Carbon filters remove contaminants from the air by a process called adsorption. Chemicals like VOCs and odor-causing molecules stick to the surface of the carbon, while clean air passes through the filter.
When the carbon becomes saturated with contaminants, it must be replaced. It may not be obvious when this happens, but following the manufacturer’s guidelines for replacement is a good idea.
Chlorine Removal
Carbon or charcoal filters can remove chlorine and other volatile organics (VOCs) from water. They can also adsorb some of the hydrogen sulfide gas that can make some well waters smell like rotten eggs. These are usually done as a prefiltration step before a semipermeable membrane or other types of filters that remove almost all dissolved solids in water.
Activated carbon is an extremely porous material. The surface of each granular or powdered block has been superheated to open up these pores, increasing its ability to bond with other chemicals. When used in a carbon filter for removing organic contaminants from water, the water particles run through the large pores of the activated carbon and bind to it. The contaminants then stick to the carbon’s surface and are unable to escape back into the water. Eventually, the contaminant will be pushed out of the filter through the pore’s surface.
For chemicals that don’t adhere to carbon’s surface, such as chlorine, the activated carbon will use a chemical reaction to eliminate it. The more reactive the activated carbon, the faster it will eliminate the chlorine molecules by converting them into chloride. This is why it’s important to choose a high-quality carbon filter that uses either coconut shell based, surface-enhanced GAC or bituminous coal-based, surface-enhanced GAC for chlorine removal.
Odor Removal
Carbon filters do a great job at removing unwanted odors in a home or commercial facility. Odor removal happens through a process known as adsorption, wherein odor molecules are physically attracted to the surface of activated carbon. This surface is made from charcoal that has been “baked” at high temperatures to create large pores, which allows for greater amounts of adsorption.
A carbon filter is an excellent choice for removing chlorine, odors, and Volatile Organic Compounds (VOC) from the home’s air. These VOCs can include household products, cleaning supplies, paints and stains, thinning compounds, and cigarette smoke. When these chemicals are inhaled they can cause a range of symptoms from nausea and headaches to long term health issues.
Carbon can be used for odor removal in home water filters, whole house water filters, and commercial drinking water systems. It is also often used to eliminate mercaptan odors at odorization stations during a pressure release event, odorant transfers or equipment failures. For this application, we recommend using a granular carbon filter that is designed for this purpose, rather than a standard carbon block. These types of filters have a much greater amount of surface area and longer residence time, which increases their effectiveness at higher flow rates. In addition, it is recommended to use a post filter housing in a series filtration fashion to catch any carbon fines that may migrate from the carbon filter under high differential pressures.
VOC Removal
VOCs, or volatile organic compounds, are gases that can be emitted into the air by a variety of sources. They can have a negative impact on indoor air quality and be harmful to humans and pets alike. The health effects of exposure to VOCs vary between individuals and are usually dependent on the length and intensity of the exposure.
Carbon filters remove VOCs by a process called ad-sorption. This differs from absorption, where pollutants are absorbed inside the structure itself-like a sponge absorbs water. With ad-sorption, the carbon has extra exterior surface area that gives gaseous molecules a chance to stick to it. This is why coconut-based bulk activated carbon is one of the most effective types of carbon for VOC removal.
Activated carbon has been treated to make it more porous, and is often impregnated with substances that help it adsorb certain chemicals, like odor-causing chemicals or VOCs. This enhances its effectiveness and extends the life of the carbon.
Carbon filters work by ad-sorption, which is when chemicals bind to the carbon at a molecular level, similar to how magnets attract and hold iron filings. Generally, the higher the molecular weight (MW), the better the carbon will perform at removing chemicals. When the adsorption capacity of the carbon is reached, it needs to be changed. The best way to determine if your carbon filter is working properly is to measure its ad-sorption capacity with an air quality monitor.
Fluoride Removal
Carbon filters remove VOCs (volatile organic compounds) and odors that other mechanical air filter types like HEPA can’t touch, including some of the chemicals in secondhand smoke or those given off by paint or cleaning products. A carbon filter also can trap toxins in the air from wildfire smoke and many common cooking smells, such as those from fish, sauteed onions, curry and fried foods.
Activated carbon works by a process called adsorption. It is different from absorption because unlike water that fills a sponge, the chemicals that adsorb onto carbon do so on a molecular level. This allows the carbon to trap gases until it is saturated, at which point it needs to be replaced.
The type of carbon used in a filter and the way it is treated (activated) affects its effectiveness. For example, some carbons are better at removing chlorine or trihalomethanes than others. Some are even specialized in removing specific heavy metals such as arsenic, chromium or lead from water.
The thickness of the carbon in a filter is important as well, because it gives it more surface area to absorb contaminants. Thicker carbon lasts longer than thinner carbon, which will need to be replaced sooner. Another factor is the concentration of organic chemicals — one carbon filter may be more effective than another at filtering high or low concentrations of certain chemicals.