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Activated Carbon Filters

Time:2017/4/28 13:48:01

 

Activated carbon (AC) is particles of carbon that have been treated to increase their surface area and increase their ability to adsorb a wide range of contaminants - activated carbon is particularly good at adsorbing organic compounds.

There two basic kinds of carbon filters Granular Activated Carbon (GAC) and Solid Block Activated Carbon (SBAC)

Contaminant reduction in AC filters takes place by two processes, physical removal of contaminant particles, blocking any that are too large to pass through the pores (obviously, filters with smaller pores are more effective), and a process called adsorption by which a variety of dissolved contaminants are attracted to and held (adsorbed) on the surface of the carbon particles. The characteristics of the carbon material (particle and pore size, surface area, surface chemistry, density, and hardness) influence the efficiency of adsorption.

AC is a highly porous material; therefore, it has an extremely high surface area for contaminant adsorption. One reference mentions" The equivalent surface area of 1 pound of AC ranges from 60 to 150 acres (over 3 football fields)".  Another article states, "Under a scanning electron microscope the activated carbon looks like a porous bath sponge. This high concentration of pores within a relatively small volume produces a material with a phenomenal surface area: one tea spoon of activated carbon would exhibit a surface area equivalent to that of a football field."

AC is made of tiny clusters of carbon atoms stacked upon one another. The carbon source is a variety of materials, such as peanut shells, coconut husks, or coal. The raw carbon source is slowly heated in the absence of air to produce a high carbon material. The carbon is activated by passing oxidizing gases through the material at extremely high temperatures. The activation process produces the pores that result in such high adsorptive properties.

The adsorption process depends on the following 5 factors:

· physical properties of the AC, such as pore size distribution and surface area

· the chemical nature of the carbon source
(the amount of oxygen and hydrogen associated with it)

· chemical composition and concentration of the contaminant

· the temperature and pH of the water

· the flow rate or time exposure of water to AC

Activated carbon filter cartridges will, become less effective over time, as the pores clog with particles (slowing the water flow) and the adsorptive surfaces in the pores become filled with contaminants (typically not affecting flow rate). 
There is often no noticeable indication that a carbon filter is no longer removing contaminants, so it is important to replace the cartridge according to the manufacturer’s instructions.

It is also important to note, particularly when using counter-top and faucet-mount carbon filtration systems, that hot water should NEVER be run through a carbon filter, as this will result in the release of trapped contaminants into the water flow, potentially making the water coming out of the filter more contaminated than the water going in.