Question

what are the steps involved in the purification of water of natural source for drinking purpose

Answer 1

The steps to purify water from a natural source are in the following order: Removal of large particles such as cobbles, rocks and sand. Coagulation of particles by adding chemicals e.g. alum and lime. Filtration to remove salt and other micro particles

Answer 2

eration

In some water treatment plants, the rst step is aeration. The raw water rst goes to aeration

tanks where large quantities of air are injected into and bubble through the raw water. Aeration

can reduce tastes and odors and can oxidize soluble iron.

Flash Mixing

The next step after aeration is ash mixing. If the raw water is not rst aerated, then the rst step

usually is ash mixing.

One or more chemicals are mixed into the raw water to neutralize or remove specic impurities

found in the raw water. The types and amounts of chemicals added depend on the types and

concentrations of impurities found in the raw water. If the water is hard (high in dissolved calcium

and magnesium), lime and sodium carbonate may be added. If ne particulates are present, alum

may be added. If bacteria and other organics are present, chlorine may be added as a

disinfectant. The raw water and the added chemicals are mixed by agitation in ash mixing

chambers. The goal is instantaneous mixing and accurate measuring of the added chemicals.

Flocculation

After ash mixing, the mixing of the chemicals and the raw water continues but at a slower pace.

The added chemicals react with the impurities in the raw water and remove the dissolved

impurities by reacting with the impurities and forming small particles of solid matter suspended

in the water. During this slow and gentle mixing, the solid particles (called oc) accumulate in

feathery white agglomerations.

Settling

Gravity and time are all that is needed to remove the oc from the water. The water is sent to

a clarier (settling basin) where the oc is allowed to settle out of the water. These settling basins

are typically twelve to eighteen feet deep and hold the water for two to four hours at a forward

velocity of 0.5 to 3 feet per minute. The settled sludge is often disposed of in a sewer.

Filtration

Allowing the partially treated water to settle may remove some, but not all, of the oc. The water

usually is then ltered through sand to remove remaining solids. Sand ltration further puries the

water by permitting additional impurities to be adsorbed (adhere) to the surfaces of the sand

particles.

During ltration, the sand particles acquire a sheath of oc. From time to time, the sand lter is

cleaned by shutting off the ow of partially treated water and then forcing puried water up

through the sand bed, in a direction of ow opposite from that used by partially treated water. The

water used for cleaning is then disposed of (usually, in a sewer) and the sand is allowed to settle

back down. The sand lter is then ready for reuse.

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PEACE