Activated carbon or carbon adsorption process is used for removing various organic substances like Oils, Radioactive Compounds, Petroleum Hydrocarbons, Poly Aromatic Hydrocarbons and various halogenated compounds like Chlorine, Fluorine, Bromine and Iodine. Apart from organic compounds it also removes inorganic compounds like Arsenic, Cadmium, Chromium, Zinc, Lead, Mercury, Copper, etc. As carbon adsorption method is effective in removing pollutants, it is used in following industrial process for water treatment:
- Ground Water Purification
- The De-Chlorination of Process Water
- Water Purification
- Wastewater Treatment
Types of Active Carbon
On the basis of physical properties activated carbon can be classified as:
Powdered Activated Carbon (PAC)
Crushed or ground carbon particles are used for making powdered activated carbon. They are so finely powdered that most of them can easily pass through a designated mesh sieve or sieve. Due to their small size they form large internal surface having small diffusion distance. PAC is normally used in processing units like, clarifiers, gravity filters, mix basins, etc.
Powdered activated carbon (PAC)
Granulated activated carbon (GAC)
Granulated activated carbon forms smaller external surface because of their larger size as compared to PAC. Granulated carbons are mainly used for treating water. Their main function includes deodorization and separation of components of flow system. GAC comes in both granular and extruded form.
Granular Activated Carbon Plant
Pelleted activated carbon
Granulated in smaller size and comes in extruded and cylindrical shaped. They are mainly used for gas phase applications.
Spherical Activated Carbon
These are made of small spherical balls and have high mechanical strength and excellent SO2 and NO2 adsorption capacity.
Impregnated Carbon
Impregnated carbon are Porous in nature and consist of various inorganic impregnant like iodine, silver, cation such as Al, Mn, Zn, etc. Activated carbon consisting of silver is used for purifying domestic water.
How does Activated Carbon Work?
The main function of the activated carbon is to remove contaminants from water. The highly porous nature of the carbon provides a large surface area for contaminants to collect. The adsorption takes place because of the attractive force between the molecules. Molecules at the surface of a solid attracts other molecules. Hence, water contaminants gets adsorbed to the surface of carbon. As the attraction of the carbon surface for contaminants is higher than the attractive forces that keep them dissolved in solution, water contaminants gets attracted. Activated carbon through adsorption also removes chemical like chlorine that combines with carbon to form chloride ions. This reaction helps not only in removing contaminants but also removes objectionable tastes and odors from drinking water.
Properties of Activated Carbon
Physical Properties
Physical attraction of the contaminants to the pore walls is one of the important aspect of the Activated carbon filtration process. The amount and distribution of pores play key roles in determining how well contaminants are filtered. Depending on pore size of the filter, contaminants are attracted differently. Contaminants having large molecules are effectively removed by AC filters.
Chemical Properties
Often the filter surface interact chemically with organic molecules. Adsorption may also result by the electrical forces between the AC surface and some contaminants. The activation process also determines the chemical properties of the adsorbing surface. The activation carbon materials that results from various activation processes will posses chemical properties that make them more or less attractive to various contaminants.
Activated Carbon Filtration Equipment Types
Activated carbon filtration units are of following types:
Pour-through AC filters
In pour through AC filters, water filtration takes place through gravity. The process is slow and can handle only small volumes of water.
Faucet-mounted AC filters
They are installed in kitchen at the end of the faucets.
High-volume AC filters
High-volume AC filters consist of more AC ac compared to pour-through or faucet-mounted models. They are normally installed under the sink and high-volume units are designed for this purpose.
Manufacturing of Activated Carbon
Various organic substances like coal, shells, sawdust, etc. can be used for the manufacturing of Activated Carbon. Molding and crushing is required to give them desired form after which they are heated at 700 to 800 degree Celsius to produce carbides. Obtained carbon substance is then reacted with with steam or carbon dioxide at 900 to 1100 degree Celsius which creates very small pores. The whole manufacturing process is called as gas activation.
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