What is Disinfection?

Disinfection is a treatment process that ensures drinking water is free from harmful organisms or pathogens.

There have 3 types of disinfection method which are:

• Disinfection by boiling

• Disinfection by chlorine

• Disinfection by solar (UV)

1. Disinfection by boiling

-Very effective though energy consuming method to destroy various pathogens such as viruses, spores, cysts and worm eggs.

-The water should be brought to a rolling boil for at least five minutes and preferably up to a period of twenty minutes. Apart from the high energy costs involved in boiling, the other disadvantage is the change in taste of water due to the release of air from the water.

-The taste can be improved by vigorously stirring the water, or shaking the water in a sealed container after it has cooled. A better water quality can be obtained by storing the boiled water, as described earlier.

2. Disinfection using chlorine

- Chlorine is a chemical most widely used for the disinfection of drinking water because of its ease of use, ability to measure its effectiveness, availability and relatively lower cost.

-When used correctly, chlorine will kill all viruses and bacteria, but some species of protozoa and helmithes are resistant. There are several different sources of chlorine for home use; in liquid, powder and tablet form.

-Chlorine is commonly available to households as liquid bleach (sodium hypo chlorite), usually with a chlorine concentration of 1%. Liquid bleach is sold in bottles or sachets, available on a commercial basis.

Chlorine must be added in sufficient quantities to destroy all the germs but not so much as to affect the taste adversely. The chemicals should also have sufficient contact time with the pathogens (at least 30 minutes for chlorine). Deciding on the right quantity can be difficult, as substances in the water will react with the disinfectant at different rates.

-Furthermore, the strength of the disinfectant may decline with time depending on how it is stored. It is therefore recommended that in emergency situations, chlorine solutions be centrally dispensed to the users by qualified personnel. Displaced people should receive standard containers for collecting/storing water, as well as simple dropper tubes or syringes.

-Technical staff should provide the instructions for mixing the chlorine solution, at the point of dispensing. See Note 1 Cleaning and disinfecting wells for details of preparing chlorine solutions.

3. Solar disinfection

- Ultra-violent rays from the sun are used to inactivate and destroy pathogens present in water. Fill transparent plastic containers with water and expose them to full sunlight for about five hours (or two consecutive days under 100% cloudy sky).

-Disinfection occurs by a combination of radiation and thermal treatment. If a water temperature of least 50oC is achieved, an exposure period of one hour is sufficient. Solar disinfection requires clear water to be effective.

An enhanced example is the SODIS system, whereby half-blackened bottles are used to increase the heat gain, with the clear side of the bottle facing the sun, as shown above.