Chlorine Dioxide

Sodium chlorite (NaClO2) is a precursor for the production of chlorine dioxide (ClO2), a chlorine compound with a high biocidal effect that is used exclusively in water purification and drinking water treatment. Chlorine dioxide is listed as an active substance in Art. 95 of EU Biocide Regulation 528/2012.

ClO2 has a short half-life once it is formed. Therefore, it is usually obtained in situ by mixing sodium chlorite, liquid or granulated, with a weak acid.

Properties of CLO2

Chlorine dioxide has been used for water treatment in public sewage treatment plants around the world since 1944. Due to its selective oxidising properties, its use is an alternative that should be considered if the organoleptic quality of the water is to be improved in addition to disinfection.

In addition, iron and manganese as well as other colouring and flavouring compounds can be removed(1).

Studies show that it is more effective than chlorine as a disinfectant against waterborne pathogens such as viruses, bacteria and protozoa under all circumstances (2).

On the other hand, unlike other products, chlorine dioxide is effective in a very wide pH range (4-10)(3)(5). Its oxidising power is better than that of chlorine, chloramine and iodine, and it is much better than ozone in already polluted water due to its effectiveness at low concentrations. In addition, due to its high solubility in water, it can act over a longer period of time, which is a great advantage over ozone, which evaporates immediately and requires constant application over a longer period of time (4).

One of the main advantages of using chlorine dioxide is that it reduces the formation of organic by-products harmful to people and the environment, such as trihalomethanes (THMs) and chloramines (4).

Chlorine dioxide in sufficient quantities is capable of oxidising phenolic compounds. (7): BPA (bisphenol-A) contamination from plastics causes damage to the body. The only functional group in BPA is two alcohols, which, if oxidised, could render BPA non-toxic. The mechanism of action of BPA has not yet been elucidated, therefore, its effect cannot be attributed to functional groups.

In addition, ClO2 does not react with ammonia or primary and secondary amines, which avoids increasing chlorine demand in distribution systems. (6)

  • Volatility: very volatile in gaseous state.
  • Solubility: one of its main characteristics is its high solubility in an aqueous medium, which is a great advantage over other substances such as ozone.
  • Liquefaction: becomes liquid at low temperatures, but may return to a gaseous state at 11°C.
  • Density: has a higher density than water and air.
  • Synthetic origin: cannot be found in nature. When mixed in aqueous solutions it can be dissipated by aeration processes, as it does not hydrolyse.
  • Colour: yellowish green.
  • Easily dissolves emulsions and hydrocarbons, so it can pass through bacterial layers.
  • Biofilm: ClO2 oxidises the polysaccharide matrix that binds the biofilm. The chlorine dioxide is converted into chloride ions, which in turn is split into parts of biofilm that remain stable. When the biofilm starts to develop again, an acidic environment is created which allows the new generation of chlorine dioxide and the complete removal of the remaining biofilm.

ADVANTAGES

  1. Obtaining high purity water, free of undesirable substances.
  2. More powerful than Chlorine in a short contact time.
  3. Higher oxidation power, which favours the elimination of odours, colours and flavours.
  4. It does not produce trihalomethanes (THMs) or chloramines.
  5. Unaffected by pH variations.
  6. Improves the elimination of iron and manganese.
  7. Controls the accumulation of silt in water reservoirs.
  8. It is capable of oxidising phenolic compounds.
  9. It is biodegradable.

DISADVANTAGES

  1. It is slightly more expensive than Chlorine.

*Effects of ClO2 on the treatment of drinking water(4)

Brief history of CLO2

Chlorine dioxide was discovered by Sir Humphrey Davy in 1814. At that time it was not very successful in industrial applications or in water treatment due to the difficulty of handling it.

In 1944 it was used for the first time in a large-scale drinking water station.

In 1955, its use became widespread in the USA for the treatment of drinking water.

It was stabilised 20 years ago in US laboratories.

Today, the use of Chlorine Dioxide continues to grow exponentially around the world, whether in water treatment and purification, odour control in wastewater, preservation of organic products or biofilm control.

On another level, ClO2 is used in industry and commerce, especially in the food sector, for cleaning and sanitising machinery and installations. Its persistence over time makes it completely effective in eliminating the biofilm present in these equipment and installations. In addition to all the properties described above, there is also a low corrosion rate in cast iron pipes.

Official recognitions of Chlorine Dioxide

Food & Drug Association E.E.U.U

It approves its use and recognises its biocidal action directed at micro-organisms, destroying their cell exchange wall and thus eliminating any bacterial, viral or fungal threat to human health.

Environmental Protection Agency E.E.U.U

Chlorine Dioxide is registered with the EPA under registration number 74986-1. It has passed the strict dis/tiss guidelines for use as a food contact surface disinfectant.

International Air Transport Association

In its guidance "General Guidance Material for Ramp Operations during COVID19", it recommends the use of chlorine dioxide in full water tanks in storage to prevent contamination of the water by micro-organisms.

U.S. Department of Agriculture

Approves Chlorine Dioxide and Sodium Chlorite for use in food processing plants for disinfection and control of bacteria and fungi.

European Union

ClO2 has been included in Article 95 of the EU Biocidal Products Regulation 528/2012.

Robert Koch Institut

It has been certified by the Robert Koch Institut, which means that it has a 99% effectiveness in the destruction of germs (effectiveness level A-D) associated with the disinfection of drinking water, general areas, human and animal consumption.

Official recognitions of Chlorine Dioxide

(1) Agencia de Protección del Medio Ambiente de los Estados Unidos (2020). Bienvenido a la base de datos de tratabilidad del agua potable. US.https://iaspub.epa.gov/tdb/pages/treatment/treatmentOverview.do?treatmentProcessId=-1277754943

(2) Ogata, N., & Shibata, T. (2008). Protective effect of low-concentration chlorine dioxide gas against influenza A virus infection. Journal of General Virology, 89(1), 60 67. doi:10.1099/vir.0.83393-0 .

(3) Chauret, C.P., Radziminski, C.Z., Lepuil, M., Creason, R., Andrews, R.C., 2001. Chlorine dioxide inactivation of Cryptosporidium parvum oocysts and bacterial spore indicators. Appl. Enviro. Microbiol. 67 (7), 2993–3001.

(4) Deininger RA, Ancheta A, Ziegler A. Chlorine dioxide disinfection. Regional symposium on water quality: effective disinfection. CEPIS/OPS. Lima. 1998; 1-14.

(5) Aieta, E. M., & Berg, J. D. (1986). A Review of Chlorine Dioxide in Drinking Water Treatment. Journal - American Water Works Association, 78(6), 62–72. doi:10.1002/j.1551-8833.1986.tb05766.x

(6) Francisco Ramírez Quirós (2005).Tratamiendo de Desinfección del Agua Potable. Water Treatment Department. Canal de Isabel II. Spain. https://www.fundacioncanal.com/canaleduca/wp-content/uploads/2015/08/Tratamiento-de-desinfeccion-del-agua-potable2.pdf

(7) Stevens, A. A. Reaction products of chlorine dioxide. Environ. Health Perspect. Vol. 46, 101–110 (1982)