore preferred for all adsorption of gases and vapours as their rate of diffusion are faster. Granulated carbons are used for water treatment, deodourisation and separation of components of flow system. GAC can be either in the granular form or extruded. GAC is designated by sizes such as 820, 2040, or 830 for liquid phase applications and 46, 48 or 410 for vapour phase applications. A 2040 carbon is made of particles that will pass through a U.S. Standard Mesh Size No. 20 sieve (0.84 mm) (generally specified as 85% passing) but be retained on a U.S. Standard Mesh Size No. 40 sieve (0.42 mm) (generally specified as 95% retained). AWWA (1992) B604 uses the 50-mesh sieve (0.297 mm) as the minimum GAC size. The most popular aqueous phase carbons are the 1240 and 830 sizes
because they have a good balance of size, surface area, and head loss characteristics.
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Granular Activated filter", also called activated charcoal or activated coal is a form of carbon that has been processed to make it extremely porous and thus to have a very large surface area available for adsorption or chemical reactions.[1]
The word activated in the name is sometimes replaced with active. Due to its high degree of microporosity, just 1 gram of activated carbon has a surface area in excess of 500 m2 (about one tenth the size of a football field), as determined typically by nitrogen gas adsorption. Sufficient activation for useful applications may come solely from the high surface area, though further chemical treatment often enhances the absorbing properties of the material. Activated carbon is usually derived from charcoal.
History of carbon filters
Carbon filters have been used for several hundred years and are considered one of the oldest means of water purification. Historians have shown evidence that carbon filtration may have been used in ancient Egyptian cultures for both air and water sanitization.[citation needed] 2000 B.C. Sanskrit text refers to filtering water through charcoal (1905 translation of "Sushruta Samhita" by Francis Evelyn Place).[citation needed] The first modern use of a carbon filter to purify potable water occurred in 1862.[citation needed] Carbon filtration was further advanced in the mid 1970's by H. Allen Rice and Alvin E. Rice when they first manufactured a porous carbon block for drinking water use.[citation needed]
Currently, carbon filters are used in individual homes as point-of-use water filters and, occasionally, in municipal water treatment facilities. They are also used as pre-treatment devices for reverse osmosis systems and as specialized filters designed to remove chlorine-resistant cysts, such as giardia and cryptosporidium.
Granular Activated filter
Activated carbon (AC) is a natural material derived from bituminous coal, lignite, wood, coconut shell etc., activated by steam and other means, and each one have different adsorption properties (e.g. bituminous carbon for high chlorine reduction capacity). We also use various blends of carbon to achieve specific water quality and contaminants reduction (e.g. coconut shell carbon for "sweet taste").
Rapid Gravity Sand Filters
The rapid gravity sand filter is a type of filter commonly used in municipal water treatment facilities. Rapid sand filters use relatively coarse sand and other granular media to remove particles and impurities that have been trapped in a floc through the use of flocculation chemicals - typically salts of aluminium or iron. Water and flocs flows through the filter medium under gravity pressure and the flocculated material are trapped in the sand matrix.
Rapid filters are usually built open with the water passing down the filter but by gravity. It has a filter rate of 4 8 m3/m2/hr. The tank is made of concrete with a depth of 3.0 to 3.5m. Coarse sand of size 0.4 to 1.5mm is used as the filter medium.
Screen Filter
A screen filter is a type of filter utilizing a rigid or flexible screen to separate sand and other fine particles out of water for irrigation or other applications. Typical screen materials include stainless steel (Mesh), polypropylene, and nylon.
