How can activated carbon remove some dissolved substances from water?

Water can look clear while containing dissolved molecules. Activated carbon can remove some of them because its many tiny pores provide a large internal surface. Suitable molecules attach to that surface as water passes through the material.

This process is adsorption. It differs from catching a large grain in a small opening: the target can be dissolved and much smaller than the channel carrying water. Interactions between the molecule, carbon and water determine how strongly attachment occurs.

Different substances attach with different strengths. Other dissolved molecules may compete for the same useful sites. Eventually a carbon bed can no longer keep removing a target effectively, even though water still flows through it.

A treatment system therefore needs appropriate carbon, sufficient contact time and monitoring. Spent carbon must be replaced or regenerated. Its value comes from a specific surface interaction within a managed process, rather than from an ability to remove every kind of contamination.