WATER DISINFECTION METHODS. Part 1

There are a number of ways of purifying water. In evaluating the methods of treatment available, the following points regarding water disinfectants should be considered:

1. A disinfectant should be able to destroy all types of pathogens and in whatever number present in the water.

2. A disinfectant should destroy the pathogens within the time available for disinfection.

3. A disinfectant should function properly regardless of any fluctuations in the composition or condition of the water.

4. A disinfectant should function within the temperature range of the water.

5. A disinfectant should not cause the water to become toxic or unpalatable.

6. A disinfectant should be safe and easy to handle.

7. A disinfectant should be such that it is easy to determine its concentration in the water.

8. A disinfectant should provide residual protection against recontamination.

Techniques such as filtration may remove infectious organisms from water. They are, however, no substitute for disinfection.

The following are specific methods for disinfecting water.

BOILING WATER

Place water in a container over heat. Bring it to the boiling point. Hold it at this temperature for 15-20 minutes. This will disinfect the water. Perhaps you have used this technique after a flood or when a water main has burst as an emergency aid. Boiling water is an effective method of treatment because no important water-borne diseases are caused by heatresisting organisms.

ULTRAVIOLET LIGHT

The use of ultraviolet light is an attempt to imitate nature. As you recall, sunlight destroys some bacteria in the natural purification of water. Exposing water to ultraviolet light destroys pathogens. To assure thorough treatment, the water must be free of turbidity and color. Otherwise some bacteria will be protected from the germ-killing ultraviolet rays. Since ultraviolet light adds nothing to the water, there is little possibility of its creating taste or odor problems. On the other hand, ultraviolet light treatment has no residual effect. Further, it must be closely checked to assure that sufficient ultraviolet energy is reaching the point of application at all times.

Advantages of ultraviolet light: automatic, no taste or odor, and low contact time.

Disadvantages of ultraviolet light: low penetration power, shielding by turbidity, slime layer develops on tube, no simple test of results, no residual effect, and ultraviolet tube gradually loses power