Granular activated carbon (GAC) has been used for centuries as an adsorbent and it is currently the only proven and realistic way to remove some, but not all, chemical contaminants from recreational drinking water.
GAC has a large number of highly reactive free valences that remove impurities by bonding with them. As a result, GAC filters or elements can remove halogens (iodine and chlorine), some fertilizers, pesticides and and other organic compounds as well as lead at concentrations normally found in groundwater.
However, GAC can only adsorb some chemicals and impurities and only until all binding sites are occupied. When the binding sites are full, impurities will pass through the filter unadsorbed or will bind to the GAC and release chemicals held by weaker bonds. Unfortunately, the only indication that a GAC element is fully saturated is a foul taste or odour in the treated water. GAC elements do not make seawater drinkable.
Some microfilters have primary or secondary elements made entirely of GAC. It is important to note that while GAC elements may remove some bacteria and viruses through adsorption, GAC is not antimicrobial and bacteria can colonize the GAC element and slough off into water coming out of the device.
GAC filters should not be solely relied upon for water treatment. However, when GAC elements are incorporated into a microfilter or purifier with primary filter elements made of other materials, they are unequalled for removing organic and inorganic chemicals, halogens and impurities that cause bad smells or tastes.
Contaminants Removed by GAC Elements in Microfilters
||Level of Removal|
|Contaminant||Level of Removal|
|Bacterial toxins||Fair to good removal|
|Benzene||Fair to good removal|
|Chlorine disinfection by-product||Good removal|
|Ethylbenzene||Fair to good remova|
|Iodine disinfection by-product||Good removal|
|Pesticides*||Fair to good remova|
|Toluene||Fair to good removal|
|Taste and odor compounds||Good removal|
*Includes: DDT, Aldrin, Dieldrin, Heptachlor, Heptachlorepoxide, 2,4-D, 2,4,5-T, Chlordane, Lindane, Methoxychlor, Benzene hexachloride, Triazine, Hexachlorobenzene, Endrin, Toxaphene and Aldicarb.