Activated Carbon Filtration( Selective Media or Adsorption)

Granular activated carbon (GAC) is commonly used for removing organic constituents and residual disinfectants in water supplies. This not only improves taste and minimizes health hazards; it protects other water treatment units such as reverse osmosis membranes and ion exchange resins from possible damage due to oxidation or organic fouling. Activated carbon is a favored water treatment technique because of its multi functional nature and the fact that it adds nothing detrimental to the treated water. 

Most activated carbons are made from raw materials such as nutshells, wood, coal and petroleum. 

Typical surface area for activated carbon is approximately 1,000 square meters per gram (m2/gm). However, different raw materials produce different types of activated carbon varying in hardness, density, pore and particle sizes, surface areas, extractable, ash and pH.  These differences in properties make certain carbons preferable over others in different applications.

There are many types of high-tech activated carbon filters available for industrial filtration systems. Activated carbon can exhibit varying performance characteristics depending upon the strata from which it is derived (e.g., bituminous or anthracite coal, bone char, coconut shell) and the way it is manufactured. The methods used to create the various AC materials are highly proprietary and lead to distinct differences across the range of media available to the industry. Water Professionals can specify high-tech filtration methods for the identified contaminates and the level of purity required. This is why it is critical to match up the correct activated carbon bed with the particular need. This will achieve the most efficient filtering and the longest use interval for the equipment.

There are two main activation methods:

  • Steam Activation – Steam activation is carried out using steam at temperatures of between 800°C and 1000°C. At these temperatures an instant Water-Gas reaction occurs, gasifying the carbonized material. Air is then introduced to burn out the gasses, without burning the carbon. This process produces a graded, screened and de-dusted form of activated carbon. Carbon activated by steam generally has a fine pore structure, ideal for adsorbing both liquid phase and vapor phase compounds.
  • Chemical Activation – With chemical activation the carbon is first filled with a powerful dehydrating agent, typically a paste form of phosphoric acid (P2O5) or zinc chloride (ZnCl2). The paste is heated to temperatures between 500°C and 800°C to activate the carbon.