Chlorine dioxide is used for a number of important purposes:
Chlorine dioxide, both in solution and in the gas phase, kills a broad range of pathogens, from viruses and bacteria to bacterial spores and encysted parasites to yeasts and fungi.
Chlorine dioxide, both in solution and in the gas phase, kills mold, including toxic molds such as Stachybotrus and Aspergillus.
Chlorine dioxide effectively penetrates biofilm, and kills the resident bacteria.
Chlorine dioxide effectively oxidizes many odor-causing compounds, especially mercaptans and sulfur compounds.
Chlorine dioxide oxidizes undesirable metals found in water—e.g., manganese, iron—and converts them from a soluble state to an insoluble state, which enables their removal by precipitation or filtering.
Chlorine dioxide effectively removes the color from many compounds, such as may be found in drinking water or wastewater.
Chlorine dioxide is used to pre-treat raw water, in order to destroy compounds that would react with chlorine in downstream processes; this reduces production of trihalomethanes (THM), haloacetic acids (HAA) and other chlorinated organic compounds.