What type of filtration method uses the principle of adhesion to purify water?

Adsorptive filtration is based on the principle of adhesion, where contaminants in water adhere to the surface of the filtration media. This method utilizes materials such as activated carbon, which have a high surface area and porous structure, allowing for the capture of impurities, organic compounds, and some metals present in water.

In this context, the effectiveness of adsorptive filtration relies on the interaction between the contaminants and the adsorbent material. The contaminants cling to, or are absorbed by, the filter medium rather than simply passing through it. This is crucial for removing substances that are dissolved in water, which might not be effectively filtered out through methods that rely purely on size exclusion.

In contrast, the other filtration methods mentioned operate on different principles. For example, sand filtration relies on size exclusion where particles are trapped by the physical size of the sand grains, microfiltration and ultrafiltration use membranes with specific pore sizes to separate particles and microorganisms based on size, rather than adhesion. Thus, adsorptive filtration stands out specifically for its principle of adhesion, making it the correct answer to the question.