Is all chlorine dioxide created equal?

Chlorine dioxide (ClO2) is often used as an alternative to chlorine for tre ating drinking water, Water utilities use ClO2 for preoxidation (e.g., for iron and manganese), to control tastes and odors, and to remove common path ogens. There are numerous technologies for generating ClO2. Utilities can c hoose the best generation process based on their regulatory and disinfectio n needs. Although each technology ultimately produces ClO2, the composition and purity of the final product can vary. Potential impurities include chl orine, chlorite ion, chlorate ion, acid, hydrogen peroxide, and, in some ca ses, perchlorate ion. Typically, the benefits of using oxidants such as ClO2 far outweigh the che mical risks. However, state and federal regulators are still concerned abou t the health effects of disinfection by-products in treated drinking water, including those that result from the use of ClO2. An understanding of the properties and reactions of ClO2 is the starting po int for maximizing ClO2 generation and minimizing unwanted by-products. Uti lities can use the information presented in this article to understand the extent of unused precursor chemicals and the formation of by-products relev ant to each ClO2 generation technology. Experimental data are also presente d to show similarities and potential differences in product composition.