How does Carbon Filtering work?

Liz Filmer
07 Sep 2021

If you grow cannabis indoors, you will no doubt be familiar with carbon filters and probably use one to keep telltale odours from seeping out of your grow room but have you ever given much thought to how carbon filtering works?

Carbon filtering uses a bed of activated carbon to remove contaminants and impurities. Each granule of carbon has a large surface area, allowing contaminants the maximum possible exposure to the active sites.

Charcoal is carbon & activated charcoal has been treated with oxygen to open up millions of tiny pores between the carbon atoms. Special manufacturing techniques result in highly porous crystals with 300-2,000 square meters per gram surface area. 

These activated charcoals are used to “adsorb” odorous or coloured substances from gases or liquids.

What is Adsorption?

When a material adsorbs something, it means that it attaches to it by chemical attraction. Activated carbon works by a phenomenon called “Adsorption”, where the odour is trapped by the activated carbon and retained.

 “Adsorption” is the sticking of atoms or molecules to a surface. The particles which get adsorbed can be from a gas, liquid or dissolved solid. Another example would be how water sticks to the surface of sand grains on a beach or particles of soil.

Adsorption differs from absorption as molecules undergoing absorption are taken inside the absorbent material (sponge, for example) and held there, rather than just sticking to the surface of it.

You can tell if a material is absorbent or adsorbent due to the volume change. A sponge, for example, will look bigger when full of water as it has taken the water inside its mass. 

With adsorption, however,, there is no visual change in the appearance of the lining. The odour molecules attach themselves chemically to the surface rather than being taken inside it.

How does “active carbon” work?

The vast surface area of activated charcoal means it has unlimited bonding sites. When certain chemicals then pass over the carbon surface, they attach to it and are trapped. Activated charcoal is good at trapping carbon (organic) based impurities and things like chlorine. Many other chemicals, however, are not attracted to carbon, such as sodium and nitrates. Therefore an activated charcoal filter will remove certain impurities while ignoring others.

Charcoal filters are used in various fashions to eliminate impurities, such as removing odours. They are also used for the purification process of liquids, including water processing facilities, coffee machines and aquariums. They are also used in air conditioning units, and exhaust fans to rid the air of unwanted odours and are available in solid carbon, impregnated foam materials, powder and cloth.

Liz Filmer