OVERVIEW

Adsorption of a substance involves its accumulation at the interface between two phases, such as a liquid and a solid or a gas and a solid. The molecule that accumulates, or adsorbs, at the interface is called an adsorbate, and the solid on which adsorption occurs is the adsorbent. Adsorbents of interest in water treatment include activated carbon; ion exchange resins; adsorbent resins; metal oxides, hydroxides, and carbonates; activated alumina; clays; and other solids that are suspended in or in contact with water.

Adsorption plays an important role in the improvement of water quality. Activated carbon, for example, can be used to adsorb specific organic molecules that cause taste and odor, mutagenicity, and toxicity, as well as natural organic matter (NOM) that causes color and that can react with chlorine to form disinfection byproducts (DBPs). NOM is a complex mixture of compounds such as fulvic and humic acids, hydrophilic acids, and carbohydrates. The aluminum hydroxide and ferric hydroxide solids that form during coagulation will also adsorb NOM. Adsorption of NOM on anion exchange resins may reduce their capacity for anions (see Chapter 9), but ion exchange resins and adsorbent resins are available that can be used for efficient removal of selected organic compounds. Calcium carbonate and magnesium hydroxide...