Chlorine Dioxide (ClO2)
What is ClO2?
Chlorine dioxide (ClO2) is a powerful yet selective oxidizing agent. It is a greenish yellow gas at room temperature that is very soluble in water.
Because ClO2 always exists as a true gas under standard conditions of temperature and pressure, whether in open air or dissolved in solution, its antimicrobial properties can be harnessed for either liquid or gaseous application. The "free radical" property of ClO2 makes it particularly useful for addressing structural microbial contamination problems. Liquid ClO2 solution can be applied directly to known areas of microbial contamination, or entire contaminated structures can be fumigated with the gas by simply stripping it back out of solution at the point of application. Once applied, ClO2 quickly decays on its own to invisible, harmless concentrations of various sodium salts including chlorite, chlorate, and chloride ion.
An Effective Biocide
The propensity of ClO2 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 triholomethanes and halogenated acidic acids, is of concern. Additionally, ClO2 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 ClO2 inactivates microorganisms is not entirely well understood. As a general matter, however, it is known that ClO2 destroys microbes by attacking their cell walls (or viral envelopes) and interfering with essential protein formation. It is also known that ClO2 is more effective against viruses than either chlorine or ozone. Furthermore, ClO2 is known to be effective against hearty waterborne protozoans such as Giardia Lambia and Cryptosporidium, the causative agents of giardiasis and cryptosporidiosis, respectively. Since ClO2 is an oxidative biocide, microorganisms cannot build up a resistance to it.
Unlike chlorine, chlorine dioxide is not a chlorinating agent and pure chlorine dioxide does not form trihalomethanes (THMs), an environmental pollutant that is considered carcinogenic. ClO2 does not chlorinate organics. It also doesn't react with water to form free chlorine or react with ammonia to form chloramine. Additionally, ClO2 is soluble in water and has efficacy across a broad pH range.
One of the most important properties of ClO2 that sets it apart from chlorine is its behavior when placed in water. Not only is ClO2 10 times more soluble in water than chlorine (3.01 grams/Liter at 25 degrees C), it doesn't hydrolyze when placed in solution. It remains as a "true" dissolved gas that retains its useful oxidative and biocidal properties throughout the entire 2 to 10 pH range.
By way of contrast, chlorine dissociates when placed in water to form hypochlorous and hydrochloric acids. Hypochlorous acid is the primary biocide in solution, which dissociates to form hypochlorite ion with increasing pH. Hypochlorite ion is only from 1/20 to 1/300 as effective in controlling microbes as hypochlorous acid. Thus, chlorine can only be an effective biocide in systems with low pH.
The high degree of solubility exhibited by ClO2 in water has also been observed in a variety of organic materials, such as oils and solvents, thereby allowing for utilization of its unique oxidative and biocidal properties in a wide range of potential applications.
High purity ClO2 has a number of physical and chemical properties that make it the ideal product for addressing liquid, surface and/or airborne microbial contamination in a safe and effective manner.
Among the properties that make ClO2 the agent of choice for addressing microbial contamination are the following:
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