Water is an excellent solvent and can dissolve almost anything. Granular Activated Carbon (GAC) has been used for water purification since the start of 20th century. GAC is made from coconut shell, coal, wood and some other products. Thermal activation of carbon (charcoal) from these products improves its pore volume, surface area, and structure making it ideal for water treatment. Because of the high percentage of unique micro pores, Coconut Shell carbons make a good choice among these.
The Adsorption Concept
GAC works through adsorption mechanism. Carbon surface has a strong attraction for organic and some other contaminants. It can reduce undesirable taste, odor and color and also effectively remove common disinfection byproducts (THMs), organic contaminants like chlorinated solvents and other industrial pollutants, pesticides, and select heavy metals such as lead and mercury. GAC can remove color bodies such as tannins also.
GAC’s capacity for organic removal is because of its very large surface area. One gram of GAC can have a surface area over 1000 m2. A pound of carbon has more than 35 acres of surface area, almost 100 football fields.
Empty Bed Contact Time (EBCT), represents the hydraulic flow rate through a GAC bed and is usually reported in “minutes”.
Another important property of GAC is its ability to catalytically reduce chlorine. This is an extremely fast reaction requiring an EBCT of only 30-40 seconds. A 10-inch cartridge with a flow of 0.5 gpm can remove 95% of incoming chlorine for 2500 gallons.
PFAS & PFOS Removal
GAC is the most common option to remove PFAS in drinking water. Carbon Block or the powdered activated carbon, which is made from same material as GAC and has smaller particle size, cannot be used in a flow through bed like GAC. And hence is not as efficient as GAC at removing PFAS.
Although, reverse osmosis (RO) treatment is effective for removal of all types of PFAS, including PFOS, PFOA, they are expensive. RO technology can be combined with GAC to achieve higher removal rates or maintain the efficiency of RO membranes.
GAC is a proven technology with high removal efficiencies (up to 99.9%) for many VOCs, including trichloroethylene (TCE) and tetrachloroethylene (PCE). In most cases, GAC can remove target contaminants to concentrations below 1 µg/l.
Radon, a radioactive gas, is the second leading cause of lung cancer in the US. It can also lead to stomach cancer. Radon in drinking water is not federally regulated. Limits in drinking water vary by state and range from 300 to 20,000 pCi/L.
GAC has been shown to achieve greater than 90% reduction of radon from treated drinking water. At low influent radon activities, EPA considers GAC to be a preferred treatment technology for POE. The Standard also limits filter life to one year.
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