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TABLE OF
CONTENTS
Table
of contents………………………………………………………..i
SR. NO. CONTENTS Page No. Introduction………………………………………………………...5
1.1 Purpose…………………………………………………………….6
1.2 Problems/Limitation…………………………………………6
1.3 Description of the scheme………………………………….7
1.4 Natural slope available………………………………………7
1.5 Ground water level…………………………………………….7
1.6 Scope…………………………………………………………………8
1.7 Elements of sewerage system……………………………..9.
Design
Criteria……………………………………………………..11
2.1 Sources of waste water………………………………………11
2.2 Sewerage treatment……………………………………..…….11
2.3 Description of sewerage system………………………….12
2.4 Assumptions…………………………………………………...….13
2.4.1 Design
period…………………………….………….13
2.5 Estimation of sewage quantities…………………………..13
2.5.1 Per capita
water consumption……………..…13
2.5.2 Per capita
water consumption for Future
Vision
Housing Society …………………………..14
2.5.3 Average
sewage flow…………………...…………14
2.5.4 Peak sewage
flow………………….………………..14
2.5.5 Infiltration………………….…………………………..15
2.6 Storm flow
capacity of a sewer………………………………15.
2.7 Design flow………………………………….………………………15
2.8 Sewer pipes and connections………………………………..16
2.9 Size of sewer…………………………………………..……………16
2.10
Minimum sewer size…………………………………………16
2.11
Slope of sewer……………….………………………………….17
2.12
Sewer design equation…………………...………………….17
2.13
Velocity of flow………………………………………………….17
2.13..1
Minimum velocity…………………………..……17
2.13..2
Maximum velocity……………………………….18
2.14
Minimum cover of sewer……………………………………18
2.15
Invert level…………………………………………………………18
2.16
Provision of manhole……..……………………………………20
2.16..1
Manholes………………………………………………21
2.16..2
Drop manholes…………………..………………….21
2.17
Direction of sewer line…………………………………………22
2.18
Inlet……………………………………………...……………………..22
2.19
Catch basin…………………………….…………………………….22
2.20
Maximum depth of sewer……………………………………..22
2.21
Joints in sewer pipe………………………………………………22
2.21..1
Bell and Spigot joints………………………………22
2.21..2
Tongue and Groove joints…………………….….23
2.22
Sewage pumping station……………………………….………23
2.23
Types of bedding………………………………………………….24
2.23..1
Sewer bedding……………………………………….24
Design of
sewerage system………………………………………..27
3.1 Design
procedure…………………………………………………..27
Conclusion…………………………………………………………………30 Reference…………………………………………………………………..31
Annexure …………………………………………………………………..3
CHAPTER1
INTRODUCTION
ENVIRONMENTAL ENGINEERING is a professional engineering
discipline that deals with the design, construction, and maintenance of the
physical and naturally built environment, including works like sewage design,
treatment plants, pumping stations and transmission lines etc. Environmental engineering is the branch of
civil engineering which is the oldest engineering discipline after military
engineering, and it was defined to distinguish non-military engineering from
military engineering.
Water is one of
the most valuable natural resources essential for human and animal life,
industry and agriculture. Wastewater causes more than 50 diseases so as an
environmental engineer it is our duty to save the environment & as well as
the human health which is affected by these diseases. In fact, there is hardly
any human activity which is not in one way or another, affected by water. Sewerage refers to the collection,
treatment and disposal of liquid waste. Sewerage system includes all physical
structures required for the collection, treatment and disposal.
The sewage, once it enters the sewers, becomes the
responsibility of the community. Small communities which have managed in the
past with on-site disposal systems may be well-advised to avoid modernization.
1.1 Purpose
The
purpose of this report is to know the various design components related to
waste water (sewage) design. Wherever high a community is planned to be established,
then waste water treatment becomes a big issue for engineers. So this report
can help us to understand the various sewage design parameters and components
which are to be used to solve various engineering problems and to perform work
in a better way.
1.2 Problems/ Limitations
In every environmental engineering
project, engineers face many problems, sometimes, problems related to
management. Time management is very important during a mega project for an
engineer. Manual working and old construction techniques delay the project
significantly and contractor has to pay for penalty on daily basis. Therefore,
engineers must learn different design software related to environmental
engineering to save the time and to solve the relevant problems in an effective
way.
1.3 Description
of the Scheme
a) Nasheman-E-Iqbal Housing
Society
Future Vision Housing
Society provides an exquisite living experience
that is situated at the shaokat khanum Road. The society is being developed
using state of the art design and incorporating all amenities of modern life.
b) Salient
Features
ü A total of 936 plots, available in
different sizes, suiting all family sizes and requirements.
ü School
ü Commercial Area
ü Disposal Station
ü Grave yard
1.4 Natural slopes
Available
From plan of
Nasheman-E-Iqbal Housing Society, we can see that the topography of this area
is almost same, the average elevation is taken as 252m. .The topography of the
area is flat according to topography of Punjab. So slope is 1 to 2%. &
Sewer must follow the natural slopes.
1.5 Ground water levels
In the given scheme the ground water table
is low. So we will use the brick ballast bedding. Mostly we do dewatering while
making trenches when the ground water table is high. Infiltration also depends
upon ground water table. We go 9m to 10m down.
1.6 Scope
As far as the scope of report is
concerned it has wide range of application in today’s field. As around the
world the idea of sewage and waste water treatment is quickly prevailing as
well as in Pakistan so this report will help in better understanding of
designing a sewage system for a community.
This
report will give the introduction and background of waste water engineering
which are necessary for performing the work at site efficiently. This report
will also provide a simplified explanation of construction method at the site.
Why Sewerage system is
required:
We use water supply system in order to provide easy
availability of water for drinking , washing etc. when this water is used it
becomes waste water called "sewage". Proper system is required for
the collection of waste water and conveying it to the point of disposal with or
without treatment called as
"sewerage.
Most of the paving types are generally
impermeable, i.e. water does not drain through them, but collects on the
surface and therefore all pavements must be designed to drain towards a gully,
a linear drain or some other handy disposal point, such as a ditch or towards
the public footpath/highway.
Failure to properly drain a
pavement can cause all sorts of problems. Water on the surface encourages
mosses, algae and other vegetation to colonize the paving. Accumulation of
water can cause growth of various micro- organisms, flies, mosquito, worms, and
protozoa etc. which are cause of various diseases. These cause over 50 diseases
to human.
So a properly designed system must be provided.
1.7
Elements of Sewerage System
The sewerage system consists of three
elements:
·
Collection
Works
·
Disposal
Works
·
Treatment
Works
CHAPTER 2
DESIGN CRITERIA
What is design?
In engineering sciences design is a term used in special meaning and is
referred to the creation or development of some system or component by
engineered manner. By McGraw-Hill Dictionary of Engineering, designing is
defined as, “A branch of engineering concerned with the creation of systems,
devices, and processes useful for the society.”
2.1
Sources of Waste Water
Following are the principal sources
of waste water
- Industrial
It is the liquid waste from the industrial
places from their different industrial processes like dying, paper matting, tanneries,
chemical industries, etc.
- Storm Water
It
includes surface runoff generated from rainfall and the street wash.
2.2 Sewage
Treatment
Sewage treatment, or domestic wastewater
treatment, is the process of removing contaminant from wastewater, both runoff
and domestic. It includes physical, chemical and biological processes to remove
physical, chemical and biological contaminants. Its objective is to produce a
waste stream (or treated effluent) and a solid waste or sludge also suitable
for discharge or reuse back into the environment. Sewage is treated to control
water pollution before discharge to surface waters.
The purpose of is the preservation of
health of the individual and the community, by preventing the communicable
diseases.
2.3 Description of Sewerage System
There are three types of
sewer system which are given below:-
Separate system
Combined system
Partially Combined system
Separate System:-
If storm water is carried separately
from domestic and industrial waste waters, the system is called separate
system. Separate systems are preferred when
- There is an immediate need for collection of sanitary sewage but not for storm water.
- When sanitary sewage needs treatment and storm water does not.
Combined System:-
It is the system in which the sewers carry
both sanitary and storm water. Combined systems are preferred when:
- Combined sewage can be disposed off without treatment
- Both sanitary and storm water need treatment
- Streets are narrow and two separate systems can’t be laid.
Partially Combined System:-
If some portion of storm or surface runoff is allowed to be
carried along with sanitary sewage, the system is known as partially combined
system.
Note: In urban areas of developing
countries, mostly partially combined system is employed as it is economical.
We have designed system as “Partially Combined System “which is
most suitable for developing countries like Pakistan.
2.4
Assumptions
2.4.1 Design Period:
Period of design is indefinite. The system is designed to
take care for the maximum development of the area. But here Design period of
our sewer system is 20 years.
Relation
of sewage Generation with Water Consumption
Around
80 to 130 % of water consumed gets into sewers.130 % sewage flow is obtained
when
v Industries having private sources of water discharge their
effluent into municipal sewer.
v When sewer joints are poor and it is laid below water table
then infiltration occurs
General range is 80 to 90 % of water consumption.
v When infiltration is taken into account then; avg rate of
sewage flow equals the average rate of water consumption i.e. 100%.
2.5
Estimation of Sewage Quantities
2.5.1 Per capita water
consumption:
It is the amount of water consumed by every
individual in a community in a day. It is usual to express water consumption in
liters per capita per day, lpcd
The amount of sewage produced from this water consumed will
be termed as per capital sewage flow. In our case we have calculated this per
capita sewage flow by taking 80% of per capita water consumption.
2.5.2 Per Capita Water Consumption for Nasheman-e-Iqbal
Housing Society
Average Per capita sewage
generationS =( 300+ sum of last two
digits of Regd. No)
=
300 + (0+7) = 307lpcd
2.5.3 Average Sewage Flow
For the present design which has
to be suggested us to use 80 % of water consumption for sewage.
2.5.4 Peak Sewage Flow
HERMAN’S FORMULA:
Like
water supply, sewage flow varies from time to time. Since sewers must be able
to accommodate Maximum Rate of Flow, the variation in the sewage flow must be
studied.
Generally
Herman’sFormula is used to estimate the ratio of Maximum to Average Flow.
P
is population in thousand
Peak sewage flow is calculated by multiplying the average
daily sewage flow by a certain factor. The factor depends on the average flow
and is given by this table.
2.5.5
Infiltration
It is amount of
water that enters into the sewers through poor joints, cracked pipes, walls and
covers of manholes.
It is nonexistent during dry weather but increases during rainy
season.
WASA
Lahore has specified following infiltration rates for design of sewer system;
Sewer
Diameter
|
Infiltration
|
225 mm to 600 mm
|
5 % of Avg. Sewage Flow
|
> 600 mm
|
10 % of Avg. Sewage Flow
|
2.6 Storm Flow Capacity of
Sewer
In the present design
the storm water flow capacity of sewer is taken as equal to peak flow.
Storm
Water Flow = Peak Flow (Qmax)
2.7 Design Flow
First of all calculate the average
sewage flow on the basis of water consumption and the population at the end of
the design period. I.e. at the full development of the area. Then the design
flow for sanitary sewer and partially combined sewers can by calculated by
using the following formulae;
For partially combined sewer: Designs = 2xPeak sewage flow +
infiltration + industrial flow
So,
Qdesign
= Qmax + 10% of infiltration + Qmax
2.8 Sewer Pipes and Connections
Different types of pipes
that are used in the sewer system are
·
PCC pipes (100mm-600mm diameter)
·
RCC pipes (225mm-4500mm diameter)
·
PVC pipes
·
AC pipes
·
C.I pipes
·
Clay
PVC and AC are employed by
households.
PCC and RCC are most widely
used in cities.
CI and Steel are used under
unusual loading conditions and in force mains.
Clay pipes were used in the
past as sewers.
We are using RCC pipes in
our system.
2.9 Size of Sewer
Use the following
relation to find the diameter of sewer
Qf = A x V
2.10 Minimum Sewer Size
225mm is taken as the minimum sewer
size. The reason being that, the choking does not take place even with the
bigger size particles, which are usually thrown into the sewer through
manholes.
2.11 Slope of Sewer
Select the minimum
velocity value and use the Manning’s formula
2.12 Sewer
Design Equation
Manning’s Equation is used for sewers
flowing under gravity
Where
V= Velocity of flow in m/sec
R= Hydraulic mean depth (A/P) = D/4 when pipe is flowing full or half full
S= Slope of the sewer
n= Coefficient of roughness for pipes
(different value for different type of materials)
2.13 VELOCITY OF FLOW
2.13.1
Minimum (Self Cleansing) Velocity
Sewage should
flow at all times with sufficient velocity to prevent the settlement of solid
matter in the sewer. Self-cleansing Velocity is the minimum velocity that
ensures non settlement of suspended matter in the sewer.
The following minimum velocities are generally employed.
- Sanitary sewer = 0.6 m/sec
- Storm sewer = 1.0 m/sec
- Partially combined sewer = 0.7 m/sec
As our design is partially combined system so
minimum velocity is 0.7 m/s.
2.14 Minimum Cover of Sewer
1m is taken as the minimum cover over
the sewers to avoid damage from live loads coming on the sewer.
2.15 Invert level (I.L)
The lowest inside
level at any cross-section of a sewer pipe is known as Invert Level at that
Cross-section.
Invert Level = NGSL/Road Level – Depth of Sewer – Thickness of Sewer – Dia. of Sewer
The
main significance of the invert level is that sewers must be designed and laid
at a specific slope to attain self -cleansing velocities. The required slope is
achieved through calculations of this invert level of the sewers at various
manholes.
Calculation of I.L
For single pipe:
§ Upstream Invert level = NGSL – Depth of sewer – Thickness of sewer –
Diameter of the sewer
§ Downstream invert level = Upstream
invert level – (Length* Slope)
Fall:
Fall is calculated by multiplying the length of the sewer by
the slope of the same particular sewer. This fall is necessary for the
calculation of the invert level at the downstream level.
Fall= Slope of sewer x Length of the sewer.
2.16 Provision of Manhole
2.16.1 Manholes:-
A manhole (alternatively utility hole, maintenance hole,
inspection chamber or access chamber) is the top opening to an underground
utility vault used to house an access point for making connections or
performing maintenance.
Purpose
of providing manhole is
- Cleaning
- Inspection
- House connection
Manholes are provided at:
- Change in sewer direction
- Where diameter of sewer changes
- Where slope of sewer changes
- It is also provided at junctions.
- One man hole for two plots
Spacing of Manhole: (WASA Criteria)
o For
pipe 225mm to 380mm
spacing = 100m
o For
pipe 460mm to 760mm
spacing = 120m
2.17 Direction of Sewer
Line
Sewers should follow as for as
possible, the natural slope so that sewage can flow easily under gravity and
minimum excavation is required which is essential for economizing the system.
2.18 Inlets
An inlet is an opening into a storm or combined sewer for entrance of
storm runoff. It is designed to permit the passage of water from the street
surface into the sewer.
Two types of inlets are
recommended for the system
a)
Curb Inlet
b) Gutter Inlet
2.19 Catch Basin
These are like inlets but
deeper enough to store the settled grit which is then removed periodically.
2.20 Maximum Depth of Sewer
The maximum
depth for sewer suggested for this area is 6-7 m
2.21 Joints in Sewer
Pipe
2.21.1Bell
and Spigot Joints
Employed for sewer
from 225mm to 760mmФ
2.21.2
Tongue and Groove Joints
Employed for sizes
> 760mmФ
We
selected ball and Spigot Joints for our design.
2.22 Sewage Pumping Station
To elevate and transport waste water when
- Continuation of gravity flow is no longer feasible.
- Basements are deep.
- Any obstacle lies in the path of sewer.
- Receiving stream is higher than the sewer.
- Sewage is to be delivered to an above ground treatment plant.
2.23
Type of Bedding
2.23.1 Sewer Bedding
If sewer is simply
laid by placing the pipe on flat trench bottom, the pipe will not be able to
support the load significantly greater than the “Three Edge Bearing test”.
However if bedding touches at least lower quadrant of sewer and backfill
material is carefully tempted, the supporting strength of pipe significantly
increases. Load factor represent this increase in strength,
Load Factor = Load Carrying Capacity/ 3-Edge
bearing strength
Sewer Bedding (Recommended By WASA):-
Three types of sewer bedding
are recommended by WASA.
(These will be used depending upon site
conditions and requirements.)
1) Brick Ballast:-
This type of bedding is used
under poor subsoil conditions, above water
table.
§ Size of the ballast
: 1-1.5 inch gauge (Broken from first class bricks)
§ Load Factor
: 1.7
2) Crushed Stone:-
It is used under poor subsoil
conditions below the water table
§ Size of the ballast
: 0.75-1.5 inch gauge
§ Load Factor
: 1.9
3)
Concrete cradle:-
It is used under increased strength
requirements.
Load
Factor : 3.0
Chapter 3
DESIGN OF SEWERAGE SYSTEM
PROCEDURE
3.1 Design Procedure
Following procedure is adopted for
design:
1) First of all we draw the layout of sewer system keeping in
view the layout of roads and streets so as to avoid overlapping of water
supply, gas and sewer pipes.
2) Represented the sewer with a line and manhole by a dot.
2)
3) Numbered the manholes and identified each sewer line.
3)
4) Then measured the length of each sewer line as per scale of
the map.
4)
5) Adopted per capita sewage flow as 80% of water consumption.
5)
6) Calculated avg. sewage flow and Infiltration for each sewer
line.(using WASA criteria)
7) Found out the peak factor for our project using WASA
criteria. For peak factor first found out the avg. sewage flow for design
population and on the basis of flow we decided the approximate peak factor from
table of peak.
8) Calculated the peak flow and finally the design flow for
sewer lines. As our system is partially combine so I have added storm flow
equal to the peak flow for design flow determination (as per WASA criteria.)
8)
9) Using method of calculation, found approximate dia and slope
for the sewer line assuming that sewer is flowing full. For back calculation I
have chosen velocity equal to 0.7 m/sec for partially combined system.(WASA Criteria)
9)
10) In the end I found out the invert levels for each sewer and
filled the
Table of calculations called “Hydraulic Statement”.
11) Draw the profiles or longitudinal-sections for sewer line
Comments
Following are the different criteria’s
that I consider while designing the sewer system
- We designed for the partially combined sewage system considering economics.
- The design flows are based on the WASA standards.
- Minimum velocity is taken as 0.7 m/sec
- Velocity must not be more than 2.4 m/sec.
- Minimum diameter is taken as 225 mm and other diameters are considered according to WASA standard.
- Minimum rate of sewage flow is taken as 50% of average sewage flow.
- Minimum clear cover of 1-m is provided above the sewer in order to avoid from impact of live loading.
CHAPTER 4
CONCLUSION
The job assigned to me by Authority, was to design the water
sewerage system for Nasheman-E-Iqbal Housing Society. The scheme has 936 residential
plots, school, commercial areas and disposal station.
I have tried to make design as much
economical as possible without compromising on safety of the system. Design is
economical because I have used RCC pipes as sewers. They possess high strength
and durability. Therefore they have longer life which ultimately makes them
suitable and economical. The strength of the system is built-in. Lower
installation cost combines with the other benefits of reinforced concrete pipe
to yield a superior drainage system. I have followed as much as possible the
natural slope. Due to those reason excavation is minimum. It also helps to
economize the system. Wherever lateral or sub main joins in a deeper sewer
excavation is also saved by providing drop manholes by keeping upper sewer at a
reasonable grade. I
have done this whole design work with the best use of my knowledge and skills
in the context of the information provided to me by my teachers. In the whole
design I have made possible that every step should be clear so that the checker
or the reader of the report could not found any difficulty in it.
I am sure to say that system has been designed with great
care and all possible circumstances have considered. Therefore I am very
confident saying that system will be working very well throughout its design
period of 20 years which is from 2016 to 2036. I am sure to say that system has
been designed with great care and all possible circumstances have considered.
Therefore I am very confident saying that system will be working very well throughout
its design period of 20 years which is from 2016 to 2036.
·
We used max diameter 530mm
for M1 to M158
·
We used min diameter 225mm.
·
Total No’s of manholes =
158
REFERENCES
References
- Water supply and sewerage by McGhee, 6th edition, McGraw Hill Inc.
- Class Lectures Notes.
- Design notes provided.
- WASA (1986) design criteria ,Water and Sanitation agency Lahore.
- Wikipedia, the free encyclopedia.
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