Water Treatment with Activated Carbon

The water-treatment problem

Activated carbon treats water by adsorbing dissolved organic molecules onto its internal pore surface — humic substances, micropollutants, taste and odor compounds, color bodies and residual solvents. Water treatment splits into two regimes that use carbon differently:

• Standing barrier — a granular carbon bed (GAC) in a contactor or filter that every liter of water must pass through, designed around empty-bed contact time. This is the municipal and industrial baseline for trace-organics compliance.
• Spike response — powdered carbon (PAC) dosed as a slurry for seasonal taste-and-odor events, algae blooms or pollution incidents, then removed with the sludge. Fast kinetics, single use.

Design ranges used in Chinese practice: PAC dosing typically 5–30 mg/L; GAC empty-bed contact time typically 8–20 minutes. Background: PAC vs GAC guide in our knowledge center.

Selection checklist

• The contaminant — name it and its concentration. "Polishing" is not a specification.
• The duty — continuous barrier or event response. GAC beds are regenerable (thermal reactivation); PAC is single-use.
• The contact conditions — flow, empty-bed contact time, temperature and competing dissolved species.
• The test method — iodine number per GB/T 7702.7, GB/T 12496.8 or ASTM D4607 are different methods; values are not directly interchangeable.
• The end-of-life route — replacement, off-site thermal reactivation, or disposal — fixed before the bed is sized.

Technical background: activated carbon in water treatment and capacity calculation in our knowledge center.