What will most likely exhaust GAC first?

• A. Taste and odor compounds
• B. Organics
• C. Chlorine
• D. Polymers

Answer: (C)

The main idea is that a granular activated carbon bed has a limited adsorption capacity, and the component that interacts with the carbon most readily will use up those sites first. Free chlorine is small and highly reactive, so it is removed from water very quickly when it hits activated carbon—often by rapid adsorption followed by chemical reduction to chloride. That rapid reaction consumes the available active sites, meaning the bed becomes exhausted for chlorine before it finishes adsorbing larger or more slowly adsorbed substances.

Taste and odor compounds and organic molecules can also be removed by GAC, but they generally need more pore space and time to occupy the sites, so they tend to exhaust after chlorine. Polymers, being larger, are even less likely to be adsorbed quickly and are not the first to exhaust the bed.