Chlorine dioxide, ClO2, is a manufactured gas that does not naturally occur in the environment. ClO2 is a highly soluble gas that does not hydrolyse immediately on contact with water and will remain as a dissolved gas for a relatively long time, eventually dissociating into Cl2 and O2.
Chlorine dioxide is a highly volatile but effective biocide that is widely used as disinfectant. Due to its volatility, it is particularly popular as a secondary disinfectant in short networks. It is especially effective against biofilms and bacteria such as Legionella.
Chlorine dioxide remains almost unchanged between pH 6-10, meaning it remains a highly effective disinfectant across a wide pH range. It can be used with short contact times and at relatively low dosages. Therefore disinfection control is important to ensure that chlorine dioxide is not being overdosed.
Chlorine dioxide does not form disinfection by-products (DBP) in the same way as chlorine, and trihalomethane (THM) production tends to be significantly lower. The major inorganic by-product of the reaction of chlorine dioxide in water is chlorite, which may be of concern in some applications.
As chlorine dioxide is highly reactive, it is often generated in situ rather than being transported in solution, which can be challenging for some applications.
Chlorine dioxide is regularly used in drinking water treatment. Sometimes as a pre-treatment for metal removal from the raw water entering a treatment plant, but more commonly at the end of the distribution network to control specific issues such as pseudomonas and Legionella.
Dosing control is critical in drinking water to ensure that the water has been effectively ‘cleaned’ but is not overdosed, posing potential danger, as well as affecting the taste of the final product.
The use of chlorine dioxide is increasingly common in food and beverage production due to its high efficacy and limited DBP formation potential. Particularly of interest in fresh produce production and the pre-treatment of raw water to be used in manufacturing bottled water.
To find out more about how chlorine dioxide is used in breweries, read our case study.
The use of chlorine dioxide is widespread in cooling waters with open systems where controlling legionella is highly important. It is particularly effective against biofilms, which more traditional disinfectants are less effective.
Other key tests for cooling waters include pH, calcium hardness, TDS and alkalinity.
Palintest offer two digital test methods for measuring chlorine dioxide: photometers and Kemio technology.
Kemio uses single use disposable sensors to generate rapid and reliable results for both chlorine dioxide and chlorite. Suitable for all sample types, Kemio can be used on samples which are turbid or discoloured.
Chlorine dioxide is an effective disinfectant that removes pathogens, but also minimizes the production of disinfection by-products (DBPs).
A potential issue for chlorine dioxide is the formation of the DBP chlorate and chlorite. However, there are methods of chlorine dioxide generation that seek to minimise these DBP. Kemio Technology measures chlorine dioxide, free chlorine and chlorite.