WATER THAT IS SUITABLE FORDRINKING IS CALLED POTABLE WATER.
1. Screening2. Sedimentation3. Coagulation4. Filtration5. Disinfection of water
In order to remove floating impuritiesscreening is carried out. screens of differentkinds such as Bar screen, drum screen, andmicro screeners are employed. These screensretain any floating impurity and are cleaned.
Sedimentations a process of removing suspendedimpurities by allowing the water to stay undistributedfor some time in large tanks when most of suspendedparticles settle down due to force of gravity. Theaccumulation of the debris at the bottom of tank isperiodically scraped and removed.•The velocity with which a particle in water falls underthe action of gravity depends upon following factors:•The horizontal flow of velocity of water•The size of particle•Temperature of water
Coagulation is a process of removing colloidal particles from water by addition of certain chemicals known as coagulants before sedimentation. Colloidal particles present in water either do not settle down at all or take a very long time. These coagulants reacts with bi-carbonates present in water and form bulky gelatinous precipitate called flock. Colloidal particles are very small sized particles possessing either positive or negative charge. colloidal particles of clay possess negative charge.
Gravity sand filter Pressure filter
•Filtration is a process of removing insoluble colloidaland bacterial impurities by passing water through abed of proper sized material.•It consists of a large shallow rectangular tank made ofconcrete. At the bottom of the tank, there is a channelof brick through filtered water goes out.•The rate of filtration after 24 hours of use becomesslow due to clogging of pores of sand layer is scrappedoff and replaced by a new sand layer. And thescrapped sand is reused.•These filters are also best for municipal water supplyand the scrapped sand is re-used after washing withwater.
•Body aid is used when the slurry is low in solids content withfine and slimy particles that are difficult to filter. To enhancefiltration coarse solids with large surface area are added to theslurry and serve as a body-aid that captures and traps in itsinterstices the slow filtering particles and produce a porouscake matrix. The amount added depends on the nature of thesolids and varies from ½ for non-compressible and up to 5times for gelatinous solids.•Precoating the plates with a 2-3 mm thick medium of a knownpermeability and its application requires skills since it takes-upeffective cake volume, lengthens the cycle time and an overconsumption can be quite costlyThe following materials serve as body-aid or are used to form a precoat: Diatomaceous Earth (also called Diatomite) consisting of silicaceous skeletal remains of tiny aquatic unicellular plants. Perlite consisting of glassy crushed and heat-expanded rock from volcanic origin. Cellulose consisting of fibrous light weight and ash less paper like medium.Special ground wood is becoming popular in recent years since it is combustible and reduces the high cost of disposal. There are nowadays manufacturers that grind, wash and classify special timber to permeabilitys which can suit a wide range of applications.
The disinfection of water can be carried out by following methods: Boiling Chlorination Aeration Removal of algae Ultraviolet rays ozonisation
Water disinfection means the removal, deactivation or killing of pathogenic microorganisms. Microorganisms are destroyed or deactivated, resulting in termination of growth and reproduction. When microorganisms are not removed from drinking water, drinking water usage will cause people to fall ill.Sterilization is a process related to disinfection. However, during the sterilization process all present microorganisms are killed, both harmful and harmless microorganisms.