Chlorine dioxide disinfection

This article discusses the application of chlorine dioxide preparation systems as a disinfection agent in the sectors of drinking water, bottle disinfection and power stations.

In the sectors of drinking water, power station water treatment or in the CIP plants of the food and beverages industry (for example bottle cleaning) a disinfection agent has to meet the following demands:

• Easy generation;
• Safe monitoring and control of the concentration;
• Safe automatic post-dosing;
• Broad spectrum of effectiveness (bacteria, yeasts, spores, viruses);
• Easy rinsing out;
• Low pollution;
• Cost saving.

When the disinfection agent is used in waterworks or power stations, the protection of the network of pipes is important. In these situations it has to provide a long-term stable disinfection effect and a low corrosion of metals.

Chlorine dioxide cannot be stored for chemical and physical reasons. Therefore, it is necessary to generate it on site, such as in the waterworks or power station. The Alldos preparation systems work according to the hydrochloric acid/sodium chlorite process (Oxiperm 166) or they generate the decontamination agent by using sodium chlorite and chlorine (Oxiperm 164).

There are a number of advantages to disinfection with chlorine dioxide. Especially in the case of drinking water, it is essential to use a chemical that poses no risk to health.

Chlorine dioxide suppresses the formation of the volatile haloforms and also reduces the generation of hardly or non-volatile organic halogen compounds. The volatile haloforms such as chloroform are primarily suspected of being harmful to health - some even carcinogenic - and to a lesser extent dichlorobromomethane, chlorodibromomethane and bromoforme.

Unlike chlorine, chlorine dioxide does not form any chlorophenoles that affect taste and smell. It also does not react with ammonium or with amino compounds. Low concentrations of chlorine dioxide are applied as chlorine, as it disinfects faster. Its effect is due to its permanency in water and its reliability in extensive networks of pipes.

The disinfection effect of inorganic agents such as chlorine dioxide depends on their redox potential. A high redox potential is decisive for effective decontamination. Chlorine dioxide is used for the oxidation treatment of water, for deodorising, fighting of algae and mucus, reduction of CSB/BSB and AOX due to its high redox potential.

The highly reactive chlorine dioxide has an oxidation capacity of more than 100 to 250% compared with chlorine.

Destruction of chloramines by oxidation means no irritation of eyes, no special smell and a pleasant ambient climate (chloramines lead to irritations of the mucous membranes, especially those of the eyes).

There is no reaction with ammonia or ammonium ions:

• Strong algicide effect of chlorine dioxide means no necessity to use organic biocides.
• The disinfecting effect is not depending on the pH in the pH range from 6 to 10. Positive effect on the skin by oxygen transfer (no degreasing, no smell).
• Destruction of dirt and microbacteria deposits at the basin or in the pipes.
• Chlorine dioxide has outstanding bactericide and bacteriostatic characteristics.
• The germicide as well as the sporicide and the virucide effect of chlorine dioxide is outstanding.

Chlorine dioxide also has a number of economic advantages as it is a very cheap disinfection agent. Thanks to the destruction by oxidation of the bonded chlorine and the reduction of the THM contents, less fresh water has to be added (usually the back-rinsing per time unit is divided by two). The consumption of water and energy is reduced to a considerable extent.

Chlorine dioxide is a cost-effective disinfection alternative. It can be integrated into process systems technologically as it can be automatically measured and controlled. In the sectors of disinfection and in the water and wastewater fields, big savings are possible, while at the same time increasing the operating safety and protection of the environment.