At advanced or tertiary treatment, chlorine is added to public drinking water. Chlorination involves adding a measured amount of chlorine to the treated wastewater. In reaction with water, chlorine residues form.
Why is water often treated with chlorine to?
When chlorine is added to your water supply, it rapidly reduces the spread of all kinds of waterborne diseases, like cholera and typhoid fever, as well as other ailments. It also makes it easier for cities and towns to purify drinking water to keep residents (like yourself) safe.
How does chlorine help purify water?
Chlorine is also used up quickly in water systems. How does chlorine help clean water? Chlorine is a disinfectant added to drinking water to reduce or eliminate microorganisms, such as bacteria and viruses, which can be present in water supplies. The addition of chlorine to our drinking water has greatly reduced the risk of waterborne diseases.
Is it safe to drink water with chlorine in it?
If regulations are followed, then yes. The U.S. Environmental Protection Agency (EPA) limits the amount of chlorine in drinking water to levels considered safe for human consumption and are unlikely to cause adverse long-term health effects. Is There a Downside to Drinking Chlorinated Water?
What are the disadvantages of chlorine in water?
- Disadvantages of chlorination. RO membranes are commercially built either from polyamide (PA) or from cellulose acetate (CA), both being very effective in desalination, but with important differences.
- Chlorine mitigation. ...
- Alternative disinfectants. ...
- Outlook. ...
- Conclusions. ...
- Change history. ...
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How does chlorine work in water treatment?
How does chlorine disinfection work? Chlorine kills pathogens such as bacteria and viruses by breaking the chemical bonds in their molecules. Disinfectants that are used for this purpose consist of chlorine compounds which can exchange atoms with other compounds, such as enzymes in bacteria and other cells.
What is the process of adding chlorine to water?
What is chlorination? Chlorination is the process of adding chlorine to drinking water to kill parasites, bacteria, and viruses.
Is chlorine added in wastewater treatment?
Chlorine is the most widely used disinfectant for municipal wastewater because it destroys target organisms by oxidizing cellular material. Chlorine can be supplied in many forms, which include chlorine gas, hypochlorite solutions, and other chlorine compounds in solid or liquid form.
What step of the treatment process is chlorine added?
Disinfection. After the water has been filtered, water treatment plants may add one or more chemical disinfectants (such as chlorine, chloramine, or chlorine dioxide) to kill any remaining parasites, bacteria, or viruses.
What are the methods 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.
Does purified water have chlorine?
Purified Water has been filtered to remove chemicals, like chlorine, and other contaminants including bacteria, algae, fungi, parasites, metals, and chemical pollutants. More often than not, it's produced using groundwater or tap water.
How is chlorine removed from wastewater?
Typically, dechlorination is accomplished by adding sulfur dioxide or sulfite salts (i.e., sodium sulfite, sodium bisulfite, or sodium metabisulfite). Carbon adsorption is also an effective dechlorination method, but is expensive compared to other methods.
Why is chlorine added to waste water?
Chlorine is added to raw water to eliminate algae and other forms of aquatic life from the water so they won't cause problems in the later stages of water treatment.
Why is chlorine required in sewage treatment?
Chlorine needs to be put into wastewater to treat it and oxidize any contaminants it once held when in the sewage system. The chlorination wastewater treatment procedure creates byproducts in treated water. Dechlorination involves removing any chlorine-based byproducts to ensure the water is truly safe.
What are the 4 main steps to water treatment?
4 Steps of Community Water TreatmentCoagulation and Flocculation. ... Sedimentation. ... Filtration. ... Disinfection.
What are the 4 steps of water treatment?
These include: (1) Collection ; (2) Screening and Straining ; (3) Chemical Addition ; (4) Coagulation and Flocculation ; (5) Sedimentation and Clarification ; (6) Filtration ; (7) Disinfection ; (8) Storage ; (9) and finally Distribution. Let's examine these steps in more detail.
What are the 7 stages of water treatment?
Figure 5.2 The seven steps often used in the large-scale treatment of water.1 Screening. ... 2 Aeration. ... 3 Coagulation and flocculation. ... 4 Sedimentation. ... 5 Filtration. ... 6 Chlorination. ... 7 Supplementary treatment.
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.
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.
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.
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 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.
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.
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 available chlorine?
Available Chlorine. "Available chlorine" is an expression of the equivalent weights of oxidizing agents, with chlorine gas as a basis , similar to the expression of alkalinity in terms of calcium carbonate equivalents. The term originated from the need to compare other chlorine-containing compounds to gaseous chlorine.
What is chlorine used for?
Chlorine is one of the most versatile chemicals used in water and wastewater treatment. This powerful oxidizing agent is used for: Disinfection. control of microorganisms. removal of ammonia. control of taste and odor. color reduction. destruction of organic matter. hydrogen sulfide oxidation.
What is free available residual chlorine?
Free available residual chlorine is the amount of chlorine which exists in the treated water system as hypochlorous acid and hypochlorite ions after the chlorine demand has been satisfied. Free residual chlorination is the application of chlorine to water to produce a free available chlorine residual.
Why is chlorine gas dangerous?
Because chlorine gas is denser than air, it stays close to the ground when released. The contents of a 1-ton cylinder of chlorine can cause coughing and respiratory discomfort in an area of 3 square miles. The same amount concentrated over an area of 1/10 square mile can be fatal after only a few breaths.
What is combined residual chlorine?
Combined residual chlorination is the application of chlorine to water to react with ammonia (natural or added) or other nitrogen compounds to produce a combined available chlor ine residual. Total available chlorine is the total of free available chlorine, combined available chlorine, and other chlorinated compounds.
How is chlorine gas generated?
Chlorine gas can also be generated by the salt process (which employs the reaction between sodium chloride and nitric acid), by the hydrochloric acid oxidation process, and by the electrolysis of hydrochloric acid solutions.
How is chlorine produced?
Chlorine is generated commercially by the electrolysis of a brine solution , typically sodium chloride, in any of three types of cells: diaphragm, mercury, or membrane.
Why should chlorine be introduced into water?
Because the effectiveness of the disinfection is a function of contact time, in each type of chlorinator the chlorine should be introduced into the water as close to the source as possible. This will allow the chlorine a longer contact time with the water. Figure 1shows a chemical feed pump chlorinator.
What happens when you add chlorine to water?
When chlorine is added to water, it reacts with microorganisms, certain chemicals, plant material, and compounds that can cause taste, odor, or color in the water. These components “tie up” some of the chlorine, which is called “chlorine demand.”.
What are the three contaminants that are tested for continuous chlorination?
For information on testing private drinking water for three common contaminants for which continuous chlorination might be considered—bacteria, iron and manganese, and hydrogen sulfide —see NebGuides Drinking Water: Bacteria (G1826), Drinking Water: Iron and Manganese (G1714), and Drinking Water: Sulfates and Hydrogen Sulfide (G1275).
What is the best way to ensure good water quality?
Treatment Principles. The bestoption for assuring good water quality is protecting the water source from contamination in the first place. If your water supply does become contaminated, removing the source of contamination is the ideal solution. Chlorination should not be a substitute for a sanitary water supply.
What is the purpose of continuous chlorination?
Continuous chlorination can treat drinking water containing pathogenic (disease-causing) bacteria, viruses, and other microorganisms, to produce drinking water considered by public health officials to be essentially pathogen free. Continuous chlorination can also be used to manage nuisance bacteria.
How to get a copy of a CCR?
A copy of the CCR can be obtained by contacting the local water utility. Public supplies must conform to federal standards established by the Safe Drinking Water Act.
Is chlorine needed for residual disinfection?
It is important to have enough chlorine in the water to meet the chlorine demand and allow for residual disinfection. Test kits are available from plumbing or water supply equipment dealers for testing chlorine in private systems. Be certain the kit used tests free chlorine, not total chlorine.
What is the best way to dechlorinate water?
Dechlorination of water is usually achieved by chemical dosing of reducing agents such as Sodium Thiosulphate or Sodium Bisulphite , which provide a high degree of control over the dechlorination process.
How long does it take for chlorine to oxidize?
However Chloramines and chlorinated organics have slower reaction times, in the range of 5 – 10 minutes.
Why is RO water dechlorinated?
When RO membranes are in use, the feed water must be dechlorinated to prevent oxidation of the membranes. The main role of dechlorination of water is the removal of high chlorine concentration levels. Chlorine is often used in water disinfection and other oxidation processes such as iron and manganese removal.
What is the chemical used in reverse osmosis desalination?
The most common dechlorination chemical used in reverse osmosis desalination is Sodium Metabisulfite (Na2S2O5). When injected, it reacts with free Chlorine and creates sodium bisulfite (NaHSO3), which reacts again with Hypochlorous acid to give Sulfuric Acid (H2SO4). In theory, 1.34 mg/L of Sodium Metabisulfite is enough to remove 1 mg/L ...
How much sodium metabisulfite is needed to remove chlorine?
In theory, 1.34 mg/L of Sodium Metabisulfite is enough to remove 1 mg/L of free chlorine, however in practice 2 mg/L are dosed per 1 mg/L of free Chlorine. Sodium Metabisulfite dosage is optimised based on the ORP potential of the feed water at the inlet of the reverse osmosis desalination plant. Sodium Bisulphite water dechlorination system.
What happens to the water before reverse desalination?
Dechlorination of water before Reverse Osmosis desalination. Membranes used in Reverse Osmosis desalination are damaged by exposure to oxidants such as chlorine. Hence, when the feed water is disinfected with chlorine or other strong oxidants, those oxidants need to be removed before any contact with the membranes.
How much chlorine can be removed with UV light?
Up to 5 mg/L of Chloramines and 15 mg/L of free chlorine can be easily removed with UV light, however the UV dosage required for dechlorination, which depends on total chlorine level, is 15 to 30 times higher than the normal disinfection dose.
Lab Effectiveness, Field Effectiveness, and Health Impact
- The most common use of chlorine in water treatment is to disinfect water. As a disinfectant, it has drawbacks, but it also has advantages. 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...
Benefits, Drawbacks, and Appropriateness
Implementation Examples
Economics and Scalability
Additional Resources