Chlorine Dioxide

Chlorine dioxide is highly effective when used to control:

  • Bacterial spores
  • Legionella (Legionnaires' disease)
  • Biofilm
  • Tuberculosis
  • Salmonella
  • Cryptosporidium
  • Giardia cysts
  • Coliforms
  • MRSA
  • VRE
  • Listeria
  • Shigella
  • Algae
  • Amoebae
  • Taste and odour
  • THM/HMM formation
  • Planktonic and sessile organisms

Chlorine Dioxide

Chlorine dioxide exists as a gas at normal temperatures and pressures and has the chemical formula ClO2. It is a highly effective, eco-friendly microbiocide that carries a number of important regulatory approvals from several international organizations including the US EPA, FDA and UK Government for many of its uses. For more useful information about chlorine dioxide please review the FAQ area of our website.

Chlorine dioxide is a strong bactericide and virucide at concentrations as low as 0.1 ppm. It will eliminate both planktonic and sessile bacteria; disinfect surfaces; and rapidly destroy problematic biofilm. With minimal contact time, it is highly effective against many pathogenic organisms including bacterial spores, Legionella, Tuberculosis, MRSA, VRE, Listeria, Salmonella, amoebal cysts, Giardia cysts, E. coli, and Cryptosporidium. Importantly, chlorine dioxide also destroys biofilm so bacterial re-growth is significantly impeded.

Chlorine dioxide has long been recognized as a very effective biocide and sterilizing agent for both large and small scale industrial and commercial applications. It is approved and recommended by the United States Environmental Protection Agency (US EPA) as an environmentally friendly drinking water additive to replace chlorine (which is known to form carcinogenic by-products).

The criteria for disinfection, as defined by the US EPA, are as follows:
a 99.9% reduction in giardia lamblia (3 log reduction).
zero lactose fermenting coliform.
less than 10 cfu/ml non-lactose fermenting coliforms.
99.99% reduction in enteric virus (4 log) concentrations.

Chlorine dioxide meets these criteria and is now used extensively across the US, UK and Europe. In the UK, the Building Services Research and Information Association (BSRIA) has recommended chlorine dioxide as the best available technology for the control of Legionella bacteria in hot and cold water systems.

Microbial infection is responsible for thousands of deaths and many more illnesses across the world each year. Frequent outbreaks of disease have been linked to food handling and processing (Listeria, Salmonella, Shigella, and E. Coli), drinking water (Giardia, Cryptosporidium) and hotels, cruise ships (Noro virus), hospitals and office buildings (MRSA, Legionella). The incidence of Legionellosis is frequently misdiagnosed as common pneumonia. This under-reporting of Legionella has recently come to light as more and more international health organisations recognize the need for control plans against this potentially deadly disease.

Chlorine dioxide is shown to be an effective disinfectant at residual concentrations between 0.2 and 0.8 ppm. Chlorine dioxide acts to penetrate the cell wall of microorganisms and disrupts metabolic function. This is more efficient than other oxidisers that just “burn” the surface of whatever they come in contact with. This allows for lower effective concentrations of Chlorine dioxide to be used when compared to other oxidiser products.

Chlorine dioxide, like ozone, is a dissolved gas that penetrates biofilm by molecular diffusion. However, unlike ozone, Chlorine dioxide is stable and soluble, allowing it to travel to the base of the film where it attacks microorganisms and destroys the biofilm at its point of attachment. Other oxidisers react mostly on the surface of the biofilm to form an oxidised layer, like charring on wood. This precludes further penetration. No other biocide has proved to control biofilm better than Chlorine dioxide.

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 chlorine dioxide to be effective over a wide pH range. For example, the pH dependent speciation of chlorine produces hypochlorite ion and hypochlorous acid (HOCl). Hypochlorite is only 1/30 to 1/200 as effective as HOCl. Chlorine dioxide being a neutral species with rapid disinfection kinetics, is 100% available for disinfection in hard or soft water.

Chlorine and bromine react rapidly with microbiological species and chemicals in water. This reactivity is both their strength and weakness. Rapid reaction with microbiological species means a quick and effective kill; rapid reaction with chemicals such as scale and corrosion inhibitors in cooling towers means consumption of the product for other than microbiological control. Since chemical reactions are usually the first to take place, only the small residual of the product remaining after the chemical reaction is completed is available for microbiological control.

Chlorine and bromine have other limitations in addition to low residual “killing power”. They exhibit poor biofilm control. They do not retain their biocidal efficiency over wide pH ranges. They are also relatively unstable. Chlorine has the potential to damage the environment and create health hazards when it combines with naturally occurring organic materials such as organic acids from leaves, to form trihalomethanes (THMs) which are suspected carcinogens. When chlorine and bromine react with chemicals such as ammonia, nitrogen, and corrosion and scale inhibitors in cooling tower water they form objectionable by-products while reducing their effectivity (HAAs).

In summary, chlorine dioxide is a very safe and potent biocide. It is effective over a wide pH range in both hard and soft water and does not react with most other water treatment chemicals. Many of its uses are US and UK Government approved and highly recommended by many researchers.