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DisinfectionWater disinfection means the removal, deactivation or killing of pathogenic microorganisms. Microorganisms are destroyed or deactivated, resulting in termination of growth and reproduction. When microorganisms are not removed fromdrinking water, drinking water usage will cause people to fall ill.

Sterilization is a process related to disinfection. However, during the sterilization process all present microorganisms are killed, both harmful and harmless microorganisms. **

Properties of Good DisinfectantMust destroy pathogens in reasonable period of time.Non toxic to human and animalEasily dispensableSafe and easy to transport and handle Must persist in sufficient concentration to provide possible recontamination.

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Water Disinfection Methods

Physical : Formation of mutagenic and carcinogenic agents in water and wastewater effluent treated with chlorine has prompted research to seek alternative disinfecting methods that would minimize environmental and public health impacts. Some techniques are already available commercially. This category is represented by techniques employing such physical principles for disinfection as 1. Radiation 2. Ultrasound3. Ultrafiltration 4.Reverse osmosis5. Heating 6.Freezing7. ionizing radiation. Disinfecting small quantities of water by pasteurizing with heat or solar energy is a technology with some potential, but requires further chemical

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Chemical Methods of Disinfection of WaterChemical methods depend mostly on selected chemicals with oxidizing and biocidal properties. Their practical applications range from removing undesirable constituents to disinfecting water supplies, wastewater treatment effluent, or industrial waters. The most commonly used chemicals include OzoneChlorine and some of its compoundsPotassium permanganateHydrogen peroxide.**

Chemical Water Disinfection

Two of the most common chemical water disinfecting agents, which may be used in an emergency situations, are chlorine and iodine (halogens).Chloramines and Ozone are also used by water treatment plants. In order for chemical disinfection to be effective, the water must be filtered and settled first. Chemical disinfection often leaves an undesirable taste in water, which an activated carbon filter can remove post-treatment. Otherwise, you can minimize bad taste and odor by reducing the disinfectant concentration and increasing contact time before drinking.**

Another option to remove the taste of chlorine and iodine from water is to add a pinch of ascorbic acid, which is available in crystal or power form. This converts chlorine into chloride and iodine into iodide, both of which have no taste or odor.Chlorine may be used in gas, liquid or solid form to disinfect water. Because chlorine gas is highly toxic and can be dangerous if released into the atmosphere, this form of disinfection must be done in a very controlled environment. Otherwise, the danger is avoided by the use of chlorine in liquid form (sodium hypochlorite) or solid form (calcium hypochlorite). **

Household bleach is made up of 3-6 percent sodium hypochlorite and the EPA recommends using it to disinfect water in emergency situations. While chlorine is a highly effective and widely used method of water disinfection, it reacts with organic compounds in water, forming trihalomethanes (THMs) and haloacetic acids, which are carcinogenic in large quantities. The best way to avoid this is to remove as many organics as possible, prior to disinfection. If necessary, some commercial water filters also remove chlorine and its by product,s post-treatment.

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Chlorination

Cl2 + H20 --> HCl + HOCl

HOCl --> H+ + OCl-

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Draw backs of chlorinationDisinfection by chlorination can be problematic, in some circumstances.

Chlorine can react compounds found in the water supply to produce dangerous compounds, known as disinfection byproducts (DBPs). The most common DBPs are trihalomethanes (THMs)

products are carcinogenic .**

Theories Chlorine disinfection action Chlorine reacts with water and nascent oxygen is producedAction of chlorine is due to complete oxidative destruction of organismCl reacts with protein and amino acid and destroys the protoplasmHOCl penetrates cell walls.

chemical reaction of HOCl with an enzyme system in the cell which is essential to the metabolic functioning of the organism.

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Important factorsThe influencing factors to be considered in chlorination practices are the following:

chlorine concentration,contact time,pH,temperature, andinterfering substances**

Boiling

Waterborne illness is caused by bacteria, viruses and parasitic often found in rivers, lakes and other dirty water sources. Heating the water to boiling point kills these disease-causing microorganisms and is the surest way to make contaminated water safe for drinking. TheCenters for Disease Control (CDC)and theEnvironmental Protection Agency (EPA)both recommend that you boil water vigorously for one minute, to ensure that all microorganisms are killed. Boiling will not rid the water of any unpleasant taste. However, aeration of the water may improve bad taste.. In developed countries, boiling is usually the recommended solution in emergency situations where accidental water contamination has been reported. However, if boiling is not an option, residents often resort to drinking bottled water.*

UV Water Purification

Ultraviolet radiation penetrates the cell walls of microorganisms and disrupts their DNA, making them unable to reproduce. Though they remain present in the water, they are inactive, and thus, leave no risk of waterborne illness. UV light is effective against viruses and bacteria but may not inactivate parasitic cysts. As with ozone, a secondary method is often necessary to prevent the regrowth of organisms, post-treatment. s. **

Filtration

Filtration is often the first and last step taken in these common methods of water disinfection. It isrecommended prior to the disinfection of water to remove particles that hinder the disinfecting process. Following disinfection, filtration may also be used as a secondary method to remove cysts, along with the bad taste and odor caused by chemical byproducts.**

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