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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. Using or drinking water with small amounts of chlorine does not cause harmful health effects and provides protection against waterborne disease outbreaks.
What happens when chlorine is added to water?
Chlorine will react in water to form hypochlorous acid, which can then dissociate into hydrogen and hypochlorite ions, according to Eqn (1). This reaction is very important, as the disinfecting power of HOCl, hypochlorous acid, is about 40–80 times that of OCl−, hypochlorite.
How does chlorination system work?
Metering pumps are used to inject a small amount of chlorine (sodium hypochlorite solution, or calcium hypochlorite solution) into the water, usually in conjunction with a contact tank. The pumps draw chlorine bleach from a solution tank and pump it into a pipe under pressure.
What kind of chlorine is used in water treatment?
The three most common chlorine-containing substances used in water treatment are chlorine gas, sodium hypochlorite, and calcium hypochlorite. The choice of the chlorine type to be used often depends on cost, on the available storage options and on the pH conditions required.
Why is chlorine in drinking water?
Chlorine is added to drinking water to protect against harmful microbes and waterborne diseases. Treating drinking water is not a new process, but the transition to chlorination of water sources represents an important shift that had immense public health consequences.
What is chlorine used for in disinfection?
Chlorine reacts with organic matter to disinfection byporducts, such as trihalomethanes (THM) and halogenated acetic acids (HAA). Chlorine can be added for disinfection in several different ways. When ordinary chlorination is apllied, the chlorine is simply added to the water and no prior treatment is necessary.
How is chlorine produced?
Finally, chlorine can be produced by means of molten salts electrolysis and, mainly in laboratories, by means of hydrochloric acid and manganesedioxide oxidation: MnO2+ 4HCl -> MnCl2+ 2H2O + Cl2. When gaseous chlorine is added to water the following hydrolysis reaction takes place: Cl2+ H2O = H++ Cl-+ HOCl.
When was chlorine first made?
Chlorine (Cl2) was first prepared in pure form by the Swedish chemist Carl Wilhelm Scheele in 1774. Scheele heated brown stone (manganesedioxide; MnO2) with hydrochloric acid (HCl). When these substances are heated the bonds are broken, causing manganese chloride (MnCl2), water(H2O) and chlorine gas (Cl2) to form.
What are the elements that react with halogens?
Other halogens are fluorine(F), bromine(Br), iodene(I) and astatine(At). All halogens react with other elements in the same way and can form a large quantity of substances. Halogens often react with metals to form soluble salts. Chlorine atoms contain 17 negative electrons (negatively charged particles).
How many electrons does chlorine have?
It can also cause an extra eletron to form (a covalent bond; a chlorine bond), causing the outer shell to complete. Figure 2: chlorine atoms contain 17 electrons. Chlorine can form very stable substances, such as kitchen salt (NaCl). Chlorine can also form very reactive products, such as hydrogenchloride (HCl).
Where can chlorine be found?
Most chlorine can be found dissolved in seas and salty lakes. Large quantities of chlorine can be found in the ground as rock salts or halite. The properties of chlorine. Chlorine (Cl2) is one of the most reactive elements; it easily binds to other elements.
Is chlorine a disinfectant?
Chlorine is one of the most widely used disinfectants. It is very applicable and very effective for the deactivation of pathogenic microorganisms. Chlorine can be easily applied, measures and controlled. Is is fairly persistent and relatively cheap.
What is chlorination in water?
Chlorination is a water treatment process that is used to eliminate certain pathogens, particularly in drinking water, such as dysentery and typhoid. Water treatment processes such as coagulation, filtration and sedimentation are used to battle waterborne diseases. For over a century, however, chlorination has been used to create water ...
What is chlorine used for?
Chlorine is most commonly used in water treatment for as a disinfectant, though seldom in its pure form. Chlorine gas, sodium hypochlorite and calcium hypochlorite are the three most common chlorine compounds used in water treatment.
When was chlorine first used in water?
The use of chlorine in water treatment has been around since 1893 and permanent water chlorination began in 1905. Hamburg, Germany was the first to attempt chlorinating drinking water, shortly followed by Maidstone, England, as a way to make water completely germ-free.
When is chlorination performed?
Chlorination can also be performed during any part of the water treatment process, including: Pre-chlorination – almost immediately after water enters the treatment facility. After sedimentation and prior to filtration. During the disinfection stage of the water treatment process – most of the time, chlorination occurs at this stage.
Is sodium hypochlorite bleach?
Easiest to handle of all three compounds, sodium hypochlorite can most easily be recognised as household bleach. A light-yellow liquid, it has a short shelf life compared to the other two compounds. Sodium hypochlorite also increases the pH of the water it is being used to treat, though lower concentrations are needed compared to calcium hypochlorite or chlorine gas.
What is the most common compound used in water treatment?
Calcium hypochlorite: Chlorine hypochlorite is the most common compound of chlorine used in residential water treatment. Calcium hypochlorite increases the pH of the water it is being used to treat and can be sold as calcium hypochlorite pellets or granules. Calcium hypochlorite should also be handled with care as it is capable ...
What is calcium hypochlorite used for?
The fact is though, calcium hypochlorite is much more than a pool chemical. It is used to disinfect drinking water throughout many communities across the developed world.
How does chlorination work?
The effectiveness of chlorination depends on various factors, including water temperature, water pH, water turbidity, general water quality and contact time. The contact time is the time available to complete the reaction between the chlorine and untreated water. A longer contact time results in more effective disinfection.
What is the best treatment for drinking water?
Drinking Water Treatment – Chlorination. Chlorination may be effective in removing pathogens, including certain viruses and bacteria, from your well water system. EFFECTIVE AGAINST: Pathogens, including certain viruses and bacteria .
What is the EPA standard for drinking water?
Environmental Protection Agency (EPA) has given a Secondary Drinking Water Standard of 0.3 milligram per liter for iron and 0.05 milligram per liter for manganese. Hydrogen sulfide is a nuisance contaminant that gives water a ‘rotten egg’ odor.
What minerals are dissolved in groundwater?
As it moves through rock, groundwater dissolves iron and manganese that occur naturally in the rock. In dissolved form, these minerals are colorless. Chlorine oxidizes iron and manganese into red-brown or black particle and hydrogen sulfide into yellow particles. These particles can then be filtered.
Does chlorine increase contact time?
As the chlorine concentration increases, the required contact time decreases. Chlorination is more effective at a high temperature and a low pH. Particles in the water decrease the effectiveness of chlorination, as microorganisms may ‘hide’ behind particles and avoid disinfection. The quality of the untreated water affects the chlorine demand.
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.
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 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 chlorine pellet?
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.
Is chlorine gas toxic to humans?
Chlorine gas, of course, is a deadly weapon when used in chemical warfare. It is a respiratory irritant and can irritate skin and mucous membranes and can cause death with sufficient exposure. Because of chemical changes that occur when it is introduced into water, chlorine gas is no more toxic to humans when used to treat drinking water than other forms of 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 the best bleach to use?
Sodium Hypochlorite. Sodium hypochlorite is a chlorine-containing compound most easily recognized as household bleach. It is a light yellow liquid that has a relatively short shelf life. It is the easiest to handle of all the types of chlorine. Sodium hypochlorite also increases the pH of the water being treated.
Does sodium hypochlorite increase pH?
Sodium hypochlorite also increases the pH of the water being treated. A lower concentration of chlorine in this form is needed to treat water than with calcium hypochlorite or chlorine gas.
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.
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.
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.
How long does it take for chlorine to react with water?
This reaction time is called the contact time. For most water systems, the best contact time is usually 30 minutes. To ensure continued protection against harmful organisms, a certain amount of chlorine must remain in the water after treatment. The remaining chlorine is known as a residual chlorine.
When did chlorine start in drinking water?
Health officials began treating drinking water with chlorine in 1908 . Previously, typhoid fever had killed about 25 out of 100,000 people in the U.S. annually, a death rate close to that now associated with automobile accidents. Today, typhoid fever has been virtually eliminated.
What disinfectant kills microorganisms?
Chlorine and chlorine-based compounds are the only disinfectants that can efficiently kill microorganisms during water treatment, and maintain the quality of the water as it flows from the treatment plant to the consumer's tap.
When was the EPA Act amended?
The law was amended in 1986 to expand the EPA's role in protecting public health from contaminated drinking water. The amendments require the agency to control specific disease-causing organisms and indicators that may be present in drinking water and to require public water suppliers to disinfect water.
Does chlorine destroy bacteria?
Researchers postulated that chlorine, which exists in water as hypochlorite and hypochlorous acid, reacts with biomolecules in the bacterial cell to destroy the organism. Further work led to the so-called "multiple hit" theory of chlorine inactivation.
Does chlorine kill microorganisms?
Proponents of this idea suggested that chlorine exposure might destroy the cell wall--by altering it physically, chemically and biochemically--and so terminate the cell's vital functions, killing the microorganism.
Is chlorine a problem in water?
Chlorine can combine with natural organic compounds in raw water to create some undesirable by-products; on its own, however, it does not usually pose a problem to public health.
Why do pools smell?
Chloramine and its byproducts create vapors that exit the water. This is why chloramines, especially dichloramines and trichloramines, can produce that “swimming pool” smell. All chloramines are respiratory irritants, with trichloramines most toxic and monochloramines least toxic. Here are some of the consequences:
Is chloramine better than chlorine?
As we mentioned above, chloramine is a less effective disinfectant than chlorine. This means that chloraminated water is more likely to contain dangerous pathogens than chlorinated water. This poses a serious risk to people with weakened immune systems, including:
