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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.
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.
Chlorine forms hydrochloric acid when added to water which reacts through oxidization with micro-organisms and kills them.
Three things can happen when chlorine is added to water:
#Some chlorine reacts through oxidization with organic matter and the pathogens in the water and kills them. This portion is called consumed chlorine.
#Some chlorine reacts with other organic matter and forms new chlorine compounds. This portion is called combined chlorine.
#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.
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.
==History and social context==
==Suitable conditions ==
Unlimited amounts of water can be processed at a time, depending on the amount of active chlorine.
{{Potential_Treatment_Capacity_table
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==What is a Sodium hypochlorite?Technical specification==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.
The effectiveness of chlorine contact time should be increased to 1 hour when the temperature is affected by turbidity, organic matter, between 10˚ and 18˚C. It should be increased to two or more hours when the temperature and pHfalls below 10˚C.
====Treatment efficiencyEfficiency====
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Toxoplasma oocysts and cryptosporidium oocysts are highly resistant to chlorine disinfection <ref name=cdcp07/>). Chlorine alone should not be expected to inactivate these pathogens in drinking water.
==Operating criteria==*'''Flow rate:''' Not applicable*'''Batch volume:''' Unlimited*'''Daily water supply:''' Unlimited The manufacturer’s instructions for specific sodium hypochlorite products need to be followed. The required dose and contact time varies with water quality (e.g. turbidity, pH, temperature). Use a 30 minute minimum contact time. If the pH is above 7.5, a higher FRC concentration of 0.6 mg/litre should be used and the contact time should be extended to 1 hour. The contact time should be increased to 1 hour when the temperature is between 10˚ and 18˚C. It should be increased to two or more hours when the temperature falls below 10˚C. <!--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. --> Maintenance==Robustness==
Free residual chlorine protects against recontamination. Most users cannot determine the dosing quantity themselves; proper use requires simple instructions from the manufacturer. Users often use less than the recommended dose to save money.
Chlorine requires a supply chain, market availability and regular purchase. It also requires quality control process to ensure product reliability. Sourcing suitable plastic containers to manufacture chlorine solutions can sometimes be a challenge. ==Estimated lifespan==Chlorine deteriorates over time, especially in liquid form. Liquid chlorine products should be used within 3 months of being manufactured. ==Manufacturing requirements==
=====Local production=Manufacturing====Can be made locally using salt water solution and electrolysis equipment.
* Generator with electrolysis equipment
* Plastic bottles and labelling equipment
* Water
Trained workers needed to produce and test the sodium hypochlorite.
Chlorine fumes and contact with skin are hazardous. 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.
==Maintenance requirements==Estimated Lifespan====Chlorine deteriorates over time, especially in liquid form. Liquid chlorine products should be stored in a cool, dark place in a closed containerused within 3 months of being manufactured. ====Suppliers====There are many producers of chlorine solutions all around the world. <!--See CAWST’s Sodium Hypochlorite Product Sheets for further details. -->
==Cost==
Note: Program, transportation and education costs are not included.
==OtherCountry experiences==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. ==Manuals==
==Movies==
==External linksLinks==
*[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)]
*[http://www.cdc.gov/safewater/publications_pages/pubs_chlorine.htm Centers for Disease Control and Prevention]
*[http://www.psi.org/child-survival Population Services International (PSI)]
==Footnotes==
<references/>
==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> {{Joinus}}
