Why Chlorine Dioxide?

For many years, Chlorine has been the most commonly used chemical for water treatment due to its ability to effectively kill bacteria and viruses.

However, ClO₂ (Chlorine dioxide) has emerged as a popular alternative in recent years due to its unique and superior properties.

Chlorine dioxide is a powerful and efficient oxidising agent that can effectively eliminate waterborne pathogens, including viruses, bacteria, and parasites, without producing harmful by-products such as trihalomethanes (THMs) and haloacetic acids (HAAs).

Our team has conducted extensive research and compiled a list of some of the significant benefits of ClO₂, which make it a better option for water treatment needs.

Higher yield & greater cost efficiencies

Chlorine Dioxide has a higher oxidation capacity, and a lower oxidation strength than most species of chlorine, making it at least 2.6 times more powerful per ppm according to WHO CT values.

No carcinogenic by-products & no bad taste occurrences in water

Chlorine Dioxide acts only by oxidation and does not combine with organic compounds to form environmentally hazardous by-products such as Trihalomethane and other chlorinated organic compounds that have been listed as potentially carcinogenic.

Less corrosive

Chlorine Dioxide has a lower oxidation potential and does not hydrolyse to form an acid, and therefore is less corrosive.

Works over a wide pH

The effectiveness of chlorine is very pH dependent, and is almost ineffective above pH8. Chlorine Dioxide is effective at all pH’s below 12.

Overall, ClO₂ offers a safer and more effective solution for water treatment needs and is an excellent choice for those who prioritise safety and efficiency.

Oxidising biocides such as ozone, hydrogen peroxide and peracetic acid are known for their instability and difficulty in safely handling and applying.

Chlorine Dioxide belongs to the same family of biocides as the oxidising biocides, sharing more in common with them than its “chlorine” namesake.

Chlorine Dioxide has several advantages over other oxidising biocides, making it more suitable for many water treatment applications.

When compared with other oxidising biocides, Chlorine Dioxide has a significantly lower oxidation strength – this means that it reacts with fewer compounds, such as organic compounds and ammonia, yet is strong enough to attack the disulphide bonds found in the membranes of bacteria and other biological material.

This “selective oxidation” process allows the Chlorine Dioxide biocide to be targeted where it is needed most, disinfecting areas quickly and at lower dose rates, leading to greater cost efficiencies.

As an example, where Hydrogen Peroxide-based products have been promoted for use in water treatment, this is often at dose rates 10-30 times greater than ClO₂, leading to difficulties in handling peroxide-based products >15% that are now listed as “Explosives Precursors” under EU Regulations.

Due to its radical structure, Chlorine Dioxide has a particular reactivity – different from chlorine or ozone.

The electrophilic nature of chlorine or hypochlorous acid can lead, through reaction of addition or substitution, to the formation of organic species while the radical reactivity of chlorine dioxide mainly results in oxycarbonyls.

Generally, Chlorine Dioxide (ClO₂) rapidly oxidises phenol-type compounds, secondary and tertiary amines, organic sulphides and certain hydrocarbon polycyclic aromatics such as benzopyrene, anthracene and benzoathracene.

In general, Chlorine Dioxide will not react on double carbon bonds, aromatic cores, quinionic and carboxylic structures, primary amines, and urea.

Commercial applications have shown that Chlorine Dioxide can effectively oxidise many compounds considered waste and water pollutants.

The table below lists a selection of pollutants found in various industries from our files and demonstrates the wide range of possible applications for Chlorine Dioxide. Scotmas possesses over 25 years of application expertise in chlorine dioxide technology in challenging applications.

The oxidising properties and the radical nature of Chlorine Dioxide make it an excellent virucidal and bactericidal agent in a large pH range.

In alkaline media the permeability of living cell walls to gaseous chlorine dioxide radicals seems to be increased allowing an easier access to vital molecules.

The reaction of chlorine dioxide with vital amino acids is one of the dominant processes of its action on bacteria and viruses.

Compounds within the cells and on the surface of cell membranes that contain oxidisable material react with chlorine dioxide, causing cell metabolism to be disrupted. Chlorine dioxide also reacts directly with disulphide bonds in the amino acids and the RNA in the cell.

Unlike non-oxidizing disinfectants, chlorine dioxide kills microorganisms even when they are inactive. The oxidative load placed on the cells by the action of chlorine dioxide mean that most microorganisms are unable to build up resistance to chlorine dioxide.

Environmental safety is a key advantage of chlorine dioxide when comparing with alternative biocides such as chlorine.

Unlike chlorine, ClO₂ will react to form mainly inorganic disinfection by products, the predominant species being chlorite.

Chlorite will subsequently reduce to form harmless chloride. The speed of this reaction depends upon a number of factors, however within saltwater conditions this can be as low as 5 minutes.

Poorly designed or tuned chlorine dioxide generation equipment can lead to the production of chlorate as a disinfection by product. Scotmas systems are extensively tested to minimise the production of chlorate, since this reduces the biocidal efficiency of the process.

Generally, it is the concentration of chlorite residuals that is the “monitored” DBP of chlorine dioxide. Modern generation systems such as those produced by Scotmas are able to monitor the downstream residual DBP and adjust the dose rate to ensure that environmental limits are not breached. In special cases, downstream reactions can be used to remove excess chlorite residual from the water stream.

It is important to note that the disinfection by products of chlorine dioxide are easily managed with the correct experience and advice, and do not present nearly the same scale of problem as found with other biocides with a higher oxidation potential. Unlike ozone (O3), chlorine dioxide does not oxidise bromide (Br-) ions into bromate ions (BrO3-) which have been identified as carcinogenic. Additionally, chlorine dioxide does not produce large amounts of aldehydes, ketones, or other disinfection by products that originate from the ozonisation of organic substances.

While chlorine dioxide has “chlorine” in its name, its chemistry is radically different from that of chlorine.

As we all learned in high school chemistry, we can mix two compounds and create a third that bears little resemblance to its parents.

For instance, by mixing two parts of hydrogen gas with one of oxygen – liquid water is the formed. We should not be misled by the fact that chlorine and chlorine dioxide share a word in common. The chemistries of the two compounds are completely different.

Chlorine and chlorine dioxide are both oxidising agents (electron receivers). However, chlorine has the capacity to take in two electrons, whereas chlorine dioxide can absorb five. This means that, mole for mole, ClO₂ is 2.6 times more effective than chlorine.

If equal, if not greater importance is the fact that chlorine dioxide will not react with many organic compounds, and as a result ClO₂ does not produce environmentally dangerous chlorinated organics. For example; aromatic compounds have carbon atoms arranged in rings and they may have other atoms, such as chlorine, attached to these rings, to form a chlorinated aromatic – a highly toxic compound that persists in the environment long after it is produced.

Chlorine dioxide’s behaviour as an oxidising agent is quite dissimilar. Like ozone, the predominant oxidation reaction mechanism for chlorine dioxide 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). This means that chlorinated organic compounds such as THMs and HAAs are not produced as a result of disinfection using chlorine dioxide.