What You Need to Know About a Carbon Filter

A Carbon filter is a very versatile water filtration medium. It is available in granular or block form and can be injected with heat, steam or chemicals to increase its surface area, which makes it better at adsorbing specific contaminants.


A single pound of activated carbon has a surface area equivalent to the size of 125 acres. This surface area allows carbon to remove most contaminant particles by physical adsorption.

Activated Carbon

Activated carbon is a porous material that works by absorbing chemicals, gases and odors. Its enormous surface area provides countless bonding sites for unwanted molecules. The molecules stick to the activated carbon and are removed from the environment. The process is akin to a sponge soaking up water. The difference is that the water is fully absorbed and is not just sticking to the top of the sponge. Activated carbon is made from a variety of materials including bituminous coal, lignite coal, wood and coconut shell. It is processed (activated) to create small pores that increase its surface area and porosity.

Most commonly, carbon is used in air and water filters to remove volatile organic compounds (VOCs) from vapor and liquid streams. Chemicals like benzene, toluene, xylene and oils are common VOCs that can be removed from fluid streams using carbon.

Other large applications include removing color contamination in foods and beverages. Activated carbon can remove the unpleasant colors from juices, wines and soft drinks. Carbons with a combination of macropores and mesopores are best at removing color contaminants.

Another common use of activated carbon is in filtration systems to reduce the concentration of radon in groundwater. Carbon adsorption is an efficient and inexpensive method for reducing radon in drinking water. Activated carbon is also used in cigarette filters and to remove bad taste from bottled water.

Particle Size

The size of carbon particles is crucial because it affects how long the air spends in contact with them. This is referred to as “dwell time” and is a good indicator of when the carbon filter needs to be replaced. The longer the air stays in contact with the carbon, the more contaminants it will remove from the air.

Generally, particle size is measured using particle density distributions. These are calculated by dividing the number of particles in each measurement class into the total sample quantity and multiplying by the median value (or d10), the 50% level (or d50) or the 90% value (or d90).

These measures are usually tabulated and reported as mean values or as percentages of the distribution. They can also be represented in terms of standard deviations, or span values, which describe the distance between a typical value and the maximum/minimum value.

Measurements of the shape of the particles are also useful, particularly for assessing accuracy of light scattering and obscuration methods that assume that all particles are spherical in form. Other particle sizing techniques that incorporate the measurement of shape include sieve analysis and laser diffraction. However, these tend to be more complex and labor intensive than other methods.

Flow Rate

The higher the water pressure, the faster the water moves through a carbon filter. This can cause the filter to work too quickly and not remove all of the contaminants from your water. Ideally, your water pressure should be below 100 psi to ensure that your carbon filter works at its best.

Filter flow rate is also known as volumetric flow rate, which is the volume of a fluid that passes through a surface in a given unit of time, defined as the change in the volume V of the fluid (V – V/t) and can be expressed as cubic meters per second or standard cubic centimeters per minute (SCCM). In US customary units and imperial units, it is commonly represented as gallons per minute, 1 MGD, and sometimes as litres per minute (L/min).

Solid carbon block filters use an adsorption method to remove tastes, odors and other contaminants from drinking water. They are a popular technology for Point Of Use (POU) drinking water treatment systems and can be used alone or in conjunction with other filtration technologies. To optimize performance, most manufacturers of carbon block water filters include a Performance Indication Device (PID), which measures actual usage and not just water capacity to indicate when the filter needs to be replaced. NSF certification requires that any manufacturer making claims about a carbon block filter’s performance must prove their claim using independent testing.

Micron Rating

The micron rating measures how well the filter can stop contaminants of a specific size. For example, a filter with a five-micron rating will prevent all contaminants from passing through the filter that are bigger than a fifth of a millimetre in diameter. This is about the size of a red blood cell and is far smaller than a human hair.

There are two common ways to express a micron rating; either absolute or nominal. An absolute micron rating will state that the filter will catch all particles that are larger than a certain amount, such as 99.9% of those larger than a given micron rating. Nominal ratings are more general and often refer to the percentage of particles that are larger than a given micron rating. For example, a filter with

A low micron rating is a good choice for well water filters as it will remove sediment and other particles that can cause poor taste and odor in drinking water. It will also trap bacteria such as E coli and Salmonella which can have serious health consequences when ingested over time. However, lower micron rated filters can struggle with flow rate loss and unnecessary clogging which may result in frequent cartridge replacement. This is why it is important to use a filter with a micron rating that is right for your application.