Activated Carbon Adsorption
The process of “adsorption” is highly different from the definition of
“absorption.” Where “absorption” occurs when a substance penetrates a
solid, “adsorption” refers to a substance adhering to the surface of a
solid. Activated carbon is utilized in the adsorption process, and is
most often involved in the purification of drinking water. It can be
made from several materials, of which, the most popular are coal, wood,
and coconut shells due to the large size of their surfaces and the
extent to which they are porous. The bigger the pores, the longer the
activated carbon functions at a time.
Once the material to be used is chosen, it is then dehydrated and carbonized by an oxidation process that involves slowly heating the material at extremely high temperatures. It is then “activated” by exposing it to other oxidizing substances, such as, chemicals and gases. The activated carbon is then categorized by such characteristics as density and hardness.
When the activated carbon is prepared, it undergoes a series of tests to determine its “breakpoint.” This is the point in time when the activated carbon begins to lose its power as an adsorbent. This characteristic occurs in all activated carbon and the determination of when it occurs aids the user in knowing when it needs to be replaced. This is extremely important information; especially when used to remove contaminants from drinking water.
As the activated carbon is placed in the water (usually in powder or granule form), the adsorption process works in three stages. First, the contaminating substances adhere to the surface of the carbon. Next, the substances move into the large pores. Finally, they are adsorbed onto the inner surface of the carbon. When the carbon hits its breakpoint, it is referred to as “spent,” and is then removed and sent off to be re-activated. Since powdered activated carbon (PAC) is too small for re-activation, granular activated carbon (GAC) is typically the only form of activated carbon to be sent back for the treatment. The “spent” carbon is then mixed with newly activated carbon and sent back to the facility for reuse.
Once the material to be used is chosen, it is then dehydrated and carbonized by an oxidation process that involves slowly heating the material at extremely high temperatures. It is then “activated” by exposing it to other oxidizing substances, such as, chemicals and gases. The activated carbon is then categorized by such characteristics as density and hardness.
When the activated carbon is prepared, it undergoes a series of tests to determine its “breakpoint.” This is the point in time when the activated carbon begins to lose its power as an adsorbent. This characteristic occurs in all activated carbon and the determination of when it occurs aids the user in knowing when it needs to be replaced. This is extremely important information; especially when used to remove contaminants from drinking water.
As the activated carbon is placed in the water (usually in powder or granule form), the adsorption process works in three stages. First, the contaminating substances adhere to the surface of the carbon. Next, the substances move into the large pores. Finally, they are adsorbed onto the inner surface of the carbon. When the carbon hits its breakpoint, it is referred to as “spent,” and is then removed and sent off to be re-activated. Since powdered activated carbon (PAC) is too small for re-activation, granular activated carbon (GAC) is typically the only form of activated carbon to be sent back for the treatment. The “spent” carbon is then mixed with newly activated carbon and sent back to the facility for reuse.