Adsorption

Dissolved organic compounds in water (e.g., atrazine, an herbicide, and industrial waste products) can pose a significant health threat, and may affect the taste and odor of drinking water. To remove them, the process of adsorption is used. Adsorption is a process in which one substance is attached to the surface of another substance (Figure 8). Powdered activated carbon (PAC), a finely ground charcoal, is used for this process. When PAC is added to the water, the organic compounds attach to the surface of the powder granules. The granules of PAC have irregularly shaped surfaces, which gives PAC a very large surface area to attract organic compounds. It is estimated that 1 pound of PAC has a surface area of 100 acres! The carbon can then be removed by filtration, taking the unwanted organic compounds with it.

Figure 8 This figure shows the irregular surface area of powdered activated carbon (PAC). Organic molecules, such as the dioxin (a toxic byproduct of chemical bleaching and a precursur to powerful pesticides) shown here, adhere to the surface of the PAC granules. When the PAC is removed by filtration, the adsorbed organic molecules are removed with the carbon.