Actived carbon filtration
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 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, extractables, ash and pH. These differences in properties make certain carbons preferable over others in different applications.
The two principal mechanisms by which activated carbon removes contaminants from water are adsorption and catalytic reduction. Organics are removed by adsorption and residual disinfectants are removed by catalytic reduction.
Actived carbon filter
Activated carbon filters are typically used to remove organic compounds and/or free chlorine from water to make water suitable for use in manufacturing or discharge. Removing organics like fulvic and humic acid from potable water prevents these acids from chemically reacting with chlorine to form a class of carcinogens known as trihalomethanes.
As with any water treatment method, activated carbon (AC) filtration is not suitable for removing every type of contaminant. AC filtration is not able to remove sodium, fluoride, microbes, or nitrates. AC filters also do not soften water. Only a specific type of activated carbon water treatment is able to remove heavy metals, such as lead, and this AC filter is typically only utilized in household point of-use filters.
Organic sources of activated carbon include coal (bituminous or anthracite) and coconut shells. Carbon is formed when the organic source is burned in an environment absent of oxygen, driving off heavy organic molecules and leaving about 30%of the original mass intact.. Next, the carbon must be "activated" for use in water treatment. The activation process further drives off unwanted molecules, as well as opens up the carbon's huge number of pores. These pores are what allow for contaminant absorption. The absorption rate of a surface area of just one pound of AC is equivalent to 60 to 150 acres!
Self-Source Auto-Backwash is achieved by using the filtered raw water from two (2) or three (3) of the filtered cells and diverting over to the remaining cell. All cells are backwashed in sequence. The filtration process will continue while in the backwash cycle so the system is not "down" while backwashing. An independent backwash water supply is not required. Self-source system typically three or four filters to allow enough flow to reach 12-15 gpm/ft2 of filter bed surface back wash flow rate. During these periods (which typically last for several minutes per filter), the amount of filtered effluent flowing downstream of the filter is reduced or stopped completely by the amount of water required for backwashing, although the process flow into the system continues to while backwashing. It is easy to operate and maintain and a pressure sensor, timer or manual initiation can be used to initiate the backwash cycle.
Filtration Equipment <o:p>
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. As described above, there are a host of variables that must be considered in designing a filtration system and selecting the best carbon for the application.
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