Design Concept of Water Treatment Plant

Components of Water Treatment Plant, Methods of Water Treatment, Process of Water Treatment such as Aeration, Sedimentation, Filtration and Disinfection etc.

1. DESIGN CONCEPTS OF
WATER TREATMENT PLANT

2. Water Availability
Water is the vital fluid essential for Life.
Water is available in nature. 2/3
rd
Earth Surface is
covered by water bodies. However most of this is not
fit for consumption.
Water fit for consumption is mainly available from
surface water bodies like rivers, lakes, ponds etc and
from Sub surface sources.
Water is never available in its purest form as it
readily absorbs impurities from air and soil.

3. Usage
Water is used for
•Domestic water supply
•Industrial water supply
•Agricultural supply
•Stock and wild life water requirement
•Propagation of fish and other aquatic life
•Shell fish Culture
•Swimming and bathing
•Boating and other recreation
•Water power and Navigation etc.

4. Quality
Quality of water depends on the ultimate use it is put to.
WHO has put down certain guidelines for quality of water to be used for domestic purposes especially
drinking. The standards with respect to major impurities is as given below::
S. No.Characteistics Acceptable Cause for rejection
1 Turbidity (NTU) 1.0 10
2 Colour 5 25
3. Taste & Odour Objectionable Objectionable
4. pH 7.0 – 8.5 < 6.5 & > 9.2
5. Total Dissolved Solids (PPM) 500 2000
6. Total Hardness as CaCO
3
(PPM) 200 600
7. Chlorides as Cl 200 1000
8. Sulphates as SO4 200 400
9. Flourides as F 1.0 1.5
10. Nitrates as NO3 45 >45
11. Calcium as Ca 75 200
12. Magnesium as Mg < 30 150
13. Iron as Fe 0.1 1.0
14. Manganese as Mn 0.05 0.5
15. Copper as Cu 0.05 1.5
16. Zinc as Zn 5.0 15.0

5. Unit Operations
Sl. No. Operation Target
1 Aeration a. Dispel Dissolved gases like
CO2, H2S
b. Remove dissolved Minerals
like Fe, Mg, Mn
c. Dissolved Organic matter
2 Screening Floating matter
3 Sedimentation
a) Plain,
b) Aided with Coagulation
a. Larger and Heavier Particles
b. Smaller and lighter
Suspended solids
4 Filtration Fine Suspended and colloidal matter
and living organisms like Bacteria
5 Disinfection Killing of Living Pathogens
6 Chemical Dissolved Minerals, other organic
matter, salts causing Hardness
7 Special Processes (Activated Carbon etc.) Removing Taste and odour

6. Preliminary Activities
Study to be conducted on
•Selection of site
•Source and Quality of Water

7. Various Flow Charts Which Can be Adopted
Surface Water:
1.Storage – Disinfection
2.Sedimentation – Slow sand Filtration – Disinfection
3.Pre Chlorination – Aeration – Rapid mixing – Flocculation –
Sedimentation – Rapid Sand Filtration – Post Chlorination
4. Rapid mixing – Flocculation– Rapid Sand Filtration – Post Chlorination
Ground Water:
1.Disinfection
2.Aeration - Rapid mixing – Flocculation – Sedimentation – Rapid Sand
Filtration – Post Chlorination
3.Softening - Rapid Sand Filtration – Post Chlorination
4.Rapid Sand Filtration – Softening - Post Chlorination - Demineralisation

8. Aeration
Objectives:
•To Control Taste and Odour
•To Precipitate Fe and Mn
•To expel Carbon Dioxide and Hydrogen Sulfide

9. Aeration
Methods:
•Gravity Aerators
•Spray Aerators
•Diffusers
•Mechanical Aerators

10. Gravity Aerators
Commonly termed as Cascade Aerators.
Design Parameters:
Height of structure: 1.2 – 3.0m
No. of Steps/Trays: 4.0 – 6.0
Area of Aerator : 0.015 – 0.045 sqm/cum.hr

11. Spray Aerators
Commonly Known as Pressure Aerators spray drops of water into air from stationary / moving
nozzles.
Design Parameters:
Dia of Nozzle : 1.0 – 4.0 cm
Rate of Discharge: 18 – 36 cum/hr at 2.0 to 9.0m pr.
Spacing of Nozzles : 0.5 – 1.0m or more
Aerator Area : 0.03 – 0.09 sqm/cum.hr

12. Diffusers
Compressed Air is injected into water through perforated piping under pressure
Design Parameters:
Depth of Tank : 3.0 – 4.5 m
Width of Tank : 3.0 – 9.0 m
Width to Depth ratio: < 2:1
Detention Time : 10 – 30 mins
Air requirement : 0.06 -1.0 cum/cum of water
Power Requirement : 3 – 13 W /cum.hr

13. Mechanical Aerators
Paddle Type Mixers are provided in the aeration tank to circulate the water in it and renew its air
water interface

14. Coagulation & Flocculation
Agglomeration and Settling of Particles by using Chemical Processes is called
COAGULATION.
FLOCCULATION is bringing together fine suspended particulates into groups.
This is done by using Chemical methods.
Coagulants Used:
•Alum (Aluminum Sulphate)
•Liquid Alum
•Ferric Sulfate
•Polyelectrolytes
Neutralisers used:
•Sulphuric Acid
•Lime
•Soda Ash

15. COAGULATION & FLOCCULATION

16. Equipment
Coagulation and flocculation is resorted to by rapid mixing of chemicals
with water followed by slow speed Flocculation Equipment:
Types of Flocculators:
1.Vertical Baffled Channels
2.Horizontal Baffled Channels
3.Hydraulic Jet Action Flocculator
4.Alabama Type Flocculator
5.Mechanical Type Flocculator
a) Horizontal Paddle Type
b) Vertical Paddle Type

17. Design Criteria
Rapid Mixing (Flash Mixer)
•Detention Time : 30 – 60 secs
•Velocity of Flow: 0.9 m/sec
•Depth of Tank : 1 – 3 m
•Power Requirement: 0.041 Kw/1000cum.day
Flocculator
•Detention Time : 10 – 40 mins
•Velocity of Flow: 0.2 -0.8 m/sec
•Depth of Tank : 3.0 – 4.5 m
In case of Paddle Flocculators
•Power Requirement: 10 -36 Kw/MLD
•Total Paddle area: 10 to 25% of the surface area

20. SEDIMENTATION
Separation of solids from liquids by gravity.

21. Solid – Liquid Separation
•Horizontal Flow Tanks
(Circular/rectangular)
•Vertical Flow (Hopper Bottom) Tanks
•Tube deck settling tanks

22. Rectangular Type
Clarifier

23. Circular Clarifier

24. Clariflocculator

25. Design Considerations
Rapid Mixing (Flash Mixer)
•Detention Time
Plain Sedimentation: 3.0 - 4.0 hrs
For Coagulated water: 2.0 - 2.5 hrs
For vertical upflow clarifiers1.0 – 1.5 hrs
•Velocity of Flow: 0.3 m/sec
•Depth of Tank : 3.0 m
•Power Requirement: 0.041 Kw/1000cum.day
•Surface Loading Rate
Circular Horizontal flow:30 - 40 cum/sqm.day
Plain Sedimentation: 15 - 30 cum/sqm.day
For vertical upflow clarifiers40 - 50 cum/sqm.day
•Weir Loading Rate: 100 – 300 cum/m.day
•Extra capacity for sludge25%

26. Conventional Clarifier
Tube Settler

27. Filtration
Removal of very fine colloidal particles which
cannot be removed by sedimentation. Water
after sedimentation is allowed to flow through
a bed of sand where in these particles are
filtered out.
Types:
1.Slow Sand Filters
2.Rapid Gravity Filters
3.Pressure Filters

28. Slow Sand Filtration
Provides single stage treatment. Normally no
pretreatment is required.
The filter basically consists of a supernatant
water layer, Filter media layer and a under
drain support structure. Water enters from
the top and the filtrate is removed from the
bottom.

29. Design Aspects
Rate of Filtration : 100 lph/sqm
Design period: 10 years
No. of Units:
Area in sqm No. of Beds
Upto 20 2
20 -249 3
250 – 649 4
650 – 1200 5
1201 – 2000 6
Length : Width : 2 : 1
Depth of water over sand: 1.0m
Effective size of sand: 0.2 -0.3 mm
Uniformity co efficient of sand 3.0 – 5.0
Depth of Sand Bed : 1.0m
Under Drain : Open Jointed brick masonry
Gravel Bed Gradation : Top most : 1 to 2mm, Second : 3 to 6mm, Third : 9 to 18mm and bottom
most : 27 to 54mm (Each layer is 60mm thick and total thickness is 300mm
Depth of Filter Bed : FB – 0.2m, Water Depth – 1.0m, Filter media – 1.0m, Gravel support – 0.3m,
Brick Drain – 0.2m (Total Depth – 2.7m)
Length of Filter run : not less than 6 – 8 weeks

31. Rapid Gravity Filtration
Filters designed to operate at a higher
filtration rate than rapid gravity filters are
called Rapid Gravity or Rapid Sand Filters.
It has a well designed drainage and Back Wash
System

32. Design Aspects
Rate of Filtration : 80 lpm /sqm
No. of Units : N=ÖQ/4.69 (min -2 nos.)
Area : max 100 sqm for one unit
Length : Width : 1.25 to 1.33
Depth of Filter Bed : 2.6m incl. 0.5m FB
Effective size of sand: 0.45 -0.70 mm
Uniformity co efficient of sand 1.3 – 1.7
Depth of Sand Bed : 0.75 m
Gravel Layer : 2-5mm size at top to 50mm size at bottom with a thickness of 30 – 50 cm
Under Drain : Piping grid with Manifold in the centre and laterals placed across (10 –
200 mm c/c spacing) - Details in next slide
Depth of water over sand: 1.0 – 2.0m
Back wash:
Air : 0.6 – 0.9 cum/sqm.min of filter area at 0.35 kg/sqcm. Perid – 5mins.
water : 0.4 – 0.6 cum/sqm.min
Wash water Tank : sufficient for 10 mins wash of one filter. With 9 – 11m elv above wash
water troughs
Head Loss : 2.5 – 3.0m
Note : Inlet and outlets to be designed for 100% overload.

33. Design of Under Drain System
1. Ratio of total area of orifices to filter bed area : 0.15 to 0.5% Preferably 0.3%
2. Ratio of cross sectional area of laterals to area orifices served : 2:1 to 4:1 preferably 2:1
3. Diameter of Orifices : 6mm to 18mm
4. Spacing of Orifices : 30 cm for 18mm dia to 7.5 cm for 6mm dia.
5. Ratio of area of Manifold to area of laterals served : 1.5:1 to 2:1
6. Spacing of laterals : approximately close to spacing of orifices
7. Length of Lateral on each side of the manifold : not more than 60 times its diameter
8. Orifice to be located downwards at an angle of 30 to 60 deg with vertical
Typical Velocities to be maintained in conduits / pipes:
1. Influent conduit carrying raw water : 0.9 to 1.8 m/sec.
2. Influent conduit carrying flocculated water : 0.8 – 1.8 m/sec.
3. Effluent conduit carrying filtered water : 0.9 -1.8 m/sec
4. Drainage conduit carrying spent wash water : 1.2 – 1.4 m/sec
5. Filter to waste connection ; 3.6 to 4.5 m/sec.

36. Comparision
Parameter Slow Sand Filter Rapid Sand Filter
Rate of Filtration 100 – 150 lph/sqm 80 – 100 lpm/sqm
Area Requirement High 20% of SSF considering
pretreatment units
Loss of Head 1.0 – 1.5 m 2.50 to 3.0 m
Filter Media Fine Sand Coarser sand
Flexibility in Operation Low High
Cleaning No regular cleaning Regular cleaning by
Backwash and air wash
Pre Treatment Not required Required
Post Treatment Not required Needs Disinfection
Bacterial Purification Completely eliminates
pathogens
Not effective and hence post
disinfection to be done
Removal of colour and odourNot effective Very effective

37. Other Type of Filters
•Pressure Filters
•Dual media filters
•Declining rate filtration
•Upflow Filters
•Radial flow Filters
•Valveless Automatic Gravity Filters

39. Small Contaminants Pass
Through Simple Filters
•Sand, gravel, and charcoal don’t filter
out some contaminants, like
–Bacteria
–Viruses
–Industrial pollutants
–Agricultural pollutants
–Salt

40. Disinfection
•Disinfection is Destruction or inactivation
(Sterilization) of disease-producing organisms
i.e. pathogens (Bacteria, Viruses, etc.)
responsible for water-borne diseases..
Chlorine is the most effective disinfectant that
is being used all over the world for over 170
yeas now.

41. Design Parameters
Temperature
Time of contact (15 to 20 mins)
Effect of pH
Parameters effecting chlorination:
•Colour and Turbidity more than 5-10 units
•Bacteria is not in a concentrated form and is not bedded onto
suspended solids
•Concentration of Manganese and iron should be less than 0.3 ppm
•There should not be any taste and odour producing impurities
•Minimum contact period of 15 mins

42. Types of Chlorinators
Differential Pressure Type Chlorinator
Gravity Type Chlorinators
Drip Chlorination

44. Other Systems of Disinfection
•Disinfection by Heat
•Ultravoilet Disinfection
•Ozone Disinfection
•Chlorine compounds:
–Bleaching Powder
–Hypochlorite
–Sodium Hypochlorite
–Chlorine and Iodine Tablets
–Potassium Permanganate

45. UV Disinfection
•UV Light
–Specific wavelengths have biocidal properties
(~254 nm)
–Quartz, mercury-vapor lamps
–Cleaning required
–No residual

46. UV Disinfection
a specific wavelength of light

47. UV Disinfection

48. How Can We Trap Smaller How Can We Trap Smaller
Contaminants?Contaminants?

49. Membrane Technology
•A membrane is a thin material that has pores (holes) of
a specific size
•Membranes trap larger particles that won’t fit through
the pores of the membrane, letting water and other
smaller substances through to the other side

50. Types of Membrane
•There are four general categories of membrane filtration
systems
–Microfiltration
–Ultrafiltration
–Nanofiltration
–Reverse Osmosis

52. Membrane Filter Technologies
Filter typeSymbol Pore Size,
mm
Operating
Pressure,
psi
Types of Materials
Removed
MicrofilterMF 1.0-0.01 <30 Clay, bacteria, large
viruses, suspended
solids
UltrafilterUF 0.01-0.001 20-100 Viruses, proteins,
starches, colloids,
silica, organics, dye,
fat
Nanofilter NF 0.001-0.0001 50-300 Sugar, pesticides,
herbicides, divalent
anions
Reverse
Osmosis
RO < 0.0001 225-1,000 Monovalent salts

53. Typical MF Membrane System

54. How RO Works
•Osmosis is a natural process that
moves water across a
semipermeable membrane, from
an area of greater concentration to
an area of lesser concentration
until the concentrations are equal
•To move water from a more
concentrated area to a less
concentrated area requires high
pressure to push the water in the
opposite direction that it flows
naturally
Osmosis
Reverse Osmosis

55. If RO Can Get Everything
Out That Would Make
Water Undrinkable, Why
Not Just Use RO Membranes
by Themselves?

56. RO is Not for Everything!
•High pressure is required to push the
water through the smallest pores
–RO is the most efficient filtration
system
•Because pores are so small, big
particles can clog them (called
fouling)
–This makes the filtering
membrane unusable
Pores clogged with
large objects
Fouling of RO pores

57. Virus
Protein
A Series of Filtrations
Increases Efficiency
•Filters can be sequenced from large to small pore size to decrease fouling
–They must still be cleaned regularly to remain usable

58. Merits and Demerits of Membrane
Process
Merits
• Reduces the number of unit processes in treatment systems
• Potential for process automation and plant compactness
• Much smaller foot print than the conventional plants
• Easy scale-up, expansion and retrofication
• Less or no chemical use and provides highest quality water
• No formation of secondary chemical by-products
• Less sludge production
• Water reuse and recycling
Demerits
Membrane fouling
Low membrane life time
Low selectivity
High capital and operating cost???

59. HEAVY METAL REMOVAL