Carbon filters remove chemicals by the process of adsorption. This happens when a chemical binds to the surfaces of the carbon molecules. These surfaces are a result of the extreme porous nature of granular activated carbon (GAC).
When water comes in contact with GAC, intermolecular forces draw the chemicals into the millions of pores and pockets of the carbon surface. The contaminants are then removed by the filter.
Removes Chlorine
Carbon filters remove chlorine, bad tastes and odors and organic chemicals from water to improve taste and make it safer to drink. They’re a good choice for homes with moderate to high TDS levels (total dissolved solids).
A carbon filter works by using a material called activated carbon. The carbon is typically made from coal or natural materials like coconut shells and wood that have been superheated to open up its pores. This increases its surface area to attract other contaminants. Activated carbon is safe, especially when it’s been tested and rated by a third party for material safety. It’s also effective at removing hydrogen sulfide gas (the chemical that gives well water its “rotten egg” smell) and reducing chloramines, a mix of ammonia and chlorine used as a disinfectant in some public water systems.
Depending on the manufacturer, carbon filters can be designed and certified to remove different contaminants from water. In general, the carbon will be effective in removing chlorine, bad tastes and odors, organic chemicals, THMs like chloroform and VOCs such as those found in gasoline, solvents and industrial cleaners.
However, a carbon filter will not remove bacteria or cysts like giardia and cryptosporidia. These require mechanical filtration through a finer pore size. It also won’t remove dissolved minerals and salts like calcium and magnesium, fluoride, arsenic or heavy metals such as lead or iron.
Removes Volatile Organic Compounds (VOCs)
Volatile organic compounds are carbon-containing substances that have a high vapor pressure at room temperature. VOCs are emitted from a wide variety of household and commercial items, including fuel oils, solvents, paints and varnishes, air fresheners, cigarette smoke and building materials. Many VOCs evaporate into the air, but some seep into soil or ground water where they can contaminate well and public drinking supplies. For example, perchloroethylene (found in dry cleaners) and methyl tert-butyl ether (MTBE, an additive used in gasoline to increase oxygen levels and reduce air pollution) are both VOCs found in public drinking water supplies.
VOCs can enter the human body through inhalation or skin contact, but the most common way is by drinking contaminated water. Inhaling VOC vapors from stored chemicals or cigarette smoke can also lead to long-term exposure.
Carbon filters are able to remove VOCs through a process called adsorption. As the name suggests, carbon has an affinity for organic molecules that are polar compounds. When the filter is saturated with these contaminants, they are absorbed by the filter surface and bond to it like Velcro. A filter’s ability to remove VOCs is related to the amount of time a given compound spends in direct contact with the carbon. A filter with a thick layer of carbon that offers an extended dwell time is most effective.
Removes Smells
Carbon filters trap odors and gases from smoke, fire, cooking, cleaning products and other sources. These filters are a good option for homes with children, elderly or immunocompromised family members who are especially vulnerable to VOCs.
VOCs are chemical compounds that produce odors and can also be harmful to your family’s health. Many VOCs are found in everyday household products, building materials and even outdoor air. A carbon filter removes VOCs from your indoor air by using a process called adsorption. Activated carbon, or charcoal, has been processed to make it more porous, which gives it more surface area and makes it more effective at trapping odors and VOCs from the air.
There are two types of carbon filters: loose carbon granules (granular activated carbon or GAC) and carbon block. GAC is typically found in air filters and carbon block is often used for drinking water filters. GAC is better at removing chlorine, bad tastes and odors and organic chemicals from water than carbon blocks, but both can effectively remove odors and VOCs.
The effectiveness of carbon filters is dependent on three factors: the type of contaminant, the movement of the air and the capacity of the filter. The contaminant must be attracted to the carbon and then advected onto it. Eventually, the pores of the carbon become filled with contaminant molecules and it becomes less effective.
Removes Bacteria
Carbon filters remove a variety of contaminants by a process called adsorption, whereby chemicals adhere to the carbon surface in much the same way that magnets attract and hold metal filings. This is one reason why carbon filters are so popular for home water purification. They are capable of removing a wide range of organic pollutants including chlorine, VOCs, dissolved minerals, trihalomethanes, hydrogen sulfide, pesticides, and chloramines (the mixture of ammonia and chlorine that some water supplies use to disinfect their water).
Most household carbon filters are made from granular activated carbon or GAC, which has a large number of pores that allow water to flow through quickly. Solid carbon block filters have a tighter pore size and offer a more concentrated form of carbon, which works better than GAC at trapping smaller particles. Both types of carbon filters can be effective, but a filter’s performance depends on the size and density of the carbon, the way it is constructed, and the amount of time the water stays in contact with the carbon, which is called residence time.
Despite being very good at removing chlorine, VOCs and bad tastes/odors, carbon filters don’t remove all contaminants from water. For example, carbon filters will not filter out coliform bacteria or cysts like giardia and cryptosporidia from your water. If you are concerned about these contaminants, consider installing a water softener to remove calcium and magnesium hard water minerals.