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 multifunctional nature and the fact that it adds nothing detrimental to the treated water.
Most activated carbon is made from raw materials such as coconut and coal. Typical surface area for activated carbon is approx. 1,000 square meters per gram. However, different raw materials produce different types of activated carbon varying in hardness, density, pore and particle sizes, surface areas, extractables, ash, and pH. These differences in properties make certain carbons preferable over others in different applications.
The two principle mechanisms by which activated carbon removes contaminants from water are absorption and catalytic reduction. Organics are removed by adsorption and residual disinfectants are removed by catalytic reduction.