why is chlorination used in water treatment?

Purifying water

• Sedimentation – the water is stored in a large tank or a reservoir. ...
• Filtration – the water is sprayed onto specially-prepared layers of sand and gravel. As it trickles through, smaller insoluble particles are removed. ...
• Chlorination – chlorine gas is injected into the water to sterilise it. The chlorine is poisonous and so kills microorganisms.

Full Answer

What are the benefits and risks of water chlorination?

Why chlorine?

• Pros
• Cons
• Dries skin and hair
• Fades clothes
• Dries out rubber seals in appliances, shortening their lives

Why is chlorine added during water treatment?

• Reducing many disagreeable tastes and odors;
• Eliminating slime bacteria, molds and algae that commonly grow in water supply reservoirs, on the walls of water mains and in storage tanks;
• It removes chemical compounds that have unpleasant tastes and hinder disinfection; and

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Why is chloramine used for water treatment?

• Skin Irritation
• Eye Irritation
• Foul Taste
• Bad Odor
• Rubber Deterioration
• Corrosion
• Toxic to Fish and Plants

Is chloramination an alternative to chlorination?

Removing monochloramine from water

• Ultraviolet light. The use of ultraviolet light for chlorine or chloramine removal is an established technology that has been widely accepted in pharmaceutical, beverage, and dialysis applications.
• Ascorbic acid and sodium ascorbate. ...
• Activated carbon. ...
• Campden tablets. ...
• Sodium thiosulfate. ...

Why is chlorination important in water treatment?

In order to combat waterborne diseases, different disinfection methods are used to inactivate pathogens. Along with other water treatment processes such as coagulation, sedimentation, and filtration, chlorination creates water that is safe for public consumption.

Why is chlorine added to water?

The main objective of this chlorine addition is to disinfect the water and maintain chlorine residuals that will remain in the water as it travels through the distribution system . Chlorinating filtered water is more economical because a lower CT value is required. This is a combination of the concentration (C) and contact time (T). The CT concept is discussed later on in this fact sheet. By the time the water has been through sedimentation and filtration, a lot of the unwanted organisms have been removed, and as a result, less chlorine and a shorter contact time is required to achieve the same effectiveness. To support and maintain the chlorine residual, a process called re-chlorination is sometimes done within the distribution system. This is done to ensure proper chlorine residual levels are maintained throughout the distribution system.

How is calcium hypochlorite made?

Calcium hypochlorite (CaOCl) is made up of the calcium salts of hypochlorous acid. It is produced by dissolving chlorine gas (Cl 2) into a solution of calcium oxide (CaO) and sodium hydroxide (NaOH). Calcium hypochlorite is a white, corrosive solid that comes either in tablet form or as a granular powder. Calcium hypochlorite is very stable, and when packaged properly, large amounts can be purchased and stored until needed. The chemical is very corrosive however, and thus requires proper handling when being used to treat water. Calcium hypochlorite needs to be stored in a dry area and kept away from organic materials. It cannot be stored near wood, cloth or petrol because the combination of calcium hypochlorite and organic material can create enough heat for an explosion. It must also be kept away from moisture because the tablets/granular powder readily adsorb moisture and will form (toxic) chlorine gas as a result. Calcium hypochlorite has a very strong chlorine odour – something that should be kept in mind when placing them in storage.

What is chlorine breakpoint?

Residual Chlorine, Breakpoint. Any type of chlorine that is added to water during the treatment process will result in the formation of hypochlorous acid (HOCl) and hypochlorite ions (OCl-), which are the main disinfecting compounds in chlorinated water. More detail is provided later on in this fact sheet.

What is the best way to disinfect water?

Chlorination is one of many methods that can be used to disinfect water. This method was first used over a century ago, and is still used today. It is a chemical disinfection method that uses various types of chlorine or chlorine-containing substances for the oxidation and disinfection of what will be the potable water source.

How much chlorine gas is needed for water treatment?

If the chlorine liquid is released from its container it will quickly return back to its gas state. Chlorine gas is the least expensive form of chlorine to use. The typical amount of chlorine gas required for water treatment is 1-16 mg/L of water. Different amounts of chlorine gas are used depending on the quality of water that needs to be treated. If the water quality is poor, a higher concentration of chlorine gas will be required to disinfect the water if the contact time cannot be increased.

When was chlorine first used?

Chlorine was first discovered in Sweden in 1744. At that time, people believed that odours from the water were responsible for transmitting diseases. In 1835, chlorine was used to remove odours from the water, but it wasn't until 1890 that chlorine was found to be an effective tool for disinfecting; a way to reduce the amount of disease transmitted through water. With this new find, chlorination began in Great Britain and then expanded to the United States in 1908 and Canada by 1917. Today, chlorination is the most popular method of disinfection and is used for water treatment all over the world.

Lab Effectiveness, Field Effectiveness, and Health Impact

At concentrations that are used for household water treatment programs, the hypochlorite solution is effective at inactivating most bacteria and viruses that cause diarrheal disease. However, it is not effective at inactivating some protozoa, such as Cryptosporidium.

Economics and Scalability

A bottle of hypochlorite solution that treats 1,000 liters of water costs about 10 US cents using refillable bottles and 11-50 US cents using disposable bottles, for a cost of 0.01-0.05 cents per liter treated. Education and community motivation add to program costs.

Additional Resources

For more information about chlorination for developing countries, visit:

Why is it important to chlorinate well water?

Often called “shocking” your well, a proper chlorination is crucial to ensuring your family has safe, potable water. Chlorination is a process you can do yourself, but if you’re not comfortable attempting this, you should call a professional.

What is the purpose of chlorinating a well?

Chlorinating your well, also known as shock chlorination, kills bacteria and disease-causing organisms that can enter your well.

What is the name of the acid that kills bacteria?

Since then, widespread epidemics of the most severe forms of diseases have become exceedingly rare in the U.S. When chlorine is added to water, it forms a weak acid called hypochlorous acid. This acid is very proficient at killing bacteria such as salmonella and E. coli, and it also knocks out many viruses.

How many people die from dirty water?

But in many developing countries around the world, diseases associated with dirty water kill more than 5 million people each year, according to the World Health Organization. Without proper disinfection procedures, outbreaks in the U.S. would significantly increase.

Does chlorine kill viruses?

The proteins’ functionality deteriorates, and the cell starts to die. Chlorine is also able to kill viruses, though the method it uses to kill viruses is less understood. Some experts think chlorine damages proteins inside virus cells, making viruses unable to get into human cells and cause infection.

Why is chlorine used as a disinfectant?

Chlorine and pH. In general terms, the lower the pH of the water, the more effective chlorine is as a disinfectant. Again, speaking generally, a reason for dosing effectively is that chlorination raises the pH of water, so overdosing often raises the pH to levels where chlorine does not work effectively as a disinfectant.

Which is more effective for disinfecting: chlorine or hypochlorite?

Chemically, this has to do with the relationship between the two constituents of chlorine that together are often referred to as “free chlorine”—hypochlorus acid and hypochlorite ions. Hypochlorus acid is the more effective disinfectant and it dominates at lower pH levels, so a lower pH is preferred for disinfection.

What is the best way to disinfect water?

Other methods of disinfection such as ultraviolet and ozonation are effective disinfectants but they do not provide a residual to prevent pathogen regrowth as chlorination does. When treatment plants are distant from the point of use, chlorination is the best way to provide safe water to the end user. Municipal water providers usually rely on measurements of “chlorine residual”—the amount of chlorine remaining in the water after it reaches its destination—as proof of safety. Residual requirements vary, but typical residual goal would be for 0.2 to 1 mg/L.

What is calcium hypochlorite?

Calcium hypochlorite is manufactured from chlorine gas. It is best known as chlorine pellets and granules in residential water treatment. It is a white solid with a very pungent odor and it can create enough heat to explode, so it must not be stored near wood, cloth or petroleum products. Calcium hypochlorite increases the pH of the water being treated.

How much chlorine is needed for disinfection?

Residual requirements vary, but typical residual goal would be for 0.2 to 1 mg/L. In addition to disinfection, chlorine can be effectively used to oxidize iron, manganese and hydrogen sulfide to facilitate their removal, to reduce color in water, and to aid in such treatment processes as sedimentation and filtration.

What is the best way to provide safe water to the end user?

When treatment plants are distant from the point of use, chlorination is the best way to provide safe water to the end user. Municipal water providers usually rely on measurements of “chlorine residual”—the amount of chlorine remaining in the water after it reaches its destination—as proof of safety. Residual requirements vary, but typical residual ...

Which is the least expensive chlorine?

Chlorine gas, which is actually sold as an amber-colored compressed liquid, is the least expensive form of chlorine and is, consequently, the preferred type for municipal water systems.

What is chlorine dioxide used for?

It is a chemical compound in a gaseous form possessing antimicrobial properties, which is used to disinfect water, surfaces, and a host of other areas. Comprising of one atom of chlorine and two atoms of oxygen, chlorine dioxide gets easily dissolved in water and is highly effective in destroying bacteria, parasites, algae, fungi, and other microorganisms. It can also neutralize the harmful compounds of cyanide. However, contrary to the claims by fraudsters, under no circumstances, it should not be ingested to fight ailments such as autism, cancer, HIV, or flu. According to FDA, ingesting chlorine dioxide in concentrations higher than the maximum permitted limit in potable water treatment in Buena Park can cause severe side effects like liver failure, respiratory failure, or abnormal heart rhythm.

Why is chlorine dioxide used in Buena Park?

However, the capacity of such heat sinks can suffer due to the formation of biofilm inside. The biofilm allows the disproportionate growth of pathogens and impacts the functioning of such cooling systems to trap and eliminate excess heat. However, chlorine dioxide can be used effectively in removing biofilm from the cooling water systems in Buena Park and improve their functioning.

Is water a lifeline?

Water is the lifeline for all living beings on planet earth and is their source of sustenance. However, it is available only in a limited quantity for actual usage (only 0.3 percent) given that the brackish water in oceans comprising 96.54 percent is not fit for human consumption or usage. Even the limited quantity of water for living beings is not potable and is a repository of all kinds of pollutants (industrial, municipal, and chemical) and microorganisms. And unless the water is sanitized and freed of all germs, it cannot be consumed or put into use.

Is chlorine dioxide a disinfectant?

It’s cost-effective, less toxic, and significantly better than chlorine for use as a disinfectant, fungicide, sanitizer, and algaecide.

Why is chlorine dioxide used in water treatment?

Bacteria elimination is the primary reason why organizations use chlorine dioxide to treat their water systems. Water purification is especially important in hospitals and germ-sensitive environments. Chlorine dioxide will cleanse many disease-causing particles and microorganisms from water.

Why use chlorine dioxide?

One benefit of using chlorine dioxide is its use to remove any unpleasant or nasty odors in water. Unpleasant odors might arise from nitrogen-based compounds, algae, or even the decay of organic matter.

What chemicals are used in chlorine dioxide generators?

The chemicals used typically involve sodium chlorite, hydrochloric acid, or sodium hypochlorite. Each type of chlorine dioxide generator will utilize the number of chemicals suitable for the appropriate efficiency and output.

Is chlorine dioxide a sterilant?

Chlorine Dioxide is a highly reactive compound – made from chlorine and oxygen molecules – that acts as a sterilant and disinfectant. It is not only EPA-approved but also FDA & USDA-approved for use in food processing plants to control bacteria. It has powerful properties that eliminate pathogens, such as listeria, salmonella, legionella, and more.

Is Pureline chlorine dioxide?

PureLine has been in the chlorine dioxide industry for over 20 years. As such, our organization is well-versed in the treatment of water systems using chlorine dioxide, with a variety of effective solutions. Fill out the contact form below to get in contact with a PureLine chlorine dioxide expert, and learn how to improve the quality of your organization’s water for good!

How does chlorine dioxide affect bacteria?

Chlorine dioxide reacts with the organic substances in bacterial and microbial cells, interrupting many of its internal processes. It also combines with amino acids to hamper protein synthesis in the organism . Viruses are killed by chlorine dioxide combining with peptone, a water-soluble product of hydrolysis of proteins into amino acids, thus preventing protein synthesis in the cells. It is much more effective as a biocide than other gases like ozone or chlorine.

What metals are neutralized by chlorine?

Metallic impurities like iron compounds, manganese and bromides are effectively neutralized with chlorine dioxide treatment. These metals are often found in complex compound forms in unpurified water – chlorine dioxide removes them effectively while not reacting with nitrogen, ammonia, amines and other oxidizable organic substances.

What is the best bleaching agent for paper?

Chlorine dioxide is an efficient bleaching agent – so it is used to turn wood pulp into paper. It whitens the pulp and lightens its color making it more suitable for printable paper. Today, almost 95% of kraft paper pulp is produced using chlorine dioxide in elemental chlorine-free (ECF) bleaching processes.

When was chlorine dioxide discovered?

Chlorine dioxide was discovered by Sir Humphrey in 1814. It is still produced by using similar methods. It is an unstable synthetic, green yellowish gaseous compound, turns into a reddish liquid at -59 degrees and reverts into the gas at 11 degrees. It is highly soluble in water, yet does not hydrolyze. There are many advantages of using chlorine dioxide over other gaseous purifying agents due to its stable nature in dissolved form. It is therefore used extensively in many water treatment and purification processes.

Does chlorine dioxide make water smell?

Chlorine dioxide does not give off any odor when dissolved in water in recommended quantities. Also, it removes other odorous substances such as phenols with can cause odor and taste problems in purified water.

Is chlorine dioxide soluble in water?

Chlorine was the gas of choice earlier for water purification treatments, due to its water-solubility and germicidal properties. Chlorine dioxide is ten times more soluble in cold water than chlorine making it more effective in any chlorine-related applications.

Does chlorine dioxide break down?

One of the most important attributes of chlorine dioxide is its high degree of water solubility. Also, it does not hydrolyze (break down) when dissolved in water, it stays as a gas in solution. Thus, it is easy to remove it through aeration or using carbon dioxide. These properties combined with other advantages discussed below have made it one of the most important chemicals used in cooling tower water treatment and any other water purification processes in modern times.

Lab Effectiveness, Field Effectiveness, and Health Impact

Benefits, Drawbacks, and Appropriateness

• The benefits of chlorination are:
  1. Proven reduction of most bacteria and viruses in water 2. Residual protection against recontamination 3. Ease-of-use and acceptability 4. Proven reduction of diarrheal disease incidence 5. Scalability and low cost
• The drawbacks of chlorination are:
  1. Relatively low protection against protozoa 2. Lower disinfection effectiveness in turbid waters 3. Potential taste and odor objections 4. Must ensure quality control of solution 5. Potential long-term effects of chlorination by-products The SWS and chlorination are most appropriate in area…

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Implementation Examples

Economics and Scalability

Additional Resources