An Effective Biocide

The property of chlorine dioxide to react by oxidation rather than substitution makes it a useful alternative to chlorine in drinking water disinfection
applications where the formation of potentially carcinogenic halogenated disinfection byproducts, such as trihalomethanes (THM's) and halogenated acidic acids (HAA's), is of concern.
 
Additionally, chlorine dioxide does not produce significant amounts of aldehydes, ketons, keton acids, or other disinfection byproducts that originate from
ozonation of water containing organic substances.
 
The reaction of ClO2 with microorganisms or other oxidizable substances takes place in two steps. In the first stage of the reaction, the ClO2 molecule accepts 
an electron and chlorite ion is formed (ClO2-). In the second stage, ClO2 accepts 4 electrons and chloride ion (Cl-) is formed.

The mechanism of action by which chlorine dioxide inactivates microorganisms is not entirely well understood. As a general matter, however,
it is known that chlorine dioxide destroys microbes by attacking their cell walls (or viral envelopes) and interfering with essential protein formation.
It is also known that chlorine dioxide is more effective against viruses than either chlorine or ozone. Furthermore, chlorine dioxide is known to be effective
against hearty waterborne protozoans such as Giardia Lambia and Cryptosporidium, the causative agents of giardiasis and cryptosporidiosis, respectively.
Since chlorine dioxide is an oxidative biocide, microorganisms cannot build up a resistance to it.

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