As per GTU syllabus

1. Introduction
Prepared by
Prof. R m Bhadaraka

2. What is Wastewater?
Every human society uses water for domestic, commercial
and industrial activities and as a result of that there is a
formation of wastewater.
The wastewater from residential and commercial area is
known as domestic wastewater.
The wastewater from industrial area is known as industrial
wastewater.

3. Why wastewater collection is required?
Wastewater from residential area contain human excreta
urine, micro organisms.
Domestic wastewater may have pathogenic organisms in it.
Inhygienic condition shall be developed if proper collection,
conveyance treatment and disposal system do not exist.

4. Terminology
 Sewage :
 Wastewater generated in latrines is known as Sewage.
 Sullage :
 Wastewater generated in bathrooms and kitchen is known as
Sullage.
 Soil pipe :
 Sewage convey through Soil pipe.
 Waste pipe :
 Sullage convey through Waste pipe.

5. Layout of Typical Sewerage System

6. Layout of Typical Sewerage System
Domestic Wastewater Sewage + Sullage
Municipal Wastewater
(where there is industrial zone)
Domestic wastewater + Industrial wastewater
Sewage + Sullage + Industrial wastewater
Municipal Wastewater
(no industrial zone)
Domestic Wastewater
Sewage + Sullage

7. Sewerage System
Combine System

8. Sewerage System
Separated System

9. Classification of Sewers
Brick Sewer
Stoneware or Vitrified clay Sewer
Asbestos Cement Sewer
Cement Concrete or Reinforced Cement Concrete Sewer
Plastic Sewer Pipes
Glass Fibre Reinforced Plastic Sewer Pipes

10. Brick Sewer
Quiet Cheaper
Locally available and moderately smooth surfaces.
Sewer structure like manholes easily made by it.
Construction cost is higher .
They are not rapidly constructed.
 It is found suitable for large size sewers carrying combine
wastewater system.

11. Brick Sewer

12. Corrosion of Brick Sewer
 Cement reacts with the gases liberated from faecal matter
containing wastewater and subjected to corrosion.

13. Vitrified clay Sewer
Widely used for manufacturing sewers.
Surface of it is very smooth, impervious and also high durable.
It has high resistance to corrosion and erosion.
They are used for small discharge because of their diameters are
small.
The maximum diameter is restricted up to 60cm.
It is difficult to make large size pipes and glaze it.
Another reason is their weight and difficulties in shipping and
transport.
It has a spigot type arrangement.

14. Vitrified clay Sewer

15. Cement Concrete Sewer Pipes
Very popular when size of sewer is very large
High strength with low cost.
They may precast and cast in situ.
It may be plain or reinforced cement concrete depend up on the
strength required.
Cost of construction is plausible.
Smoother and low weights.

16. Cement Concrete Sewer Pipes

17. Chemical Attack on Cement Concrete Sewer
If the sewer exposed to sewage , it is subjected to corrosion.
To resist adverse effect of above, concrete with good quality,
made from well graded aggregates, acid resistant cement.
The corrosion of sewer is mainly due to acidic industrial
wastewater and hydrogen sulphide produced due to anaerobic
decomposition of the organic matters with sulphates.

18. Precaution to Chemical Attack
Partially purification of wastewater to reduce sulphur.
Raising Oxidation reduction potential by adding nitrates compounds.
Aeration
Chlorination
Dosage of copper, iron or zinc salts to throw sulphur compounds.
Protective coating.
Good Ventilation facilities.
Sewer may be designed to full run.

19. Indian Standard 458 1971
Class of Pipes Description Condition
NP1 Unreinforced concrete non pressure
pipes
Drainage or irrigation use above
ground or shallow trenches
NP2 reinforced concrete light duty non
pressure pipes
Drainage or irrigation use for culvert
carrying light traffic
NP3 reinforced concrete heavy duty
non pressure pipes
Drainage or irrigation use for culvert
carrying heavy traffic
NP4 reinforced concrete heavy duty
pressure pipes
Drainage or irrigation use for culvert
carrying heavy traffic likes railways

20. Steel Pipe Sewer
Steel pipes used when lightness, imperviousness and resistance
to bursting pressure are the major requirement.
It also absorb shocks and high external pressures by deflecting,
buckling and flatting without failure.
Erosion and corrosive actions can be prevented by bituminous
coating to the internal surfaces.

21. Steel Pipe Sewer

22. Asbestos Cement Pipe Sewers
Manufacture with the help of cement and asbestos fibres.
Light weight smooth and durable.
It can sustain moderately good internal pressure.
The can easily cut, drilled jointed and fitted.
They are brittle, thus unable to bear the external loads.
Mostly used for rain water pipes in house drainage system.

23. Asbestos Cement Pipe Sewers

24. Cast Iron Sewer Pipes
When Extra Strength is required, cast iron pipes are used as
sewer pipes.
They are strong against internal and external pressure.
Smooth, durable and Strong.
Costly and heavy.

25. Cast Iron Sewer Pipes

26. Plastic Sewer Pipes
Mainly used in House Drainage System.
Available in various sizes Diameter between 25mm to 100mm.

27. Glass Fibre Reinforced Plastic Sewer Pipes
These are known as GRP pipes.
They are made From Polyester Resins(thermoset plastics), Glass
fibre and sometimes silica sand is used as filler.
Light weight
Easy to handle
Smooth surface hence less headloss
Repair work can be quickly done.
Faster installation

28. GRP Sewer Pipe

29. Why Estimation of Wastewater Discharge
Required?
Under Estimation Would Result In Less Diameter Of Sewer
Causing The Overflow Problems.
Over estimation of wastewater flow would result in a sewer
of large diameter which would increase the cost of sewerage
system.

30. Wastewater Discharge
Dry Weather Flow
The Flow which always available through out the year.
It is the summation of domestic supply and industrial supply.
Wet Weather Flow
It consist the combination of Dry Weather Flow And The Storm
Water flow.
It is generally estimated when the combine sewerage system has
adopted.

31. Estimation of Dry Weather Flow
Domestic Wastewater
Industrial Wastewater
Ground water Infiltration in to Sewer through Joints.
Thumb Rule : Wastewater generated from a city is the 80% of
the water supplied.

32. Factors Affect to DWF
Rate of Water Supply
Area Served
Population Growth
Infiltration as well as Exfiltration

33. Rate Of Water Supply
Sr No. Population Rate of Water Supply Rate of Sewage
Production
1 Up to 20000 110 90
2 20000 to 50000 110 to 150 90 to 120
3 50000 to 200000 150 to 180 120 to 150
4 2 lakhs to 5 lakhs 180 to 210 150 to 170
5 5 lakhs to 10 lakhs 210 to 240 170 to 190
6 Above 10 lakhs 240 to 270 190 to 200

34. Population Growth
Wastewater treatment plant should also consider population
forecasting for design period.
Waste water treatment projects designed to serve for a
period of 30 years.
Design Period should neither be too long nor to short
It should note exceed the useful life of the component
structure or equipment.

35. Area Served
Waste water generated in residential area depends upon the
water supplied per capita per day.
Waste water generated in Industrial area depends upon the
type of industries.
Sr no. Name of Industry Unit of Production Wastewater generation
1 Milk Production Ton 20000
2 Steel Ton 260000
3 Bread Ton 2100-4200
4 Automobile Vehicle 40000
5 Sugar Tonne Crushed 1000 to 2000
6 Textile 100 kg 8000 to 14000

36. Infiltration
Ground Pressure higher than pressure inside the sewer, thus
Ground water entered in inside the sewer known as
infiltration.
Depth of Sewer below the ground water level.
Size and length of sewer
Nature and type of soil
Workmanship during lying off sewer.

37. Exfiltration
Inside Sewer Pressure higher than outside Ground water,
sewage shall leak out of the sewer through the faulty joints.
There is addition in sewage due to unaccounted private
water supplies.
The Additional in sewage due to infiltration.
Water losses due to leakage
Some water is not entering the sewerage system e.g.
gardening, garages for washing cars,etc

38. Net Quantity of Domestic Wastewater
The net amount of domestic wastewater formed may vary
between 70 to 140% of water supplied.
In India Generally this value taken as 75 to 80%.

39. Variation in Sewage Flow
The generation of wastewater from the residential,
commercial and industrial areas is function of time.
Water consumption is not uniform through out the day, thus
wastewater generation also vary hour to hour.

40. Variation in Sewage Flow
Sr No Type of Sewer Peak Factor
1 Main Sewer Dia of sewer 1.25m 1.5
2 Main Sewer Dia of sewer up to 1m 2.0
3 Branch Sewer up to dia 0.5m 3.0
4 Laterals and small sewer up to 0.25m 4.0
Peak Factor : The Ratio between Peak flow to Average Flow
 Size of Sewer can be easily designed for carrying the computed maximum hourly flow
with sewer running 3/4th full.

41. Estimating Peak Storm Discharge
It is only considered if separate sewerage system is
available.
Storm Runoff : It Is A Maximum Storm Discharge Of Rainfall In Sewer.
Runoff depends on rainfall intensity, duration of rainfall and
frequency, types of soil of catchment area soil moisture
deficiency.
Proper and economical value of rainfall frequency must be
choose for design of drain.

42. Estimating Peak Runoff
It is not possible to precisely determine runoff.
It is determine with the help of empirical formulae.
Area less than or equal to 400 hectares the rational method
is more suitable.
The empirical formulae are used for very large areas.
Time of Concentration : The period after which the entire area starts to contributing to the
runoff.
Maximum runoff shall be obtained from rainfall having duration equal to time of
concentration and this is called critical rainfall duration.

43. Rational formula
Basic principle of rational formula developed by frushing,
Kuichling and Lloyd Davis.
𝑹 =
𝟏
𝟑𝟔
𝒌 𝑷 𝑨
Where R = Peak rate of runoff in cumec
k = Coefficient of runoff
A = Catchment Area
P = Critical Rainfall Intensity of design frequency
Value of k depend upon the imperviousness of soil.
k = 1for impervious soil , generally its value taken 0.9 for paved surface and 0.15
for lawns and gardens.

44. Coefficient of Runoff
Sr no. Types of Area k
1 Asphalt pavement in good condition 0.85 to 0.90
2 Water bound macadam roads 0.25 to 0.60
3 Parks lawn, garden 0.05 to 0.25
4 Unpaved streets and vacant land 0.10 to 0.30
5 Wooden land 0.01 to 0.20
6 Gravel roads and walks 0.15 to 0.30

45. Coefficient of Runoff
Sr no. Type of locality Approx. Population
density
k
1 Extreme Suburban area with 20 to
30% parking facilities
75 to 125 0.30
2 Suburban area with widely detached
houses
125 to 150 0.45 to 0.55
3 Area with 50% attached and 50%
detached houses
375 to 500 0.65
4 Closely built up area 500 to 625 0.75
5 Business area >625 0.85

46. Dicken’s Formula
𝑸 = 𝑪𝑴 𝟑/𝟒
Where Q = Peak drainage discharge cumecs
M = Catchment area in sq.m
C = A constant are in sq.km
Sr no. Area C Value
1 Kachchh 6
2 North Gujarat 6 to 11
3 Saurashtra and South Gujarat 14

47. Dredge or Burge’s Formula
𝑸 = 𝟏𝟗. 𝟔
𝑴
𝑳 𝟐/𝟑
Where Q = Maximum storm drainage discharge in cumecs
M = Catchment area in sq.km
L = Length of drainage basis in kilometer

48. Ryve’s Formula
𝑸 = 𝑪 𝑴
𝟐
𝟑
Where Q = Maximum discharge in cumecs
M = Catchment area in sq.km
C = A constant depending upon the factor affecting runoff.
Sr no. Area C Value
1 Area within 24 km from the coast 6.8
2 Area within 16 km from coast 8.8
3 Limited Area near hills 10.1

49. Inglis Formula
𝑸 =
𝟏𝟐𝟑𝑴
𝑴 + 𝟏𝟎. 𝟒
Where Q = Maximum discharge in cumecs
M = Catchment area in sq.km

50. Peak Runoff
Example 1 : Find out the peak runoff from the following data, Total area is 72 hectares and
critical rainfall intensity is 8cm/hr.
Sr No. Area % Covered Runoff Coefficient
1 Roofs 15 0.90
2 Pavements 20 0.85
3 Paved Yards of House 10 0.80
4 Macadam Roads 15 0.40
5 Garden Lawns 35 0.10
6 Wooded 5 0.50

51. Peak Runoff
Example 2 : In the pervious example the density of people/hectare = 300 and quota of water
supply is 200lpcd ,
(i) Domestic wastewater for which a sewer of separate system should be designed
(ii) Storm water for which a sewer of a separate system should be designed.
Condition Peak Consumption
Seasonal consumption 130% of avg. consumption
Monthly consumption 140% of avg. consumption
Daily consumption 180% of avg. consumption
Hourly consumption 270% of avg. consumption
150% of Daily peak consumption

52. Hydraulic Design of Sewer
Hydraulic design means finding out their section and
gradients.
Domestic and industrial wastewater contains lot of
suspended, colloidal and dissolved impurities.
The velocity of wastewater is non silting non scouring
velocity.
Normally the sewer size of greater than 0.4 m in diameter
are designed as running 2/3rd or 3/4th full at max discharge.

53. Why freeboard provided in wastewater sewer?
Freeboard provided for factor of safety against :
Low estimate of maximum flow.
Infiltration of storm water due to illegal connections and
underground water penetration through cracks leaky joints
etc.
Unforeseen increase in population and contribution of sewer
by the private water supplies.

54. Freeboard
Design Peak discharge (Cumecs) Free Board (Meter)
Below 0.3 0.3
0.3 to 1.0 0.4
1.0 to 5.0 0.5
5.0 to 10.0 0.6
10.0 to 30.0 0.75
30.0 to 150 0.9
More than 150 1.0

55. Hydraulic Design of Sewer
Chezy’s Formula
𝑽 = 𝒄 𝒓𝒔
where V = average velocity of flow in pipe
r = Hydraulic mean radius
r =
𝐴𝑟𝑒𝑎 𝑜𝑓 𝑓𝑙𝑜𝑤
𝑊𝑒𝑡𝑡𝑒𝑑 𝑝𝑒𝑟𝑖𝑚𝑒𝑡𝑒𝑟
S = hydraulic gradient
c = chezy’s constant

56. Chezy’s Constant
Kutters equation for find out C
C=
𝟐𝟑:
𝟎.𝟎𝟎𝟏𝟓𝟓
𝒔
:
𝟏
𝒏
𝟏:(𝟐𝟑:
𝟎.𝟎𝟎𝟏𝟓𝟓
𝒔
)
𝒏
𝒓
where n = rugosity coefficient depend upon roughness of surface
S = bed slope of sewer
=
Head loss between two points
𝐻𝑜𝑟𝑖𝑧𝑒𝑛𝑡𝑎𝑙 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑏𝑒𝑡𝑤𝑒𝑒𝑛 𝑠𝑎𝑚𝑒 𝑡𝑤𝑜 𝑝𝑜𝑖𝑛𝑡𝑠
r =
𝐴𝑟𝑒𝑎 𝑜𝑓 𝑓𝑙𝑜𝑤
𝑊𝑒𝑡𝑡𝑒𝑑 𝑝𝑒𝑟𝑖𝑚𝑒𝑡𝑒𝑟

57. Chezy’s Constant
Bazin’s equation for find out C
C=
𝟏𝟓𝟕.𝟔
𝟏.𝟖𝟏:
𝒌
𝒓
Sr No. Inside Surface K Value of sewer pipe
1 Very smooth surface 0.11
2 Smooth brick and concrete surface 0.29
3 Rough brick and concrete surface 0.50
4 Smooth rubble masonry surface 0.83
5 Good earthen channel 1.54
6 Rough earthen channel 3.17

58. Hydraulic Design of Sewer
Manning Formula
𝑽 =
𝟏
𝒏
𝒓
𝟐
𝟑 𝒔
𝟏
𝟐
where V = average velocity of flow in pipe
r = Hydraulic mean radius
r =
𝐴𝑟𝑒𝑎 𝑜𝑓 𝑓𝑙𝑜𝑤
𝑊𝑒𝑡𝑡𝑒𝑑 𝑝𝑒𝑟𝑖𝑚𝑒𝑡𝑒𝑟
S = hydraulic gradient
n = Manning rugosity coefficient or roughness coefficient depend upon
roughness of internal pipe surface

59. Hydraulic Design of Sewer
Manning Rugosity coefficient for different type of sewer
Sr No. Pipe Material Value of n for full depth
Good Interior surface Fair interior Surface
1 Glazed stone ware pipe 0.012 0.014
2 Cement concrete pipes 0.013 0.015
3 Cast iron pipes 0.012 0013
4 Bricks unglazed sewers 0.013 0.015
5 Plastic pipes 0.011 0.011
The Value for Lined channel is between 0.020 to 0.025

60. Shield Expression for Self cleaning Velocity
A
θ
W
D B
A
 If we take diameter of particle as 1mm and sp. Gravity = 2.65 then what will
be self cleaning velocity?
Similarly for organic particle having diameter as 5mm and sp. Gravity = 1.2
what will be self cleaning velocity?

61. National Building Organisation
Dia of sewer in meter Gradient required to generate
self cleaning velocity
Velocity in m/sec generated
in sewer when running half full
condition
100 1 in 60 0.58
150 1 in 100 0.61
200 1 in 120 0.79

62. Maximum velocities
Sr no Sewer material Non scouring or limiting
velocity m/sec
1 Vitrified tiles and glazed bricks 4.5 to 5.5
2 Cast iron sewers 3.5 to 4.5
3 Stone ware sewers 3 to 4
4 Cement concrete sewers 2.5 to 3.0
5 Ordinary brick lined sewers 1.5 to 2.5
6 Earthen channel 0.6 to 1.2
For safer side, the maximum velocity permitted is normally restricted to a value
3.0 m/sec

63. Circular Sewer
It may be widely used recently due to
Ease in Manufacture
Less difficulty in lying
Comparatively less cost in manufacture
Maximum hydraulic depth for running full and half
running condition therefore most efficient section.
Uniform curvature thus prevent possibility of deposits of
bed load.

64. Circular Sewer
Fullsection
d 0
𝐴 =
𝜋𝑑2
4
Area of section :
Wetted perimeter :
P= 𝜋𝑑
Hydraulic Mean Depth :
𝑅 =
𝐴
𝑃
=
𝑑
4
Velocity of flow :
𝑉 =
1
𝑁
𝑅2/3 𝑆1/2
=
0.3968
𝑁
𝐷2/3 𝑆1/2
Discharge :
𝑄 = 𝐴 𝑉 =
0.3116
𝑁
𝐷8/3
𝑆1/2

65. Circular Sewer
Fullsection
d 0
𝐴 =
𝜋𝑑2
4
𝛼
360
−
sin 𝛼
2𝜋
Area of section :
Wetted perimeter :
P= 𝜋𝑑
𝛼
360
Hydraulic Mean Depth :
𝑅 =
𝐴
𝑃
=
𝑑
4
1 −
360 sin 𝛼
2𝜋𝛼
c
A B
d
B

66. Proportion Relationship
Proportion depth 𝐝
𝐃
=
𝟏
𝟐
𝟏 − 𝐜𝐨𝐬
𝛂
𝟐
Proportion Area 𝐚
𝐀
=
𝛂
𝟑𝟔𝟎
−
𝐬𝐢𝐧 𝛂
𝟐𝛑
Proportion perimeter 𝐩
𝐏
=
𝛂
𝟑𝟔𝟎

67. Examples
Find minimum velocity and gradient
required to transport coarse sand with
particle size of 1m diameter and G = 2.65
through diameter of sewer 0.9m. Assume β =
0.1 and f = 0.03. The sewer run half full, take
N = 0.013 for half full condition.

68. Examples
Calculate the velocity of flow and
discharge. If circular sewer diameter 1m
laid at gradient 1 in 500. Take Sewer run
partially full at 0.6m depth. Use
manning’s formula taking N = 0.012.

69. Examples
Design a combine sewer for following data:
Area to be served = 20 sq.km
population density = 250 person/ha
average consumption of water = 300 lit/capita/day
Max flow is = 60% avg.
Rainfall equivalent = 15 mm in 24 hr as runoff
Max velocity of flow = 2 m/s

70. Examples
Design circular sewer running half full wastewater velocity 1.8
m/sec. slope 1 in 400 , N = 0.012

71. Examples
Design a Sewer running 0.75 times full at maximum discharge
for a town provided with the separate system a population of
100000 persons. Water is supplied from the water works at
rate of 135 litre per capita per day . Take a constant value of N
= 0.012 at all depth of flow. The permissible slope is 1 in 800.
Take peak factor of 2.