Activated Carbon Filters: The Key to Removing Taste, Odor, and Chemicals

If you have a water filter pitcher in your fridge or a purification system under your sink, chances are it uses Activated Carbon. It is the most common and effective technology for “polishing” water to make it safe and pleasant to drink.

But what makes this black, dusty material so special?

What is Activated Carbon?

Activated carbon (or activated charcoal) is carbon that has been treated with oxygen to create millions of tiny pores between the carbon atoms. This process dramatically increases the surface area of the material.

Fun Fact: Just one gram of activated carbon has a surface area in excess of 3,000 square meters (about half a football field). This massive surface area is what allows it to trap contaminants.

How It Works: Adsorption (Not Absorption)

Carbon filters work through a process called Adsorption (with a 'd').

• Absorption is like a sponge soaking up water (the water goes inside).
• Adsorption is like a magnet (contaminants stick to the surface).

As water flows through the carbon filter, organic contaminants and chemicals are attracted to the carbon surface and get stuck in the varying sizes of pores, leaving clean water to pass through.

The Technical Specs: Measuring Carbon Quality

Not all charcoal is "Activated." Engineers look for three key numbers when buying carbon:

1. Iodine Number (800 – 1100): Measures the surface area. A higher number means a better "sponge."
2. CTC Activity: Measures the ability to adsorb vapors/organic gases.
3. Hardness Number: Measures how much the carbon will crumble. Coconut shell carbon has the highest hardness.

Comparison: Coconut vs. Coal vs. Wood

How It Removes Chlorine (Cl₂)

Surprisingly, carbon doesn't just "soak up" chlorine—it performs a chemical reaction. When chlorine hits the carbon surface, it is converted into a tiny amount of Chloride (Cl⁻) and Carbon Dioxide (CO₂). In the process, the carbon itself is slowly "eaten" away. This is why carbon filters eventually grow lighter over years of use!

C* + 2Cl₂ + 2H₂O → C*O₂ + 4HCl

(C represents the activated carbon surface)*

Advanced: Catalytic Carbon

Regular carbon is bad at removing Hydrogen Sulfide (Rotten Egg smell) and Chloramines.

• Catalytic Carbon is a special grade where the surface has been changed (often with Nitrogen) to act as a catalyst.
• Why it matters: It converts H₂S into elemental sulfur or sulfate, locking it away. It’s essential for well-water treatment.

What it does NOT remove:

• Dissolved Minerals: It will not lower your TDS. Calcium, Magnesium, and Sodium pass right through.
• Heavy Metals: Standard carbon is poor here. However, KDF-modified carbon or Carbon blocks with Ion-Exchange resins can remove Lead and Mercury.

Types of Carbon Filters

1. Granular Activated Carbon (GAC)

Loose granules of carbon held in a cartridge.

• Pros: High flow rate, cheaper.
• Cons: Water can create "channels" through the loose granules, bypassing the carbon.

2. Carbon Block

Fine carbon powder compressed into a solid block.

• Pros: Much more effective. The tight structure prevents channeling and can filter out fine sediments.
• Cons: Restricts water flow (lower GPM).

Maintenance

Carbon filters are like sponges—eventually, they get full. Once the surface area is covered in contaminants, the filter stops working. Worse, it can begin to dump contaminants back into the water.

• Replacement: Typically every 6–12 months, or when you notice a return of bad taste/odor or a drop in water pressure.