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The available raw waters must be treated and purified before they can be supplied to the public for their domestic, industrial or any other uses. The extent of treatment required to be given to the particular water depends upon the characteristics and quality of the available water, and also upon the quality requirements for the intended use..

Lecture 5: Preliminary Treatment: Silt Excluder Design Lecture 7: Coagulation - Flocculation Theory; Lecture 8: Rapid Mixing, Coagulation - Flocculation; Lecture 9: Coagulation - Flocculation Lecture 6: Sedimentation Tank Design Lecture 10: Filtration Theory; Lecture 11: Rapid Sand Filtration Lecture 12: Disinfection Lecture 13: Treatment Plant Siting and Hydraulics Lecture 6: Sedimentation Tank Design Lecture 1: Raw Water Source and Quality Lecture 5: Preliminary Treatment: Silt Excluder Design Lecture 7: Coagulation - Flocculation Theory; Lecture 8: Rapid Mixing, Coagulation - Flocculation; Lecture 9: Coagulation - Flocculation Lecture 6: Sedimentation Tank Design Lecture 10: Filtration Theory; Lecture 11: Rapid Sand Filtration Lecture 12: Disinfection Lecture 13: Treatment Plant Siting and Hydraulics Lecture 6: Sedimentation Tank Design Lecture 1: Raw Water Source and Quality
  The layout of conventional water treatment plant is as follows:

 

Depending upon the magnitude of treatment required, proper unit operations are selected and arranged in the proper sequential order for the purpose of modifying the quality of raw water to meet the desired standards. Indian Standards for drinking water are given in the table below.

Indian Standards for drinking water

Parameter
Desirable-Tolerable
If no alternative source available, limit extended upto
Physical
Turbidity (NTU unit)
< 10
25
Colour (Hazen scale)
< 10
50
Taste and Odour
Un-objectionable
Un-objectionable
Chemical
pH
7.0-8.5
6.5-9.2
Total Dissolved Solids mg/l
500-1500
3000
Total Hardness mg/l (as CaCO3)
200-300
600
Chlorides mg/l (as Cl)
200-250
1000
Sulphates mg/l (as SO4)
150-200
400
Fluorides mg/l (as F )
0.6-1.2
1.5
Nitrates mg/l (as NO3)
45
45
Calcium mg/l (as Ca)
75
200
Iron mg/l (as Fe )
0.1-0.3
1.0

The typical functions of each unit operations are given in the following table:

Functions of Water Treatment Units

Unit treatment Function (removal)
Aeration, chemicals use Colour, Odour, Taste
Screening Floating matter
Chemical methods Iron, Manganese, etc.
Softening Hardness
Sedimentation Suspended matter
Coagulation Suspended matter, a part of colloidal matter and bacteria
Filtration Remaining colloidal dissolved matter, bacteria
Disinfection Pathogenic bacteria, Organic matter and Reducing substances

 

 

 

 

 

 

 

The types of treatment required for different sources are given in the following table:

Source
Treatment required
1. Ground water and spring water fairly free from contamination
No treatment or Chlorination
2. Ground water with chemicals, minerals and gases
Aeration, coagulation (if necessary), filtration and disinfection
3. Lakes, surface water reservoirs with less amount of pollution
Disinfection
4. Other surface waters such as rivers, canals and impounded reservoirs with a considerable amount of pollution
Complete treatment
 
 

 

 

 

Lecture 5: Preliminary Treatment: Silt Excluder Design Lecture 7: Coagulation - Flocculation Theory; Lecture 8: Rapid Mixing, Coagulation - Flocculation; Lecture 9: Coagulation - Flocculation Lecture 6: Sedimentation Tank Design Lecture 10: Filtration Theory; Lecture 11: Rapid Sand Filtration Lecture 12: Disinfection Lecture 13: Treatment Plant Siting and Hydraulics Lecture 6: Sedimentation Tank Design Lecture 1: Raw Water Source and Quality