Activated Carbon Definitions
Acid Washed – A process whereby the activated carbon is washed by acid to remove the water-soluble ash. This process will also lower the total ash content of the carbon as seen on the detailed specification sheets. Acid washed activated carbon is desirable for treating drinking water and food grade applications. Industries include municipal water treatment plants, food processing companies, breweries and distilleries among others.
Activated Carbon – A filtration media that is preferred due to its cost effective advantage. It comes in pelletized, granular and powdered forms derived from materials such as coal, coconut shell and wood. The raw charcoal is superheated to create a large internal pore structure where the organic contaminants can adsorb to. Activated carbon is used for both air and water applications. More can be found on our frequently asked questions page.
Adsorption – In the instance of activated carbon treatment, adsorption is when a molecule sticks to the surface area of the activated carbon. Activated carbon has an extremely large internal pore structure and large surface area. Molecules will stick to the surface of these pores.
Ash Content – Ash is an actual property of activated carbon. It decreases the effectiveness of the activated carbon. You will find low ash content in all activated carbon products. Water soluble ash is the ash content that can be washed away by water. Often, activated carbon that is intended for food grade applications will be acid washed to remove the water-soluble ash content. No acid is left behind in this process.
Backwashing – There is an initial backwash and then there are periodic backwashes. The initial backwash can be used to remove the fines and dust created from handling the activated carbon. To properly backwash your filter, start slowly and speed up the flow. This allows the carbon to expand gently. Do not start quickly because this will push the carbon up. Backwash for 15-20 minutes. Backwashes done periodically will help remove particles of the application that can get stuck in the activated carbon pores. For instance, one of our car wash customers has a lot of soap that goes through the filter. Occasionally they backwash the filter to get rid of the soap that could be blocking some of the activated carbon pores.
Capacity – Activated carbon capacity is the amount of space available to capture contaminants. For example, activated carbon can capture 1 gram of contaminant for every 10 grams of activated carbon. This means that for this contaminant, the activated carbon has a 10% weight on weight capacity.
Contact Time – Contact time is the amount of time the contaminants are in contact with the surface area of activated carbon. The higher the concentration, the more contact time is required. Increasing contact time decreases pressure drop. For Air phase we like greater than one and a half seconds. For Water phase we like 5 to 10 minutes but love 10 to 20 minutes.
Carbon Tetrachloride Number – A measurement of the quality of the activated carbon typically used for vapor phase carbons. It is a test to see how much CTC the carbon will remove.
Granular Activated Carbon – Like little broken pieces. They are not uniform in shape. Typically ranging from 0.295 mm to 4.70 mm. Cheaper than pelletized activated carbon.
Hazardous Activated Carbon – Activated carbon that has reached levels set out by the EPA that are deemed hazardous and must be handled in a safer condition. The material must be put in DOT approved drums or supersacks, transported by a licensed trucker and disposed or reactivated at a licensed reactivated facility. Hazardous projects cost much more than non-hazardous projects do.
Humidity – Humidity is a problem if it causes enough condensation that blocks the pores of the activated carbon and stop the carbon from being able to adsorb the contaminants. Condensation will form in a carbon bed if the dew point of the air flow is greater than the temperature of the air outside. Humidity and condensation is an issue if you have chlorinated solvents because the chemical reaction will not work well. 50% humidity is fine and 70-80% is tolerable.
Iodine – A measurement of the quality of the activated carbon typically used for liquid phase carbons. It is a test to see how much iodine the carbon will remove.
Mesh Size – a measure of the size of the granules. It is a range. For instance, 8×30 means that the largest particles are 1/8” and the smallest are 1/30”. The 8×30 means a range that the granule sizes will be in between 1/8” and 1/30”. Larger mesh size carbons are used for air treatment because there is less pressure drop. The smaller the particle the greater the pressure drop. Water applications require greater contact time and therefore use smaller particles so that the contaminants are close to always in contact to the surface area of the activated carbon.
Moisture Content – typically measured as packaged, the measurement of the amount of water in the activated carbon.
Pelletized Activated Carbon – Uniform in shaped, cylindrical carbon pellets. Typically mined into chunks of charcoal, pulverized and formed into pellets with a coal tar binder or petroleum tar binder. Used for low flow and low pressure drop applications.
pH – Acidic (0) -> Neutral (7) -> Basic (14). pH Effects the solubility of a chemical but only a drastic pH is a big concern, ie. 2 or 12. pH will rise in liquid phase applications because of water soluble ash. Higher ash content, higher pH. Since coal has more ash, it will have a higher initial spike in pH. A rule of thumb is to increase the size of the carbon bed by twenty percent for every pH unit above neutral (7.0).
Micropore – up to 100 A < 1 nm
Mesopore – Between 100-5000 A 1-500 nm
Macropore – Greater than 5000 A > 500 nm
Powdered Activated Carbon – Activated carbon in powder form. Used predominantly in water phase applications. Sizes 100-325 mesh which are smaller than 0.147 mm. Can be coal, coconut shell or wood based.
Pressure Drop – Amount of drop in velocity of air as it goes through the carbon. The less the pressure drop the better. This really is only accurate at 30-60 ft/min superficial velocity. The smaller the activated carbon particles, the greater the pressure drop will be. 12×40 will have a greater pressure drop than 8×30. Lower temperatures increase pressure drop because the water is denser.
Reactivated Carbon – Carbon that is spent and superheated in a rotary kiln to remove/lift off the contaminants so that the carbon can be used again. The reactivation process can recover up to 80% effectiveness of the carbon. Reactivated carbon is a cheaper option to treating many applications. The only applications that cannot use reactivated carbon are food grade applications.
Surface Area – Activated carbon has a deceivingly gigantic surface area. During its’ manufacturing process, it is superheated to create a large internal pore structure. Contaminants adsorb, or stick, to the surface of the activated carbon. You cannot see the pore structure with your naked eye but they look like a sponge.
Temperature – Carbon begins to lose its effectiveness for removing contaminants when the temperature reaches 90 F. At approximately 120 F, carbon will not work effectively. When liquid reaches boiling carbon will not work at all.