Water purification

Water purification is the process of removing undesirable chemicals, biological contaminants, suspended solids, and gases from water. The goal is to produce water fit for specific purposes. Most water is purified and disinfected for human consumption (drinking water), but water purification may also be carried out for a variety of other purposes, including medical, pharmacological, chemical, and industrial applications. The methods used include physical processes such as filtration, sedimentation, and distillation; biological processes such as slow sand filters or biologically active carbon; chemical processes such as flocculation and chlorination; and the use of electromagnetic radiation such as ultraviolet light.

Methods

Water purification methods vary widely, and the method chosen often depends on the nature of the water source and the intended use of the water.

Physical processes

Physical processes include sedimentation, filtration, and distillation. Sedimentation involves the settling of suspended particles, often after the addition of a chemical flocculant. Filtration can be through granular media, such as sand or activated carbon, or through membranes, such as those used in reverse osmosis. Distillation involves boiling the water and then condensing the steam.

Biological processes

Biological processes use organisms to remove contaminants. Slow sand filters rely on biological activity in a layer of sand to filter out particles and microorganisms. Biologically active carbon filters use a similar process, but with activated carbon as the medium.

Chemical processes

Chemical processes include flocculation, in which a chemical is added that causes particles to clump together and settle out of the water, and chlorination, which kills microorganisms.

Electromagnetic radiation

Ultraviolet light can be used to kill microorganisms in water. This is often used in combination with other purification methods.

Health effects

The purification of water is a crucial step in preventing waterborne diseases. Some waterborne diseases include cholera, typhoid, and dysentery.

Environmental impact

Water purification processes can have an environmental impact, particularly in terms of the energy used and the disposal of residual sludge.

See also

• Water treatment
• Waterborne diseases
• Drinking water