Cristina Tuser is associate editor for WWD. Tuser can be reached at [email protected]
Carbon adsorption is a method for removing dissolved organic substances, particularly those which cause tastes and odors.
What is Carbon Adsorption Used for?
According to the U.S. EPA, carbon adsorbers are used in applications including: “controlling volatile organic compounds (VOC) and hazardous air pollutants (HAP) emissions from storage tanks and process vents at refineries, chemical manufacturing, and pulp and paper plants, to control hydrogen sulfide and VOC emissions from municipal wastewater plants.”
The equipment life for carbon adsorbers generally falls between 15 and 25 years. There are smaller applications in which carbon adsorption is used, such as in portable soil remediation systems.
What Does Adsorption Mean?
Adsorption is a surface process that leads to transfer of a molecule from a fluid bulk to solid surface, removing VOCs from low to medium concentration gas streams.
According to the International Adsorption Society, historically, activated carbon has been used for removing nerve gasses from battlefields. Today, there are thousands of applications for adsorption.
“Adsorbents are mostly microporous, high specific surface material,” states the International Adsorption Society.
Is Carbon a Good Adsorbent?
Carbon is an effective adsorbent because it is a highly porous material and provides a large surface area where contaminants are adsorbed.
Natural carbon may not be able to treat every contaminant because there are still organics that are not able to be adsorbed by activated carbon.
What are the Types of Carbon Adsorbents?
Powder and granular activated carbons are the most well-known and used carbon adsorbents.
Powder Activated Carbon
Powdered activated carbon is generally “added before coagulation, during chemical addition, or during the settling stage, prior to sand filtration.”
An advantage is that it can be applied for short periods and is particularly useful for algal toxins, tastes and odors but it cannot be reused.
Granular Activated Carbon
Granular activated carbon is generally used for the removal of organic matter such as micropollutants, and is installed downstream of rapid gravity filters which are used for turbidity removal.
Granular activated carbon is two or three times more costly than powdered activated carbon.