The Three Basic Coal-Based Filter Carbons and Their Special Properties

The heart of most water filtration systems is filter carbon, usually called “granular activated carbon,” or GAC.   Activated carbon is the preferred treatment for a large percentage of  contaminants on the EPA’s list of monitored water issues.  Carbon is an effective treatment for a large percentage of chemical contaminants, including disinfectants like chlorine and chloramine, plus it is very effective at improving the aesthetic qualities of water like taste, odor and color.

Filter carbon is a manufactured product, but it starts from a natural source.  It can be made from any carbonaceous raw material.  Coconut shells are a common raw material used in carbon making, but by far the most common source material is coal.

Carbons made from lignite tend to have a large pore diameter. The pore diameter is measured by a property know to manufacturers as the “molasses number.”  The higher the molasses number the more suited the carbon is to remove colors from liquids.

Bituminous coal activated carbons have a broad range of pore diameters. Since these carbons have both a fine and wide pore diameter, they are well suited for general de-chlorination and the removal of a wider variety of organic chemical contaminants from water, including colors.

Because of its versatility, bituminous carbon is the most commonly used carbon for general water treatment.

In addition to the “molasses number,” qualities that are used to grade filter carbons are the so-called iodine number, the ash content, the abrasion number, the bulk density, the peroxide number, and the phosphorous content.