In modern water filtration, a highly specialized form known as Activated Carbon (AC) is the standard, found in everything from small pitcher filters to whole-house systems. This processed material is widely used for enhancing the taste and purity of drinking water. The effectiveness of AC relies entirely on a unique internal structure engineered to physically capture dissolved impurities.
The Activation Process
Activated Carbon differs from ordinary charcoal due to a manufacturing process designed to create an immense internal surface area. The process begins with carbon-rich source materials, such as coconut shells, wood, or coal. These materials undergo carbonization (pyrolysis), which involves heating them in an oxygen-free environment, typically at 600 to 900 degrees Celsius. This initial heating drives off volatile components and leaves behind a carbon-rich char.
The char is then “activated” by exposing it to gases like steam or carbon dioxide at even higher temperatures, often between 800 and 1,100 degrees Celsius. This step etches a vast network of microscopic pores into the carbon structure. A single gram of activated carbon can possess an internal surface area equivalent to over 1,000 square meters.
How Adsorption Works
The mechanism by which activated carbon cleans water is called adsorption, which is distinct from absorption. While absorption is like a sponge soaking up water, adsorption is a surface phenomenon where contaminants stick to the exterior and interior walls of the carbon’s pores. As water passes through the filter, impurities are physically or chemically attracted to the carbon’s surface.
This attraction occurs because many common contaminants, particularly organic chemicals, are non-polar molecules that are less soluble in water than they are attracted to the non-polar carbon surface. The vast network of micro- and mesopores acts like a molecular trap, providing countless sites where these dissolved substances can be captured and held.
The effectiveness of adsorption is highly dependent on the contact time between the water and the carbon, as well as the size of the contaminant molecule. Smaller pores are more effective for trapping smaller molecules, but the pores must be large enough to allow the contaminant to enter. This trapping process removes the pollutants from the water, which flows out clean while the impurities remain locked inside the carbon structure.
What Charcoal Removes
Activated carbon is effective at removing organic compounds and substances that affect the aesthetic quality of water. A primary application is the reduction of chlorine and chloramine, which are added disinfectants that cause unpleasant tastes and odors. The carbon surface chemically reacts with these substances, effectively neutralizing them.
The filter also excels at trapping Volatile Organic Compounds (VOCs), including solvents, industrial chemicals, and byproducts from disinfection. Specific examples of VOCs removed include benzene, trichloroethylene, and carbon tetrachloride. AC is also used to reduce levels of pesticides, herbicides, and compounds originating from agricultural or industrial runoff.
What Charcoal Does Not Remove and Filter Lifespan
Despite its effectiveness against organic contaminants, activated carbon has limitations concerning inorganic substances and microorganisms. AC filters are ineffective at removing dissolved inorganic minerals, such as calcium and magnesium, which cause water hardness. They also do not reliably remove highly water-soluble inorganic pollutants like nitrates, or microscopic contaminants like bacteria and viruses.
The pores eventually become full, a state called saturation, signaling the end of the filter’s useful life. When saturated, the carbon loses its ability to adsorb new contaminants and can begin to release previously trapped impurities back into the water, a phenomenon known as “breakthrough.” For typical household systems, AC filters must be replaced regularly, often every six to twelve months, to maintain performance and prevent microbial growth.