Chlorine Dioxide (ClO2) is a powerful oxidising biocide and has been successfully used as a water treatment disinfectant for several decades in many countries. Rapid progress has been made in the technology for generation of the product and knowledge of its reactivity has increased with improved analytical techniques.
Chlorine dioxide is efficient against viruses, bacteria and protozoa clumps usually found in raw water. A rise in pH level further increases its action against f2 bacteriophages, amoebic clumps, polioviruses and enterovirus. It is efficient against Giardia and has an excellent biocidal effect against Cryptosporidium which are resistant to chlorine and chloromines. It has been demonstrated that ClO2 has greater persistence than chlorine. In a recent report, for dosages 3 times lower than those of chlorine at the station outlet, the residual of ClO2 used alone was always higher than that of Cl2, which also required 3 extra injections of chlorine in the distribution system.
The reduction of bad tastes and odour with ClO2 is the result of the elimination of algae and on the negligible formation of organo-chlorinated derivatives. The latter formed under chlorination gave rise to very unpleasant odours. By its action on dissolved organic materials, without the formation of organic halogen compounds, ClO2 limits problems of taste and colour. In addition, the low dosages used in post disinfection are an advantage. When chlorine dioxide replaces chlorine in a system it may take up to 15 days for the benefits of the change to become apparent. Changes should be made gradually to avoid problems of a sudden release of slime into the system.
Chlorine dioxide and chlorine, because of their fundamentally different chemistries, react in distinct ways with organic compounds, and as a result generate very different by-products. It’s this difference that explains the superior environmental performance of chlorine dioxide in a number of industrial applications. Chlorine and chlorine dioxide are oxidising agents – electron receivers. Chlorine has the capacity to take in two electrons, whereas chlorine dioxide can absorb five. This property, along with the complex but well-known ways chlorine combines with certain organic materials to form chlorinated organics that cause numerous environmental problems, explains the superiority of chlorine dioxide based products.
Why Chlorine Dioxide (ClO2)?
ClO2 offers a number of advantages over conventional biocides. Its broad spectrum and rapid reactivity allows it to be applied in many situations at lower dose rates with fewer environmental risks.
What advantages does ClO2 have over Chlorine?
- ClO2 is a more powerful oxidant. It is 2.6 times more powerful than chlorine for every part per million dosed.
- ClO2 acts only by oxidation. Chlorine will combine to produce harmful chlorinated by-products, e.g. chlorinated phenols. THM’s, dioxins etc. Many of these by-products are recognised carcinogens.
- ClO2 does not hydrolyse to form an acid and is therefore less corrosive in-situ.
- The properties of Chlorine are very pH dependent. Chlorine Dioxide is effective at all pHs below 12.
- ClO2 has been found to be effective against complex organisms, e.g. cysts and protozoa. Chlorine is not.
- Chlorine does not remove Biofilm. ClO2 does!
