Granular Activated Carbon

Granular activated carbon (GAC)  has a relatively larger particle size compared to powdered activated carbon and consequently, presents a smaller external surface. Diffusion of the adsorbate is thus an important factor. These carbons are suitable for absorption of gases and vapors, because they diffuse rapidly. Granulated carbons are used for water treatment, deodorization and separation of components of flow system and is also used in rapid mix basins. GAC can be either in granular or extruded form.

GAC is designated by sizes such as 8×20, 20×40, or 8×30 for liquid phase applications and 4×6, 4×8 or 4×10 for vapor phase applications. A 20×40 carbon is made of particles that will pass through a U.S. Standard Mesh Size No. 20 sieve (0.84 mm) (generally specified as 85% passing) but be retained on a U.S. Standard Mesh Size No. 40 sieve (0.42 mm) (generally specified as 95% retained). AWWA (1992) B604 uses the 50-mesh sieve (0.297 mm) as the minimum GAC size.


The most popular aqueous phase carbons are the 12×40 and 8×30 sizes because they have a good balance of size, surface area, and head loss characteristics.

GAC is normally placed in a pressure vessel or gravity filtration tank through which raw water passes. The carbon filters mechanically strain out dirt, sediment, algae, bacteria, microscopic worms, cryptosporidium, and asbestos.  When the surface area of the carbon granules is clogged with the contaminants due to adsorption, pressure differential increases and the filter bed is back washed.

Optional Granular Activated Carbon filtration system can be a single treatment step or can be combined with other processes to remove free chlorine and dissolved organics from:

  • Municipal Water
  • Municipal Wastewater
  • Surface Water
  • Ground Water
  • Industrial Wastewater

Granular Activated Carbon market places here


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