Describe the various steps involved in getting clear water from wastewater.

Explanation

The purification of water basically involves two steps:
(i) Removal of suspended impurities.
(ii) Removal of microorganisms.
(i) Removal of suspended impurities
(a) Sedimentation: River water is pumped into settling tanks and allowed to settle without any disturbance. The suspended impurities being larger particles settle down on standing.
(b) Addition of chemicals: The above process makes water only semi clear. This is passed into mixing chamber where alum and lime are added to water and it is agitated with huge mechanical blades. Later on, this water is pumped into sedimentation tank. Alum hastens the process of precipitation of suspended impurities. During the precipitation process, some bacteria also get trapped and removed.
(c ) Filtration through sand and gravel: The clear water obtained is pumped into sand and gravel filter. This removes all remaining traces of suspended impurities.
(ii) Removal of microorganisms
Addition of bleaching powder releases chlorine which helps in killing the harmful bacteria and the pure water obtained is stored in storage tanks.
The water so obtained at the end of the above purification process is devoid of suspended impurities and harmful bacteria. This water is fit for drinking and is called potable water. Potable water contains dissolved gases such as `O_(2)` and `CO_(2)` and also some dissolved salts especially common salt. These salts play an important role in the metabolic activities. They also provide taste to water. Therefore this water is very much suitable for human consumption.