Activated carbon is made of organic material porous particulates containing a maze of small pores, which account for the substance’s highly developed surface. One gram of activated carbon has a surface of up to 1 000 m2. Organic molecules dissolved in water may enter the pores and bind to their walls due to van der Waals forces. The adsorption process is controlled by the diameter of the pores in the carbon filter and by the diffusion rate of organic molecules through the pores. The rate of adsorption is a function of molecular weight and the molecular size of the organics.
Removes dissolved organics and chlorine effectively.
Long life due to high binding capacity.
Does not efficiently remove ions and particulates.
Limited capacity due to a high, but limited, number of binding sites.
Can generate carbon fines.
Activated carbon used in water purification is available in two forms:
Natural activated carbon produced by treating vegetal products such as coconut shells at high temperature. The result of this process is a fine powder made of irregularly shaped grains. Natural activated carbon contains a high concentration of ionic contaminants and is therefore used only as a pretreatment step to remove excess chlorine from tap water by a reduction reaction and, to some extent, to reduce organic contamination.
Synthetic activated carbon is made by the controlled pyrolysis of polystyrene spherical beads. This cleaner material is used for the removal of trace organics of low molecular weight.
Activated carbon is usually used in combination with other treatment processes. The placement of carbon in relation to other components is an important consideration in the design of a water purification system.