Chlorine Dioxide is becoming an increasingly popular choice for biocidal applications in industries around the world.

Although lower chemical costs and better generation equipment have increased its market profile significantly over recent years, the core chemistry is well established and far from new.

Here we cover what is ClO2, key facts about the chemical, and its development and use over time as a powerful disinfectant.


What is Chlorine Dioxide?

Chlorine Dioxide is a small, volatile and very strong molecule consisting of 1 Chlorine atom and 2 oxygen atoms.

Abbreviated to ClO2, Chlorine Dioxide exists as a free radical in dilute solutions

  • Molecular weight of 67.45.
  • It is a gas at normal temperatures and pressures.
  • Melting point of -59oC.
  • Boiling point of 11oC.
  • Yellowish/green colour and has an odour similar to that of Chlorine.
  • Denser than air and is water soluble at standard temperatures and pressures up to 2500ppm.
  • Explosive in air at concentrations >10%. It is therefore normally generated in-situ within an aqueous solution at <0.2%
  • Some pre-mixed solutions are sold on the market at concentrations of 0.6%, however these are hazardous to transport and costly. Most ClO2 is applied using on site dosing and generation equipment from companies like Scotmas.
  • It will decompose in the presence of UV, high temperatures >70oC, and high alkalinity (>pH12).

Chlorine Dioxide Timeline



First discovered by Sir Humphrey Davey


First commercial application. Used as a biocide/taste and odour control agent in domestic water at Niagara Falls in the USA.


Three thousand municipal water systems achieving biological control using Chlorine Dioxide.


Chlorine Dioxide gradually replacing Chlorine in many industries.

  • Pulp and Paper industry – used as a bleaching agent.
  • Industrial water treatment – used as a biocide and as an odour control agent.
  • Food processing – used as a sanitiser.


Increasingly used for the secondary disinfection of potable water.


New generation equipment and control technology introduces ClO2 as a practical alternative to many industrial applications.

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