Activated Carbon Filtration
Activated carbon filtration is a specialized filtration which removes chlorine and dissolved organic contamination by adsorption.
To use a simple analogy,
If someone give you a cream pie and you eat it, you are absorbing it.
If someone sticks a cream pie in your face you are adsorbing it.
Chlorine and organic contamination "sticks" to the surface of the carbon.
Uses for Activated carbon :
Chlorine removal prior to Thin Film Composite Reverse Osmosis Membranes
Because thin film composite reverse osmosis membranes are especially sensitive to chlorine, and also somewhat to fouling from dissolved organics, active carbon is placed in two places in these units.
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Info from Dakota State University