Chlorine Dioxide Disadvantages

Chlorine dioxide can kill a wide variety of microorganisms, but it also has disadvantages.

Chlorine dioxide (ClO2) belongs to a class of compounds called free radicals, which means that it has an unpaired electron, but no net charge. By acquiring a single electron, it can become the chlorite ion, (ClO2-), so it tends to react by taking electrons from other reactants. This chemical serves as a highly effective water disinfectant, but it also has a number of disadvantages.

Production

Chlorine dioxide is explosive under pressure, so it can neither be stored nor shipped. Consequently, if you want to use this chemical, you must make it on-site. Typically, chlorine dioxide production involves combining sodium chlorite with chlorine gas, or reacting sodium chlorite with hydrochloric acid. These processes require technical know-how, expensive equipment and the use of toxic or dangerous chemicals.

Byproducts

Using chlorine dioxide to disinfect water generates chlorite, chloride and chlorate, with chlorite as the main byproduct. According to the EPA, total concentration of chlorine dioxide, chlorate and chlorite in the final product should not exceed 1 mg per liter. Also, excess levels of chlorine dioxide can cause taste and odor problems for consumers, so it's necessary to monitor the amount of ClO2 in drinking water carefully.

Reactivity

Chlorine dioxide is a very reactive compound, which is one of the reasons it's such a good disinfectant. However, its reactivity also makes it dangerous to produce and handle. At higher concentrations, it can react violently with chemicals that give away electrons (i.e., reducing agents), or it can decompose violently, releasing a substantial amount of energy. In addition, concentrated aqueous ClO2 solutions may release hazardous levels of gaseous ClO2.

Processing

Unlike chlorine, ClO2 does not react with organic matter to generate hazardous compounds called trihalomethanes. Although chlorine dioxide is highly effective at destroying most waterborne pathogens, however, it is less effective at deactivating rotaviruses and E. coli. Moreover, it does not remove minerals, salts and other kinds of contaminants, so wastewater will always require further treatment steps in addition to chlorine dioxide disinfection.

References

• EPA: Chlorine Dioxide
• Virginia Tech Civil Engineering Department: Water Disinfection With Chlorine Dioxide
• Lenntech: Disinfectants - Chlorine Dioxide