Activated Carbon Filters
Activated carbon filters are generally employed in the process of removing organic compounds and/or extracting
free chlorine from water, thereby making the water suitable for discharge or use in manufacturing processes. Eliminating
organics in potable water, such as humic and fulvic acid, prevents chlorine in the water from chemically reacting with the
acids and forming trihalomethanes, a class of known carcinogens.
Activated Carbon (AC) filtration, as with any water treatment method, is not capable of removing every possible type of contaminant. For example, sodium, microbes, fluoride, and nitrates cannot be removed with AC filtration. Water softening also cannot be achieved with AC filters. In addition, heavy metals, such as lead, can only be removed with a very specific kind of activated carbon water treatment, which is typically used only in residential point-of-use filters.
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. Chemical activation produces activated carbon with a very open pore structure, making it more suitable for adsorbing large molecules
Activated carbon filters are similar to those used in multi-media filtration, except without the air scour step in the backwash process. Since certain organics require an extended exposure time to the filter to be removed, higher filter vessel sideshells may be used to provide deeper carbon beds for extended reaction times. Carbon beds should be backwashed to help remove trapped silt, prevent packing and head loss, and to remove carbon fines produced by friction between granules.