What is the principal mechanism by which activated carbon removes contaminants?

• A. Adsorption
• B. Filtration by size exclusion
• C. Oxidation
• D. Biodegradation

Answer: (A)

Activated carbon removes contaminants mainly through adsorption, where molecules are drawn to and held on the surface and within the pores of the carbon. The material has an enormous surface area and a network of micro- and mesopores, providing countless sites for contaminants to attach. This is a surface phenomenon driven by interactions between the contaminant molecules and the carbon, so dissolved organics and other compounds are removed as they partition onto the carbon rather than being blocked by particle size alone. Oxidation would require chemical reactions that break down or transform contaminants, which isn’t how activated carbon works; biodegradation relies on microbes breaking substances down, not on the carbon surface adsorbing them. The effectiveness depends on the properties of both the contaminants and the carbon (pore size distribution, surface chemistry), and the carbon bed must be regenerated or replaced as it becomes saturated.