By:

Anand Kadali,

Hari Prasad Gollapalli,

Kalyanam Sudheer Kumar.

What is Raw Water?

What is the need for treatment of raw water?

Industrial Waste WaterAgricultureNatural CalamitiesRadioactive WastesOil Spills etc.

Characteristics of Raw Water are classified as:

1) Physical Characteristics2) Biological Characteristics3) Chemical Characteristics

Physical Characteristics:

1) Colour2) Odour3) Temperature4) Turbidity

Biological Characteristics:

1) Viruses2) Algae/Fungi3) Animal/Plant Tissues

Chemical Characteristics:

Organic Inorganic Gases

Carbohydrates Alkalinity Hydrogen SulphideFats, Oils & Grease Acidity MethanePesticides Chlorides OxygenPhenols Heavy MetalsProteins PhosphorousSurfactants Sulphur

Toxic Compounds

Impurities present in river water can be classified into:

1) Suspended Solids (Dirt, Silt, Mud, Plankton, Coloured Organic Matter)

2) Iron & Dissolved Solids (Calcium, Magnesium, Iron, Nitrate, Chlorides, Silica & Sulphates )

3) Dissolved Liquids & Gases (CO2, NH3, o2, Hydrogen Sulphide & Oils)

RAW WATER INTAKE SYSTEM:

Koradi TPS: IEPL BELA TPS:

No. of Raw Water Intake pumps=7 No. of Raw Water Intake pumps=3(6 running / 1 standby) (2 running / 1 standby)Motor ratings: 6.6 KV, 1000 KW Motor ratings: 440V, 180A (max)Discharge capacity: 15000 cubic meter/hr Discharge capacity:1200 cubic meter/hr

Screening:

To prevent floating material of fairly large size.

Coarse Screens made of steel bars of 25mm diameter spaced about 100 mm Apart are provided to restrict the entry of any floating material.

Fine Screens are normally fitted immediately after coarse screens of order 6mm.

Pre Chlorination:

Chlorine is injected into raw water at a dosing rate of 2-5 mg/liter.

Pre chlorination destroys bacteria & kills algae.

Oxidizes and precipitates iron and manganese.

Reduces color and slime formation.

Raw Water Storage:

Raw Water stored as a backup of 7 to 8 days in plant’s reservoir.

This is sufficient to reduce pathogenic bacteria, suspended solids & river algae.

Raw water quality is noticeable purely as a result of retention of water provided.

Aeration:

Gases are absorbed or liberated from water.Excess CO2 and H2S are lost.oxygen is picked up from atmosphere.Volatile substance liberated by algae growth or decomposing organic

matter can be released out. Fe & Mn are oxidized and precipitated out.Taste , Odour and Corrosion Properties of water can be maximum controlled.

Coagulation:

A process by which small particles in suspension join together to form larger agglomerate. Fine suspended particles and colloids carry positive & negative charges.

For agglomeration fine particles should come in contact with each other. Mixing promotes the effect but violent mixing breaks down the attraction between the particles.

Coagulation Aids Poly Acryl amideActivated Silica

Flocculation:

Aluminum & Iron Salts gives good flocks normally slight acidic pH.5-6 pH for Fe and 6-7 pH for Al.

Al2(SO4)3+6H2O Al(OH)3+3H2SO4

When pH of water come down below coagulation pH, then Lime Ca(OH)2 is added to raise the pH level.

Clarifiers:

Water is cleared from most of the suspended particles. It consists of a flash mixer & settler in separate compartments.

Flash Mixer Chemicals dozed + high speed agitation + retentionFlocculation Chamber Gentle agitation + 20-60 minutes retention.Settling Chamber Collection of suspended particles.

Filtration:

Rapid Sand Filters consists a bed of graded sand of 30mm to 15mm mesh about 0.6m depth and gravel sizes of 2.5mm to 25mm.

The filter operates between 5-10 cubic meter/Hr and capable of removing particles of size 10 microns.

The filter are designed to backwash once/twice a day by filtered water only .

Activated carbon filter :

Granular carbon is used as a filter bed through which water is passed.

Limitations of ACF:

Filtration is a slow process.Bacterial growth Cl2 + H2O 2HCl + ½ O2

Conclusion:

Thus after the filtration process the water is stored in a filtered water storage tank and this water is called portable water/general service water and suitable for drinking and cooling of some auxiliaries and other purposes. This water is further sent to post treatment in DM Plant.