What principle underlies carbon adsorption in water treatment?

The principle underlying carbon adsorption in water treatment is based on the adherence of contaminants to the surfaces of activated carbon. Activated carbon has a highly porous structure with a vast surface area, which allows it to attract and hold various organic and inorganic substances present in the water. This process is driven by physical interactions such as van der Waals forces and in some cases, chemical bonding.

During water treatment, when contaminated water comes into contact with activated carbon, the contaminants present in the water are drawn to the carbon's surfaces and become trapped, effectively removing them from the water. This mechanism is the core of adsorption, distinguishing it from other processes such as absorption, where a substance is taken up into the bulk of another material.

In contrast, the other options describe different mechanisms that are not applicable to carbon adsorption. For instance, the absorption of chemicals through membranes typically refers to a different filtration or separation process, while filtration by size exclusion pertains to removing particles based on size rather than through interaction with surface areas. Decomposition of pollutants by heat refers to thermal processes, which are not part of the adsorption process. Thus, the adherence of contaminants to activated carbon surfaces is the correct explanation for the principle underlying carbon adsorption.