Chlorine Dioxide: the practical choice for water treatment in the UK

Chlorine Dioxide: the practical choice for water treatment in the UK

Chlorine Dioxide the practical choice for water treatment in the UK

Chlorine Dioxide: the practical choice for water treatment in the UK

What is Chlorine Dioxide?

Chlorine dioxide (ClO2) is a yellow or reddish-yellow gas. It’s a highly reactive compound, especially when heated. When exposed to the air, sunlight breaks it down into chlorine gas and oxygen. Chlorine gas is toxic if inhaled. Chlorine dioxide turns to liquid below 11ºC   and can be frozen into an orange-colored solid, for instance for shipping, although it must be carefully monitored during transit.

As chlorine dioxide is such a volatile compound, difficult to store or transport safely, it is usually manufactured in solution form at the point of use, as and when required. It does not occur naturally. Chlorine dioxide, when dissolved in water, is an efficient disinfectant and is used around the world to make drinking water safe. Chlorine dioxide solution has many other industrial and agricultural applications, including bleaching paper and fabric, and disinfecting food processing equipment.

How is Chlorine Dioxide made?

Chlorine dioxide can be explosive and cause burns in gas form, so it is most commonly manufactured as a stable solution. Chlorine dioxide solution is generated through the acidification of sodium chlorite. This process involves adding sodium chloride crystals or flakes to water (producing sodium chlorite NaClO2) and a food-grade acid (e.g., phosphoric acid, hydrochloric acid, citric acid, malic acid, or sodium hydrogen sulfate). This combination generates chlorous acid (HClO2), which decomposes to a specific and controlled mix of chlorite (ClO2), chlorine dioxide (ClO2) and chloride (Cl ̄).

Alternatively, a stabilized chlorine dioxide solution is “activated by adding small doses of a strong acid. This releases low quantities of gaseous chlorine dioxide over a period of time.

Why is Chlorine Dioxide such an effective water treatment?

Although chlorine is usually the chemical associated with water treatment, chlorine dioxide is a better choice for many reasons. Both chlorine and chlorine dioxide are highly reactive, but chlorine dioxide has the advantage in that it only reacts with a narrow range of chemicals. It remains stable across a wider range of pH values than chlorine: it’s only active in the pH4-10 range. It does not react with the vast majority of organic compounds therefore it is easier to control and has more of an effect at lower residual levels than either chlorine or another competitor, ozone.

One of the main reasons for sanitizing the water supply is to destroy biofilms, the slimy collection of molds, viruses, and bacteria that may be found growing on the surface of equipment. Biofilms often build up in pipework, or in the warm environments offered by hot and cold water systems in buildings and cooling towers.

The microorganisms in biofilms include disease-causing pathogens such as E.coli, Salmonella, Campylobacter and Listeria so it’s important to prevent their development and stop the spread of any spores. The microorganisms cluster together and secrete a protective polysaccharide “glue” that helps them to resist outside elements.

Chlorine dioxide penetrates this slimy outer layer by breaking down the inert sugars. Unlike other biocides, chlorine dioxide then continues reacting with the proteins that the microorganisms are built from, disrupting cell function and preventing them from reproducing. Chlorine dioxide is particularly effective at preventing the build-up of Legionella, Giardia Lambia and Cryptosporidium oocysts in public drinking water supplies.

Another reason to choose chlorine dioxide over chlorine is that it does not form disinfection by-products (DBPs) such as chloramines and halogenated compounds (Trihalomethane or THMS). Chloramines can taint the water, causing an unpleasant taste and/or odour. Obviously, it’s crucial that the water used in agricultural and food processes is odourless and tasteless so it doesn’t contaminate the product. Chlorine dioxide disinfects without side-effects.

Finally, chlorine dioxide oxidises swiftly as it only reacts with a narrow range of chemicals. This means it goes to work on the problem more quickly than other disinfectants and at lower residual levels. Chlorine dioxide is a much more precise, fast-acting water treatment solution than chlorine and its other competitors. 

Looking for Chlorine Dioxide Generators? 

What is Chlorine Dioxide?

Chlorine dioxide (ClO2) is a yellow or reddish-yellow gas. It’s a highly reactive compound, especially when heated. When exposed to the air, sunlight breaks it down into chlorine gas and oxygen. Chlorine gas is toxic if inhaled. Chlorine dioxide turns to liquid below 11ºC   and can be frozen into an orange-colored solid, for instance for shipping, although it must be carefully monitored during transit.

As chlorine dioxide is such a volatile compound, difficult to store or transport safely, it is usually manufactured in solution form at the point of use, as and when required. It does not occur naturally. Chlorine dioxide, when dissolved in water, is an efficient disinfectant and is used around the world to make drinking water safe. Chlorine dioxide solution has many other industrial and agricultural applications, including bleaching paper and fabric, and disinfecting food processing equipment.

How is Chlorine Dioxide made?

Chlorine dioxide can be explosive and cause burns in gas form, so it is most commonly manufactured as a stable solution. Chlorine dioxide solution is generated through the acidification of sodium chlorite. This process involves adding sodium chloride crystals or flakes to water (producing sodium chlorite NaClO2) and a food-grade acid (e.g., phosphoric acid, hydrochloric acid, citric acid, malic acid, or sodium hydrogen sulfate). This combination generates chlorous acid (HClO2), which decomposes to a specific and controlled mix of chlorite (ClO2), chlorine dioxide (ClO2) and chloride (Cl ̄).

Alternatively, a stabilized chlorine dioxide solution is “activated by adding small doses of a strong acid. This releases low quantities of gaseous chlorine dioxide over a period of time.

Why is Chlorine Dioxide such an effective water treatment?

Although chlorine is usually the chemical associated with water treatment, chlorine dioxide is a better choice for many reasons. Both chlorine and chlorine dioxide are highly reactive, but chlorine dioxide has the advantage in that it only reacts with a narrow range of chemicals. It remains stable across a wider range of pH values than chlorine: it’s only active in the pH4-10 range. It does not react with the vast majority of organic compounds therefore it is easier to control and has more of an effect at lower residual levels than either chlorine or another competitor, ozone.

One of the main reasons for sanitizing the water supply is to destroy biofilms, the slimy collection of molds, viruses, and bacteria that may be found growing on the surface of equipment. Biofilms often build up in pipework, or in the warm environments offered by hot and cold water systems in buildings and cooling towers.

The microorganisms in biofilms include disease-causing pathogens such as E.coli, Salmonella, Campylobacter and Listeria so it’s important to prevent their development and stop the spread of any spores. The microorganisms cluster together and secrete a protective polysaccharide “glue” that helps them to resist outside elements.

Chlorine dioxide penetrates this slimy outer layer by breaking down the inert sugars. Unlike other biocides, chlorine dioxide then continues reacting with the proteins that the microorganisms are built from, disrupting cell function and preventing them from reproducing. Chlorine dioxide is particularly effective at preventing the build-up of Legionella, Giardia Lambia and Cryptosporidium oocysts in public drinking water supplies.

Another reason to choose chlorine dioxide over chlorine is that it does not form disinfection by-products (DBPs) such as chloramines and halogenated compounds (Trihalomethane or THMS). Chloramines can taint the water, causing an unpleasant taste and/or odour. Obviously, it’s crucial that the water used in agricultural and food processes is odourless and tasteless so it doesn’t contaminate the product. Chlorine dioxide disinfects without side-effects.

Finally, chlorine dioxide oxidises swiftly as it only reacts with a narrow range of chemicals. This means it goes to work on the problem more quickly than other disinfectants and at lower residual levels. Chlorine dioxide is a much more precise, fast-acting water treatment solution than chlorine and its other competitors.

What are the types of chlorination used in water treatment?

There are three main methods of chlorinating water, depending on the strength of the disinfectant required. Chlorine compounds can be added to the water as:

  • Liquid (in the form of sodium hypochlorite);
  • Solid, in the form of powder, granules, or tablets, made from calcium hypochlorite, chlorinated isocyanurates or lithium hypochlorite;
  • Gas (highly toxic and only used under special conditions).

When chlorine or a chlorine compound is added into water it releases hypochlorous acid, HOCl. The hypochlorous acid commonly disassociates into other forms, such as the chlorite ion, OCl-, depending on the pH of the water. The amount of chlorine in the water in these forms is referred to as Free Chlorine. The reaction of chlorine with organics to form compounds such as chloramines is referred to as combined chlorine.

How is Chlorine Dioxide applied in water treatment?

Chlorine dioxide water treatment is a versatile process that can be adapted to many different types and sizes of facilities. Depending on the strength and speed of biocidal action required, chlorine dioxide can be generated on site and on demand from tablets, solutions, or via electrochlorination. This allows the operator to control the concentration of chlorine dioxide within their water system. The most common type of generators form chlorine dioxide as an aqueous solution of consistent product strength from the controlled reaction of Hydrochloric Acid and Sodium Chlorite.

As mentioned above, chlorine dioxide can also be stored and used in the form of Stabilised Chlorine Dioxide. This is an aqueous buffered solution of chlorine dioxide, activated through the addition of an additional acid solution. Some facilities find this to be a more convenient method of chlorination. 

What are the benefits of Chlorine Dioxide water treatment to industry?

As a swift and efficient biocide, chlorine dioxide has many applications. It destroys bacteria, viruses, fungi and other pathogens on hard surfaces and within water supply systems. It can be added to any hot or cold water system, including cooling towers, swimming pools, and spas to destroy problem bacteria and viruses such as Pseudomonas, MRSA, E-coli, and cryptosporidium. 

Chlorine dioxide is a vital component of the sanitization process at every stage of agricultural production, storage, and distribution. It’s also valued as a disinfectant for large buildings, such as office blocks, hotels, laboratories, and hospitals – especially those which might be vulnerable to legionella growth within their water supply. It’s employed across the hospitality sector as an all-round sanitizer and antimicrobial agent.

If you have questions about the use of Chlorine Dioxide in water treatment, please contact us. The Prodose team has more than ten years of expertise in this area and we can advise on all aspects of your water disinfection system. We offer end-to-end water treatment service, designing and installing your system, supplying chemicals, and servicing. Prodose is your one-stop shop for Chlorine Dioxide water treatment.

 

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If you are interested in upgrading your system in this way, please get in touch with us at Prodose. We’d be very happy to talk to you confidentially and on a no-pressure basis.

Major UK Stadium Case Study

Major UK Stadium Case Study

Major UK Stadium Case Study

Case Study: Stadium water supply

The dosing of water supplies with chlorine dioxide is a very common and effective method of preventing Legionella within buildings and facilities.

Prodose has recently specified and installed a chlorine dioxide generation system in a large, well-known sports stadium in the UK. This will help the venue to ensure a safe supply of water across all of the site facilities at all times.

The building management team got in touch with us because they were routinely finding low levels of chlorine dioxide in toilet facilities throughout the site.

We looked at the frequency and volume of water use within the stadium. As is usually the case with such venues, demand for water was extremely high during events but also very low at other times. This meant that, during long periods when water within the system was either not flowing or hardly at all, the levels of residual chlorine dioxide dropped down to unacceptably low levels.

We recommended the installation of a larger chlorine dioxide generator and an emissions-proof water storage tank. The large capacity of the generator would be able to keep up with the spikes in water demand during events, for example at half time when many audience members all visit the toilet facilities at the same time.

The water storage tank needs to be emissions-proof in order to prevent chlorine dioxide fumes from entering the plant room. The tanks are very large in order to cope with peak demands. This does however mean that water can be standing static in them at other times, so it is important to be able to monitor this water for chlorine dioxide level to ensure residual levels do not drop too low.

To enable this, we installed a tank recirculating line with a chlorine dioxide residual analyser. This constantly monitors the levels of chlorine dioxide and tops them up when they drop below a predetermined level.

The system has now been up and running for a period of time and the client has been very pleased to now be recording consistent levels of chlorine dioxide throughout the site. This has remained steady at all times, regardless of how long it has been since a large audience attendance.

Further Case Studies

Major UK Stadium Case Study

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Bagged Salad Producer

A supplier of bagged salads approached us in 2015 to see if we could help them streamline their disinfection process and save costs. The company produces various products for a number of clients. This includes privately labelled items for some well-known supermarkets....

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Recent Articles

What part does chlorine play in food safety?

What Part Does Chlorine Play In Food Safety?21st century food production, processing and delivery relies on a constant source of clean water to disinfect machinery, containers, work surfaces and the products themselves. This prevents the spread of foodborne diseases....

read more

New Salad Project

New Project Bagged salad producer approaches Prodose.We’ve just received a new order from a producer of pre-bagged salad. It looks like this project will be an interesting case study for any similar food supplier. This client currently uses three flume washers to...

read more

Focus on Food Washing

Food washing: Do you monitor your disinfection levels?In the food industry, it is common for food suppliers and processors to disinfect fruit, salad leaves and vegetables by washing them in water that has been treated with disinfectant. This is an essential part of...

read more

Is the chlorine dioxide dosing system within your facility providing you with sufficient residual levels to be sure your employees or visitors are protected at all times? If you have any doubts about the effectiveness of your system, or would like to find a smarter way to control your chlorine dioxide dosing, please get in touch with us. We can cover every aspect, from initial consultation to final commissioning of a new system.