What is the purpose of chlorination in water treatment?
The main purpose of chlorination is to disinfect water, but it also has many other benefits. Unlike some of the other disinfection methods like ozonation and ultraviolet radiation, chlorination is able to provide a residual to reduce the chance of pathogen regrowth in water storage tanks or within the water distribution system.
Is chlorination still used today?
Along with other water treatment processes such as coagulation, sedimentation, and filtration, chlorination creates water that is safe for public consumption. 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.
What is chlorine re-chlorination?
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.
When was chlorination invented?
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.
Is chlorination a stage in water treatment?
Chlorination may also be done as the final step in the treatment process, which is when it is usually done in most treatment plants. 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.
What is chlorination in water treatment?
Chlorination is the process of adding chlorine to drinking water to kill parasites, bacteria, and viruses. Different processes can be used to achieve safe levels of chlorine in drinking water.
What are the method of chlorination?
The different types of chlorine disinfection are batch disinfection, simple chlorination, super-chlorination followed by dechlorination, and shock chlorination. They vary in the amount of chlorine used.
Which water treatment process is done after filtration of water?
DisinfectionWhich water treatment process is done after filtration of water? Explanation: Disinfection is a process which is done to kill microorganism present in the water after the filtration process.
What is post chlorination?
Post chlorination is the normal process of applying chlorine in the end, when all other treatments are completed but before the water reaches the distribution system. At this stage, chlorination is meant to kill pathogens and to provide a chlorine residual in the distribution system.
Why is prechlorination important?
In addition, the chlorine has a much longer contact time when added at the beginning of the treatment process, so prechlorination increases safety in disinfecting heavily contaminated water. Pre-chlorination is generally applied to the water before coagulation. It improves the coagulation and reduces load on filters.
What is the term for adding chlorine to water after the break point?
The addition of chlorine beyond break point is called break point chlorination . The residual of free chlorine, appearing after break point, is not usually removed except by sun light and therefore, it takes care of the future recontamination of water.
What is pre chlorine?
Pre-chlorination is the addition of chlorine to the raw water prior to treatment to produce residual chlorine after meeting chlorine demand. The residual chlorine is useful in several stages of the reatment process – aiding in coagulation, controlling algae problems in sedimentation basins, reducing odor problems, and controlling mud-ball formation in filters. In addition, the chlorine has a much longer contact time when added at the beginning of the treatment process, so prechlorination increases safety in disinfecting heavily contaminated water.
What is chlorine used for?
But the chlorination can also be used for taste and odor control, iron and manganese removal, and to remove some gases such as ammonia and hydrogen sulfide. Chlorination is currently the most frequently used form of disinfection in the water treatment field. However, other disinfection processes have been developed. Like several other water treatment processes, chlorination can be used as a pretreatment process (pre-chlorination) or as the final treatment of water (post -chlorination).
What does de chlorine mean?
De-chlorination means removing the chlorine from the water. This is generally required when super-chlorination has been practiced. The de-chlorination process may either be carried out to such an extent that sufficient residual chlorine of 0.1 to 0.2 mg/L only remains in water after de-chlorination.
Why is pre chlorination always followed by post chlorination?
The pre-chlorination is always followed by post chlorination, so as to ensure final safety of water. Until the middle of the 1970s, water treatment plants typically used both pre-chlorination and post-chlorination.
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:
What is the final step in chlorine treatment?
Typically, chlorine is added to public drinking water as the final stage of treatment, often following an upstream filtration step which removes sediment that can tie up chlorine and shield organisms from its effect .
What is the process of adding chlorine to water?
Chlorination. Chlorination involves adding a measured amount of chlorine to water to produce a residual sufficient to kill bacteria, viruses, and cysts.
What are the reactions between free chlorine and these acids?
Reactions between free chlorine and these acids may produce a class of compounds called trihalomethanes. Strategies to reduce these in public water supplies include enhanced filtration for better organic removal and use of ammonia together with chlorine to produce chloramines for use in lieu of chlorine.
What is the chemical that is added to water to make trihalomethanes?
Chloramines have longer half-life in the water and are less likely to produce trihalomethanes. Chlorine is typically added to water using chemical feed systems to inject liquid sodium hypochlorite (bleach) solution or added as gaseous chlorine (typical of larger public water treatment plants).
Can chlorine be used in water?
Chlorine cannot be used in most high purity water loops without contaminating the process or interfering with the end use of the water. These systems often rely on ultraviolet disinfection as an alternative to water chlorination.
Does chlorine react with organic compounds?
Unfortunately, chlorine reacts with many organic compounds to form chlorine disinfection by-products that are recognized as potent carcinogens at low levels of concentrations. Such organic compounds include humic and fulvic acids, which derive from rotting vegetation common in surface waters.
When was chlorine first used?
Chlorine was first used in the United States as a major disinfectant in 1908 in Jersey City, New Jersey. Chlorine use became more and more common in the following decades, and by 1995 about 64% of all community water systems in the United States used chlorine to disinfect their water.
Where is chloramine used?
Chloramine has been used as a drinking water disinfectant in the United States in places like Cleveland, Ohio, Springfield, Illinois, and Lansing, Michigan since 1929. In 1998, an EPA survey estimated 68 million Americans were drinking water disinfected with chloramine.
What is the process of adding chloramine to drinking water to disinfect it and kill germs?
Chloramination is the process of adding chloramine to drinking water to disinfect it and kill germs. It is sometimes used as an alternative to chlorination. Chloramines are a group of chemical compounds that contain chlorine and ammonia.
What is the EPA's water treatment system?
The U.S. Environmental Protection Agency (EPA) allows drinking water treatment plants to use chloramine and chlorine to disinfect drinking water. Water system pipes develop a layer of biofilm (slime) that makes killing germs more difficult.
What is the EPA's hotline for chloramine?
EPA provides guidance for local water authorities switching to chloramine on how to minimize lead and copper levels. If you are concerned about lead or copper levels in your household water, call EPA’s Safe Drinking Water Hotline at 800-426-4791 for testing information.
Is chlorine good for drinking water?
The U.S. Environmental Protection Agency (EPA) allows drinking water treatment plants to use chloramine and chlorine to disinfect drinking water. Research shows that chloramine and chlorine both have benefits and drawbacks. Chlorine is a highly effective method of disinfection.
Is chloramine toxic to fish?
Chlorine and chloramine are toxic to fish, other aquatic animals, reptiles, and amphibians. Unlike humans and other household pets, these types of animals absorb water directly into the blood stream. Don’t keep these animals in water that contains these disinfectants.
What is chlorine added to?
During the treatment process, chlorine is added to drinking water as elemental chlorine (chlorine gas), sodium hypochlorite solution or dry calcium hypochlorite. When applied to water, each of these forms “free chlorine,” which destroys pathogenic (disease-causing) organisms.
Why should microbial pathogens be placed as the highest priority in water treatment?
For this reason, The American Academy of Microbiology (Ford and Colwell, 1996) has recommended, “the health risks posed by microbial pathogens should be placed as the highest priority in water treatment to protect public health. ”.
How much chlorine is in sodium hypochlorite?
Sodium Hypochlorite, or bleach, is produced by adding elemental chlorine to sodium hydroxide. Typically, hypochlorite solutions contain from 5 to 15% chlorine, and are shipped by truck in one- to 5,000- gallon containers.
What is the purpose of a water purifier?
Reduces many disagreeable tastes and odors; Eliminates slime bacteria, molds and algae that commonly grow in water supply reservoirs, on the walls of water mains and in storage tanks; Removes chemical compounds that have unpleasant tastes and hinder disinfection; and. Helps remove iron and manganese from raw water.
Why is clean water important?
Abundant, clean water is essential for good public health. Humans cannot survive without water; in fact, our bodies are 67% water! Both the U.S. Centers for Disease Control and Prevention and the National Academy of Engineering cite water treatment as one of the most significant advancements of the last century.
Does the EPA require water to be chlorinated?
New regulations from the U.S. Environmental Protection Agency (EPA) will require water systems to monitor Cryptosporidium and adopt a range of treatment options based on source water Cryptosporidiumconcentrations. Most water systems are expected to meet EPA requirements while continuing to use chlorination.
Is chlorination a disinfectant?
Despite a range of new challenges, drinking water chlorination will remain a cornerstone of waterborne disease prevention. Chlorine’s wide array of benefits cannot be provided by any other single disinfectant. While alternative disinfectants (including chlorine dioxide, ozone, and ultraviolet radiation) are available, all disinfection methods have unique benefits, limitations, and costs. Water system managers must consider these factors, and design a disinfection approach to match each system’s characteristics and source water quality.
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…
Implementation Examples
- The Safe Water System has been implemented in over 35 countries. Social marketing organizations, such as Population Services International (PSI), sell hypochlorite solution in over 20 countries. Since 1998 over 125 million bottles of hypochlorite solution, a volume of product sufficient to treat approximately 118.7 billion liters of household drinking water, were sold (as o…
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. SWS programs can achieve full cost recovery (charging the user the full cost of product, marketing, distribution, and …
Additional Resources
- For more information about chlorination for developing countries, visit: 1. Population Services Internationalexternal icon 2. WHO Household Water Treatment and Safe Storageexternal icon