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[[Image:safe_water_systems_icon.png|thumb|right|150px]]
[[Image:chlorine disinfection.jpg|thumb|right|300px|A women using chlorine to disinfect water]]
Sodium hypochlorite is one form of chlorine used for water disinfection. It can be manufactured in most locations since it can be obtained through the electrolysis of salt water. Bottles can be purchased for household water treatment from many manufacturers in various sizes. Chlorine concentrations range from 0.5 to 10% and each product should have its own instructions for correct dosing of contaminated water. Liquid household bleach also contains sodium hypochlorite, and is widely available.
#Excess chlorine that is not consumed or combined remains in the water. This portion is called free residual chlorine (FRC). The FRC helps prevent recontamination of the treated water.
Chlorine began to be widely used as a disinfectant in the early 1900’s. It revolutionized drinking water treatment and dramatically reduced the incidence of waterborne diseases. Chlorine remains the most widely used chemical for water disinfection in the United States.
==Suitable conditions==
Unlimited amounts of water can be processed at a time, depending on the amount of active chlorine.
Some users complain about the taste and odour that chlorine may cause in water. Chlorine reacts with organic matter naturally present in water to form by-products such as trihalomethanes (THMs), which are potentially cancer-causing. Lantagne et al. (2008)<ref>[[#lantagne08|Lantagne et al. (2008)]]</ref> indicate that THM levels produced during household chlorination may fall below World Health Organization (WHO) guideline values.
The use of household bleach products for household water treatment is not recommended in the absence of ongoing quality control testing, due to poor quality control of most sodium hypochlorite bleaches. If household bleach is used, the concentration should be regularly tested and an appropriate dosage strategy (2 mg/l for waters of turbidity 0-10 NTU, 4 mg/L for water of turbidity 10-100 NTU) should be developed by the recommending organization.
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- Uncertain concentration and shelf life, susceptibility to gaps in supply chain, high transportation costs, and difficulty in dispensing precise quantities <br>
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==History and social context==
Chlorine began to be widely used as a disinfectant in the early 1900’s. It revolutionized drinking water treatment and dramatically reduced the incidence of waterborne diseases. Chlorine remains the most widely used chemical for water disinfection in the United States.
==Suitable conditions ==
Unlimited amounts of water can be processed at a time, depending on the amount of active chlorine.
Some users complain about the taste and odour that chlorine may cause in water. Chlorine reacts with organic matter naturally present in water to form by-products such as trihalomethanes (THMs), which are potentially cancer-causing. Lantagne et al. (2008)<ref>[[#lantagne08|Lantagne et al. (2008)]]</ref> indicate that THM levels produced during household chlorination may fall below World Health Organization (WHO) guideline values.
The use of household bleach products for household water treatment is not recommended in the absence of ongoing quality control testing, due to poor quality control of most sodium hypochlorite bleaches. If household bleach is used, the concentration should be regularly tested and an appropriate dosage strategy (2 mg/l for waters of turbidity 0-10 NTU, 4 mg/L for water of turbidity 10-100 NTU) should be developed by the recommending organization.
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==Technical specificationConstruction, operations and maintenance==
====Operation====
There are several different brands of chlorine products that have been manufactured specifically for household water treatment. Each product should have its own instructions for correct dosing and contact time.
<!--See CAWST’s Technical Brief on Chlorine Disinfection of Drinking Water for information on how to determine the chlorine dose and contact time using household bleach. -->
====Manufacturing====
It can be manufactured in most locations since it can be obtained through the electrolysis of brine. Bottles can be purchased for household water treatment from many manufacturers in various sizes
Hypochlorite solution for household water treatment can be manufactured in four ways, in order of decreasing quality control: 1) chlorine gas injection into a stream of water, 2) dilution of higher concentration sodium hypochlorite solution, 3) dilution of calcium hypochlorite powder; and, 4) electrolytic generation of sodium hypochlorite from salt, water, and electricity. In all cases: 1) distilled or deionized water should be used for manufacturing; 2) the solution should be stabilized to pH over 11,9 to ensure adequate shelf- life of a minimum of 12 months; and, 3) each batch should be tested for chlorine concentration and pH. For national scale programs, it is recommended to work with a local company to manufacture the solution using high-quality processes
Skin and eye protection should be used when handling chlorine solutions. Work should be conducted in a well ventilated area or in the open air. Trained workers needed to produce and test the sodium hypochlorite.
====Treatment Efficiency====
Chlorine should be stored in a cool, dark place in a closed container.
====Manufacturing====
It can be manufactured in most locations since it can be obtained through the electrolysis of brine. Bottles can be purchased for household water treatment from many manufacturers in various sizes
Hypochlorite solution for household water treatment can be manufactured in four ways, in order of decreasing quality control: 1) chlorine gas injection into a stream of water, 2) dilution of higher concentration sodium hypochlorite solution, 3) dilution of calcium hypochlorite powder; and, 4) electrolytic generation of sodium hypochlorite from salt, water, and electricity. In all cases: 1) distilled or deionized water should be used for manufacturing; 2) the solution should be stabilized to pH over 11,9 to ensure adequate shelf- life of a minimum of 12 months; and, 3) each batch should be tested for chlorine concentration and pH. For national scale programs, it is recommended to work with a local company to manufacture the solution using high-quality processes
Skin and eye protection should be used when handling chlorine solutions. Work should be conducted in a well ventilated area or in the open air. Trained workers needed to produce and test the sodium hypochlorite.
====Estimated Lifespan====
There are many producers of chlorine solutions all around the world. <!--See CAWST’s Sodium Hypochlorite Product Sheets for further details.-->
==CostCosts==
{{Treatment_Cost
|CapCost=US$ 0
Note: Program, transportation and education costs are not included.
==Country Field experiences==
==Manuals== ==Movies== ==LinksReference manuals, videos, and links==
*[http://www.cawst.org CAWST (Centre for Affordable Water and Sanitation Technology)]
*[http://www.enpho.org/drinking_water_quality.htm Drinking water quality information from Environment and Public Health Organization (ENPHO)]
==Acknowledgements==
This article is based on a factsheet from [http://www.cawst.org/ Centre for Affordable Water and Sanitation Technology (CAWST)], which is gratefully acknowledged.
==References==
* <cite id=CDCP07>Centers for Disease Control and Prevention (CDC 2007). Effect of Chlorination on Inactivating Selected Pathogens. Available at:www.cdc.gov/safewater/about_pages/chlorinationtable.htm </cite>
* <cite id=Lantagne08>Lantagne, D.S., Blount, B. C., Cardinali, F., and R. Quick (2008). Disinfection by-product formation and mitigation strategies in point-of-use chlorination of turbid and non-turbid waters in western Kenya. Journal of Water and Health, 06.1, 2008.</cite>
* <cite id=luby01>Luby, S., Agboatwalla, M., Razz, A. and J. Sobel (2001). A Low-Cost Intervention for Cleaner Drinking Water in Karachi, Pakistan. International Journal of Infectious Diseases; 5(3): 144-150.</cite>Cambodia.</cite>
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