This presentation includes the basic introduction to sewage/ wastewater, quantity estimation, the basic terms commonly used in the sewerage system, Types of sewer, sewage, and sewerage system.

1. Wastewater/ Sewage
Resource Person
Engr. Sidra Rashid
sidradar9@gmail.com

2. Textbook
WATER SUPPLY AND SEWERAGE
By
E.W. Steel and T.J. McGhee
6th Edition
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3. Wastewater/ Sewage
Sources
Types
Quantities
Characteris
tics
Design of
sewerage
system
Hydraulics
Treatment

4. Introduction
Wastewater, a combination of liquid and water-
transported wastes along with any groundwater
infiltration, surface water and stormwater inflow that
may enter the sewer system.
Waste may come from homes, commercial buildings,
industrial facilities, and institutions
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5. Cont.
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Sewer: Pipe or conduit
which carries sewage.
Sewage: Waste matter
carried off by the sewer
Sewerage: Refers to
physical facilities
through which sewage
flows.

6. Cont.
Collection system (network of sewer pipes)
Disposal Works (sewage pumping stations, outfalls)
Treatment works (for interpreting wastewater that is
safe for environment and life)
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Components of Sewerage System

7. Sources of Wastewater
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1.Domestic
Sewage
• Wastewater
produced due to
human activities
in households
• i.e., residential
buildings, offices,
hotels and
institutions etc.
Industrial
Wastewater
• It includes the
liquid discharges
from industrial
processes.
Storm
Sewage
• It include
surface run off
generated by
rainfall and the
street wash.

8. Factors Affecting Sewage Generation
Size of City
Population Characteristics
Industries and Commerce
Climatic Conditions
Metering
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9. Types of Sewers
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1.
House
Sewer
A pipe conveying wastewater from an
individual structure to a common
sewer or some other point of disposal.
2.
Lateral
Sewer
A common sewer with no tributary
flow except from house sewers.
3.
Submain
Sewer
It collects flow from one or more
laterals or house sewers.

10. Cont.
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4.
Main/
Trunk
Sewer
It collects flow from several submains as
well as lateral and house sewers
5.
Force
Main
A pressurized sewer lines which convey
sewage from a pumping station to another
main or to a point of treatment or disposal.
6.
Outfall
Sewer
It receives discharge from all collecting
system and convey it to the point of final
disposal (e.g., a waterbody etc.)

11. Cont.
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12. Types of Sewer Systems
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1.
Separate System
If storm sewage is
carried separately
from domestic and
industrial
wastewaters
2.
Combined System
A system of sewers
that carry both
sanitary as well as
storm sewage.
3.
Partially Combined
System
If some portion of
storm or surface run
off is allowed to be
carried along with
sanitary sewage
NOTE: In urban areas of developing countries, mostly partially combined system is used.

13. Cont.
Separate sewers are preferred when
 There is an immediate need for collection of
sanitary sewage but not for storm sewage
 When sanitary sewage needs treatment but storm
sewage does not
 Costly construction and requires extra
maintenance
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14. Cont.
Combined sewers are preferred when
 Combined sewage can be disposed off without treatment
 Both sanitary and storm sewage need treatment
 Streets are narrow and two separate sewers cannot be laid
 Preferred in present construction except previously
constructed old combined sewers
 But in Pakistan combined sewers are preferred as sewage is
disposed of in Canals, rivers and for
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15. Sewage Flow / Quantity
Domestic and industrial sewage is derived from water
supply, so it has a relationship with amount of water
consumption. Generally
 About 70-90% of the total water supplied to a community
becomes wastewater
 Illicit drains and water use from privately owned source
may produce quantities of sewage larger than public water
withdrawals.
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16. Relation between Sewage Generation and
Water Consumption
Following relation prevails among the water supply
and sewage generation.
 Around 70 – 130 % of the water consumed
1. Higher percentage (130%) is as industries (wet processes)
rely on private water sources but discharge their effluent
into municipal sewer system.
2. Moreover, it is aided by Infiltration form poor joints and
pipes laid under GWT.
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17. Cont.
 Variations in sewage flow presents no fixed relation
between sewage production and water supply.
 However generally it ranges from 70 – 90 % of the
water consumption.
After taking into consideration the rate of infiltration, the
average rate of sewage flow equals the average rate of
water consumption.
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18. Cont.
 Infiltration is non-existent in dry weather but increases during rainy
seasons.
 WASA considers following infiltration rates
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Infiltration
The water which enters
the sewers form ground
through poor joints,
cracked pipes, and the
walls of the manholes.
Inflow
The water which enters
the sewers from surface
through perforated
manhole covers, roof
drains connected to the
sewers, and drains from
the flooded cellar etc.
Sewer Dia. (mm)
225 – 600
5 % of Average Sewage flow= Infiltration
Sewer Dia. (mm)
>600
10 % of Average Sewage flow= Infiltration

19. Cont.
Amount of Storm Sewage
Rainfall is the primary source of storm flow. Estimation
of flow is the first step to design the Storm sewer.
 Rational Method is widely used
 Based on rainfall data.
 Most widely used formula for urban areas
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