What is the typical hydraulic loading for activated carbon beds in gal/min per ft2?

• A. 0.5-1
• B. 20-30
• C. 2-10 gal/min/ft2
• D. 50-100

Answer: (C)

Hydraulic loading is the rate at which water moves through the activated carbon bed per unit area, expressed as gal/min per ft^2. For adsorption to work effectively, you need enough contact time for organics to diffuse to and bind with the carbon, but you also need to avoid pushing water so fast that it channels through preferential paths and wastes bed capacity.

The typical range of 2-10 gal/min per ft^2 provides that balance: low enough to maintain good contact and prevent premature breakthrough, and high enough to keep the process efficient and the headloss manageable. If you go much lower, the bed isn’t used efficiently; if you go much higher, channeling and reduced adsorption occur, degrading performance. This is why 2-10 gal/min/ft^2 is the best fit for common activated carbon beds.