Activated carbon (AC) filters contain either granular activated carbon (GAC) or powdered block carbon (PAC). The amount of AC in a filter is one of the most important characteristics affecting the amount and rate of contaminate removal. More carbon in a cartridge means more capacity for chemical removal, resulting in longer cartridge lifetime.
Because AC systems are limited in the types of compounds they can effectively remove,it is essential that the homeowner determine which water contaminants are present before purchasing any type of water purification system.
AC is most effective at removing organic compounds such as volatile organic compounds, pesticides and benzene. It can also remove some metals, chlorine and radon. As with any treatment system, it cannot remove all possible drinking water contaminants.
AC can be extremely effective for the removal of emerging contaminants. In the study described here, both PAC and GAC were capable of removing nearly all compounds evaluated by greater than 90%.
Rust, scale, sand or other sediments can clog any AC filter. A solution to this problem is to place sediment
filter between the cartridge and incoming water. When sediment filters become clogged, they will cause a pressure drop and need to be replaced.
An AC filter must be deep enough so that the pollutants will adsorb to the AC in the time it takes the water to move through the filter. The appropriate filter depth depends on the flow rate of water through the filter. The slower the flow rate, the better the removal.
AC filters can be excellent places for bacteria to grow. Conditions for bacterial growth are best when the filter is saturated with organic contaminants, which supply the food source for the bacteria, and when the filter has not been used for a long period of time. It is still unclear whether the bacteria growing on the carbon poses a health threat. Some manufacturers have placed silver in the AC in order to prevent the growth of bacteria.
Some cartridges are sold with predictions about their longevity. These are generally only crude estimates since they do not take into consideration factors that are characteristic to a specific water source, such as pollutant concentration.
