Difference Between Granular Activated Carbon and Anthracite
Anthracite filter media is used in the filtration process. It is used to remove matter that precipitates out of solution. Also, it is chemically treated to make it more filterable. It doesn’t work well at the molecular level because its pores are very small. And, they’re far smaller than most of the molecules that must be eliminated. GAC (granular activated carbon) is built up of PAC (powdered activated carbon) particles collected together.
Driving out smelly chemicals and burning away carbon to increase the size of the pores in carbon particles until they look like a molecular sponge produces PAC. Activated carbon can even be processed. This allows elimination of particular compounds while leaving others behind, depending on the pore size. Adsorption onto the surface of the carbon particle, followed by diffusion into and absorption in the pores, causes molecules to be removed by this pore structure. In this instance, precipitation is not needed. Backwashing, on the other hand, will not remove the debris that has been soaked up into the pores. A re-generation process is the only way to get rid of it.
By adsorption, anthracite filter material removes particulate debris from the flow. However, this is just the tip of the iceberg. Diffusion into the pores is generally not present. In an equal way, the accumulate liquids on the surface are easily removed by agitation during backwashing.
Anthracite or Sand in a Mono-Media Filter?
Slow sand and quick sand filters are the two most common forms of mono-media filters. Slow sand filters are not backwashed and usually operate at a rate of.2 gpm/ft2 (.3 m/hr). As a result, there is likely no benefit to using anthracite in them.
Rapid filters and high-rate filters operate from around 2 to 5 gpm/ft2 (3 to 7.6 m/hr). Depending upon their purpose, there can be advantages to utilizing anthracite. Although the first cost might be higher, overall costs are usually lower due to longer filter runs and lower operating costs.
Crushed, angular materials have greater filtering properties than spherical materials, according to studies. When good quality is desired, this would appear to encourage the use of anthracite. However, anthracite fluidizes at a far slower speed than sand of similar size, which could cause media loss in some shallow bed applications like traveling bridge filters. To collect all of the potential benefits of this design, rough, deep bed filters run at rates as high as 15 gpm/ft2 (23 m/hr) and require rough, deep beds of very uniform (i.e. low uniformity coefficient) anthracite.
Anthracite is sometimes chosen for its essentially inert properties, as well as its attraction for or resistance to particular build-ups. Because anthracite has a lower concentration of silicates than sand, boiler condensate water is usually filtered over beds of anthracite (including support layers). Because anthracite has a strong affinity for iron, especially when coated with potassium permanganate, it is commonly used to remove iron and manganese. The removed hardness-causing deposits are easier to remove from anthracite than from sand in lime softening applications.
