Activated carbon filters are very similar to multi media filters and other pressure filters in construction and operation. The purpose of an activated carbon filter is to remove free chlorine, an oxidizing agent that will damage most resins and/or membranes in a water treatment system. A chemical injection system using sodium bisulfite (a reducing agent) can be used in place of an activated carbon filter to remove chlorine.
Granular activated carbon is a particularly good adsorbent medium due to its high surface area to volume ratio. One gram of a typical commercial activated carbon will have a surface area equivalent to 850-1.000 square meters. This high surface area permits the accumulation of a large number of contaminant molecules.
Some drinking water may be disinfected with chlorine or chloramines. During disinfection the reaction of chlorine with organic matter during drinking water chlorination can produce compounds such as trihalomethanes (THMs) as byproducts. These disinfection byproducts may increase the risk of certain cancers. AC filtration can be effective in removing chlorine, chloramines, and some disinfection byproducts. Activated carbon periodically becomes contaminated with large amounts of bacteria. In industries where bacteria generation in the filtration system is a problem, the activated carbon can be sterilized with steam.