Chlorine dioxide

Your Guide to Chlorine Dioxide (ClO₂)

Chlorine dioxide (ClO₂) is a yellowish-green, gaseous chemical compound with a strongly oxidising effect. Chemically speaking, chlorine dioxide is an unstable molecule that decomposes easily, particularly at higher temperatures or under the influence of light. For this reason, it is usually produced directly on-site in solution. The discovery of chlorine dioxide is generally attributed to Humphry Davy, who first obtained it in 1811 through the disproportionation (splitting) of chloric acid (HClO₃), making it the first known halogen oxide.

Chlorine Dioxide and Drinking Water Disinfection

Chlorine dioxide (ClO₂) is successfully used worldwide for drinking water disinfection. It acts as a powerful oxidising and disinfecting agent that reliably kills bacteria, viruses, fungi, parasites and some protozoa by destroying cell membranes and enzymes. Unlike chlorine, chlorine dioxide reacts more selectively with organic substances and does not form toxic organochlorine by-products such as trichloromethane or other trihalomethanes, which improves water quality.

ClO₂ is also effective at higher pH levels and in cool water, remaining stable over longer periods, allowing it to develop a lasting disinfection effect throughout the distribution network. It is frequently used in municipal waterworks, hospitals, hotels and the food industry. Since it decomposes easily, chlorine dioxide is usually generated on-site through a chemical reaction (e.g. from sodium chlorite and acid) and added to the water at controlled concentrations (typically < 0.4 mg/L).

The drinking water regulations set limit values to prevent health risks. It is interesting to note that these limits vary considerably across Europe. For this reason, they are also listed on our AQUARIUS pro life products CDSpure® and CDLpure®.

Conclusion

Overall, chlorine dioxide offers an efficient, low-odour and more environmentally friendly alternative to conventional chlorination, particularly where biofilms or Legionella bacteria need to be reliably eliminated.