Activated Carbon — Frequently Asked Questions

Because it determines pore structure, and adsorption happens inside the pores. Coconut shell carbon is predominantly microporous, suiting small molecules, gas-phase work and chlorine removal. Coal-based carbon has a broader distribution including mesopores, suiting the mixed contaminants of wastewater. Wood-based carbon is largely meso and macroporous, suiting large molecules such as colour bodies in sugar and oil refining.

Iodine number measures micropore capacity, using a small molecule that only fits in fine pores, and it is the standard index for water treatment carbons. Molasses number measures macropore capacity using a large molecule, and it predicts performance in decolourisation. A carbon can have a high iodine number and still perform poorly on large molecules, which is why both are quoted.

Yes. Thermal reactivation heats the spent carbon in a controlled atmosphere to drive off and destroy the adsorbed material, restoring most of the capacity. Reactivation is economic for large granular carbon installations and reduces both cost and waste, though some carbon is lost each cycle and capacity declines gradually. Powdered carbon is normally used once and disposed of with the sludge.

Granular carbon is used in fixed beds with water flowing through, giving continuous treatment and allowing regeneration, but requiring vessel infrastructure. Powdered carbon is dosed directly into the water, contacted and then removed with the sludge, which needs no vessels and allows dose to be varied day to day, but cannot be regenerated and adds to sludge volume.