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 • It has a molecular weight of 67.45.
- It is a gas at normal temperatures and pressures.
- It has a melting point of -59oC.
- It has a boiling point of 11oC.
- It is yellowish/green and has an odour similar to that of Chlorine.
- It is denser than air and is water soluble at standard temperatures and pressures up to 5000ppm.
- It is explosive in air at concentrations > 10%
- It is prohibited from road and sea transport in its “free” form, and is normally generated at the point of application using 2 precursor chemicals.
- It will decompose in the presence of UV, high temperatures, and high alkalinity (>pH12)
How does ClO2 work?
ClO2 is an oxidizing biocide. It deactivates micro organisms by attacking and penetrating their cell wall, disrupting the transport of nutrients across the cell wall and inhibiting protein synthesis. Since this action occurs regardless of the metabolic state of the organism, oxidizing biocides are effective against dormant organisms and spores (Giardia Cysts and Poliovirus) also.
Is CDD 5000/CDL 7500 the same as Chlorine or Hypochlorite?
Although they have similar names and elements they are very dissimilar. The commonality of the name arises from the fact that they all contain the element chlorine, but their properties are quite different. Chlorine and Hypochlorite are very powerful oxidizing agents but more importantly their reaction with organic matter can lead to unacceptable concentrations of chlorinated organic compounds via substitution reactions. Some of these compounds such as the by-products of reactions with phenolic compounds are either odoriferous (such as 2, 6-dichlorophenol) or extremely carcinogenic like dioxin. Chlorine Dioxide on the other hand is incapable of causing such chemical transformations. Chlorine Dioxide is non-mutagenic, non-carcinogenic and relatively non-irritating unlike Chlorine and Hypochlorite.
Why Microorganisms are Unable to buildup resistance to ClO2?
When the cell wall is penetrated by chlorine dioxide, Organic substances within cells and on the surface of cell membranes react with chlorine dioxide, causing cell metabolism to be disrupted. Chlorine dioxide also reacts directly with amino acids and the RNA in the cell. This reaction is not dependent on reaction time or concentration. Unlike non-oxidizing disinfectants, chlorine dioxide kills microorganisms even when they are inactive. Microorganisms are unable to build up resistance to chlorine dioxide, in practical terms.
How can ClO2 remove Biofilm?
Many biocides have particular problems in penetrating this biofilm, due to the polysaccharide “glue” that is secreted by the bacteria to hold the biofilm together. Unlike most biocides, chlorine dioxide can effectively penetrate biofilm to provide complete protection. Chlorine dioxide kills viruses by preventing protein formation. ClO2 reacts with peptone, a water-soluble substance that originates from hydrolysis of proteins to amino acids.
What are Disinfection By-Products of ClO2?
The DBPs of chlorine dioxide reactions are chlorite (ClO2-) and chlorate (ClO3-), and eventually chloride (Cl-). The fate of any disinfection by-products depends largely on the conditions at the time, such as concentration, temperature and the presence of other molecules.
Unlike ozone (O3), chlorine dioxide does not oxidise bromide (Br-) ions into bromate ions (BrO3-). Additionally, chlorine dioxide does not produce large amounts of aldehydes, ketones, or other disinfection by-products that originate from the ozonisation of organic substances.
Is ClO2 pH dependant ?
Because chlorine dioxide is a dissolved gas, it does not ionise to form weak acids (as chlorine and bromine do) in aqueous solutions. This allows ClO2 to be effective over a wide pH range from Acidic to Alkaline (4-10).
Is there free chlorine in CDD 5000/CDL 7500?
No, there is no free Chlorine in CDD 5000/CDL 7500. Although Chlorine Dioxide has the word Chlorine in its name but two chemicals have completely different chemical structures of its revolutionary formula. The additional oxygen atom radically changes the molecule and creates completely different chemical behaviours and by-products. Their differences are as profound as those between hydrogen, the explosive gas, and hydrogen combined with oxygen, which creates di-hydrogen oxide – commonly called water.
Can I use CDD 5000/CDL 7500 in hospitals and healthcare facilities?
Because of its biocidal characteristics, ClO2 is ideal for water hygiene applications in hospitals and healthcare facilities. It has consistently been shown to be the best molecule for eradicating the causative organism of Legionnaires’ disease. In the UK, the Building Services Research and Information Association (BSRIA) has recommended chlorine dioxide as the best available technology for control of Legionella in hot and cold water systems.
Can I use CDD 5000/CDL 7500 for waste-water treatment?
Chlorine dioxide safely oxidises phenols, cyanides, aldehydes, and mercaptans, reduced sulphur compounds and some pesticides. It is useful in both waste-water treatment and scrubber systems. Chlorine dioxide is an eco-friendly oxidant that is preferred by many regulating water utilities and supply authorities for final discharge disinfection.
Can I use CDD 5000/CDL 7500 for ultrapure water treatment?
YES. Ultrapure water is used to process pharmaceuticals and WFI, to rinse silicon microchips, and to feed high-pressure boilers and turbines in power plants and chemical processing installations. Ultra-pure water delivered at the process level must have between 99.9% and 99.99% of typical fresh water impurities removed. In addition to other contaminants, process-piping systems must be free of bacteria and biofilm.
If Chlorine Dioxide is only an Oxidising agent, why not use Peroxide or Ozone?
Why not indeed! Ozone is a very powerful oxidizing agent. In acidic environments its oxidizing power is only exceeded by fluorine, which dissolve’s glass! Ozone will react with most substances at 25° C, but accidental skin or eye contact would lead to immediate, irreparable tissue damage. It only has a half-life of 2 minutes so must be produced where you want to use it and cannot be stored. It is generally manufactured as a dilute water solution, on-site, but there is a high production cost. Hydrogen Peroxide on the other hand is very stable, if correctly handled. Contact with even trace amounts of metal ions (Mn+2, Fe+2) can cause rapid, explosive decomposition. Dilution with anything other than distilled or de-ionised water will lead to unstable solutions. Contact with any metal other than passive stainless 316L will also cause decomposition. It is a powerful oxidising agent and accidental contact would again result in immediate, irreparable tissue damage. Chlorine Dioxide is nowhere near as powerful oxidising agent, but is sufficiently strong to act as a biocide. It is safe for all uses and contact with skin will cause no damage. It is used as a mouthwash and pet deodoriser. For the extremely chemically minded, the oxidation potential of chlorine dioxide is only 0.954 EoV, compared with acidic ozone 2.07, Hydrogen Peroxide 1.77, Hypochlorite 1.48 and Chlorine 1.36.
Why can Chlorine Dioxide be used at lower concentrations than Peroxide or hypochlorite even though they are more powerful?
Peroxide and Hypochlorite are more powerful and that is their problem. They are unselective and easily consumed by all manner of materials present in the environment As a result; large quantities must be used to ensure there is a sufficient residue to act as a biocide. Chlorine Dioxide is a relatively weak oxidising agent. It only reacts with some sulphur compounds; selected amines and other reduced organic compounds. As a result, low levels can be used to eliminate microorganisms, as it is not consumed attacking non-target compounds.
Is Chlorine Dioxide Safe and Environmentally Friendly?
Yes. There are many reasons why Chlorine Dioxide is safe and friendly. Environmentally, the by products formed when using Chlorine Dioxide are benign. Compare this to chlorinated by products formed when using Chlorine or Hypochlorite and you can see why so many Pulp and Paper Mills use Chlorine Dioxide. They have virtually eliminated trichloromethanes, chloroacetic acids, chlorinated dioxins and furans from their waste streams, all of which used to pose significant risks in the environment. In its reaction, Chlorine Dioxide oxidizes (removes electrons) other compounds and is itself reduced (gains electrons) to the Chlorite anion (CLO2). Toxicological studies have shown the Chlorine Dioxide and its disinfection by-product, Chlorite, pose no significant risk to human, animal or fish health. Chlorine Dioxide was first introduced for drinking water disinfection in 1944 at the Niagara Falls. Today over 1000 municipal water treatment processes use Chlorine Dioxide.
How Does Chlorine Dioxide react when it oxidises?
The predominant oxidation reaction mechanism for chlorine dioxide (and for ozone as well) proceeds through a process known as free radical electrophilic (i.e.: electron-attracting) abstraction rather than by oxidative substitution or addition (as in chlorinating agents such as chlorine or hypochlorite). It has this ability due to unique one-electron exchange mechanisms. One electron is transferred and chlorine dioxide is reduced to chlorite (ClO2-).The term “oxidation strength” is used to describe how strongly an oxidizer reacts with an oxidizable substance. Ozone is generally regarded as having the highest oxidation strength and reacts with every substance that can be oxidized. In practical terms, this is often undesirable since a number of side reactions can take place causing undesirable disinfection byproducts.Chlorine dioxide has a lower oxidation strength than ozone, but is more powerful than chlorine. Less chlorine dioxide is normally required to obtain an active residual disinfectant. Unlike ozone, ClO2 can also be used when a large amount of organic matter is present.For more information on the specific reaction of chlorine dioxide with a number of compounds, click here