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Chlorine Dioxide Versus Chlorine: What’s the Difference?

10 June 2014

Byron Stein, Editor of 'Drumstick', explores the differences between conventional chlorination and chlorine dioxide for water sanitation.

One of the large poultry processors in Australia recently required some growers to change from using conventional chlorination to chlorine dioxide for sanitising their bird water supplies.

This article explores what some of the reasons for this change might be by looking at the differences between conventional chlorination and chlorine dioxide.

So what is chlorine dioxide?

Chlorine dioxide is a greenish-yellow gas which easily mixes with water. Because chlorine dioxide is a relatively unstable gas it cannot be transported and sold in its pure form and must be generated on site. It is therefore supplied as a chemical compound in either stable liquid or solid form. This stable liquid or solid is then mixed with another chemical (sometimes called an activator) at the site of the water treatment. The chemical reaction of the liquid or solid product and the activator produces chlorine dioxide.

How effective is chlorine dioxide in sanitising water?

Chlorine dioxide is extremely effective and is one of the most powerful water sanitising agents available. It is highly effective in killing bacteria, viruses, protozoa, spores, yeasts, moulds and other disease-causing organisms.

How is chlorine dioxide different from chlorine (sodium hypochlorite or calcium hypochlorite)?

Although both chemicals have the chlorine in their names, they have different chemical structures. This means they have also have different properties. It is these properties which make all the difference when comparing the two chemicals.

So chlorine is not an effective water sanitiser?

Chlorine is a very effective water sanitiser, and has been used for many years with very good effect. However, the effectiveness of chlorine is very much dependent on water quality and pH. Chlorine is also far more reactive in water and is more prone to lose it’s effectiveness over time than chlorine dioxide.

Another way of thinking about this is if we consider chlorine to be a very friendly, happy chemical. As soon as we add it to water, it has a tendency to bind and react with many other chemicals in the water. Once this happens, its chemical structure is changed and it becomes less effective in killing viruses and other diseases.

Chlorine dioxide on the other hand is less friendly and tends to stick to itself. This means there is more chlorine dioxide in the water to attack and kill viruses, bacteria and other organisms.

Is it true chlorine dioxide is better at killing avian influenza than chlorine?

No and yes. Both chemicals are very effective at destroying avian influenza viruses. However, while chlorine dioxide remains effective in a range of water pH values and in variable water quality, chlorine becomes less effective as pH rises and as water becomes more contaminated with organic material and other chemicals, including ammonia.

In other words, chlorine dioxide remains effective under a wide range of water quality conditions while chlorine is ‘fussier’ and is effective only if water is relatively clean and the pH of water is below 7.5.

Important Differences between Chlorine Dioxide and Chlorine

1. Water quality

Chlorine dioxide is much less sensitive to poor water quality than chlorine. This means that chlorine dioxide is more effective as a sanitiser in water of variable quality.

Chlorine is effective when water is relatively free of other chemicals and contaminants such as salts, organic material, silt and dirt and other water contaminants. As water quality declines, then so does the effectiveness of chlorine.

Chlorine dioxide is also more effective in cleaner water, but can cope with more water contamination than chlorine can.

2. Water pH

Water pH is the measure of how acid or alkaline water is.

Chlorine dioxide is much less sensitive to water pH than chlorine is and can operate in a relatively broad range of pH levels (pH 5 to 10).

Chlorine is much more sensitive to pH and becomes less effective as pH rises, in other words, as water becomes more alkaline (greater than pH 7.5).

3. Speed

Chlorine dioxide is a more powerful sterilising agent than chlorine and has a much faster sanitation rate, especially as water pH rises.

4. Biofilm

Biofilm is the layer of slime containing bacteria and other organisms that build-up on the insides of water pipes and equipment. This layer of slime protects bacteria and other disease causing organisms from sanitisers and chemicals.

Chlorine dioxide is able to penetrate the biofilm and effectively remove it from your water system. Chlorine is not able to do this.

Summary

Chlorine and chlorine dioxide are both excellent water sanitising agents. Whilst chlorine dioxide is more powerful, chlorine still produces good results and will kill the key pathogens of concern to the poultry industry.

However, chlorine’s weakness is that it is only truly effective under relatively narrow conditions. If your water is pretty clean, free of natural organic matter, low in salts and ammonia and other chemicals, then chlorine is a relatively cheap and cost effective sanitiser.

Chlorine dioxide however is a safer bet. Chlorine dioxide lasts longer, is effective in a range of water qualities (although is still most effective in clean water) and a range of pH ranges and crucially can penetrate and remove biofilm in water lines and equipment.

Some material in this article is adapted from the National Water Biosecurity Manual Poultry Production (2009).

This article was first published in The Drumstick newsletter from the New South Wales Department of Primary Industries.

June 2014



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