Question

Please explain the science behind municipal water treatment including chlorination and alternatives to chlorination (UV radiation, etc).

Answer 1

Removal of undesirable impurities from municipal waste is called as municipal water treatment. The methods can be classified as

1. Physical processes such as filtration, sedimentation, and distillation

2. Biological processes such as slow sand filters or biologically active carbon;

3. Chemical processes such as flocculation and chlorination and the use of electromagnetic radiation such as ultraviolet light.

Chlorination is effective against many pathogenic bacteria, but at normal dosage rates it does not kill all viruses, cysts, or worms. When combined with filtration, chlorination is an excellent way to disinfect drinking water supplies.

Chlorine is a strong oxidant that rapidly kills many harmful micro-organisms. Because chlorine is a toxic gas, there is a danger of a release associated with its use. This problem is overcome by the use of sodium hypochlorite, which is a relatively inexpensive solution used in household bleach that releases free chlorine when dissolved in water.

UV radiation can be described as invisible light. UV energy penetrates the outer cell membrane, passes through the cell body and disrupts its DNA preventing reproduction. UV treatment does not alter water chemically; nothing is being added except energy. The sterilized microorganisms are not removed from the water. UV disinfection does not

remove dissolved organics, inorganics or particles in the water.

The degree of inactivation by ultraviolet radiation is directly related to the UV dose applied to the water and is measured in microwatt second persquare centimeter