INTERMEDIATE
VOCATIONAL COURSE
SECOND YEAR
ENVIRONMENTAL
ENGINEERING
FOR THE COURSE OF
WATER SUPPLY AND
SANITARY ENGINEERING
STATE INSTITUTE OF VOCATIONAL EDUCATION
DIRECTOR OF INTERMEDIATE EDUCATION
GOVT. OF ANDHRA PRADESH
2005
Intermediate Vocational Course, 2nd Year :
ENVIROMENTAL ENGINEERING (For the Course of
Water Supply and Sanitary Engineering)
Author : Sri P. Venkateswara Rao,
Editor : Sri M. Vishnukanth.
©
State Institute of Vocational Education
Andhra Pradesh, Hyderabad.
Printed and Published by
the Telugu Akademi, Hyderabad on behalf of
State Institute of Vocational Education
Govt. of Andhra Pradesh, Hyderabad.
First Edition : 2005
Copies :
All rights whatsoever in this book are strictly reserved and no
portion of it may be reproduced any process for any purpose
without the written permission of the copyright owners.
Price Rs:
/-
Text Printed at ……………………
Andhra Pradesh.
AUTHOR
Puli Venkateshwara Rao, M.E. (STRUCT. ENGG.)
Junior Lecturer in Vocational, WS & SE
Govt. Junior College, Malkajgiri,
Secunderabad.
EDITOR
M. VISHNUKANTH, B.TECH.(Civil)
Junior Lecturer in Vocational, WS & SE
Govt. Junior College, Huzurabad,
Karimnagar Dist.
IVC
WATER SUPPLY AND SANITARY ENGINEERING
SECOND YEAR
ENVIRONMENTAL
ENGINEERING
STATE INSTITUTE OF VOCATIONAL EDUCATION
DIRECTOR OF INTERMEDIATE EDUCATION
GOVT. OF ANDHRAPRADESH
Introduction
Page 1
CHAPTER 1
ENVIRONMENTAL ENGINEERING
INTRODUCTION :
1.0
GENERAL INTRODUCTION:
Originally the term Environment was used to mean the
surroundings in which the man lives, works and plays including
the physical factors without giving much importance to living
components. But in the changed situations of rapid
industrialization and consequent pollution and other problems,
the dimensions of total environment were enlarged to include not
only the physical factors, but also factors as components of the
environment.
Thus the term environment is defined as all the systems
namely atmosphere, lithosphere, hydrosphere (non living
components) and biosphere (living components) surroundings us.
It includes air, water, food, the pollutions, waste materials and
other ecological problems, which effect the life and health of
human beings and other life.
Environmental engineering is concerned with the control
of all those which exercise or may exercise deleterious effect on
his development, health and sundial with the consideration of the
physical, economic and social impact of the control measures
applied. Environmental engineering deals with the application of
engineering principles to the control, modification and adaption
Page 2
Environmental Engineering
of the physical, chemical and biological factors of the
environment in the interest of man’s health, comfort and social
wellbeing. In this textbook, some aspects of environmental
engineering, such as ecology, water supply systems, waste water
treatment and disposal, rural sanitation and air pollution are
presented.
If proper arrangements for the collection, treatment and
disposal of all the wastes produced from the town or city such as
water from bathroom, kitchens, lavatory basins, house and street
washings, from various industrial processes semi liquid wastes of
human and animal excreta, dry refuse of house and street
sweepings, broken furniture, crockery, wastes from Industries etc
are not made, they will go on accumulating and create
(i)
Buildings and roads will be in danger due to accumulation
of spent water in their foundation
(ii)
Disease causing bacteria will bread up in the stagnate
water
(iii)
Drinking water will be polluted.
Total insanitary conditions will be developed in the town
or city and it will become impossible for the public to live in the
town or city. Therefore in the interest of the community of the
town or city it is most essential to collect, treat and dispose of all
the waste products of city in such a way that it may not cause any
problem to the people residing in the town. Table 1.1. illustrates
waste products of town or city (outlines of sanitary engineering).
Table 1.1 outlines of sanitary engineering
Introduction
Page 3
Page 4
1.1
Environmental Engineering
OBJECT OF PROVIDING SEWERAGE WORKS:
The following are the aims and objects of sewage disposal.
1.
Proper disposal of human excreta to a safe place, before
its starts decomposition and may cause insanitary
conditions in the locality
2. To take out all kinds of wastewater from the locality
immediately after its use, so that mosquitos, files, bacteria
etc may not breed in it and cause nuisance.
3. Final disposal of sewage on land or in near by watercourses after some treatment so that receiving land or
water may not get polluted and unsafe for its further use.
4. As far as possible the fertilizing elements of sewage may
be used in growing crops through farming and getting
some income in addition to the disposal of sewage
5. In unsewered areas, the treatment of sewage from
individual houses, should be done by septic tank or other
suitable means and the effluent should be disposed of.
6. If the sewage is disposed of on land, it should have such s
degree of treatment that it may not affect the sub-soil in
anyway.
1.2
DEFINITIONS OF TERMS-SULLAGE, SEWAGE, SEWER
AND SEWERAGE:
Sullage: The liquid waste from latrines, Urinals stable etc is
known as sullage.
Introduction
Page 5
Sewage: The term sewage is used to indicate the liquid waste
from the community and it includes sullage, discharge from
latrines, urinals, stable etc industrial waste and storm water.
Sewer: The underground conducts or drains through which is
conveyed are known as the sewers.
Sewerage: The entire science of collecting and carrying sewage
by water carriage system through sewers is known as sewerage.
Garbage: The term indicates dry refuse which includes decayed
fruits, grass, leaves, paper pieces, sweepings, vegetables etc.
Refuse: The term refuse is used to indicate all kinds of dry
wastes of the community (i.e.,) street and house sweepings,
garbage etc.
1.3
CLASSIFICATION OF SEWAGE:
1. Storm Sewage: Which includes surface runoff developed
during and immediately after rainfall over the concerned area.
2. Sanitary Sewage: Which includes the liquid wastes of
domestic and industrial places. This sewage is extremely foul
in nature and required to be disposed of very carefully.
1.4
SYSTEMS OF SEWERAGE METHODS:
1. Conservancy System: In this system various types of refuse
and storm water are collected, conveyed and disposed off
separately by different methods in this system. This method is
also called dry system and is in practice from very ancient
times. This is method is adopting in small towns, villages and
Page 6
Environmental Engineering
undeveloped portions of large city even it is out of date
system.
In this method garbage or dry refuse is collected from the
dustbins and conveyed by trucks or covered carts once or
twice in a day. All the uncombustible portions such as sand,
dust, clay, ashes etc are used for filling low lying areas and
combustible portions such as dry leaves, waste paper, broken
furniture etc… are burnt. The decaying fruits, vegetables,
grass are first dried and then disposed of by burning or in the
manufacture of manure. Human excreta or night soil is
collected in separate liquid and semi-liquid wastes by animal
drawn carts, trucks or tractor trailors and buried in trenches.
After 2-3 years the buried night soil is converted into an
excellent manure which can be used for growing crops. In
this system sullage and storm water are also carried
separately in closed or open drains upto the point of disposal,
where they are allowed to mix up with streams, rivers or sea.
ADVANTAGES AND DISADVANTAGES:
ADVANTAGES:
1. Initial cost is low, because storm water can pass
through open drains.
2. The quantity of sewage reaching at the treatment plant
before disposal is low.
3. The sewer section is small and no deposit of silting
because storm water goes in open drains.
Introduction
Page 7
DISADVANTAGES:
1. Possibility of storm water may mix with sewers
causing heavy load on treatment plant.
2. In crowded lanes it is difficult lay two sewers or
construct drains roadside causing great inconvenience
to the traffic.
3. More land is required for human excreta.
4. Liquid refuse may get on access in the sub soil and
pollute the underground water.
5. Aesthetic appearance of city cannot be increased.
6. Decomposition of sewage causes insanitary conditions
which are dangerous to the public health.
7. This system is completely depends upon the mercy of
sweepers at every time and may possibility of
spreading of diseases in the town if they are on strike.
2.
WATER CARRIAGE SYSTEM:
In this system, the excremental matters are mixed up in
the large quantity of water and are taken out from the city
through properly designed sewerage systems where they are
disposed off after necessary treatment in a satisfactory manner.
The sewage so formed in water carriage system consists of 99.9
percentage of water and 0.1 percentage of solid matters. All the
solid matters remain in suspension in the sewage and donot
change the specific gravity of water. So all the hydraulic
formulae can be directly used in the design of sewerage system
and treatment plants.
Page 8
Environmental Engineering
MERITS AND DEMERITS OF WATER CARRIAGE SYSTEM:
The following are the merits of water carriage system.
1. It is hygienic method because all the excremental matters
are collected and conveyed by water only.
2. There is no nuisance in the streets of town and risk of
epidemics reduced because of underground sewerage
system.
3. Less space is occupied in crowded lane as only one sewer
is laid
4. Self cleaning velocity can be obtained even at less
gradients due to more quantity of sewage.
5. The land required for the disposal work is less as
compared to conservancy system.
6. This system doesnot depend on manual labour at every
time except when sewers get choked.
7. The usual water supply is sufficient and no additional
water is required in water carriage system.
8. Sewer after proper treatment can be used fro various
purposes.
DEMERITS
1. This system is very costly in initial cost.
2. The maintenance of this system is also costly.
3. During monsoon large volume of sewage is to be treated
compared to remaining period of year.
COMPARISION OF CONSERVANCY AND WATER-CARRIAGE
SYSTEMS:
Introduction
CONSERVANCY SYSTEM
1. Very cheap in initial
cost
2. Due to foul smell from
latrines, they are to be
constructed away from
the living room
3. The
aesthetic
appearance of the city
cannot be increased
4. Storm water is carried
in usually surface
drains,
hence
no
problem of pumping
the storm water
5. The quantity of waste
liquid reaching the
disposed point is less,
hence it can be
disposed of without
any treatment.
6. This system is fully
dependent
on
the
human agency
7. As sewage is disposed
of
without
any
treatment
it
may
pollute the natural
water courses
8. For
burying
of
excremental
matter,
large area is required.
Page 9
WATER-CARRIAGE
SYSTEM
1. It involves high initial
cost
2. As there is no foul
smell, latrines remain
clean and neat and
hence are constructed
with room.
3. Good
aesthetic
appearance of the city
can be obtained.
4. Sewage
is
treated
before disposing of ,it
may or may not require
pumping it depends on
the topography of the
town.
5. Large
quantity
of
sewage highly polluted
in nature, it requires its
treatment
before
disposal so it is costly
process.
6. This system is not
dependent
on
the
human agency
7. Sewage is treated upto
required degree of
sanitation.
8. Less area is required as
compared
to
conservancy system.
Page 10
1.5
Environmental Engineering
TYPES OF SEWERAGE
SUITABILITY:
SYSTEM
AND
THEIR
The sewerage system are classified as follows:
(a) Combined system
(b) Separate system
(c) Partially separate system
(a)
COMBINED SYSTEM:
This system is best suited in areas having small rainfall,
which is distributed, throughout the area, because at such
places self-cleaning velocity will be available in every season.
As only one sewer is laid in this system, it is best suited for
crowded area because of traffic problems. The combined
system can also be used in area having less sewage, to obtain
the self-cleaning velocity.
MERITS AND DEMERITS OF COMBINED SYSTEM:
The following are the merits of combined system
1. There is no need of flushing because self-cleaning velocity is
available at every place due to more quantity of sewage.
2. The sewage can be treated easily and economically because
rainwater dilutes the sewage.
3. House plumbing can be done easily only one set of pipes will
be required.
DEMERITS:
The following are the demerits of the combined system.
Introduction
Page 11
1. The initial cost is high as compared to seperate system
2. It is not suitable for areas having rainfall for smaller period of
year because resulting in the silting up of the sewers due to
self velocity is not available
3. During heavy rainfall, the overflowing of sewers will
endanger the public health
4. If whole sewage is to be disposed of by pumping, it is
uneconomical
(b)
SEPERATE SYSTEM:
When domestic and industrial sewage are taken in one
set of sewers, where as storm and surface water are taken in
another set of sewers, it is called seperate system.
MERITS AND DEMERITS OF COMBINED SYSTEM:
The following are the merits of the seperate system
1. Since the sewage flows in seperate sewer, the quantity to be
treated is small which results in economical design of
treatment works.
2. Separate system is cheaper than combined system, because
only sanitary sewage flows in closed sewer and storm water
which is unfoul in nature can be taken through open channel
or drains, whereas both types of sewage is to be carried in
closed sewer in combined system
3. During disposal if the sewage is to be pumped, the separate
system is cheaper
4. There is no fear of steam pollution.
Page 12
Environmental Engineering
DEMERITS:
1. Flushing is required at various points because self-cleaning
velocity is not available due to less quantity of sewage
2. There is always risk that the storm water may enter the
sanitary sewage sewer and cause over-flowing of sewer and
heavy load in the treatment plant
3. Maintenance cost is more because of two sewers
4. In busy lanes laying of two sewers is difficult which also
causes great inconvenience to the traffic during repairs
(C)
PARTIALLY SEPERATE SYSTEM:
In the seperate system, if a portion of storm water is
allowed to enter in the sewers carrying sewage and the
remaining storm water flows in seperate set of sewers, it is
called partially seperate system
MERITS AND DEMERITS OF PARTIALLY SEPERATE
SYSTEM:
MERITS:
1. It is economical and reasonable size sewers are required
because as it is an improvement over seperate system.
2. The work of house-plumbing is reduced because the rain
water from roof, sullage from bath and kitchen, can be taken
in the same pipe carrying the discharge from the water closets.
Introduction
Page 13
The water from all other places can be taken in seperate sewer
or drain.
3. No flushing is required because small portion of storm water
is allowed to enter in sanitary sewage.
DEMERITS:
1. Cost of pumping is more than seperate system when pumping
is required because portion of storm water is mixed.
2. There are possibilities of over-flow.
3. In dry weather, the self cleaning velocity may not develop.
Page 14
Environmental Engineering
SYNOPYSIS
1. Environmental engineering is deals with the application
of engineering principles to the control modification and
adaption of the physical, chemical and biological factors
of the environment in the interest of mans health;
comfort and social well being
2. The term used in sewerage
a. Sullage – liquid waste from latrines, urinals
b. Sewage – liquid waste from community include
sullage, discharge from latrines, urinals,
industries and storm water
c. Garbage – dry refuse which include decayed
fruits, grass, leaves, paper pieces, sweepings,
vegetable etc
d. Refuse – all kinds of dry wastes of community of
street and house sweepings, garbage etc
e. Sewer – The underground conduct or drain
through which waste water is conveyed
3. The sewage is classified as
1) Storm sewage
2) Sanitary sewage
4. The system of sewerage methods are
1. Conservancy system – refuse and storm water collected
separately and disposed
2. Water carriage system – Properly designed sewerage
system
5. The types of sewage systems are
1. Combined system
2. Separate system
3. Partially separate system
Introduction
Page 15
SHORT ANSWER TYPE QUESTIONS
1. Define the terms
(a) Sewage
(d) Sullage
(b) Sewerage (c) Sewer
2. Define the terms
(a) Garbage
(b) Refuse
3. What are the main objects of sewage disposal?
4. What are the methods collection of sanitation?
5. What are the main types of sewage?
6. What is conservancy system?
7. What is water carriage system?
8. What are sewerage systems?
ESSAY QUESTIONS
1. Explain the objects of sewage-disposal.
2. Why it is necessary to collect, treat and dispose of waste
products of town?
3. Explain the methods of collection of sanitation.
4. Compare the methods of collection of sanitation of
conservancy & water carriage systems.
5. Explain the merits and demerits of sewerage systems.
6. Discuss the comparative merits and demerits of seperate
system and combined system.
Page 16
Environmental Engineering
CHAPTER 2
QUANTITY OF SEWAGE
In order to find out suitable section of sewer, it is necessary to
determine the quantity of sewage that will flow through the sewer. The
sewage consists of dry weather flow and storm water.
2.1
QUANTITY OF DISCHARGE IN SEWERS:
The quantity of discharge in sewers is mainly affected by
the following factors.
(i)
Rate of water supply
(ii)
Population
(iii) Type of area served as residential, industrial or commercial
(iv) Ground water infiltration
(i)
RATE OF WATER SUPPLY:
The rate of sewage may be 60 to 70 percent of water
supply due to various reasons such as consumption, evaporation,
use in industries etc. This may be changes daily, seasonal and
also standard of living of people.
(ii)
POPULATION:
As the population increases the quantity of sewage also
increases because the consumption of water is more.
(iii)
TYPE OF AREA SERVED:
The quantity of sewage depends upon the type of area as
residential, industrial or commercial. The quantity is depends on
population if it is residential, type of industry if it is industrial.
Quantity of Sewage
Page 17
Commercial and public places can be determined by studying the
developing of other such places.
(iv)
GROUND WATER INFILTRATION:
When sewers laid below the water table in the ground, the
ground water may percolate in the sewer from the faulty joints
and cracks in the pipelines. The quantity of infiltration water in
the sewer depends upon the height of the water table about the
sewer invert, permeability of soil, size and nature of the faults or
cracks in the sewer line. As per the U.S.A. reports
(i)
4.5 to 45 cum/hectare area/day
(ii)
11 to 225 cum/hectare area/km length of the sewer
line
(iii)
0.7 to 7.2 cum/day/cm of dia of the sewer.
DRY WEATHER FLOW:
The sanitary sewage, which includes wastewater from
residences and industries, is known as Dry Weather Flow
(D.W.F)
VARIABILITY OF FLOW:
Practically the average sewage never flows in the sewer, it
continuously varies from hour to hour of the day and season to
season. The consumption of water in summer is more than in
winter or rainy season and this change in consumption of water
directly affects the quantity of sewage. Practically it has been
Page 18
Environmental Engineering
seen that the maximum to average flow of sewage is between 1.5
to 1.0 and average to minimum is between 1.2 to 1.0
2.2
DETERMINATION OF STORM WATER FLOW:
The quantity of storm water, which is known as the wet
weather flow (W.W.F), that will enter the sewer is to be carefully
determined. The following are the factors mainly affect the
quantity of storm sewage.
(i)
Intensity of rainfall
(ii)
Characteristics of catchment area
(iii) Duration of storm
(iv) Atmospheric temperature, wind and humidity
Generally two methods are used to calculate the quantity
of storm water.
(i)
(i)
Rational method
(ii)
Empirical formulae method
RATIONAL METHOD:
In this method , the storm water quantity is determined by
the rational formula
C.i.A
Q = --------360
where Q=quantity o storm water in m3/sec
C=Coefficient of runoff from table
I=intensity of rainfall in mm/hour
Quantity of Sewage
Page 19
A=drainage area in hectares
* The runoff coefficient ‘C’
is calculated (overall)
∑AC
A1C1 + A2C2 + ---------+ AnCn
= -------------------------------------- =
-----------∑A
A1 + A2 + --------------+ An
Where A1, A2, A3 ------- An are the different types of areas
And C1, C2, C3 ------- Cn are their runoff coeff. respectively from
table.
(ii)
EMPIRICAL FORMULAE METHOD:
For determining runoff from very large areas under
specific conditions such as slope of land, imperviousness, rate of
rainfall etc. These formulae are derived after long practical
experience and collection of field data.
(A)
Burkli – Zeighar formula (used in switzerland)
4
C.I.A
√S
Q = ----------------
-----
141.58 A
(B)
Mc.Math Formula (used in U.S.A)
C.i.A
5
√S
Q = ---------- ----148.35
(C)
Fuller’s Formula
A
Page 20
Environmental Engineering
C. M 0.8
Q = -------------13.23
(D)
Funnig’s Formula
Q = 12.8 M 5/8
(E)
Tallbot’s Formula
Q = 22.4 M 1/4
Where Q = runoff in cum/sec
C = runoff coefficient
i = intensity of rainfall in cm/hour
S = slope of the area in metre per thousand metre
A = drainage area in hectare
M = drainage area in square km
2.3
SURFACE DRAINAGE:
The sullage from kitchens, bathrooms and storm water,
which passes through the surface drains, is called surface
drainage. They are less hygienic as they are open and exposed to
atmosphere
REQUIREMENTS:
1. The inner surface of surface should be plastered
2. The joints of drains should be properly and neatly finished
Quantity of Sewage
Page 21
3. The drain should be laid such a gradient that self-cleansing
velocity is developed
4. They should be laid on easy curves
5. They should be properly designed with reasonable provision of
free board
SHAPES OF SURFACE DRAINS:
The following are the four shapes, which are commonly
adopted in the construction of surface drains as shown in fig 2.1.
1. Rectangular surface drains
2. Semi-circular surface drains
3. U-shaped surface drains
4. V-shaped surface drains
Fig 2.1 Types of Surface drains
Page 22
1.
Environmental Engineering
RECTANGULAR SURFACE DRAINS:
These drains are suitable for carrying heavy discharge.
They however donot develop the required velocity when depth of
flow is small and they get easily deposited.
2.
SEMI-CIRCULAR SURFACE DRAINS:
These are suitable for streets where the discharge to be
accommodated is of small quantity. These drains are readymade
semi-circular sections of stoneware or concrete or asbestors
cement pipes.
3.
U-SHAPED SURFACE DRAINS:
These drains are easy to construct and they combine the
advantages of semi-circular drains and rectangular surface drains.
4.
V-SHAPED SURFACE DRAINS:
These drains posses better hydraulic properties but they
are difficult to construct. These drains will carry fluctuating to
construct. These drains will carry fluctuating discharge without
depositing solids at any point and capable of producing a good
velocity.
These drains are constructed either in brick masonary or
stone masonary in cement mortar. The inside surface is smoothly
plastered with rich cement mortar. The drains are provided with
suitable gradients to meinatin the velocity within the range so as
to avoid either silting or scouring.
Quantity of Sewage
2.4
Page 23
Use of nomograms as per IS 1742 to determine the unknown
values of gradient, diameter, discharge and velocity.
In the design of sewerage scheme for a town, the
calculations have to be done for every sewerline to obtain the
necessary gradients, the given self cleansing velocities and
estimated discharge use of the formula for every calculation and
thus number of calculations flow whole scheme becomes a
cumbersome job. This work is simplified by adopting tables,
nomograms, partial flow diagrams etc prepared on the basis of
the appropriate formula.
Nomogram shown in fig 2.2 is very commonly used in the
design of sewers. This nomogram is based on mannings formula
in which value of ‘n’ is taken as 0.013. The values given in the
Nomograma are for sewers running full. As per IS 1742, the
Nomogram shown in fig can be used conveniently. For example
if the required discharge of a sewer for which n=0.013 is 224
lit/sec, and the grade is 0.00125, a line is drawn through these
two values. The intersection of this line on velocity scale and
diameter scale gives the corresponding values. Thus for this
example diameter of sewer is found to be 600mm and the
velocity to be maintained is 0.765 m/sec. Hence if two values are
known, the remaining two values can be easily got from the
nomogram.
Page 24
Environmental Engineering
Fig 2.2 Nomogram
Quantity of Sewage
Page 25
SYNOPYSIS
1. The determination of quantity of sewage is essential for the
design of system of collection, pumping, treatment and disposal
2. The sanitary sewage is called dry weather flow (DWF) which
depends upon the following factors
a. Rate of water supply
b. Population
c. Type of area
d. Infiltration of ground water into sewers
e. Exfiltration
3. The variations in the flow of sewage may be seasonal, monthly,
daily and hourly and to get maximum flow rate the average flow
rate of sewage is to be multiplied by a peak factor
4. Nomograms are used in the design of sewers for calculating the
gradients, diameter of pipes, velocities and quantities of sewage
based on mannings formula
5. The factors affecting storm water flow are
a. Intensity and duration of rainfall
b. Area of catchment
Page 26
Environmental Engineering
c. Store and shape of catchment
d. Nature of soil
e. Initial moisture content in the soil
f. Number and size of ditches available in the area
6. Determination of storm water flow by
1. Rational formula
2. Empirical formulae
7. The types surface drains used are
a. Rectangular
b. Semi-circular
c. U.shaped
d. V-shaped
Quantity of Sewage
Page 27
SHORT ANSWER TYPE QUESTIONS
1. Define dry weather flow
2. What are the factors affecting dry weather flow?
3. What do you understand by self cleaning velocity?
4. Mention the three factors considered to fix gradient for the
sewer?
ESSAY TYPE QUESTIONS
1. Explain different types of surface drains
2. Explain different factors that effect quantity of discharge in
sewers
3. How do you estimate the storm water by rational method and
empirical formulae method?
Page 28
Environmental Engineering
CHAPTER 3
SEWERAGE SYSTEMS
Sewerage are closed conducts are called sewers and are laid
under ground for conveying foul discharges from water-closets of public
and domestic buildings, chemical mixed water from industries without
creating any nuisance outside the town.
Sewers should have such cross-section that self-cleaning velocity
should be developed even during dry weather flow. No deposit should
settle down in the bed of sewers under any circumstances. These should
be laid in the town at such a slope that water in case of flood in river at
the outlet should not come out from manholes and cause insanitary
conditions
3.1
DIFFERENT
SHAPES
OF
CROSS-SECTIONS
FOR
SEWERS CIRCULAR AND NON CIRCULAR
Generally the sewers of circular shape are adopted because of
following facts
1. Circular shape affords least perimeter and hence construction cost
is minimum for the same area of other shape
2. Deposition of organic matter are reduced to minimum because of
no corners
3. They are easy to manufacture or construct and handle
Sewerage Systems
Page 29
4. Because of circular shape, these are subjected to hoop
compression hence the concrete required is minimum and no
reinforcement is required
5. They posses excellent hydraulic properties because they provide
the maximum hydraulic mean depth when running full or half
full.
The circular sewers prove to be best when the discharge
doesnot vary too much and the chances of sewers running with
very low depths (less than half) are less.
However the sewers of non-circular shapes are also used
for the following reasons
1. To bring down the cost of construction
2. to improve the velocity of flow when the depth of sewage
is low
3. to secure more structural strength
4. to simplify the process of construction
5. to make them large enough for a man to enter for cleaning
or repairing
SHAPES OF NON-CIRCULAR SHAPES:
The following are the non-circular shapes, which are commonly,
used for sewers.
1. BASKET HANDLE SECTION: In this type of sewer, the upper
portion of sewer has got the shape of a basket-handle as shown in
fig. 3.1. The bottom portion is narrower and carries small
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Environmental Engineering
discharges during mansoon and combined sewage is carried
through the full section. This shape of sewer is not generally used
at present.
Fig 3.1
2. CATENARY-SHAPED SECTION: In this type of sewer, the
shape of sewer is in the form of a catenary and only gravity force
is acted upon this sewer. This is suitable for tunnelling work.
3. EGG-SHAPED OR OVOID SECTION: This type of sewer is
suitable for carrying combined flow. The main advantage of this
type of sewer is that it gives slightly higher velocity during low
Fig 3.2
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Page 31
flow than a circular sewer of the same capacity. But construction
of this section is difficult and less stable than circular section.
Inverted egg-shaped sewer gives better stability and carries heavy
discharges. The details are as shown in fig 3.2.
4. HORSE-SHOE SECTION: This type of sewers are used for
the construction in tunnel to carry heavy discharges, such as truck
and outfall sewers. This is also suitable when the available
headroom for the construction of sewer is limited. The invert of
the sewer may be flat, circular or paraboloid and top is semicircular with sides vertical or inclined as shown in fig 3.3.
Fig 3.3
5. PARABOLIC SECTION: This type of sewers are suitable fro
carrying comparatively small quantities of sewage and
economical in construction. The invert of sewer may be flat or
parabolic and upper arch of the sewer takes the form of parabola
as shown in fig 3.4.
Fig 3.4
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6. RECTANGULAR OR BOX TYPE SECTION: The
rectangular or box type section of sewer is stable and it is easy to
construct as shown in fig 3.5. It is some times used to work as a
storage tank during the tide it becomes necessary to store the
sewage for some period.
Fig 3.5
7. SEMI-CIRCULAR: This type of sewers are suitable for
constructing large sewers with less available headroom and it
posses better hydraulic properties as shown in figure 3.6.
Fig 3.6
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8. SEMI-ELLIPTICAL SECTION: This type of the section is
suitable to carry heavy discharges and adopted for soft soil, as it
is more stable. The dia of sewer may be more than 1.8m and
posses good hydraulic properties except at low depths as shown
in fig 3.7.
Fig 3.7
9. U-SHAPED SECTION: The shape of this section is the true
shape of letter as shown in fig. Or small trench of U shape can be
setup in the larger section of sewer as shown in fig 3.8. The
trench is known as the cunette and adopted for a combined sewer
having predominant flow of storm water.
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Environmental Engineering
Fig 3.8
3.2
BRIEF DESCRIPTION AND CHOICE OF TYPES OF
SEWERS
The following factors are to be carefully considered while
making selection for the materials of sewer.
1. Cost: The cost should be moderate and reasonable
2. Durability: The material should be durable
3. Imperviousness: The material of sewer should be impervious
nature
4. Resistance to Abrasion: The material should possess enough
resistance to abrasion caused due to grit moving with high
velocity.
5. Resistance to corrosion: The material should be capable of
offering resistance to the corrosion because the sewage posseses
corrosive qualities
6. Weight: The material should possess moderate weight so as to
make easy handling and transportation.
The following are the various materials, which are used for sewers
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Page 35
(i)
Asbestos cement sewers
(ii)
Brick sewers
(iii)
Cast-Iron sewers
(iv)
Cement concrete sewers
(v)
Corrugated iron sewers
(vi)
Plastic sewers
(vii)
Steel sewers
(viii) Stoneware sewers
(ix)
Wood sewers
STONEWARE SEWERS:
The stoneware sewers are also known as the vitrified clay sewers
or salt-glazed sewers and they are prepared from various clays and
shapes in required proportion, allowed to dry and then burnt in a kiln. A
small quantity of salt is added to kiln get glass like glaze on the surface
of pipes.
ADVANTAGES:
1. These pipes are strong enough to take backfilling and traffic
2. The interior surface of sewers are smooth and impervious
3. The overall performance is very good
4. These sewers are cheap and easily available
5. These sewers are durable and better resistance to corrosion &
erosion
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Environmental Engineering
6. These sewers are capable of withstand hydraulic pressure upto
0.15N/mm2 and bear a load of soil of about 4.5 m depth
DISADVANTAGES:
1. These are brittle in nature and may damage in handling or
transport.
2. These are not strong enough to allow sewage under pressure.
3. These are difficult to handle or transport because of heavy
weight.
CAST IRON SEWERS:
The cast sewers possess high strength and they are durable. These
are available in sizes from 150mm to 750mm diameter. These sewers
can resists the action of acids in sewage if the inner surface is coated
with paint or cement concrete.
The cast-Iron sewers are used for following special purpose
1. Danger of contamination against leakages.
2. Expensive road surface like C.C. can be avoided.
3. Heavy external loads under railway lane, foundation.
4. Under high pressure.
5. The places subjected to considerable differences in temperature.
6. Where the ground is likely to subject to heavy movements and
vibrations.
7. Where wet ground required to reduce infiltration.
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DISADVANTAGES:
1. Cost is high
2. Transportation and handling is difficult
CEMENT CONCRETE SEWERS:
The cement concrete sewers may be plain or reinforced. The
plain cement concrete sewers are used upto the diameter of 600mm and
beyond 600mm reinforcement is provided.
ADVANTAGES:
1. These are strong and imperivious.
2. Larger diameter can be made.
3. Inner surface of sewer is smooth.
4. For attack of chemical and errosive actions the inner surface
should be lined with vitrified clay.
DISADVANTAGES:
1. Heavy weight transportation and handling is difficult.
2. Joints should be carefully filled.
4.
A.C.PIPES: These sewers are made from a mixture of asbestos
fibres and cement. They are available upto sizes of 900mm.
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ADVANTAGES:
1. Easy to cut and join.
2. Durable and good resistance to corrosion.
3. The inside surface is smooth.
4. Light in weight and hence easy to handle.
DISADVANTAGES:
1. Brittle and cannot stand impact forces during handling
operations.
2. The structural strength is poor and hence cannot be laid to resist
heavy external loads.
3.3
LAYING OF SEWERS:
The construction of sewer consists of the following works
a) Marking center lines of sewers.
b) Excavation of trenches.
c) Checking the gradient.
d) Preparation of bedding.
e) Laying of sewers.
f) Jionting.
g) Back filling.
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MARKING CENTER LINE OF SEWER:
The centre line of a sewers are marked on the streets and roads
from the plans starting from the lowest point or outfall of the main
proceeding upwards. The setting out of work is done by means of chain
and theodolite or compass. For checking the centre line during the
construction generally wooden pegs or steel spikes are driven at 10
meters intervals on a line parallel to the centre where while laying
sewers, they will not disturb them. For checking the levels of sewer pipes
and their alignment temporary benchmarks are established at 200-400
metres intervals. The reduced level (R.L) of these benchmarks should be
calculated with respect to G.T.S benchmarks. On the centre line position
of sewer appurtenances are also marked
EXCAVATION TRENCHES:
After marking the layout of the sewer lines on the ground, the
first step is the removal of pavement, which starts from the lower end of
the sewers and proceeds upwards. Pickaxes, spade or pneumatic drills
can be used in case of removing concrete pavements. After removing
pavements, the excavation of trenches is done manually or machinery.
The width of trench depends upon the dia of sewer and depth of sewerline below the ground level. The width of sewerline is 15cm more than
external diameter of sewer for easiness in lowering and adjusting the
sewerpipe. The minimum trench width of 60 to 100cm is necessary for
conveniently laying and jointing of even very small size sewers. The
excavation of trench sides require shoring and shuttering and also
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Environmental Engineering
dewatering is done by gravity method or pumping method as shown in
fig. 3.9.
Fig 3.9 Excavation of Trenches
PREPARATION OF BEDDING:
Trenches are excavated with proper grade so that sewage may
flow in sewer due to gravitational flow only. The centre line of sewers
and their grades are transferred from the ground by means of sight rail
and boning rod shown in fig no. 3.10.
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Fig 3.10 Laying of Sewer Pipes
When a sewer has to be laid in a soil underground strata or in a
reclaimed land, the trench shall be excavated deeper than what is
ordinarily required trench bottom or rock. In the case of very bad soil the
trench bottom shall be filled in with cement concrete of appropriate
grade. In areas subject to subsidence the pipe sewer shall be laid on a
timber platform or concrete cradle supported on piles. In the case of castin-site sewers and R.C.C section with reinforcement, bearing capacity is
encountered and soil stabilization shall be done either by rubber,
concrete or wooden crib. The various types of Pipe-Beddings are as
shown in Fig. 3.11.
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Fig 3.11 Various types pipe-bedding
LAYING:
Smaller size pipes can be laid by the pipe-layers directly by hand
only. But heavier and larger size pipes are lowered in the trenches by
passing ropes around them and supporting through hock.
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Page 43
It is the common practice to lay the pipes with their socket end
upgrade for easiness in joining. After lowering the pipes these are
brought near and spigot end of one pipe is placed in the socketed end of
the other after properly placing and arranging the pipes they are suitably
joined. The joints are carefully cured for sufficient time.
JOINTING OF SEWERS:
The C.I.Pipes shall be examined for line and level and the space
left in the socket shall be filled in by pouring molten piglead of bestquality as for IS:782 and IS 3114.
For concrete pipes, the collars shall be placed symmetrically over
the end of two pipes and the annual space between the inside of the
collar and the outside of the pipe shall be filled with hempyarn soaked in
tar or cement slurry tamped with just-sufficient quantity of water to have
consistency of semi-dry condition, well packed and thoroughly rammed
with caulking tools and then filled with cement mortar 1:2. The joints
shall be finished off with a fillet slopping at 45° to the surface of the pipe
and cured for 24 hours. Any plastic solution or cement mortar that may
have squeezed in the pipe shall be removed to leave the inside of the pipe
perfectly clean.
For stoneware pipes, all the joints shall be caulked with tarred
gasket in one length for each joint and sufficiently long to entirely
surround the spigot end of the pipe. The gasket shall then be filled with
1:2 cement sand mortar in a semi-dry condition and a fillet shall be
formed round the joint with trowel forming an angle of 45° with the
barrel of the pipe as per IS 4217. Rubber gasket may also be used for
jointing.
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TESTING OF SEWERS:
Following two tests are done for testing of sewer pipes.
1.
WATER TEST:
Each section of the sewer is tested for water tightness preferably
between the manholes. To prevent the change in alignment and
disturbance after the pipes have been laid, it is desirable to backfill the
pipes upto the top, keeping atleast given length of pipe at the joints.
Testing of sewers done by plugging the upper end with a
provision for an air outlet pipe with stopcock. The water is filled
through a funnel connected at the lower end provided with a plug. After
expelling the air through the air outlet, the stopcock is closed and water
level in the funnel is raised to 2m above the invert at the upper end.
Water level is noted after 30 minutes in the funnel and quantity of water
required to restore the original water in the funnel is determined. The
pipeline under pressure is then inspected while the funnel is still in
position. There should not be any leak in the pipe or the joint except
small sweating on the pipe surface which is allowed. Leakage in 30
minutes determined by measuring the replenished water in the funnel
should not exceed 15ml for smaller and 60 ml for larger diameter pipes
for 100m length.
2.
AIR TESTING:
This testing is done in large dia. Pipes when the required quantity
of water is not available it is done by subjecting the stretch of pipe to an
air pressure of 100mm of water by means of hand pump. If the pressure
is maintained at 75mm, the joints shall be assumed to be water tight. In
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Page 45
case drop is more than 25mm the leaking joints shall be traced and
suitably treated to ensure water-tightness. The exact position of leak can
be detected by applying soap solution to all the joints in the line and
looking for air bubbles.
BACK-FILLING OF TRENCHES:
After testing and removing defects of pipeline, the trenches are
back filled with excavated soil after removal of pebbles, stone-pieces and
lamps by ramming the soil in layers using with water. When the height
reaches to 60cm above the crown of the pipe, back filling is stopped for
atleast one weak for weathering. After a week, again backfilling is
started in layers and the trench is filled 15cm above the ground level.
During the course of time the back filled soil gets compacted and the
filled soil comes to the ground level. Back filling will be after 7 days for
precast pipes and 14 days after in the case of cast-in-site sewers.
Reinstatement of the pavement is carried out after about two months
after the proper consolidation of the backfill material and there is no
danger of risk of crank or settlement in the pavement.
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SYNOPYSIS
1. Sewers are closed conduits which are laid underground for
conveying sewage
2. Sewers of circular shape are adopted because
a. Construction cost is minimum for same area of other
shape
b. Deposition of organic matter are reduced to minimum
c. Poses excellent hydraulic properties
d. Easy to manufacture, construction and handle
3. The Non-circular shapes generally used are
a. Basket handle section
b. Catenary-shaped section
c. Egg shaped section
d. Horse shoe section
e. Parabolic section
f. Rectangular or box type section
g. Semi circular section
h. Semi-elliptical section
i. U-shaped section
4. The factors like cost, durability, impervious, resistance to
abrasion, resistance to corrosion, weight considered in making
selection for the material of sewer
5. The materials used for the manufacture of sewers are
a. Asbestos cement sewers
Sewerage Systems
b. Brick sewers
c. Cast-Iron sewers
d. Cement concrete sewers
e. Corrugated iron sewers
f. Plastic sewers
g. Steel sewers
h. Stoneware sewers
i. Wood sewers
6. Laying of sewers involves the following works
a. Marking center lines of sewers
b. Excavation of trenches
c. Checking the gradient
d. Preparation of bedding
e. Laying of sewers
f. Jointing
g. Back filling
7. Testing of sewers are done by the following
1. Water test
2. Air test
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Environmental Engineering
SHORT ANSWER TYPE QUESTIONS
1. Name the different type of non-circular sewers.
2. Name any four material used for sewers.
3. Name the types of tests required for sewers.
Write short notes on
4. Concrete pipes.
5. A.C. Pipes.
6. Horse-Shoe type sewer.
7. Egg-Shaped Sewer.
8. Define sewer.
9. What are the advantages of circular type of sewers over noncircular type of sewers?
10. Draw the neat sketch of egg-shaped sewer.
ESSAY TYPE QUESTIONS
1. Explain different type of non-circular sewers with neat sketches.
2. What are the factors should be considered for selecting the
material of sewer?
3. Explain in the following
1. Stoneware sewers
2. Cement concrete sewers
3. A.C. Sewers
4. Cast Iron sewers
4. Explain the laying of sewers.
5. What are the tests required for testing of sewers? Explain.
Sewer Appurtenances
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CHAPTER 4
SEWER APPURTENANCES
Sewer system require various types of appurtenances for their
proper functioning and maintenances. If sewerage system will not be
maintained properly, salt, ashes, fats, oils and greasy matters etc will
choke the sewerline. Therefore for the proper operation and maintenance
of sewerage system, various devices like manholes, lamp holes, drop
manholes, street inlets, flushing tanks, catch basins, ventilating shafts
and storm role of works etc are essential, which should be inaccessible to
the public.
1.1.1
MANHOLES
LOCATION:
Manholes are provided at every change of alignment, gradient or
diameter of the sewer.
FUNCTION:
Manholes are provided for inspection, cleaning, repairs and
maintenance of the sewer.
CONSTRUCTION:
A Manhole consists of
a) Working chamber.
b) An access shaft and
c) A strong cover on the top flush with the road level.
a) WORKING CHAMBER:
The working chamber has such a size, so that necessary
examination and cleaning can be done easily. The minimum internal size
of the chamber are as follows.
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Environmental Engineering
(i)
For depth of 0.8m or less __________ 0.75m x 0.75m
(ii)
For depth between 0.8m and 2.1m _____1.2m x 0.9m
(iii)
For depth more than 2.1m __________ 1.2m x 0.9m
or 1.4dia circular chamber.
b) ACCESS SHAFT:
The access shaft provides an access to the working chamber. The
shaft is formed, by corbelling the working chamber on three as shown in
fig no. 4.1. So that the cover frame can be fitted in the opening, the
minimum internal dimensions of the access shaft are 0.5 x 0.5m
Fig no. 4.1 Manhole
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COVER:
At the top of manhole, the manhole cover of cast iron or R.C.C is
provided to cover the opening depending upon the type of traffic on the
road. The manhole covers are provided flush with the road level. The
bottom of the manhole is usually made of concrete slightly sloped at the
top towards the open channels, which are in continuation of the sewer
line. The channels are sometimes lined with half-round sewer pipe
section. The top surface of the concrete is called benching and the man
stands on its top during cleaning and inspection of the sewerlines over
the cement concrete walls not less than 20cm thickness are constructed.
Circular shape is structurally more stable and stronger though it is
difficult in construction. The maximum distance between two manholes
should be 30m and the distance between the manhole and gully
chambers should not exceed 6m.
4.1.2
DROP MANHOLE:
If the difference in level between the branch sewer and main
sewer is within 60cm and there is sufficient roof within the working
chamber, the connecting pipe may be directly brought through the
manhole wall by providing a ramp in benching. Such manholes which
drop the level of invert of the incoming sewer, by providing a vertical
shaft are called drop manholes.
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Environmental Engineering
The main purpose being to avoid the splashing of sewage on the
man working and on the masonary work. The branch sewer line is
connected to the manhole in such a way that it can be cleaned and rodded
when necessary. For inspection of the incoming sewage and cleaning of
vertical shaft, the vertical shaft is taken upto the ground level as shown
in fig no. 4.2.
Fig No. 4.2 Drop Manhole
4.1.3 STREET INLETS
Street inlets or gullies are the openings in the street a or b or
gutter to collect the storm water and surface wash flowing along the
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street and convey it to storm or combined sewer by means of stoneware
pipes of 25 to 30cm diameter. Fig No.4.3 shows the most useful location
of street inlet at the street junction in such way that the storm water may
not flow across any of the streets or flood the cross walks causing
interference with the traffic street inlets are of three types.
Fig No. 4.3 Street Inlets
1. CURB INLET: In which an opening is provided in the road curb
for the entrance of storm water. The gutter opening bars are
provided to prevent the passage of dry-leaves, papers etc in the
sewer line as shown in fig no. 4.4.
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Environmental Engineering
Fig 4.4 Curb Inlet
2. GUTTER INLET: These are placed directly below the road
gutter and storm water directly enters them from the top. Such
inlets catch very large volume of water and are most suitable in
roads having steep slopes. These inlets are provided with cast
Iron gratings at their top to prevent floating matters entering the
sewer. The top grating should be sufficiently strong the bear the
traffic loads. The main difficulty with such inlets is that of the
heavy cost and these are mostly stolen and the pit remain
uncovered as shown in fig no. 4.5.
Fig No. 4.5 Gutter Inlet
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3. COMBINED GUTTER AND CURB INLET: These inlets in
which the storm water enters from both the gutter and curb as
shown in fig no. 4.6.
Fig 4.6 Combined Gutter and Curb Inlet
4.1.4
CATCH BASINS:
These are small masonary chambers (75 to 90cm in
diameter and 75 to 90cm deep) which are constructed below the
street inlet to prevent the flow of grit, sand or debris in the sewer
lines. The outlet pipe of catch basin is fixed about 60cm above
bottom as shown in fig no. 4.7. The outlet pipe is provided with a
trap to prevent the escape of odours from the sewer to the catch
basins. Catch basins are provided in the following sections.
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Environmental Engineering
Fig 4.7 Catch Basins
1. When the sewers are laid at very small gradient and velocity of
flow is less than self-cleaning velocity.
2. When the drains are passing along the water bound mechadam
road or in sandy area and market.
Catch basins collect the solids from the storm water.
These solids are to be removed at frequent intervals for the
proper functioning of the catch basin otherwise they will block
the passage of storm water in the sewers resulting in the flooding
of the streets creating nuisance. Nowadays catch basins are not
providing and street inlet may be directly connected with the
sewers.
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4.1.5 FLUSHING TANKS:
These are masonary or concrete chambers to flush the
sewers when the sewers gradients are flat and velocity of sewage
is very low. These are usually provided at the beginning point of
the sewers and may be either are automatic or worked by hand.
In automatic flushing tank, the water is automatically
released from the tank at required intervals, which can be
adjusted by supply tap and flushes the sewer as shown in fig no.
4.8. It consists of U-tube with bell cap at its one end connects the
chamber with sewer. With the water level reaches certain level in
the chamber, siphonic action takes place and the whole water of
the chamber rushes to the sewer pipe and flushes it. The capacity
of these tanks is usually 9 to 14 litre and may be adjusted in such
a way as to work twice or thrice a day depending upon the
quantity of deposits in the sewer and size of sewer.
Fig 4.8 Automatic Flushing Tanks
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Environmental Engineering
Table 7.1 gives the capacity of the flushing tanks for
flushing 65m long sewer of different diameters.
S.No. Dia of the sewer
Gradient of
Sewer
Capacity of
flushing tank
1
150mm
1 in 100
1.30 cum
2
225mm
1 in 185
2.80 cum
3
300mm
1 in 270
4.50 cum
Table 4.2 gives the approximate quantities of water
required for flushing the sewer lines.
Slope
Quantity of flushing water in litre
200mm sewer
250mm sewer
300mm sewer
0.0050
2300
2500
3000
0.0075
1500
1800
2300
0.0100
1300
1500
2000
0.0200
500
800
1000
0.0300
400
500
700
4.1.6 REGULATORS:
The structures constructed to divert part of sewage in the
case of combined sewers are known as the storm water regulators
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OBJECT:
The main object of providing a storm water regulator is to
divert the excess storm water to the natural stream or river. The
excess sewage will be mainly composed of storm water and it
will therefore be not foul in nature and hence decrease in load on
the treatment units or pumping stations.
TYPES:
1. LEAPING WEIR:
Leaping weir is used to indicate the gap or opening in the
invert of a combined sewer. The intercepting weir runs at right
angles to the combined sewer. If the discharge exceeds certain
limit, the excess sewage leaps or jumps across the weir and it is
carried to the natural stream or river as shown in fig no. 4.9.
Fig 4.9 Leaping Weir
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Environmental Engineering
2. OVERFLOW WEIR:
The excess sewage is allowed to overflow in the channel
made in the manhole as shown in fig no. 4.10 and conveyed to
the storm water sewer or channel. In order to prevent the escape
of floating matter from the combined sewer channel, adjustable
plates are provided. In another arrangement, the openings at
suitable height above invert are provided along the length of
combined sewer as shown.
Fig 4.10 Overflow Weir
3. SYPHON SPILLWAY:
The arrangement of diverting excess sewage from the
combined sewer by the syphonic action is most effective because
it operates on automatically and requires least maintenance.
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However it is likely to be clogged due to narrow passage as
shown in fig no. 4.11.
Fig 4.11 Syphone Spill Way
4.1.7
INVERTED SIPHON:
Inverted siphon is a sewer section which is constructed
lower than the adjacent sewer section and which runs full under
gravity with pressure greater than atmosphere as shown in Fig.
No. 4.12.
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Environmental Engineering
Fig 4.12 Inverted Syphone
PURPOSE:
The main purpose of inverted siphon is to carry the
sewerline below obstructions such as ground depressions,
streams, rivers, railway etc.
Siphon is so designed that a self-cleaning velocity of
about 90cm/sec during achieved the period of minimum
discharge. For this purpose, the siphon is usually made of three
pipe sections-one for carrying minimum discharge, the other for
maximum discharge and the third for combined flow in
mansoons. The inlet chamber contains three channels, one for
each pipe section. When channel no. 1 overflows, the sewage
enters in channel no. 2 and pipe no. 2 comes into commission.
Similarly, when channel no. 2 also overflows the sewage enters
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channel no. 3 and pipe no. 3 comes into commission as shown in
fig no. 4.12. The inlet chamber should be provided with screens
to remove silt, grit etc from sewage before enters the siphon
DISADVANTAGES OF SIPHON:
1. As the down gradient is not continuous in inverted siphon; the
silting takes place.
2. It is not possible to give side connections to inverted siphons.
3. If inlet chamber is not properly designed, the floating matter
contained in sewage will separate out and it will accumulate in
the inlet chamber results in the inefficient functioning of the
inverted siphon.
4.2
NECESSITY OF PUMPING SEWAGE-LOCATION AND
COMPONENT PARTS OF PUMPING STATION.
In sewerage system at some places the sewage cannot
flow under its gravitational force only and requires lifting in
following circumstances, it is becomes necessary to pump the
sewage.
1. If some portion of the town is low-laying and the sewage cannot
flow by gravity.
2. When basements are provided in the buildings, the sewage is
pumped to the sewerline.
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Environmental Engineering
3. If a ridge intervenes, sometimes it is economical to pump sewage,
instead of providing a funnel.
4. When the land is flat and it not possible to get self-cleaning
velocity, the sewers are laid at the required slope and after some
interval they are allowed to flow under gravity.
5. At the treatment plants to rise it upto the plant for treatment.
6. At the outfall while disposing it is required to be pump if the
level of the water course is higher than the outlet of the sewer.
LOCATION OF PUMPING STATION:
The following points should be considered while locating the site
of pumping station
1. The topographical conditions of the city should be thoroughly
studied to locate the best site of pumping station
2. If the quantity of sewage is very large, the site should be near to
the disposal point or at a place where the sewage can be directly
disposed off during emergencies
3. The site should be such that during flexed, it should not flooded
with river water or seepage from the ground.
4. Provision should be made to pump all the sewage which will be
received during worst conditions of rains
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ELEMENTS OF PUMPING STATION:
Every sewage pumping station consists of the following
1. Preliminary screening and grit chambers
2. Sump or wet well
3. Pumproom or dry well
4. Pumps with driving engine or motar
5. Miscellaneous accessories such as pipes, valves, fittings, flow
recorder, emergency over-flow etc
The capacity of pumping station is determined by the
present and future sewage flows based on a designed period of
15years. While designing the pump house, provisions should be
made for easy removal and installation of pumps and motars for
periodical repairs and replacements
(i)
PRELIMINARY SCREENING AND GRIT CHANNELS:
The sewage contains large amount of sand, gravel , rags ,
paper, leaves etc should be removed before pumping so as to
prevent the wear and tear of pumping machinery and increasing
its life. Large floating matter are removed by passing the see page
through flat bar screens. After passing through the screens, the
sewage goes into grit channel where heavier inorganic solid
matters are removed because of low velocity is maintained
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(ii)
Environmental Engineering
SUMP OR WET WELL:
The sewage from the city is received at pumping station
in a tank known as sump or wet well. The tank having capacity of
20-30cm per minutes average flow is designed in modern
practice. The sump well is an underground, ring or circular shape
placed at such a level that sewage from trunk sewer can flow into
it by gravity only. The bottom of the tank is given a 1:1 slope
towards a central pit where the end of section pipe of the pump is
placed.
The depth of the well depends upon the depth of incoming
sewage of inlet. The main storage inside the well should be free
fall inside the wet well to avoid the save harging and back flow.
Guide pipes filled with flats, switches of motars, cables of
electric motars, sewage level indicators etc should be placed in
the wet well at suitable places. Gate valves should be fitted on the
incoming sewer lines to stop the sewage flow during inspection ,
repairs and cleaning of the wet well etc. At the top of the wet
well manhole with ladders are provided for cleaning, inspection
and maintenance as shown in fig no. 4.13. The overflow weirs
and by-pass arrangements are also provided in the wet wells for
diverting the sewage during emergency floods.
Sewer Appurtenances
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Fig 4.13 Components of a Pumping Station
(iii)
PUMP ROOM:
This is also called as dry-well and placed in a convenient
location such that the pumps can easily function
The pump-room is an underground masonary or rccroom
with circular or rectangular shape and sewage pumps, their
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Environmental Engineering
driving units, control valves etc are installed in it. The size of the
dry well should be sufficient for the movement of operator ,
maintenance repair and installation of pumps etc. In some cases a
small pump is also provided to pump the leakages from the wet
well in this well
(iv)
PIPES VALVES, FITTINGS etc:
Cast Iron pipes with flanged joints should be in all
installation works at pumping station so that the dismantling and
repair of pumping station equipment. The size of pipe should be
such that the sewage can flow at a velocity of 0.6 to 0.9m/sec so
as to prevent the settlement of solids in the sewage. The length of
the pipe is kept small so as to avoid anerobic deterioration and
also head due to more number of valves, bends, junctions etc
should be kept small as possible.
Check valve should be provided in the sewerline to
prevent the back flow of sewage during floods in the rivers or
discharge area.
Gate valve should be provided on the sewerline before
wet well and on the section and discharge pipe to close the flow
of sewage during maintenance, inspection and repair of the
pump.
Sewer Appurtenances
Page 69
Pressure gauge is note the section pressure and discharge
pressure should be installed at the appropriate position to record
section and delivery pressure.
Sewerage level indicator should also be filled in the wet
well to record the level of the sewage.
(iv)
PUMPS WITH DRIVING ENGINE OR MOTOR:
The following are the requirements of good sewage pump.
1. It can pump the sewage upto required elevation.
2. It can pump the required quantity of sewage even in emergency
period.
3. It should be reliable.
4. It should be cheap in initial cost and maintenance.
5. It should not corroded by the organic and inorganic wastes of the
sewage.
6. It should not be damaged or worn out by the presence of sand ,
gravel, stone etc in the sewage.
7. It should require less spacing for installation.
8. It should not made more noise during working.
9. It should not require high skills in its maintenance and operation.
Generally centrifugal pumps are used for pumping of
sewage provided with automatic or remote control devices and
fulfill most of the requirements of the sewage pumps.
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Environmental Engineering
The pumps can be placed
(i)
Directly in the wet well in the submerged position
(ii)
In the dry well above the sewerage level in the wet
well driving unit is gasoline or steam engine
(iii)
In the dry well below the sewage level in the wet well
driving unit is electric motar
The B.H.P of the driving unit is calculated by the formula,
W.Q.H
B.H.P. = ----------------------------75 x np x nm
where Q = discharge
H = Water head
np = efficiency of pump
nm = efficiency of driving engine of motar
SAFETY MEASURES:
The following safety measures shall be taken at the sewage
pumping stations
1. Rating should be provided around manholes and openings
2. Gaurds should be provided on and around all mechanical
equipment
3. Staircases with landing should be provided in place of ladders
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4. The steps of the stair cares should be of non-slippery to prevent
slippage
5. Fire extinguishers first aid boxes and other safety devices should
be provided
6. To prevent explosure gas leakage, wet well should not be directly
connected by any opening to dry well or super structure.
7. All electrical equipment and wiring should be properly insulated
and grounded.
8. To minimize the possibilities of cross connectors, the pipes
should be given different colours.
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SYNOPYSIS
1. For proper functioning and maintenance of sewer system,
requires various types of appurtenances like manholes,
lampholes, drop manholes, street inlets, flushing tanks, catch
basins, ventilating shafts and storm relief works etc are essential
2. Manholes are provided at every change of alignment, gradient or
diameter of the sewer for inspection, cleaning, repairs and
maintenance of the sewer.
3. Street inlets or gullies are the openings in the street curbs or
gutter to collect storm water and surface wash flowing along the
street and convey it to storm or combined sewer by means of
stone ware pipes of 25 to 30 cm diameter.
4. Catch basins are small masonary chambers constructed below the
street inlet to prevent the flow of grit, sand or debris in the sewer
lines
5. Flushing tanks are masonary or concrete chambers to flush the
sewers when the sewer gradients are flat and the velocity of
sewage is very low
6. Regulators constructed to divert part of sewage in the case of
combined sewers are known as the storm water regulators
7. Inverted siphon is a sewer section which is constructed lower
than the adjacent sewer section and which runs full under gravity
with pressure greater than atmosphere
8. The location of sewage pumping station selected based on
1)tropographical conditions of city b) should be near to
disposal point c) the site should be such that during the flood it
should not flooded with river water or see page from the ground
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9. The elements of pumping station are
a. Preliminary screening and grit chambers
b. Sump or well
c. Pump room or dry well
d. Pumps with driving engine or motar
e. Mislaneous accessories such as pipes, valves, fittings,
flow recorder, emergency over-flow etc
10. The following safety measures should be taken at the pumping
station
a. Railing should be around the manholes and openings
b. Guard should be provided on and around all mechanical
equipment
c. Staircase with landing should be provided in place of
ladders
d. Non-slippery type steps of stair case should prevent
slippage
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Environmental Engineering
SHORT ANSWER TYPE QUESTIONS
1. What is the
appurtenances?
necessity
of
providing
following
sewer
a. Street inlet.
b. Siphon spillways.
c. Lamp hole.
d. Manhole.
2. Write short notes on catch pits.
3. under, what circumstances it becomes necessary to pump the
sewage?
4. What are the requirements of sewage pump?
5. What is the purpose of providing catch basins?
6. What is the purpose of inverted siphon?
7. Name any four safety measures taken in the pumping of sewage.
ESSAY QUESTIONS
1. State the different sewer appurtenances used in the sewerage
scheme and state the location and utility of each.
2. Describe the following with neat sketch
a. Manhole
b. Flushing tanks
Sewer Appurtenances
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3. What do you understand by the drop manhole? Explain it with
neat sketch
4. What points should be kept in mind while locating the site of
pumping station? What are the requirements of a sewage pump?
5. What are the elements of pumping station? Describe each of them
6. Draw the neat sketch of pumping station and mention the purpose
of each unit.
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Environmental Engineering
CHAPTER 5
SEWAGE CHARACTERISTICS
GENERAL INTRODUCTION:
Sewage is a dilute mixture of the various types of wastes
from residential; public and industrial places. Sewage contains
99.9% of water and small portion of solids present in the sewage
pose threat as they are offensive in nature, undergo changes by
bio-degradation causes nuisance and pollution. So an
understanding the nature of physical, chemical and biological
characteristics of sewage is essential in planning, design and
operation of treatment and disposal facilities and in the
engineering management of environmental quality.
5.1
STRENGTH OF SEWAGE: The strength sewage is its
potential to produce nuisance to the man and his environment. It
is expressed in terms of B.O.D. The nuisance is caused by the
oxidizable organic matter, which is unstable in nature, undergoes
biodegradation produces very bad odour and causes insanitary
and unhealthy environment. If the sewage contains more organic
matter is more strong and if the sewage contains less organic
matter is considered as less strong.
5.2
SAMPLING OF SEWAGE:
The constituents of sewage continuously change with the
time. So it is necessary that a sample collected for analysis should
be fairly representative of the sewage. Hence, the samples of 100
to 150 C.C. are collected at various depths and at frequent
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Page 77
intervals of time (half hourly or hourly collection) samples are
taken beneath the surface where particles are mixed due to
turbulence. Such sampling is called “grab sampling”. Different
grab samples collected at frequent intervals in equal volume or
proportionate to flow mixed are called “composite sample”,
which gives the indication of true strength of sewage. All the
samples collected are kept in cool place so that the
bacteriological activities may not change the character of sewage
before its examination.
Samples should be tested immediately as the
characteristics are liable for change with the time. For certain
samples, preservatives like chloroform; formaldehyde, sulphuric
acid etc are also added. But care should be taken in selection of
preservatives so that the selected preservative does not change
the characteristics of sample.
Thoroughly cleaned and sterilized bottles of quartz are
used for sample collection. The bottles should be completed filled
without leaving any air in the bottle. The stopper should be firmly
inserted and tied with a piece of cloth. Each sample should carry
a tag or lable which consists of the following details (a) Source
(b) Date (c) Time (d) Preservative added (e) Collectors Identity
5.3
CHARACTERISTICS OF SEWAGE:
Following are the characteristics of sewage
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a. PHYSICAL CHARACTERISTICS:
1) Colour: It indicates the condition of sewage as fresh,
stale or septic. Yellow, grey or light brown colour
indicates fresh sewage. Black or dark brown colour
indicates stale sewage. Other colours in sewage are
due to the presence of industrial wastes, dyes etc
2) Odour: It also indicates whether the sewage is fresh or
stale. Fresh domestic sewage has slightly soapy or
oily smell but the stale sewage has of offensive odour
due to liberation of hydrogen sulphide and other
sulphur compounds
3) Temperature: temperature of sewage is measured by
means of ordinary thermometers, which should be
able to read upto 0.1°c. If the temperature of sewage is
more, biological activity is more
4) Turbidity : It is caused due to the presence of
suspended matter and colloidal matter. Sewage is
normally turbid resembling dirty dish water or waste
water from baths having other floating matter, faecal
matters etc.
b. CHEMICAL CHARACTERISTICS:
1) Solids: The sewage contains both organic and
inorganic solids in the form of settleable suspended
solids, colloidal particles and dissolved solids. The
settleable solids can be removed by sedimentation but
removable of dissolved and colloidal solids required
some biological treatment. It is estimated that 1000kg
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of sewage contains approximately 0.45kg of solids of
which 0.225kg is indissolved form, 0.112 kg in
suspension and 0.112kg in settleable form. Further it
is noted that 100parts of solids contains approximately
45 parts of organic solids and 55 parts of inorganic
solids. However for a given sample the parameters are
to be determined by analysis only
2) Other chemical substances: The sewage contains
chlorides, compounds of nitrogen, phosphorous,
sulphur, alkaline substances, toxic compounds and
heavy metals. The sewage may also contain proteins,
carbohydrates, fats, oils, greases, phenols etc.
3) Gases: The sewage contains dissolved oxygen,
hydrogen sulphide, carbondioxide, methane etc.
c. BIOLOGICAL CHARACTERISTICS :
The sewage may contains micro-organisms like
viruses, bacteria, algae, fungi, protozoa, rotifers etc.
These organisms may be aerobic, anaerobic or facultative
in nature.
“Aerobic bacteria” are those, which can live and grow
in the presence of oxygen dissolved in water medium but
anaerobic bacteria can survive and grow in absence of
oxygen. “Facultative bacteria” are those, which survive
and grow both in presence and absence of oxygen.
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5.2
Environmental Engineering
ANALYSIS OF SEWAGE:
The analysis of sewage test samples is to determine the
nature and concentration of physical, chemical and biological
parameters. The information is required for planning, design ,
operation and maintenance of treatment of sewage of city/town
SIGNIFICANCE OF TESTS:
5.2.1 TOTAL SOLIDS:
The total solids are the quantity of suspended, dissolved
and colloidal solids in the sewage and the nature may be organic
or inorganic. The total solids are the important indicator of the
strength of sewage.
The quatitative determination of all these forms is very
significant in the sewage treatment depends upon the nature,
amount of settleable solids and determined by means of
imhoffcone. Amount of dissolved solids influence the design of
biological treatment units like trickling filters; activated sludge
process. The quantity of biodegradable organic matter influences
the design of sludge digestion units
5.2.2
C.O.D.:
The amount oxygen consumed for chemical oxidation of organic
matter with potassium permanganate or potassium dichromate in
an acid solution is called chemical oxygen demand (C.O.D.).
Using this test, the amount of carbon in organic matter is
measured. It is useful in identifying the performance of various
steps of treatment plants. It is also useful in determining the
strength of industrial waters in sewage, which cannot be
Sewage Characteristics
Page 81
determined by B.O.D. test. The limitation of this test is its
inability to differentiate between the biologically oxidizable and
biologically inert material. C.O.D. test takes only 5 hours for
determination where as B.O.D takes 5 days. C.O.D test is also
easy and not affected by interference as in B.O.D test.
5.2.3
B.O.D:
The amount of oxygen required for biochemical oxidation
of the decomposable matter at specified temperature within the
specified time under aerobic conditions is known as “Biological
oxygen Demand”. B.O.D. indicates the strength of sewage and if
B.O.D is more, the nuisance producing capacity of that sewage
also increases
The complete oxidation of organic matter takes about 2-3
months. The oxidation process proceeds in two stages. In the first
stage carboneous matter is oxidized and in the second stage the
nitrogen matter is oxidized.
But it is found that nearly 70 to 80 percent of total B.O.D.
is satisfied within 5 days at a temperature of 20°. Hence the
B.O.D5, B.O.D. at 5 days period, incubated at 20°C is taken as
standard value in actual practice.
B.O.D. is the important parameter in sanitary engineering
and influences the planning design and operation of biological
units in treatment works
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Environmental Engineering
Sometimes for more accurate results the sample of
diluting water is also incubated in the same incubator along with
the sewage for 5 days.The difference in dissolved oxygen content
in the incubated sewage sample and plain water in the sewage is
the B.O.D. of the sewage . This test is very delicate and much
care is required while conducting the test
B.O.D5 = Depletion of oxygen in ppm x diltion factor
5.2.4
PH:
PH value is defined as the logarithem reciprocal of
hydrogen iron concentration. The PH value of sewage is
determined for regulating the various operations of treatment
works. It also indicates the capacity to neutralize base or acid and
the activity of hydrogen ions. In chemical and biological process
of treatment, the PH value is so adjusted that each process is
carried out efficiently.
5.2.5
CHLORIDES:
Chlorides are stable and hence not a measure of degree of
treatment. The normal chloride concentration in sewage is
120mg/lit. The excess of chlorides indicates the presence of
industrial waste of infiltration of sea water. The sources of
chlorides for domestic waste water are kitchens, urinals and water
closets.
Sewage Characteristics
5.3
Page 83
CHARACTERISTICS OF INDUSTRIAL WASTE WATER:
The characteristics of industrial waste cannot be so easily
generalized as in the case of domestic wastewater. The
characteristics of industrial waste vary with the type of industry
and also plant to plant producing same type of end products.
They depends upon the actual manufacturing process in the
industry. The pollutants in the industrial sewage include the raw
materials, end products, process intermediates process by
products and process chemicals. However, the pollutants and
characteristics are used as follows
1. The organic substances that deplete the dissolved oxygen (D.O)
content of stream into the which the industrial wastes are
disposed. These organic substances impose greater load on the
biological units of treatment plants
2. The inorganic substances like carbonates, chlorides, nitrogen etc
that make the receiving water body unfit for further use and also
encourage the growth of micro-plants in the body of water
3. Acids and alkalis which endanger the growth of fish and other
aquatic life and also cause difficulties in the operation of
treatment plants
4. Toxic substances such as sulphides, cyanides, acetylene, alcohol,
petrol etc which cause damage to the flora and fauna of receiving
streams and also affect the treatment processes and some times
endanger the safety of the workmen
5. Colour producing substances like dyes, which aesthetically
objectionable when present in water supplies
6. Oils, fats and greases and other floating substances which will
make the receiving streams unsightly and interfere with the self
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Environmental Engineering
purification of the same. These substances also render the
treatment operations difficult.
PRINCIPLES OF TREATMENT:
Depending upon the way in which the industrial wastes
are discharged and the nature of the constituents, the treatment
may consists of any one or more of the following processes
5.3.1 REDUCTION OF VOLUME AND STRENGTH:
The following are the methods for the reduction of volume and
strength are
a. Segregation of uncontaminated wastes from contaminated
wastes
b. Conservation of water
c. Implementing process changes to minimize wastes
d. Reusing treated waste water for processes requiring lesser
quality of water
e. Reduction of strength of waste by process changes equipment
modifications, segregation, equalization and by-product
recovery
5.3.2
EQUALIZATION:
When the characteristics of industrial waste water vary in
a day and also when the discharge rate is not uniform or
continuous, the waste may require equalization before treatment.
The equalization consists of holding the waste for some designed
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period in a continuously mixed basin, which produces an effluent
of fairly uniform characteristics.
5.3.3
NEUTRALIZATION
When the industrial waste contains excessively acidic or
alkaline substances the waste water requires neutralization. This
becomes very essential particularly in the case of acidic wastes.
In the neutralization process the waste is held in the tanks and its
PH value is adjusted suitably by either adding alkaline or acidic
substances as the case may be.
5.3.4
PROPORTIONING
When the industrial waste is treated along with municipal
sewage, the waste may be subjected to proportioning.
Proportioning consists of control of the discharge of the industrial
waste into the receiving stream or sewer in a fixed proportion to
the flow of domestic waste water
This helps not only in protecting the treatment device
from shock load, but also improving the sanitary quality of the
treated effluent.
5.3.5
PHYSICAL TREATMENT
The physical treatment consists of unit methods like
sedimentation by which settleable solids are sedimented and
floatation in skimming tanks by which finer particles, oils etc are
brought to the surface and then removed
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5.3.6
Environmental Engineering
CHEMICAL TREATMENT
The following are the chemical and physico-chemical
processes employed in the treatment of industrial waste are
a. Chemical precipitation
b. Chemical oxidation
c. Reverse osmosis
d. Electrodialysis
e. Adsorption
f. Ion Exchange
g. Thermal reduction
h. Air stripping
BIOLOGICAL TREATMENT:
In addition to the conventional biological processes like
trickling filters, activated sludge process, sludge digestion tanks
etc special processes involving acclimatized micro-organisms are
also employed Biological processes like aerated lageons,
Anaerobic lagoons, oxidation ditches etc are also used for
treatment of industrial wastes.
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SYNOPSIS
1. If the sewage contains more organic matter, then the sewage
is said to be strong (i.e.,) B.O.D. is high
2. Samples are collected beneath the surface where the particles
are mixed due to turbulence is called grab sample for the
analysis of sewage
3. Different grab samples collected at frequent intervals in equal
volume or proportionate to flow mixed are called “Composite
Sample”.
4. Thoroughly cleaned and sterilized bottles of quartz are used
for sample collection. The bottle should be completely filled
with sample without air and stopper should be firmly inserted
and tied with a piece of cloth
5. The characteristics of sewage are
(i)
Physical – Colour, Odour, temperature, turbidity
(ii)
Chemical
gases
(iii)
Biological characteristics – aerobic, anaerobic or
fraculative
- solids, other chemical substances,
6. The analysis of sewage is to determine the nature and
concentration of physical, chemical and biological parameters
and also useful in planning, design, operation and
maintenance of treatment units
7. Significance of tests:
(i)
Total solids: Size sedimentation/imhoffcone
trickling filters, activated sludge process
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Environmental Engineering
(ii)
C.O.D. – The amount of carboneous matter in
organic matter is measured and useful in
identifying the performance of various steps of
treatment plant.
(iii)
B.O.D – The amount of oxygen required for
biochemical oxidation of the decomposable matter
and it is an important parameter in palnning,
design and operation of biological units in the
treatment of sewage
(iv)
PH-The logarithem of reciprocal of Hydrogen Ion
concentration. It is determined for regulating the
various operations of treatment works
(v)
Chlorides – the normal chloride concentration in
sewage is 120mg/lit and excess chlorides indicates
presence of industrial sewage
8. The principles of treatment of industrial sewage are
a. Reduction of volume and strength
b. Equalization
c. Neutralization
d. Proportioning
e. Physical treatment
f. Chemical treatment
g. Biological treatment
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SHORT ANSWER TYPE QUESTIONS
1. Define B.O.D.
2. Define C.O.D.
3. What is meant by strength of sewage?
4. What is composite sample?
5. What is meant by grab sample?
6. What are the precautions should be taken while collecting
samples for analysis?
7. What is the significance of B.O.D value?
8. What is meant by equalization?
9. What is meant by neutralization?
10. What is meant by proportioning?
ESSAY QUESTIONS
1. Explain the method of collecting samples and precautions taken
in sampling of sewage.
2. Explain physical, chemical and biological characteristics of
domestic sewage.
3. Explain the significance of following
1) B.O.D
2) C.O.D
3) PH
4) CHLORIDES
4. List the characteristics of industrial sewage.
5. List the principles of treatment of industrial waste water and
explain any two methods.
6. List the physico-chemical methods used in treatment of industrial
sewage.
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Environmental Engineering
CHAPTER 6
SEWERAGE TREATMENT AND DISPOSAL
The sewage contains various types of impurities and disease
bacteria is disposed of by dilution or on land after its collection and
conveyance. If the sewage is directly disposed of, it will acted upon the
natural forces, which will convert into harmless substances. The natural
forces of purification cannot purify any amount of sewage within the
specified time. If the quantity of sewage is more than receiving water
will become polluted or the land become sewage sick under such
circumstances it becomes essential to do some treatment of the sewage
so that it can be accepted by the land or receiving water without any
objection.
The main object of the treatment limits is to reduce the sewage
contents (solids) from the sewage and remove all the nuisance causing
elements and change the character of the sewage in such a way that it can
be safely discharged in the natural course applied on the land.
Practically the treatment of sewage is required in big cities only
where the volume of the sewage is more as well as the quantity of
various types of solids, industrial sewage etc. The degree of treatment
will be mostly be decided by the regulatory agencies and the extent to
which the final products of treatment are to be utilized.
The sewage treatment units can be broadly classified as
a) Primary treatment
b) Secondary treatment
Sewerage Treatment & Disposal
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c) Final treatment
Table 6.1 shows relative efficiencies of various types of treatment units
Percentage removal of
S.No.
Treatment Unit
Suspended
Solids
Bacteria
B.O.Dat
5 day
20°C
1.
Screens
5 to 20
10 to 20
5 to 10
2.
Plain sedimentation
35 to 65
30 to 70
25 to 40
3.
Sedimentation with
chemicals
70 to 90
90 to 95
80 to 95
4.
Trickling filter
followed by plain
sedimentation (low
rate)
70 to 90
90 to 95
80 to 95
Trickling filter
(High rate)
proceeded and
followed by plain
sedimentation
65 to 92
80 to 95
70 to 95
Activated sludge
process followed by
plain sedimentation
(ordinary)
85 to 90
90 to 98
75 to 96
Activated sludge
process followed by
plain sedimentation
(high rate)
65 to 96
95 to 96
65 to 96
5.
6.
7.
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Environmental Engineering
8.
Sedimentation
85 to 95
95 to 98
90 to 95
9.
Intermittent sand
filtration
-
95 to 98
18 to 30
10.
Chlorination of
settled sewage
-
-
98 to 99.2
Table 6.1
The treatment plant should be located as near the point of
disposal as possible. If the sewage is to be disposed of finally in the river
or natural streams the treatment plant should be located on the river bank
and it should be down stream side of city and sufficiently away from the
water intake works. The layout of the treatment plant is as shown in fig
no. 6.1 and table 6.2 shows the various types of impurities and required
treatment processes.
Fig 6.1 Layout of Sewage Treatment Plant
Sewerage Treatment & Disposal
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Impurity
Process used for removal
1. Bulky floating and suspended Racks and screens
matters
2. Oils and greese
Floating tanks (skimming tanks)
3. Heavy and coarse suspended Grit chamber, detritus tanks and
matter
sedimentation tanks
4. Non-settlable suspended and Chemical flocculation
some dissolved solids
5.
Colloids and
organic matter
dissolved Biological Growth
6. Pathogenic bacteria
Disinfection
Table 6.2
6.1
PRIMARY TREATMENT:
In primary treatment, the larger solids from the sewage are
removed during the treatment process. The more complex compounds
are broken up and converted into simpler compounds by decomposition.
The primary treatment includes screen, grit chambers, detritus tanks
skimming tanks and sedimentation tanks with or without use of
chemicals.
PURPOSE:
The main purpose of the installation of screens is to remove the
floating matter of comparatively large size to prevent the possible
damage of pumps and other equipments
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Environmental Engineering
LOCATION:
The screens should preferably be located just before grit
chambers at an angle of 30° to 60° with the direction of flow. The
screens are some times accommodated in the body of grit chambers. The
screening element may consists of parallel bars, rods, gratings or wire
meshes or perforated plates and openings may be of any shape generally
they are circular or rectangular.
TYPES OF SCREENS:
(i)
Racks or bar-screens
(ii)
Perforated or fine screens
(iii)
Comminuters or cutting screens.
The classification can also be done based on
a. Opening size as course, medium or fine screen
b. Shape as disc, band , drum, wings or cage
c. Hand or mechanical cleaned screens
Bar screens coarse or medium size in which bars are palced 5 cm
or above and remove rags , sticks, dead animals etc from the sewage
and prevent the sewage pumps against damage as shown in fig no.6.2
Sewerage Treatment & Disposal
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Fig 6.2 Bar Screens
Fine screens have perforations of size about 1.5 mm to 6mm.
They produces a noticeable effect on the strength of sewage and they
considerably reduce the load on subsequent treatment units. Fine
screens may be of drum or disc type and mechanically operated.
These screens are less common now-a-days because of low
efficiency , high maintenance cost and difficulty in the disposal of
screening materials fig no.6.3 shows disc type fine screen
Fig6.3 Fine Screen
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Comminuters or cutting screens which are very popular in
modern sewage works due to their high efficiency and less
maintenance cost. Fig No. 6.4 shows communiter in which
cutting screen drum continuously revolves and removes the fine
suspended impurities from the sewage. The disposal screenings
may be burial, incenevation or digestion.
Fig 6.4 Communiter
2. SKIMMING TANKS:
These tanks are used to remove oil, greese, soap; wood
pieces; fruit skins etc. Fig No. 6.5 shows typical skimming tank.
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Fig 6.5 Skimming Tank
DESIGN ASPECTS:
(i)
AIR DIFFUSERS: Air diffusers are provided at the
bottom of the tank for efficient working of skimming
tank. The period of aeration and quantity of air will
depends upon the quality of sewage. The compressed
air sets up the currents and it results in the floating
matter of sewage
(ii)
COLLECTION OF FLOATING SUBSTANCES:
The floating substances collected at the top of tank are
removed either with hand or with the help of
mechanical equipment
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(iii)
DETENTION PERIOD: The detension period of
about 3 to 5 minutes are designed
(iv)
OUTLET: The submerged outlet is provided to
prevent the floating substances into the outlet channel
(v)
SHAPE: The shape skimming tank may be elliptical
or circular and depth may be about one metre or so
The disposal of the skimming obtained from skimming
tanks can be done for the manufacture of the soap,
lubricants, wax, pitch and other non-edible products. The
skimmings are usually disposed of burning or burying in
the ground
3.
GRIT CHAMBERS:
The purpose of providing grit chamber in the sewage
treatment process is to remove grit, sand and other organic matter
by reducing velocity of flow so that the heavier organic materials
settle down at the bottom of grit chamber and the lighter organic
materials are carried forward for further treatment.
LOCATION:
The grit chambers are placed after pumping stations and
before screens or may be changed to suit the local requirements.
NATURE OF GRIT:
The grit has a specific gravity of about 2.0 to 2.5. The
weight of dry gret is about 300kg/m3 and the weight of wet grit is
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about 1600kg/m3. The grit contains voids to the extent of 35 to 40
percent.
SOURCES OF GRIT:
The grit in the sewage is obtained from domestic sewage, floors
of garages, obtained from domestic sewage. Floors of garages, service
stations, fast storm of the season etc.
VOLUME OF GRIT:
The following factors which affect the volume or quantity of grit
in the sewage
1. Area of unpaved surface in the locality.
2. Characteristics of ground.
3. Design of suit chambers.
4. Intensity of cleaning the streets.
5. Occurance of storms and their intensity.
6. Provision of catch basins.
7. Systems of sewage – combined or separate.
NUMBER:
The grit chambers are provided in duplicate. A stand by unit is
essential for the smooth and efficient working of the grit chamber.
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TYPES:
The grit chambers may be horizontal flow or vertical flow type.
The horizontal flow grit chamber is more popular as shown in fig no. 6.6.
Fig 6.6 Grit Chamber
CLEANING DEVICES:
The grit deposited at the bottom of the tank is to be periodically
cleaned by
1. Hand cleaning.
2. Hydraulic cleaning.
3. Mechanical cleaning.
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DESIGN ASPECTS:
1. CLEANING INTERVAL: depending upon the local conditions
cleaning interval varies from one to two weeks.
2. DEPTH: A minimum of 300mm should be provided and depth to
length ratio should be about 1/16.
3. DETENSION PERIOD: The grit chambers are designed for a
detension period of about 1 minute.
4. SPACE FOR ACCUMULATION OF GRIT: It is necessary to
provide sufficient space at the bottom of grit chamber for
accumulation of grit which may be 12 to 27 litres per one million
litres of sewage.
5. VELOCITY OF FLOW: The velocity of flow in the grit
chamber is kept 200 to 300 mm per sec. This is obtained by
dividing the grit chamber into compartments.
DISPOSAL OF GRIT:
The disposal of grit is used to reclaim the low lying land. It can
also mixed with poor soil to condition it and acts as good manure for
garden crops.
6.2
PRIMARY TREATMENT – PLAIN SEDIMENTATION :
OBJECTS:
1. The process of sedimentation reduces the strength of sewage to
the extent of about 30 to 35%.
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2. The quantity of settleable solids in the sewage reduces to the
extent of 80 to 90%.
3. There is a reduction in B.O.D to the extent of about 30 to 35%.
4. The sewage after being treated in the sedimentation becomes fit
for further treatment processes.
SEDIMENTATION PROCESS:
When the velocity of flow is decreased or when sewage is
allowed to stand at rest, the suspended particles carried by the
sewage tend to settle at the bottom of tanks. The material
collected at the bottom of sedimentation tanks is known as sludge
and partially treated sewage is known as effluent, both require
further additional treatment to make them an objectionable.
TYPES OF TANKS:
1. According to the nature of working
a. Fill and draw type.
b. Continuous flow type.
2. According to the location
a. Primary clarifies before grit chambers.
b. Secondary clarifies after filters or activated sludge
process.
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a.
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PRIMARY CLARIFIES OR PRIMARY SEDIMENTARY
TANKS:
The overall features of primary clarifies are more or less
the same as those tanks which are provided in the water supply
schemes. The following are the design aspects of the primary
clarifies.
1.
INLET AND OUTLET ARRANGEMENTS:
The following points should be noted in the design of
inlet and outlet arrangements.
(i)
The rate of inflow and outflow are equal.
(ii)
The sewage should diffused equally across the entire
section of tank.
(iii) The outflow should be as thin as possible.
(iv) The distance between inlet and outlet channel should
remain constant.
2.
SHAPE OF TANK:
(i)
Rectangular tanks: The ratios of length to width is about
4 to 5 and the ratio of width to depth is about 2 to 3. A
rectangular tank with horizontal flow is a s shown in fig
no. 6.7.
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Fig 6.7 Rectangular Settling Tank
(ii)
Circular tank: The circular tanks are with vertical flow
and it is possible to install conveniently the mechanical
scrapers to collect the sludge at bottom of tank as in the
case of dorr clarifier.
(iii)
Hopper bottom tank: These tanks may be with
horizontal or vertical flow. Hopper bottom tank with
vertical flow is as shown in fig no. 6.8.
Fig No. 6.8
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(3)
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CAPACITY OF TANK:
The capacity of tank is determined by considering the
detension period and overflow rate. For primary clarifiers are
generally designed for a detension period of 1 to 3 hours (average
2 hours) The overflow rate is generally taken as 1000 to 2000 lit
per hour per m2.
(4)
SCUM BUFFLES:
The scum baffles in the form of troughs or boards are to
be provided to prevent the entry of floating substances into the
outlet channel.
(5)
SCUM REMOVAL DEVICES:
The primary clarifiers should be provided suitable scum
removal devices. The floating thus caught are sent for further
treatment or for final disposal.
(6)
SLUDGE REMOVAL:
The sludge collected at the bottom of settling tanks should
be periodically removed by the following methods.
(i)
Hand cleaning – suitable for rectangular tank with flat
bottom.
(ii)
Hydraulic Cleaning – This method is suitable for
hopper bottom settling tank with vertical flow. In this
tank the sludge is conveyed to a manhole through
sludge removal pipe under hydraulic pressure.
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(iii)
Mechanical cleaning – This method is suitable for
rectangular and circular tanks.
ADVANTAGES:
1. The sludge is removed continuously there is no chance to become
septic.
2. The sludge obtained by this method is dense.
DISADVANTAGES:
1. Power required to run the mechanical equipment.
2. The steelwork is increased.
3. The efficiency of tank may be reduced due to disturbing effects
of the mechanical equipment.
(2)
MISLANEOUS CONSIDERATIONS:
The velocity of flow should be about 300 mm per minute.
The clarifies should be provided with suitable facilities such as
handrails, ladders, passages etc for easy access and maintenance
of the tanks.
6.3
SECONDARY TREATMENT
The effluent that is coming out from primary clarifies
contains 45 to 50 percent of the unstable or organic matter
originally present in the sewage as solution or suspension or
colloidal matter. The sewage to this extent is prepared to receive
the secondary treatment.
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The main function of the secondary treatment of sewage
is to convert the remaining organic matter into stable form by
oxidation or nitrification. The secondary treatment involves the
following methods.
1. Filtration.
2. Activated sludge process.
The filters which are commonly employed in the secondary
treatment of sewage are of following types
1. Contact beds.
2. Intermittent sand filters.
3. Trickling filters.
6.3.1
TRICKLING FILTERS:
Trickling filters are used for the biological treatment of
domestic and industrial wastes, which are amenable to aerobic
biological process. The sewage is allowed to sprinkle or to trickle
over bed of coarse, rough, hard material and it is then collected
through the under drainage system. The oxidation of the organic
matter is carried out under aerobic conditions.
A bacteria film known as bio film is formed around the
particles of filtering media and for the existence of this film
oxygen in supplied by intermittent working of the filter and by
provision of suitable ventilation facilities in the body of the filter.
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The colour of film is blackish, greenish and yellowish and
consists of bacteria, algae, fungi, lichens, protozoa etc.
The trickling filters are broadly divided into the following
categories.
1. Standard rate trickling filter.
2. High rate trickling filter.
1. STANDARD RATE TRICKLING FILTER:
(i) STRUCTURAL FEATURES:
(a) SHAPE – The shape of trickling filter may be circular or rectangular,
the former is being very common
(b) FILTER MEDIA - The filter media of trickling filter may consists
of exushed rock or clinker or specially manufactured material of uniform
size varies from 30mm to 80mm approximately cubical in shape and free
from flat, elongated pieces, dirt or any other undesirable materials
(c) FLOORS – The floor of trickling filter is generally made of R.C.C.
of 100 to 150 mm thick and slope towards central drain or towards
periphery of filter as shown in fig 6.9.
Fig. 6.9
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(d) UNDER DRAINAGE SYSTEM: The trickling filter should be
provided with suitable under drainage system to collect the sewage after
it has passed through the filter media at the bottom of filter and sent for
further treatment or disposal.
The under drains consists of specially manufactured blocks or
half-round tiles which supports filter media; ventilation and lead the
effluent to main channel.
(e) VENTILATORS: The ventilation should be provided for successful
working of trickling filter by
1. Forced ventilation by mechanical equipment.
2. Natural draft ventilation by vent pipes etc.
3. Under drains and effluent channel designed to permit free
passage of air.
(f)
DISTRIBUTORS:
The function of distributor is to spread the influent evenly
on the filtering media. The distributors are divided into two
categories
1. MOVABLE DISTRIBUTORS:
a) Rotary distributors: These are rotate around a
central support and suitable for circular filters.
b) Rectilinear distributors: These are move back and
forth from one to other end, suitable for rectangular
filters.
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2. FIXED DISTRIBUTORS:
These are spry nozzles discharge the sewage in the form
of fine drops, which are fixed on the surface of filter at
appropriate distances and suitable for small installations.
Dosing tank: The automatic siphonic dosing tanks are
provided for the application of sewage on the surface of filter
for 3 to 5 minutes and stopped or discontinued for a period of
about 3 to 10 minutes.
(ii)
TREATMENT OF SEWAGE :
To achieve better results from the trickling filter plant it is
desirable and essential to provide primary sedimentation which
removes the suspended particles and hence clogging of filter
media is avoided. Secondly post filtration treatment is required
because trickling filter change the character or nature of the
suspended solids rather than to remove them totally from sewage.
This is done providing secondary clarifies.
(iii)
DESIGN ASPECTS:
1) DEPTH : The effective depth of trickling filter is generally kept
1.8m to 2.4m. The depths smaller than 1.8m are adopted only
under circumstances such as to avoid pumping etc.
2) NUMBER: Minimum of two trickling filters should be provided
so that one can be stand by unit.
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3) RATE OF FILTER LOADING:
i) Kg of B.O.D per hectare-metre per day
1000 to 2000
ii) Kg of B.O.D per day per 100m3 of filter media
15 to 30
iii) Million litres per hectare of surface area
25 to 40
(IV)
ADVANTAGES
1) It requires smaller volume of water for dilution because of the
effluent is highly nutrified and stabilized.
2) Wear and tear is small because of less mechanical equipment.
3) It requires less power.
4) The trickling filters are flexible in operation.
5) It may reduce the B.O.D and colloidal matter to the extent of 75
to 80 percent.
6) The working of trickling filter is simple and doesnot require
skilled supervision.
7) The moisture content of sludge obtained from the trickling filter
is as high as 99 percent or so.
(V)
DISADVANTAGES
1) Cost of construction is high.
2) The loss of head in the filter is high and hence siphonic dosing
tanks are essential.
3) The process may develop fly nuisance and bad odour.
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4) The process requires primary treatment of sewage and hence raw
sewage cannot be purified by this process.
5) It requires large land area.
II.
HIGH RATE TRICKLING FILTERS
High rate trickling filters all similar to the standard rate
trickling filters except the rate of loading for high rate trickling is
more. The rate of loading increased by adopting.
COMPARISION BETWEEN STANDARD RATE AND HIGH
RATE TRICKLING FILTERS
No.
Feature
Standard Rate
High rate trickling
Trickling filter
filter
1.
Cost of operation
It is more
It is less for equal
performance
2.
Depth
1.8m to 2.4m
0.9m to 1.8m
3.
Dosing interval
Generally
3
to
10minutes intervals
and not applied
continuously
It is not more than
15sec and sewage
is to be applied
continuously
4.
Land
requirement
More
Less
5.
Method
aeration
of Less flexible and More flexible and
requires less skilled requires
more
supervision
skilled supervision
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6.
Quality
of It is black and It is brown and not
secondary sludge highly oxidized with fully oxidized with
slight fine particles
fine particles
7.
Rate of
loading
filter
I) Kg of B.O.D
per hectare meter
1000 to 2000
per day
ii) Kg of B.O.D
per
day
per
3
100m of filter
15 to 50
media
iii) Million litres
per hectare of
surface area per 25 to 40
day
8000 to 14000
above 45
100 to 300
8.
Effluent
The
effluent
is The effluent is
highly nitrified and nitrified upto nitrite
stabilized
stage only and
hence it is of
inferior quality
9.
Recirculation
system
It is generally not It always included
included but it can However, in some
be adopted
types it may be
used daring periods
of low & low only
10.
Size of
media
filter 30mm to 80mm
30mm to 60mm
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DISADVATAGES:
1. The effluent is not highly nitrified and hence it requires high
volume of water for dilution.
2. Raw sewage can be treated as the process requires sewage treated
with primary treatment.
6.3.2 ACTIVATED SLUDGE PROCESS:
The term activated sludge is used to indicate the sludge
which is obtained by settling sewage in presence of abundant
oxygen. The activated sludge is biologically active and it contains
a great number of aerobic bacteria and other micro-organisms
which have got an unsual property to oxidize the organic matter.
The following are the properties of activated sludge.
1. The activated sludge contains fertilizing constituents.
2. The colour of activated sludge indicates the degree of
aeration.
Light brown – under aerated sludge.
Golden brown - well aerated sludge.
Muddy brown – over aerated sludge.
3. Moisture content of activated sludge is about 95 to 97 percent
Fig 6.10 shows the flows diagram of activated sludge process.
The following three basic operations are involved in the
activated sludge process.
(1) Mixing of activated sludge : The activated sludge is mixed
properly with raw or settled sewage of primary clarifier
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(2) Aeration: The effluent is agitated or aerated in the aeration
tank and various methods are employed
6.3.3
OXIDATION DITCH:
Dr. Pasveer of netherland developed this method for
treatment of sewage of small estates and colonies. For the
aeration of sewage to the extended type of activated sludge
process mechanical system is used.
The oxidation ditches are aeration units in the shape of
long channels 150 to 1000m long, 1 to 5 m wide and 1 to 1.5m
deep. Mechanical aeration devices consists of cylindrical cage
about 75cm in diameter made of C.I. is kept at such a level that
about 10 to 15cm of them remain dipped in sewage and rotated at
about 75 r.p.m.
Detension period of 12 to 15 hours is normally provided.
The loading of sewage can be 0.8 to 2.5 cum/kg of B.O.D for
treatment of 150cum of sewage standard mechanical aeration is
sufficient which aerates the sewage as well as move it and
generate a velocity of more than 30cm/sec. It keeps the solid
contents of the sewage in suspension condition.
After aeration the sewage is allowed to settle in the
settling tank. The activated sludge is returned back to the aeration
units. For economy purpose sometimes the aeration units also
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acts as the settling units. The rotars are stopped for 2 hours to
settle the suspended solids in the bed. The effluent is taken out
and disposed of with or without treatment.
The efficiency of the oxidation ditch is more than 95% for
suspended solids and more than 98% for B.O.D. These ditches
requires about 4.4 km/kg of B.O.D present in the raw sewage.
The power consumption in rotating rotars is very high, but as the
primary settling tanks and the anerobic digestion processes are
eliminated, hence it is compensated. When the land is costly and
it is very costly to construct oxidation ditch method can be
economically used. The details are as shown in fig no. 6.10.
Fig 6.10 Oxidation Ditch
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6.3.4
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OXIDATION PONDS:
An artificial pond of shallow depth formed for the
retention of sewage for sufficient time is known as an oxidation
pond. These ponds are used to treat raw sewage or partially
treated sewage. Oxidation ponds are suitable for small towns
situated in tropical regions with dry climate and warm
temperature.
ACTION: The oxidation ponds purify the sewage by dual
action of aerobic bacteria and algae. The aerobic bacteria obtain
oxygen from the atmosphere and use it in the decomposition of
organic matter of sewage. The carbondioxide produced in the
decomposition of sewage is broken up by algae by the process
of photosynthesis into carbon and oxygen. The carbon is used
in producing more carbohydrates and the released oxygen
keeps the dissolved oxygen content of water at high level.
CONSTRUCTION: The oxidation ponds are constructed with
shallow depths of about 900 to 1500mm, which permits the
sunlight to penetrate into the body of sewage for the growth of
algae. It is desirable to provide a free board of about one metre
or so. The pond is constructed into compartments of suitable
sizes and the sewage is allowed to flow in zigzag manner
through these compartments as shown in fig no. 6.11.
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Fig 6.11 Oxidation Pond
DESIGN ASPECTS: The detention period of 2 to 6 weeks
should be provided for proper development of algae. The
loading may be expressed in terms of B.O.D. varies from 150
to 300 kg per hectare.
ADVANTAGES:
1. Cost treatment in oxidation ponds is low
2. Maintenance and operation of oxidation ponds are simple
and easy
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3. These are highly efficient in removal of B.O.D (90%) and
califorms(99%)
4. The oxidation ponds prove economical where land is
cheaply available and suitable dry climate exists
DISADVATAGES:
1. These may give objectionable odours and cause the
nuisance of mosquitoes. Hence they constructed away from
the residential locality
2. These oxidation ponds may sometimes become septic due
to overloading or unfavourable badly season
6.3.5
AERATED LAGOONS AND ANAEROBIC LAGOONS:
AERATED LAGOONS: An aerated lagoon is an earthen basin
about 2.5 to 4.0 m deep in which sewage is filled and aerated by
means of diffused air or mechanical aerators. Commonly
mechanical aerators are used and fixed on permanent foundation
sewage is sent in these lagoons after passing through the grit
chamber, without giving any primary treatment. The aerated
lagoon acts as a settling cum aeration tank, where artificial
aeration replaces algal oxygenation of the waste stabilization
ponds.
The initial cost of construction varies from Rs. 15 to Rs.
25 per capita, therefore these are most suitable for middle size
towns. The waste water industries such as paper, straw board and
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food industries can also be easily treated by the aerated lagoons.
The cost of construction can be reduced by constructing the side
walls of lagoons in simple earth work. The floats should be
manufactured from the non-carrodible water for maximum
durability as well as less maintenance cost. All the electrical
wires, cables supplying power to the mechanical aerations should
be taken overhead for safety as well as low maintenance purpose
The shape of lagoons are normally rectangular. The
capacity of lagoon is provided about 30 cum per 2.0 kg to
domestic sewage. The oxygen capacity varies from 1.5 to 2.5 kg
of oxygen / H.P. / hour at 20°C.
6.3.6
ANAEROBIC LAGOONS:
These lagoons are anaerobic throughout their depth
except for an extremely shallow surface zone. The lagoons are
constructed to a depth of about 6m so that the heat energy is
conserved and an aerobic conditions are maintained stabilization
of sewage is brought about by the combination of sedimentation
and anaerobic conversion of organic wastes to methane, carbon
dioxide and other gaseous and products of organic acids and cell
tissues. B.O.D. conversion efficiency is about 70% in routine and
under optimum operating conditions it is raised upto 85%.
6.4
SEPTIC TANK:
In order to provide satisfactory disposal of sewage received or
obtained from isolated buildings, small institutions, big hotels,
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camps etc or undeveloped areas of the locality where municipal
sewers are not laid, the septic tanks may be adopted
THEORY:
The septic tank is just like a plain sedimentation tank but
in septic tank, bio-chemical reactions by anaerobic bacteria take
place as in the case of sludge digestion tanks. During the
detention period, the sewage is purified and the effluent is taken
to soak pits for disposal. The septic tank is provided with cover at
top for avoiding the bad smells occur during the digestion period
of sludge.
CONSTRUCTION:
1. The septic tank should be water tight and material used are
resistant to corrosion
2. The septic tank should be such that the direct currents are not
established between inlet and outlet by using submerged
pipes or buffle walls near the inlet. The scum boards may be
provided near the inlet and outlet ends to prevent the escape
of scum. The level of outlet is about 150mm lower than inlet
as shown in fig 6.12.
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Fig 6.12 Septic Tank with Soak Pit
3. The septic tank should provide proper ventilation by air vent
pipes.
4. The top cover of septic tank should be made of R.C.C and a
manhole is provided in RCC slab for the purpose of
inspection and cleaning. If necessary, C.I. steps may be
provided.
5. The sludge is allowed to be accumulated at the bottom of tank
and it is removed at intervals either by manual labour or by
pumping.
Sewerage Treatment & Disposal
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6. The septic tanks may be constructed in series to act like two
stage sludge digestion tanks but the single stage septic tanks
are very popular.
7. A septic tank thus combines the functions of sedimentation
tank, a sludge digestion tank and a sludge storage tank.
8. The accumulation of sludge at the bottom of tank decreases
its storing capacity and hence the septic tanks should be
cleaned every 6 to 12 months.
DESIGN ASPECTS:
1. CAPACITY: The volume of septic tank is decided by taking the
consideration of quantity of flow and detention period. It is also
designed based on per capita basis which varies from 60 to 110
litres per person to be served by the septic tank. The space for
sludge is kept usually at the rate of 15 to 45 litres per capita per
year.
2. DETENSION PERIOD: The detension period varies from 12 to
72 hours commonly being 24 hours.
3. FREE BOARD: This should be about 400 to 600 mm.
4. SHAPE: The shape is generally rectangular with length breadth
ratio 2:4.
DISPOSAL OF EFFLUENT:
The effluent of septic tanks is highly odors and it should
therefore carefully discharged by the following methods.
1. Absorption trenches.
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2. Gardening.
3. Natural Waters.
4. Soak pits.
5. Soak wells.
6. Sub-surface irrigation.
7. Surface irrigation.
8. Trickling filters.
SOAK PIT:
It is a circular or square pit of sufficient dimension. The
total depth of soak pit varies from 1.2 to 1.8m. The pit is filled
with bric bats or coarse aggregates. The effluent is applied into
the pit so that aerobic bacteria film on the surface of brick bat
oxidizes the dissolved organic matter. The waste water then
percolates into the ground and thus finally disposed. The size of
the pit depends upon the quantity of effluent and permeability of
subsoil. The details of soak pit is as shown in fig.6.11.
ADVANTAGES:
1. It doesnot require special attention or skilled super vision.
2. The cost is reasonable.
3. It removes about 90% B.O.D. and 80% suspended solids.
4. There is reduction in the volume of about 60% and 30% less in
weight.
5. The sludge, effluent and scum obtained from septic tank can be
disposed off easily without causing serious nuisance.
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DISADVANTAGES:
1. The leakage of tank causes air pollution.
2. The working of septic tank is unpredictable and non-uniform.
3. It requires excessive size for serving more persons.
4. If tank is not properly functioning the effluent is dark and foul
smelling worse than influent.
6.5
SEWAGE DISPOSAL:
The liquid effluent of treatment plant has to be disposed
properly to avoid further adverse effects. There are following
methods available.
1. Disposal on land
2. Disposal in water
3. Direct and indirect reuse of waste water
4. Artificial methods
1.
DISPOSAL ON LAND:
Before disposing on to the land it is to be verified
whether the effluent is treated and removed off the pollutants to
such an extent as to satisfy the standards for disposal. The liquid
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effluent can be advantageously used for irrigation purposes. The
methods by which land irrigation (sewage farming) is done are
(a) Broad irrigation or surface irrigation in which the sewage is
allowed to flow over cultivable lands to grow crops like
plantains, cotton etc. The amount of waste water that can be
disposed depends on the climatic conditions, infiltration capacity
of soil, types of crops grown etc.
(b) Sub surface irrigation in which sewage is allowed to enter the
land through distributors. The drain pipes are laid below ground
so as to collect it after evaporation, filtration by biological action
etc. during which the sewage gets purified.
(c) Ridge and furrow method in which the land is ploughed into
ridges and furrows. The furrows are filled with sewage and crops
are grown on ridges.
The continuous disposal of sewage on land may lead to the
conditions, what is called "Sewage sickness". By such
continuous application, the pores of soils get clogged, preventing
free circulation of air. This prevents aerobic biological action and
thus the purifying capacity of land is reduced. Such adverse
phenomenon can be stopped by (1) Applying pretreated sewage
instead of raw sewage (2) Stopping the application of sewage on
to those lands for certain period (3) By rotation of crops.
The land disposal can also be done by evaporation ponds in
which the sewage is filled in ponds and is made to evaporate.
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2.
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DISPOSAL IN WATER:
This is also called dilution technique. The method
involves disposing sewage in the natural body of water, taking
the advantage of its "Self Purification" capacity due to natural
aeration. The mechanisms responsible for self purification of
water bodies are (a) Dilution (b) Sedimentation (c) Oxidationreduction (d) Sun light. This phenomenon of automatic
purification of natural water in due course is called selfpurification.
However, car should be taken to see that the effluents
are treated for the removal of pollutants below tolerance limits
before being discharged into natural water bodies. In this
method, the effluent may be discharged into any one of the
nearby water bodies.
i. Disposal in to lakes, ii. Disposal in to rivers and
streams.
iii. Disposal in to estuaries i.e. zones where rivers meet
the sea.
iv. Disposal in to the sea.
3.
DIRECT AND INDIRECT REUSE OF WASTE WATER:
It is generally impossible to reuse a waste water
completely or indefinitely. The reuse of treated effluent by
direct or indirect means is a method of disposal that
complements the other disposal methods. Water reuse maybe
classified according to use as
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1. Municipal reuse for park, lawn, golf course watering.
2. Industrial reuse such as cooling tower water, boiler feed
water and process water.
3. Agricultural reuse i.e., for irrigation of certain crops,
orchards, forests and leaching of soils.
4. Recreational reuse such as forming artificial lakes for
boating etc.
5. Ground water recharge which is one of the most common
methods of disposal of treated effluent to replenish ground
water supplies, and to stop sea water intrusion into the
aquifers.
4.
ARTIFICIAL METHODS:
In addition to the above three methods, the untreated
sewage may also be treated and disposed by the following
methods
a. Oxidation ponds
b. Oxidation ditches
c. Aerated lagoons
d. Anaerobic lagoons
These methods are called low cost treatment and disposal
methods.
Sewerage Treatment & Disposal
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SYNOPYSIS
1. The main object of the treatment units is to reduce the sewage
contents (solids) from the sewage and remove all the nuisance
causing elements
2. The sewage treatment units can be broadly classified as
a) Primary treatment
b) Secondary treatment
c) Final treatment
3. The primary treatment includes screen, grit chamber, detritus
tanks, skimming tanks and sedimentation tanks in which larger
solids are removed during the treatment process. Move complex
compounds are broken up and converted into simpler compounds
by decomposition
4. The types screens based on
Size – Coarse, medium or fine screen
Shape – disc, hand, drum, wings or cage
Mechanism – hand or mechanical
Operation – fixed, moving or movable
Generally
a) Racks or bar – screens
b) Performed or fine screens
c) Comminuters or cutting screens
5. Skimming tanks are used to remove oil, greese, soap, wood
pieces, fruit skins etc
6. Grit chambers remove grit, sand and other organic matter by
reducing the velocity of flow
7. By the plain sedimentation reduces the strength of sewage to the
extent of about 30 to 35%, settleable solids 80 to 90% and B.O.D
30 to 35%.
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8. The material collected at the bottom of sedimentation tank is
known as “sludge” and partially treated sewage is known as
“effluent”.
9. The types of sedimentation tanks according to
a) Nature of working
– Fill and draw type
- Continuous type
b) Location
– Primary clarifiers
- Secondary Clarifiers
10. The primary clarifiers may have following features
Shape – Rectangular, circular or hopper bottom
Capacity – detention period 1 to 3 hours (generally 2 hours)
overflow rate 1000 to 2000 lit per hour per no2
Slum buffler & removal – to prevent the entry of floating
substances into outlet channel and provided some suitable
devices
Sludge removal – removed by hand, hydraulic or mechanical
cleaning
11. The effluent coming from primary treatment contains 45 to 50%
of unstable organic matter and the main function of secondary
treatment is to convert into stable form by oxidation or
nitrification by filtration and activated sludge process.
12. The filters generally employed in the secondary treatment are
1. Contact beds
2. Intermittent sand filters
3. Trickling filters
13. In activated sludge process, the micro-organisms like bacteria
oxidize the organic matter by the basic operations
a) Mixing of activated sludge
b) Aeration
14. The methods of disposal of sewage are 1) disposal on land
2) Disposal in water 3) Direct & Indirect reuse of waste water
4) Artificial methods
Sewerage Treatment & Disposal
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SHORT ANSWER TYPE QUESTIONS
1.
2.
3.
4.
5.
6.
7.
8.
9.
What is the purpose of screens?
What is the use of skimming tanks?
What are the objects of primary treatment?
What are the treatment methods in the secondary treatment?
What are the advantages of oxidation pond?
What is the purpose of soak pit?
What are methods of sewage disposal?
What is the purpose of grit chamber?
What is the use of plain sedimentation?
ESSAY TYPE QUESTIONS
1. Explain the different units of treatment of sewage?
2. Explain the following
a) Screens
b) Skimming tanks
3. Explain the grit chamber with the help of meat sketch.
4. Explain the standard rate trickling filter.
5. Compare the standard rate trickling filter with high rate trickling
filter
6. Explain the following
a) Oxidation ditch
b) Oxidation pond
7. Explain activated sludge process
8. Explain septic tank with the help of neat sketch
9. Explain the methods of disposal of sewage
10. Explain the following
a) Aerobic lagoon
a) Anaerobic Lagoon
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CHAPTER 7
SOLID WASTE DISPOSAL
7.1
GENERAL INTRODUCTION:
The solid waste of the community is known as "refuse".
The term "refuse" includes all the solid or semi solid waste matter
except the night soil. The refuse may contain both organic and
inorganic matter. The organic matter undergoes biological
degradation and becomes offensive in nature, causing nuisance to
the public and effect the health. The accumulation of solid waste
in the streets and surroundings of houses, promotes the growth of
house flies, which are the transmittes of diseases like typhoid,
diphtheria, diarhoae etc Insanitary conditions are developed by
the indiscriminate throwing of solid waste in the streets and
surroundings. Hence it necessary, that the solid waste is properly
collected and disposed.
7.1.1 COMPOSITION AND SOURCES:
1.
Garbage is putrescible wastes from obtained from kitchens,
hotels, restaurants etc.
2. Ashes are the waste products of coal and other fuels from
industries
3. Rubbish denotes all non putrescible wastes like cans, papers,
brush, cardboard wood, scrap metals, crokery etc from dustbins,
houses etc
4. Dead animals - The dead animals of dog,
birds etc collected from municipalities
cows,
goats,
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5. Street Sweepings - Waste materials collected from street
surfaces
6. Industrial solid waste - The waste materials from different
industries distillery, dye, hospitals etc.
7.1.2 SYSTEM OF COLLECTION OF REFUSE:
The dry refuse is generally collected in the following systems
1. One-bin system
2. Two-bin system
3. Three-bin system
In one-bin system the dust-bins are placed in streets at
suitable places. This system is not properly functioning because
people are not taking care in throwing the refuse in the bins and
removal of refuse from the bins is also not being properly
attended and hence insanitary conditions around the bin.
In two-bin system, every house is provided with two
metal or plastic bins having top covers. The garbage is collected
in one bin and the remaining refuse in the other bin. Once or
twice in a week, the municipal workers collect the refuse in
separate trucks from every house and then take away for disposal.
The success of this system depends upon the prompt collection of
the refuse from the houses
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In three-bin system, similar to the two-bin system with
covers, meant for receiving a) Garbage b) Inorganic ash, grit
etc and c) other rubbish.
In this system the bins are regularly collected once or
twice in a week and disposed separately.
The following factors, which affect the collection of
refuse for disposal, are
1.
Location of dustbins
2.
Type of bin system
3.
Frequency of collection
4.
Population density
5.
Number of workers per truck
6.
Time of collection
7.
Collection routes
8.
Cost of collection
7.1.3 TRANSPORTATION
The vehicles used for transporting the refuse from the
collection points to the disposal point are
1) Auto-rickshaws of capacity 0.5. to 0.75 tonnes
2) Trailers of capacity 2 to 3 tonnes
3) Trucks of capacity 5 to 10 tonnes
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7.1.4 DISPOSAL METHODS:
Dry refuse requires careful disposal otherwise results in
the unhygienic conditions and puts public health in danger. A
careful analysis, qualitatively and quantitatively, of dry refuse
becomes essential to arrive at a satisfactory methods of following
dry refuse.
1. DUMPING - The method of filling low laying areas by
refuse is called dumping. This method is suitable if the refuse
contains ashes, street sweepings and rubbish. If the refuse
contain garbage, it causes serious problems to the public
health due to the breeding of mosquitoes, flies, scattering of
papers and bad smell
2. SANITARY LANDFILL - This method is better than
dumping method. This is the simple effective and cheap
method of refuse disposal. The trenches are dug out for a
depth of about 3 to 5 m and about 6m wide excavated and
refuse is placed in trench in layers to a depth of 1.5m. Each
layer is compacted with rooters or bulldozers and then
covered 150mm layer of earth at the end of each working day
when the total height becomes 2.5m, it is covered with
600mm thick earth layer. The organic matter in the refuse, is
decomposes slowly by the time of 2 to 3 years
This is an efficient method but requires constant super
vision for proper carrying out of filling operations. The
reclaimed area obtained by filling of low lying areas with
refuse can be used for parks, golf courses, other recreational
purposes, godowns, buildings and overhead tanks, if proper
care not taken sanitary landfill is reduced to ordinary
dumping
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3. INCINERATION:
This is the best method of disposal of combustible
refuse. This process is carried out in an incinerator, which
consists of a furnace provided with grating and a chimney.
An ash pit is provided below the grating. The refuse is
charged through the charging door. The burnt ash is removed
through ash door. This method is particularly suitable for
thickly populated area where the site for land filling is not
available and used to reduce volume of refuse can be
completely destroyed. The main disadvantage of this method
is, its emission of large amount of smoke causes air pollution
COMPOSTING:
The process of making of organic matter along with cattle
dung, night soil by the controlled microbial reactions to stable
end product which is used for reclaiming waste land or growing
crops is known as composting.
In India, two methods namely Bangalore method and
Indore method popular
(i)
BANGALORE METHOD: It is an anaerobic and simple
method first non-combustible materials like cans, glass etc
are separated then the refuse and night soil / cow dung with
some water are placed in alternate layers in earthen trenches
of size 10 x 1.1 x 1.5m. The material is covered with 15cm
layer of earth and left for decomposing. After 4 to 5 months
time, the compost become ready for use. This method is
effective in killing the larva of the flies and pathogenic
bacteria in the mass
(ii)
INDORE METHOD: This is modified method of Bangalore
method and involves aerobic decomposition. The refuse and
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night soil/cow dung are filled n alternate layers in the pit or
trench except the top 600mm. The top portion is not filled
with refuse. Turning of the mass is carried out for the period
of 5 to 7 days twice or thrice by showels or other mechanical
equipment. Thus the mass is decomposed aerobically under
the action of atmospheric oxygen and aerobic bacteria.
Because of turning of the mass subjected to higher
temperature hence pathogenic organism and larva of flies are
more thoroughly destroyed. By the time period of 15 to 20
days the compost become ready for use.
Composting can also be done on large scale for the
disposal of large quantities of refuse of cities by using
mechanical equipment as shown in fig 7.1
Fig 7.1 Composting Process of City Refuse
i.
Trucks, tippers ..... for transporatation.
ii.
cranes..... lifting and loading of refuse into hoppers.
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iii.
Hoppers.....seperation
of
refuse
compostable
&
non-compostable.
iv.
Screens .....seperation according to the size.
v.
Separators
.....magnetic separators separate the
non-compostable iron materials.
vi.
Grinders ..... coversion of finer particles and sludge.
vii.
Conveyors.....belt conveyors working on rollers used
to transport the pulverized material from grinders to
digesters.
viii.
Mechanized
silo
digesters...
prepared by aeration in 3 to 5 days.
compost
is
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SYNOPYSIS
1. Refuse is the solid waste of community consists of ashes, cinder,
rubbish, vegetable and animal waste materials, street sweepings,
solid waste of industries etc should be properly collected and
disposed otherwise decomposition refuse causes diseases like
diptheria, typhoid, diarrhoea etc
2. The refuse is collected by
1. One-bin system
2. Two-bin system
3. Three-bin system
3. The refuse is transported to disposal place by auto-rickshaws, trailers
& trucks
4. The refuse is disposed by
1. Dumping
2. Sanitary landfill
3. Incineration
4. Composting
5. Composting of refuse can be done by
1. Bangalore method
2. Indore method
6. Composting of refuse of big cities can be done on large scale by
using mechanical equipment like storage hoppers, grinders,
conveyers etc.
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SHORT ANSWER TYPE QUESTIONS
1. Define Refuse.
2. What is meant by garbage?
3. What are the sources of refuse?
4. Name the systems of collection of refuse.
5. Name the list of equipment used in composting of city refuse.
6. What is meant by composting?
7. Name the two methods of composting of refuse?
8. What is dumping?
ESSAY TYPE QUESTIONS
1. Explain different systems of collection of refuse.
2. What is meant by comsposting? Explain the methods in detail.
3. What are the different methods of disposal of refuse? Explain.
4. Explain the composting of city refuse with the help of neat sketch.
5. Explain the preparation of sanitary land fill what are the advantages
over dumping?
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CHAPTER 8
DRAINAGE AND SANITATION IN BUILDINGS
GENERAL INTRODUCTION:
In order to maintain in healthy environment, the waste
water coming from the kitchens, bathroom, water closet, urinals
of the building has to be drained properly. If the waste is not
drained properly, it leads to stagnation in and around the building
causing nuisance, effect on the health. Hence, necessary
arrangements have to be provided in the building for effective
drainage of waste water. This chapter covers the entire sanitary
arrangements above and below he ground in the building.
8.1
AIMS OF BUILDING DRAINAGE
1. To drain away the liquid waste produced as quickly as
possible so as to avoid nuisance.
2. To prevent the entry of foul gases from the sewer line.
3. To provide facilities for the quick removal of foul matter
such as human excreta from the water closets.
4. To collect the sewage systematically for its further
conveyance, treatment and disposal.
5. To provide healthy and aesthetic environment in the
building.
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REQUIREMENTS OF GOOD DRAINAGE SYSTEM IN
BUILDINGS:
The following are the requirements of good drainage
system in a building.
1. The drainage pipes should be strong and durable.
2. The pipes should be of non-absorbent materials.
3. The pipes and joints should be airtight to prevent the leakage
of waste water or gases.
4. The network of pipes should have sufficient accessibility for
inspection, cleaning and removing the obstructions.
5. The levels of building, sewer and other points of outlet should
be fixed accurately.
6. The system should not give scope for air locks or self or
induced syphonage, deposits, obstructions etc. which interfere
with the functioning of drainage.
7. As per as possible drains should not pass under the buildings.
8. The drains should be given proper ventilation to avoid air
locks and syphonage.
9. The system should have traps at all necessary points.
10. The foul matter should be quickly removed away from the
sanitary fixtures so as to avoid the putrefaction and
production of bad smelling gases.
11. The drainage system should be able to prevent the entry of
gases, vermin etc from the sewer into the building.
12. The branch drains should be as short as possible
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13. The drains should not pass near or under the trees to avoid the
damage of pipes by the roots
8.3
PRINCIPLES OF PLANNING AND DESIGN OF HOUSE
DRAINAGE
For the proper design and construction of house drainage
system the following general principles are adopted.
1. It is advisable to lay sewers by the side of building rather than
below the building.
2. The drains should be straight between the inspection
chambers or manholes.
3. The entire system should be properly ventilated.
4. The house drain should connect to the public sewer only if
the public sewer is deeper than house drain otherwise reverse
flow from public sewer to the house drain.
5. The house drain should contain enough number of traps at
suitable points for efficient functioning of it.
6. The joints of sewers should be water tight.
7. The lateral sewers should be laid at proper gradient so that
they develop self-cleaning velocity.
8. The layout of house drainage system should permit easy
cleaning and removal of obstructions.
9. The material of sewer should not absorb the sewage and
should be provided to protect then from external loads by
earth cushioning.
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10. The possibilities of formation of air locks, siphonage, undue
deposits etc should be properly studied and adequate
remedies should be accommodated in the design to avoid
them.
11. The rain water from houses is collected from roofs and
convey it to storm water drain through catch basins or inlets.
12. The sewage formed should be conveyed as early as possible
after its formation.
13. The size of lateral sewers should be such that they will not
oveflow at the time of maximum discharge.
8.1.4
GENERAL LAYOUT OF SANITARY FITTINGS TO
HOUSE DRAINAGE ARRANGEMENTS
The following should be kept in mind in planning the
layout of drainage connections to the various fittings.
1. The layout should be simple and direct (both horizontal and
vertical).
2. Horizontal pipes should lay at designed slope.
3. Concrete pads should be provided to support the pipes laid on
earthfill.
4. Long or short sweep quarter bends or two 45° or eight bends
for making 90° turn should be provided.
5. Only sanitary fees and quarter bends are used for a change of
pipe from horizontal to vertical
6. Manholes should be provided at all points of intersections and
change of direction of pipes
7. All soil pipes, waste pipes and ventilating pipes may be
graped in shafts or ducts for easy inspection and maintenance
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8. A clear minimum distance of 5cm should be maintained from
walls to all surface pipes.
9. The waste pipes should be separated from house drain by
means of gully traps to prevents entry of foul gases, vermin
etc into the building.
10. Traps are required for every sanitary fixture and they should
be as close to the fixture as possible.
The typical layout of single storeyed building drainage
system is shown in the fig no 8.1.
Fig 8.1 Plan of the Layout Drainage in Single Storeyed Building
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In the case of multistoried building , sanitary blocks are arranged
one above the other on different floors. This facilitates the same soil pipe
or waste pipe or vent pipe to serve the various fixtures in different floors.
Inspection chamber is provided at the ground where the solid pipe joins
the house drain avent pipe or anti syphonage pipe is also provided to
preserve the waste seals of sanitary fittings. The soil pipes and vent pipes
are provided with wire cage at the top to avoid the birds making nests in
the pipe fig 8.2 shows the drainage system of multi storeyed buildings.
The drainage system in the building is as per IS1172-1971 and IS17421972.
Fig 8.2 Layout of Drainage System in Multistoreyed Building
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The following technical terms are used in the house
drainage
1. Anti-siphonage pipe – The pipe used in the house drainage
to preserve the water seal of traps is known as the antisiphonage.
2. Cowl - The top of vent pipe provided with slits or narrow
openings to escape.
3. fresh inlet – The last manhole which connects the house
drain with the public sewer is provided with an inlet of fresh
air to dilutes the sewage gases.
4. Soil pipe – The pipe which carries discharges from soil
fittings such as urinals, water closets etc.
5. Ventpipe – The pipe installed for the purpose of ventlation is
known as ventpipe through which foul gases escape into
atmosphere.
6. Waste pipe – The pipe which carries discharges from
sanitary fittings such as bathrooms, kitchens, sinks etc.
8.2
SANITARY FITTINGS:
The sanitary fittings are required in house drainage for the
efficient collection and removal of waste water from the house to
house drain. The following are some of the sanitary fittings.
1. Traps.
2. Water closets.
3. Flushing cisterns.
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4. Urinals.
5. Inspection chambers.
6. Wash basins.
7. Sinks.
8. Bath tubs etc.
8.2.1
TRAPS A trap is a depressed or bent sanitary fitting which always
remains full of water (water seal). The function of a trap is to
prevent the entry of bad smelling gases into the house. The
effectiveness depends upon the depth of water seal, which varies
from 25 to 75mm
Requirements of good trap:
1. It should be capable of being easily cleaned.
2. It should be easily fixed with the drain.
3. It should be of simple construction.
4. It should possess self-cleansing property.
5. It should posses adequate water seal to fulfil the purpose of
installation.
6. It should be free from any inside projection which are likely
to obstruct the passage of flow of sewage.
7. The internal and external surfaces should be of smooth finish.
TYPES OF TRAPS:
1. Classification according to shape as shown in fig 8.3.
a. P-trap.
Drainage & Sanitation in Buildings
b. Q-trap.
c. S-trap.
Fig 8.3 Traps according to shapes
2. Classification according to use as shown in fig 8.4.
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Fig 8.4 Floor trap ,Gully trap & Intercepting trap
a. Floor trap – made of cast iron and placed in bathrooms,
kitchens, sinks etc.
b. Gully trap - made of stone wave and C.I. grating is
provided. It is placed near the external face of wall and
kept slightly higher level than ground level.
c. Intercepting trap – This trap has water seal of about
100mm and provided in the last manhole of house
drainage system. It thus conveys sewage from house to
the public sewer.
8.2.2
WATER CLOSETS:
The water closet is a sanitary fitting which is designed to
receive human excreta directly from the person using it. The
room in which it is installed is also sometimes referred by the
term water closet.
The water closets are of following two types
1. Indian type water closet
2. European type water closet
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INDIAN TYPE WATER CLOSET –
This is fixed in squatting or sitting position. The overall length of
this varies from 450 to 675mm. The width near the one end is 150mm
and it is increased to 225 to 280mm near the other end. The overall
height is including the trap is about 400 to 500mm. It requires atleast 10
litres of water for flushing. Hence its flushing rim is connected to a
flushing cistern fixed above the water closet. Two foot rests are fixed on
either side of the closet. The Indian type is usually made of porcelain.
The details are as shown in fig. 8.5.
Fig 8.5 Indian Type Water Closet
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EUROPEAN TYPE WATER CLOSET:
Fig 8.6 shows the details of a typical European type water
closet. It is made of porcelain and fixed above floor level. The
pan has flushing rim, which is connected to the flushing cistern.
A cover is provided at its top. Overall lengths varies from 500 to
600mm and height 350 to 400mm.
Fig 8.6 European Type Water Closet
8.2.3
FLUSHING CISTERNS:
In order to flush the water closets and urinals the
arrangement made is called flushing cistern. These are made of
cast-iron or porcelain with a capacity of 5 to 15 litres. It consists
of a bell connected to flushing chain through a lever. When the
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chain is pulled, the bell is lifted up and the water in the tank
rushes through the flushing pipe by syphonic action. The float
valve now allows the water from the inlet into the cistern and
thus the cistern is ready for next flushing. The details are as
shown in the fig 8.7.
Fig 8.7 Flushing Cistern
8.2.4 URINALS – The arrangements provided to receive the urine.
They are mainly two types.
1. Bowl type.
2. Stall or Slab type.
1. BOWL TYPE – The bowl type has a lipped basin with a
flushing rim fixed at a convenient height about 0.6m. It is flushed
through hand operated symphonic type flushing cistern
2. STALL OR SLAB TYPE – It comprises of a flat wall with slab
with partitions on sides. It has a floor channel to drain off the
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discharge through trapped outlet. The stall type urinal range may
be flushed by automatic flushing cistern with a capacity of 10 to
15 litres. The details are as shown in fig 8.8.
Fig 8.8 Stall type Urinal with 3 units
8.2.5
INSPECTION CHAMBERS:
Inspection chamber is a masonary chamber similar to
manhole to provide access for the cleaning, inspection and repair
of the drain. This chamber is provided with C.I. cover. The size
of this chamber depends on the depth and number of branch
connections. The size may be about 60 x 75cm and 90cm deep.
They should be constructed at all junctions, bends and at about
10m interval on straight runs of the drains.
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8.2.6
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ANTI-SYPHONAGE PIPE:
These pipes are provided to prevent syphonage action and
consequent sucking of water seals. Particularly if several lavatory
blocks are situated on different storeys discharging in the same
soil pipe or waste pipe, the anti syphonage pipe has to be
necessarily provided. Because, the flushing in upper floors
creates partial vaccum in the pipe at lower region, inducing
syphonic action and thus the water seals are sucked in the lower
floors. Hence antisphonage pipe or vent pipe is connected to all
traps, so that when the partial vaccum occurs due to flushing, it
may be immediately broken by suction if air from the vent pipe
and seals of traps remain infact.
8.2.7
PLUMBING SYSTEMS:
There are three system of plumbing as shown in fig 8.9
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Fig 8.9 Plumbing Systems of House Drainage
1. SINGLE STACK: In this system, the waste water from
bathroom, kitchen, wash basin, urinals etc and human excreta
from water closet is discharged through a singh soil pipe and also
this pipe acts as ventilating pipe. The traps should have water
seals at all times at least to a depth of 75mm.
ADVANTAGES:
1. Simplicity of layout, design and plumbing.
2. More economical.
3. Improved external appearance because of single pipe.
4. Compact plumbing.
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DISADVANTAGES:
1. Water seals may be evaporated during dry weather.
2. Possibility of self or induced syphonage leads sucking of water
seals.
3. Due to blockage or bad design, the waste water from drainage
pipes may be forced up through traps by back pressure..
2. ONE PIPE SYSTEM:
This is same as single stack system but in addition to this there is
a separate vent pipe connected to the fittings and the water seals
are protected. This is costlier than single stack system.
3. TWO PIPE SYSTEM: In this system, the soil pipe is connected
to all water closets and urinals and the other waste pipe is
connected to bath, kitchen and wash basins etc. Both soil pipe
and vent pipes are separately ventilated by vent pipes. This
system provides very effective and trouble free drainage. But this
is costly system.
3.2.8
INSPECTION OF BUILDING DRAINAGE SYSTEM:
The following points should be observed for the inspection of
building drainage system.
1. The flow through the drains should be observed by
opening the inspection chambers, gully traps.
2. If there are any damp spots, they should be detected as the
indicated leakages.
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3. The water closets, flushing cisterns, traps should be
examined.
4. Emission of bad smell if any from the sanitary block
should be detected.
5. A detailed survey of the entire system is made and then
completely checked.
3.2.9
TESTING OF DRAINAGE SYSTEM:
The following are the tests, which commonly employed
a. Airtest – in this test, air is blown into the drain after plugging the
ends. This soap solution is then applied. The formation of
bubbles indicates leakages
b. Hydraulic test or water test – the drain is plugged at the lower
inspection chamber and the water is filled under the pressure of
0.015 W/mm2. There should not be any visible drop in water
level within ten minutes
c. Smell Test- Air is mixed with some smelling gas and is allowed
to pass through the drainage pipe. Leaky joints can be detected by
smelling.
d. Colour-water test – Colour water is added from one side. The
leakage can be easily seen
e. Smoke test – This test is used to detect leakage of rain water
pipes and other vertical waste pipes. In this test smoke is forced
into the pipe. Leakage can de detected by smell or vision of the
smoke through the joint
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8.2.10 MAINTENANCE OF BUILDING DRAINAGE SYSTEM –
The house drainage system should be properly maintained and
cleaned at regular intervals for its efficient working. The
following points should be carefully noted.
a. Entry of undesired elements – The substance like sand,
grit, decayed fruits, pieces of cloth, leaves should not
allowed into the sewers and collected separately.
b. Flushing – Inorder to maintain the house drainage system
in proper working order, it is advisable to flush it once or
twice a day.
c. Inspection – The various units of house drainage system
should inspected at regular intervals and damaged pipes /
washer of leaky taps should be replaced.
d. Use of disinfectants – To maintain good sanitary
conditions in the building, phenol or disinfectants should
be used.
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SYNOPYSIS
1.
The term “house drainage’ covers entire sanitary arrangements
above or below the ground in the building.
2.
Building drainage is provided for
a. To prevent the entry of foul gases into sewer lines.
b. To provide facilities for quick removal of foul matter such
as human excreta from water closets.
c. To collect sewage systematically.
d. To provide healthy and aesthetic environment in the
building.
3.
The pipes used in the drainage arrangement are
1.
soil pipe – which collects human excreta.
2.
waste pipe – which collects liquid waste from kitchens,
bathrooms, wash basins etc.
3.
vent pipe – which provides flow of air into or from a
drainage system in order to protect water seal.
4.
The sanitary fittings used in the drainage system of building
are traps, water closets, flushing cisterns, urinals, inspection
chambers, wash basins, sinks, bath tubs etc.
5. The traps Depressed or bent sanitary fitting holding always water
in the bend so that foul gases cannot pass through this water seal
or barrier which are generally used according to shape are
1) P-trap
2) Q-trap
3) S-trap
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b) according to use
1) floor trap 2) gully trap 3) intercepting trap
6.
The water closets generally used are
a) Indian type water closet .
b) European type water closet .
7.
The plumbing systems are mainly
a) single stack system .
b) one pipe system.
c) two pipe system.
8.
Inspection of building drainage system by
a) Check the flow through drains by opening gully
traps and inspection chambers.
b) Detection of damp spots.
c) Water closets, flush traps should be examined.
d) Emission of bad smell should be detected from
any sanitary block if any.
9.
Testing of drainage system are done by
a) Air test by leakage test.
b) Water test indicates drop in water.
c) Smoke test leakage of rain water pipes.
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d) Coloured water test leakage test.
e) Smell test leaky joints.
10.
Maintenance of building drainage system by
a) Washers of leaky taps etc.
b) Entire drainage system should be cleaned once
in a month.
c) Sand, grit etc shout not allowed in the sewers.
d) Phenol or any other approved disinfection
should be used regularly to maintain sanitary
conditions.
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SHORT ANSWER TYPE QUESTIONS
1. Define soil pipe and waste pipe.
2. What is the function of trap?
3. What is meant by single stack system?
4. Name the types of traps according to the shape .
5. Classify the traps according to the use.
6. What is the significance of air test?
7. Name the different systems of plumbing.
8. What are the requirements of good trap?
9. Name the different types of water closets
10. Name any four sanitary fittings.
ESSAY TYPE QUESTIONS
1. Name the types of water closets and explain with neat sketches.
2. List out the aims of the drainage of buildings.
3. Sketch the layout of drainage in single storeyed building and
name the components
4. State the requirements of good drainage system in building.
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5. Explain with neat sketches
1) Floor trap 2) Intercepting trap
6. State any six principles of planning and design of house drainage.
7. What are the points to be borne in mind during the inspection of
drainage system?
8. Explain the tests, which can be, conducted in house drainage
system.
9. How you maintain the drainage system?
10. Explain with sketches “one pipe system and two pipe system” of
plumbing.
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CHAPTER 9
RURAL WATER SUPPLY AND SANITATION
GENERAL INTRODUCTION:
The protected water supply system is only available in
urban areas to some extent. But the country like India is
essentially a village based country and majority of population
lives in villages. Most of the rural population not yet provided
protected water supply systems. They are mostly depending upon
the conventional sources like wells, ponds and streams etc are
generally in polluted condition. So people consuming this water
without any treatment they are made to suffer from water borne
diseases like typhoid, dysentery, cholera, poliomyelitis, Jaundice,
gunia worm etc. The rural water supply system aim to provide
reasonable quantity of protected water to satisfy demands of
people and safe guard against the health in the initial stage but
comprehensive long ranged planning is quite essential.
9.1
DISINFECTION OF WELLS:
The some of the sources of water supply to the rural
population are wells, ponds and streams. At present the wells are
major sources of water requirements in villages. The wells
without parapet walls and concrete platform with drain around
them are sure to be polluted. The spilled water around the well
and surface runoff, percolate into the well and pollute it. Hence it
is necessary to provide sanitary protection to the well and lift
arrangements may be in the form of a permanent rope and bucket
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or a pump or a wind mill etc instead of individual rope and
bucket. Fig 9.1 shows protected dug well.
Fig 9.1 Protected Dug Well
NEERI (National Environmental Engineering Research
Institute), Nagpur has evolved a method called “double pot
system” for the application of beaching powder to the rural well.
The dosage of the bleaching powder depends on the extent of
pollution in the well and the required residual chlorine in the
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water. The dosage upto 4mg/litre may be sufficient for this
purpose. Fig 9.2 shows double pot system. In this method, the
container with bottom inlet hole is taken and filled with the
mixter of sand and bleaching powder in the ratio of 2:1. The top
of this container is closed at top and kept in another bigger
container. The outer container is also provided with hole at
bottom. The top of this container is also closed with a polythene
paper and the whole arrangement is kept in an immersed position
in the well, by hanging it with a rope. The water slowly and
continuously comes into contact with bleaching powder and
dissolves chlorine, effecting disinfecting water. The mixture of
bleaching powder and sand may be replaced by every 15 days or
so.
Fig 9.2 Double part system of disinfection of wells
For ponds and streams, the practices like cattle cleaning,
bathing, washing of clothes etc should be stopped and a
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watchman can be arranged disallowing the uses except for
drinking purpose. Water from the pond or stream can be pumped
to a tank, disinfected and then supplied through taps. Proper
education should be given to the village regarding the danger of
water borne diseases and need for protected water.
9.2
RURAL SANITATION
GENERAL INTRODUCTION:
The term rural sanitation is used to indicate the
development or maintenance of sanitary conditions in rural areas.
At present the sanitation in and around the villages is generally
poor. Indiscriminate and unscientific disposal of the liquid and
solid wastes causes environmental pollution and consequent
health hazards. Some of the observations and precautions to be
taken in this regard are
1. Stagnation of liquid wastes promotes the growth of mosquitos
which communicates the diseases like malaria; filarial and also
causes pollution of wells. So this has to be taken care of by
disposing liquid waste by land treatment or soakage pits etc.
2. Storing of cow dung in an open pits leads to the cause of like
typhoid, ophthalma, cholera, diahhera etc caused by house files.
So cowdung can be properly disposed by composting; biogas
plant etc.
3. Using cow dung for the preparation of cow dung cakes used as
fuel is also to be discouraged because these leads to the air
pollution and seriously affects the health of village women
4. Open disinfection leads to the pollution of environment and open
wells are polluted by surface wash of faecal matters. By the result
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the occurrence of hookwarm disease to the people who are not
using foot wear. It is necessary to go for atleast rural sanitary
latrines in the absence of systematic water carriage system to deal
with human excreta
5. Improper thowing of solid waste materials also causes insanitary
conditions due to fly nuisance, spread of diseases etc. So the solid
waste can be affectively disposed by sanitary land fill,
composting etc and avoid nuisance
6. Ignorance, illiterancy, superstitions, lack of sanitary sence etc are
highly prevalent among the rural masses, which have to be
tackled and eradicated for the success of maintaining healthy
environment in villages.
SANITARY LATRINES:
The following are the various types of privies or latrines which
are constructed to dispose off human excreta without the help of water
carriage system
a) PIT PRIVY
b) BORE-HOLE LATRINE
c) AQUA PRIVY
d) CESS-POOLS
A.
PIT PRIVY:
Fig 9.3. shows pit privy, which consists of a pit 1.3 x
1.0m in plan and 1.5 to 2.8m deep. At the top of the this pit the
squatting seat is provided in a compartment. The super structure
is of temporary nature with A.C. sheets is constructed over the
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pit. A little earth is thrown every time after the use of latrine.
When the pit is completely filled, it is closed from the top by
60cm thick earth layer and a new pit is excavated by the side of
it. The squatting pan along with the compartment is shifted to
new trench. A 10cm dia pipe is also provided to take the foul
gases.
Fig 9.3 Pit Privy
This is cheap and construction is simple but there will be
some bad odours, which can be reduced by the use of lime. To
avoid ground water pollution, the pit should be located at least
30m away from the well. The contents of pits can be taken out
after about couple of months and may be used as manure.
(b)
BORE HOLE LATRINE:
It is similar to the pit privy but in place of pit there is a
bore-hole. The size of the hole is 200 to 300mm dia and 4 to 8 m
deep. The bottom of the bore-hole should be 1 to 2m above the
highest water table in the locality so that the excreta may not the
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pollute the ground water. The hole should be lined from inside.
When the hole is completely filled up, the top is covered with a
thick layer of soil, and another hole is dug by the side of it. Fig
9.4 shows the bore hole latrine. This method is suitable for the
regions where sandy soils are suitable for the regions where
sandy soils are available in which, making a bore-hole with
handauger is easy. For avoiding the bad odour water seal trap is
provided.
Fig 9.4 Borehole Latrine
(c)
AQUA-PRIVY:
The construction is based on the principle of septic tank.
It consists of a rectangular water tight tank over which the latrine
is constructed.
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The sludge sedimentation on the tank undergoes
anaerobic digestion. The effluent is percolated into the ground
through soak pit or absorption field. The digested sludge after
being filled completely has to be removed. The drop pipe
attached to squat plate is made to submerge in the liquid thus
avoiding bad smell. Fig 9.5 shows the details of aqua-privy.
Fig 9.5 Aqua - Privy
(d)
CESS POOLS:
The cess pools consists of a pit or chamber lined with dry
bricks or stones as shown in fig 9.6. The bottom is unlined and
allows the liquid to percolate. Only solid matter remain in the
cess pool, undergoing anaerobic digestion. The cess pool is
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periodically cleaned. One cess pool can serve the function of
more than one building depending upon its capacity. This is an
inferior method, as it produces bad smell and polluted the ground
water. So wells should not be located near these cesspools.
Fig 9.6 Cess Pools
DESCRIPTION AND OPERATIONAL DETAILS OF BIO GAS
PLANT:
For rural uplift, with respect to energy crises, the bio-gas
seems to be a good alternative. These plants help in the
maintenance of healthy environment in villages. These are also
called GOBAR GAS PLANTS. These bio-gas plants solves the
problem of energy and fertilizer in rural areas and also solves to
some extent the problem of sanitation and air pollution.
The following materials can be used as raw materials for
the production of combustible gas methane (CH4), which has a
calorific value of 4400 to 6200 K.Cala in bio-gas plants.
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1. Cattle dung from cow, bulls, buffaloes, ship, pigs etc.
2. Human excreta and urine from latrines.
3. Agriculture waste like paddy, groundnut, sugarcane, cotton waste
etc.
4. Forest litter.
The bio-gas production by anaerobic digestion involves
hydrolysis and methane formation. For the best results the
following factors should be considered.
1. Temperature – 30° to 60°C.
2. PH Value – 7.0 to 7.2.
3. Effect of nutrient deficiency – carbon and nitrogen ratio
should lie between 30:1 to 50:1.
4. Quality of raw materials.
5. Influent solid materials : optimum gas production is
obtained with 1:1 slurry of cow dung and water
6. Toxity: the slurry does not contain any toxic materials
which may destroys anaerobic bacteria.
The effluent of bio-gas plant is an excellent organic
manure with enriched nutrients for plant growth and humas
materials to improve soil structure for aeration.
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TYPES OF BIO-GAS PLANTS:
Number of institutes and organizations developed
different models of bio-gas plants. The following are the models
of bio-gas plants used in rural areas.
1. KVIC MODEL
2. JANATA MODEL
I.
KVIC MODEL:
It consist of a circular tank constructed with brick
masonary in cement mortar 1:4 on concrete floor. The inside of
tank is plastered with C.M. 1:3 and acts as an anaerobic digester
which is divided into two parts by a vertical partition wall
A gas holder made of steel sheets in the shape of a
circular dome is placed on the top of digester. The dome is
supported on a horizontal beam. The steel dome rests on this
beam when there is no gas accumulation in it and floats in the
slurry when sufficient gas accumulates
The digester is provided with an inlet and outlet pipes
made of A.C. or masonary as shown in the fig. 9.7.
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Fig 9.7 KVIC Model Bio-gas Plant
Cow dung is mixed with water in the ratio 1:1 and fed to
the digester through inlet tank. The slurry makes a slow vertical
movement, then over flows the partition and finally reach the
outlet pipe through which it comes out from the outlet tank. The
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volume of digester is so designed as to hold the slurry for 55
days, an average 10kg of dung per day (per cattle 4 to 6 kg)
during which period the cow dung slurry is digested
anaerobically and produce bio-gas satisfies the requirements of
family of 8 members. The accumulated gas is taken out through a
pipe to the kitchen.
For successful operation and production of gas it is
necessary that the plant is well maintained without allowing any
clogging etc. The steel dome is likely to be corroded and get
damaged so periodic painting of the steel dome is carried out.
2.
JANATA MODEL:
The Janata Bio-gas plant is as shown in the fig 9.8 with
3m capacity can serve a small family of 5 members. The weight
of the dung required is 45kgs, 3 to 4 cattle can yield this quantity
of dung. This model was developed by gobar gas research station,
ajitmal, Lucknow, in view of its reduced cost.
3
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Environmental Engineering
Fig 9.8 Janata Model
Janata bio-gas plant can be constructed with the locally
available materials like bricks, cement mortar and concrete. The
tank is constructed on concrete floor, which acts as digester is
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provided with a dome shaped roof constructed with brick
masonary. The digester and fixed dome remain below the ground
level. At the middle of the depth of digester, there are two
rectangular openings facing each other and coming upto a little
above the ground level, acts as inlet and outlet of the plant the
dome shaped roof is filled with a pipe at the crown. This pipe acts
as an outlet for the gas
The mixed slurry of 1:1 ratio of cattle dung and water is
filled with digester through inlet chamber for 50 days and by
anaerobic digestion bio-gas is produced. The gas in the dome
exerts pressure on the slurry thus displacing from the digester to
the inlet and outlet tanks.
The gas is supplied to the kitchen through the pipe. The
difference of slurry levels in the inlet, outlet and digester depicts
the pressure of gas. The Janata Model bio-gas plant is cheaper
than KVIC model because of locally available materials without
use of steel
ADVANTAGES OF BIO-GAS PLANTS:
1. The energy generated by the plant can be used for cooking,
lighting and running pumps.
2. The digested sludge acts as good manure.
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Environmental Engineering
3. Unstable and putrescible organic solids are reduced into
stable acceptable form.
4. Handling & disposal of digested sludge becomes easy
because no bad odour coming out.
5. Ground water pollution is prevented.
6. Asthatic value.
7. The pathogenic organisms are destroyed during digestion.
8. Housefly and mosquito breeding is eliminated.
9. Destruction of weed seeds present in the dung.
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SYNOPYSIS
1. People in rural area consuming water from wells, ponds and
streams without any treatment they are made to suffer from water
borne diseases like typhoid, dysentery, cholera, jaundice,
guniaworm etc. so rural water system aim to provide reasonable
quantity of protected water to satisfy demands of people and
safeguard against the health
2. NEERI (National Environmental Engineering Research Institute),
Nagpur has evolved a method called “double pot system” for the
application of bleaching powder to the rural well.
3. Rural sanitation is used to indicate the development or
maintenance of sanitary conditions in rural area
4. The disposal of human excreta without the help of water carriage
system in rural areas by using
a. Pit privy
b. Bore hole latrine
c. Aqua privy
d. Cess pools
5. Bio-gas plants solve the problem of energy and fertilizer in rural
areas and also solves to some extent the problem of sanitation
and air pollution
6. The models of bio-gas plants used in rural areas are 1. KVIC
model 2. JANATA model.
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SHORT ANSWER QUESTIONS
1. Name any four water-borne diseases.
2. What are the reasons for pollution of wells?
3. What is double pot system?
4. What are the precautions to be taken to avoid the pollution of
streams and lakes?
5. Name the various types of privies constructed in the rural areas.
6. What are the raw materials used for the production of bio-gas?
7. What are the important stages of anaerobic digestion of bio-gas?
8. What are the factors considered in the bio-gas production for
getting good results?
9. Name any two models for the production of bio-gas in rural
areas.
10. What are the advantages of bio-gas?
ESSAY TYPE QUESTIONS
1. How do you carry out disinfection of wells?
2. Explain the pit-privy with the help of neat sketch.
3. Explain the construction of borehole latrine and draw the figure.
4. Draw the neat sketch of K.V.I.C. model of bio-gas plant and
explain the construction.
5. Explain the construction and working of Janata bio-gas plant with
neat sketch.
6. Draw the neat sketch of sanitary protected well.
Air Pollution & Ecology
Page 183
CHAPTER 10
AIR POLLUTION AND ECOLOGY
10.1 GENERAL INTRODUCTION:
The term air pollution may broadly defined as the presence in the
outdoor atmosphere of one or more contaminants like dust, mist,
smoke, colour etc in quantities, of characteristics and of duration.
Such as to be injurious to human beings, plants, animals or
properties or which unreasonably abstruct the comfortable
enjoyment of life and property. It also alters the environment
unfavorably, Hence the study of causes, effects, preventive
measures and control methods of air pollution has become
important for environmental engineers
10.1.2COMPOSITION OF AIR:
The
atmosphere
air
contains
the
constitutions expressed in percentage by volume
1. Nitrogen
-----
78.10
2. Oxygen
-----
20.90
3. Carbondioxide
-----
0.04
5. Water Vapour,ozone,
organ, krypton, carbon
monoxide,ammonia etc
----
0.96
---------100.00
----------
following
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10.1.3 SOURCES OF AIR POLLUTION:
Following are the main sources of air pollution
(i)
(i)
Natural sources
(ii)
Man made sources
NATURAL SOURCES:
The following are the natural sources of air pollution
a. Electrical storms producing oxides of nitrogen
b. Volcanic eruptions
contributing
hydrogen
fluoride.
hydrogen chloride etc
c. Desert/winds causing the spread of dust particles
d. Aerosols of natural origin by volcanic action, smoke
obtained by forest fires
e. Natural radio activity of atmosphere due to radioactive
minerals in the earth crust and action of cosmic rays.
f.
Natural chemical reactions,
bio-chemical
reactions
releasing carbon dioxide, hydrogen sulphide etc into the
atmosphere
(ii)
MAN MADE SOURCES:
(a) FUEL BURNING OPERATIONS: The combustion of fuel
in industries, commercial and domestic purposes produces
large quantities of carbon dioxide, carbon monoxide, sulphur
dioxide, nitrogen oxide etc
(b) AUTOMOBILE POLLUTION: The exhaust emissions
from transport vehicles of petrol, diesel or kerosene oil,
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include road vehicle, diesel locomotives, ships and aeroplanes
change the quality of air and results the formation of smog
(smoke + fog) which seriously affecting the visibility.
(c) INDUSTRIAL POLLUTION: The waste gases like
carbondioxide, carbon monoxide, hydrocarbons, sulphur
dioxide, nitrogen oxides etc, dust particulate matter and heat
from the industries like chemical manufactures, Iron, brick,
cement manufacture, quarries rice mills, flour mills, cotton
mills and electric power generating stations etc causes serious
air pollution.
The factors like wind speed & direction, atmospheric
diffusion, temperature distribution, topographical features of
area, the quality & quantity of pollutants will severity of air
pollution.
10.1.4 EFFECTS OF AIR POLLUTION:
The adverse effects of air pollution can be classified as
follows
(i)
Effect on human health
(ii)
Effect on physical properties of
atmosphere
(iii)
Effect on plants and animals
(iv)
Effect on materials and property
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(i)
Environmental Engineering
EFFECT ON HUMAN HEALTH
a. Carbon monoxide from automobile emission, cigarette smoke,
domestic heat combines with hemoglobin of the blood and forms
carboxyheamoglobin in the blood. If the level reaches 10%,
headache & lassitude and it reaches to 20%, impairs the transfer
of oxygen
b. Sulphurdioxide from petroleum, thermal power stations, sulphuric
acid plants etc results increased symptoms in cardiac and
pulmonary diseased patients when the sulphur dioxide
concentration is more than 500 µg/m3 for 24 hours.
c. Carbon dioxide from coal Industries, automobiles etc at higher
concentrations can causes death.
d. Hydrogen Sulphide from tunnels, petroleum, sewerage system,
paper industry is toxic in nature and causes serious odour
problem
e. Hydrocarbons from petroleum, rubber industry etc effects un eyes
leading to lachrymation and polynuclear hydrocarbons may
produce cancer.
f. Nitrogendioxide results from electrical discharges solar radiations,
acid manufacture etc causes respiratory illness in children.
g. Chlorine from textile industry cause photo chemical oxidants
results from atmospheric reactions lead to asthematic attacks in
the people. They also causes irritation of eyes, nose and throat.
h. Halogenated solvents from fertilizers industry attacks the lever
and sometimes lead to death.
Air Pollution & Ecology
(ii) EFFECT
ON
ATMOSPHERE
a.
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PHYSICAL
PROPERTIES
OF
The emissions of automobile exhaust gases, smoke from the
industries forms smog which seriously effect the visibility on
roads and leads to accidents.
b. The rise of carbondioxide in the atmosphere rises the temperature
which leads global warming.
(iii)
EFFECT ON PLANTS AND ANIMALS:
a. The sensitive vegetation may severly damaged by the even
low concentrations of ozone, nitrogen dioxide and
sulphurdioxide.
Ex. Standing crops, orchards, sugarcane etc.
b.
Hydrogen fluoride, chlorine, hydrogen sulphide hydrocarbons also causes damage to vegetation.
c. Radioactive substances also causes genetic changes in
animals.
d. The oxides of nitrogen and sulphur forms acid rains
which causes severe effect on vegetation results in
reduction is yield of the crop and also effect on wild life.
(iv)
EFFECT ON MATERIALS AND PROPERTY
The materials and property are deteriorated by the following
four ways
(1) Abration
(2) Corrosion
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Environmental Engineering
(3) Deposition and removal
(4) Chemical attack
And also fading away of colours may takes place by the
pollution
10.2 CONTROL OF AIR POLLUTION - METHODS
The control of air pollution can be done independently or
combination with the other. The following are the methods
1. Air pollution prevention at source
2. Air pollution by zoning
3. Air pollution by control devices
4. Air pollution control by stacks and
vegetation 10.2.1 Air pollution at
source
This method is more effective than control equipment method
and avoids the capital and maintenance cost of the control
equipment. Prevention of air pollution at source can be effected
by two ways
(i)
CHANGE IN RAW MATERIALS:
Emission of pollutions reduced by the substitute raw
materials or its structure. The raw material, which is responsible
for pollution is replaced by other material in which the
ingradients responsible for emission of pollutants are absent.
Example:
a. Lead removed petrol can be used for vehicle instead of
ordinary petrol.
Air Pollution & Ecology
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b. Low sulphur fuels instead of high sulphur fuels to
reduce the emission of SO2.
c. Electricity or methane gas instead of petrol or
diesel eliminates the carbon monoxide pollution.
(ii) CHANGE IN PROCESS:
A particular conventional process of manufacture with results in
heavy pollution of air may be replaced by the new process or
modified process
Example:
a. Adoption of two stage combustion for reducing
the emission of NO2.
b. Recycling
of
non-condensable
gases
for
additional reactions .
Eg. Polymerization and alkylation of hydrocarbons.
c.
By reducing excess air from 15% to 1% during
burning of fossil fuels to reduce oxidation of SO2 to
SO3 avoids the formation of H2SO4.
c. Use of electrical furnace instead of open hearth
furnace in steel industry.
10.2.2 AIR POLLUTION CONTROL BY ZOING
In this method, the industrial areas are classified into separate
groups depending on factory size, no. of workers, quality and
quantity of air pollutants released by them while planning the city
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Environmental Engineering
each group is zoned and located in such a manner that they are
separated from each other as to avoid impact of pollution on
residential areas
At present following two methods of zoning
1. Exclusive zoing system
2. Performance standard zoning system
In performance standard zoing system, the industrial areas
classified as below.
a.
Group - 1 - The small industries, which the emissions are less
effect on environment and the variety of products having close
relation to cities can be located on the fringer of town and cities
b. Group - 2 - Cottage and small scale industries, which have no or
least adverse effect on environment located in the city
c. Group - 3 - Big industries are more adverse effect on environment
are located at a distance of 3 km or more from the residential area
The performance standard zoning system is based on
characteristics as industrial nuisance include dust, noise, smoke,
odour, heat, fire, hazardous gases etc., traffic congestion,
obnoxious and hazardous character of industry. It is necessary to
place the neat industries away from the obnoxious industry.
10.2.3 AIR
POLLUTION
CONTROL
DEVICES AND EQUIPMENT
BY
CONTROL
The emission of particulate matter into the atmosphere can be
controlled by the installation of certain devices. The selection of
device depends upon the following factors.
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1. Characteristics of the gas like pressure, humidity, temperature
density, dew point, viscosity etc.
2. Operational factors
service requirements.
like
space
required, corrosion,
3. Process factors like concentration of particulate matter,
pressure drops, discharge of gas, efficiency required etc.
4. Characteristics of particulate matter like size, shape,
density. Electrical conductivity, toxicity, corrosiveness etc.
The design of the equipment is influenced by the following
factors
1. Initial cost, operational and maintenance.
2. Space requirement of the controlling equipment.
3. Availability of materials for construction and operation.
4. Removal of efficiency of the plant.
CLASSIFICATION OF THE EQUIPMENT:
Depending upon the method by which the participate matter is
collected the equipment is classified as
1.
Internal seperators - fabric filters, gravity settling chamber,
cyclone
2.
Wet collection device - Spray chambers, cyclone scrubbers
venturi scrubbers
3. Electro static precipitator - single stage precipitator.
- two stage precipitator.
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1. GRAVITY SETTLING CHAMBER:
The gravity settling chamber is simplest form of pollution control
devices. It consists of an enclosed chamber, where the velocity of
the dust laden gas is considerably reduced (0.3 to 3m/sec), which
allow the dust particles to settle down by gravitational force. At
such reduced velocities the particles settle down to the hopper
bottom and dust is removed from dust outlet. The dust free gas is
taken out through outlet. The gravity settling chamber is effective
in particle size of 100µ. The gravity settling chamber is shown in
fig 10.1
Fig 10.1 Gravity settling Chamber
ADVANTAGES:
1. It is simple in construction and operation.
2. It is cheapest device and hence can be used where larger particles
are to be separated.
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3. It acts as preliminary screening device before the treatment is
more effective.
DISADVANTAGES
1. The settling chamber can be used only to remove larger sized
particles.
2. It is not by itself a solution for controlling of air pollution.
2.
CYCLONE:
The cyclone works on the principle of separating the
particles from the gas by transforming the inlet gas velocity into
double vertex. The entering gas spirals down at the inner surface
and then spirals upward at the central portion of the cyclone as
shown in fig 10.2. Due to inertia, the dust particles tend to
concentrate on the surface of the cyclone wall, from where they
are led to the receiver. These are cheaper in cost and best suited
to dry dust particles of size 10-40µ. The cyclones can handle a
wide range of physical and chemical conditions of operations as
compared with other collection equipments.
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Environmental Engineering
Fig 10.2 Cyclone
3.
FABRIC FILTER:
The fabric filter method is the older and often the most
reliable method. When the dust laden gas passes over fabric bags,
the direction of streams of gas is changed. The inertial dust
particles of size 0.01µ size are caught by the bag. The collection
of the particles on the fibres is due to several collecting
mechanism such as inertial impaction interception, diffusion,
sedimentation and electrostatic seperation. The dust particles thus
deposited on the inner side of the fabric filter are cleaned by
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sending compressed air in the fabric filter are cleaned by sending
compressed air in the reverse direction and removed through dust
outlet. Fabric filter is also called "Bag Filter" or cloth filter as
shown in fig 10.3.
Fig 10.3 Fabric Filter
ADVANTAGES:
1. Efficiency of collection is high (about 99%)
2. Moderate pressure drop and power consumption.
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Environmental Engineering
3. Recovery of dust in a dry and often reusable form.
4. No water is required for exhaust gases.
DISADVANTAGES:
1. Maintenance cost high due to bag replacement
2. Suitable for moderate temperatures only
3. Not suitable for situations when liquid condensation occurs
4. They require more space for installation
ELECTRO STATIC PRECIPITATORS:
The electrostatic precipitator is one of the most widely used
collection device for both solid and liquid particulates very effectively.
Electrostatic attraction is used as the basic force for seperation of
participate matter from the gas.
The electrostatic precipitators may be two types
namely a. Single stage precipitators
b. Two stage precipitators
Fig 10.4 shows the single stage cylindrical electrostatic
precipitator consists of cylindrical container with an inlet and outlets. It
has a centrally arranged discharge electrode with a weight at bottom. The
wall of the container is earthened so as to make it a collector electrode.
The discharge electrode is supplied with power. There is a hopper at the
bottom with an outlet to remove the collected particulates.
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Fig 10.4 Single Stage Cylindrical Electrostatic Prespitater
The particles move upward along with the stream of air and the
particles are charged in an electric field generated by the discharge
electrode. The charged particles move to the inner surface of the
container and are caught by the surface. The cleaned gas then emerges at
the top. The collected dust is removed periodically from the surface by
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rapping it. This dust then falls to the dust hopper and is accumulated
there for periodic removal
ADVANTAGES:
1. The range of the size of precipitators is enormous.
2. The efficiency of collection is high as 99.99%.
3. It can operate at high temperature and pressure.
4. Power requirement is low.
DISADVANTAGES:
1. Certain dusts can be collected by the precipitator only with great
difficulty.
2. It cannot collect gaseous pollutants.
3. The precipitator requires certain gaseous pollutants to be present
along with particulate matter, for good collection efficiency.
10.3
AIR POLLUTION CONTROL BY STACKS AND
VEGETATION
a. STACKS:
The stacks work on the principle of dilution of gases with
huge quantities of atmospheric air. The atmosphere can
assimilate a small quantity of pollutant without producing a
noticeable adverse effects
Stack is a chemney constructed to a sufficient height so
that it releases the polluted gases at a great height into the
atmosphere producing no ill effects. The polluted gas, after
release from the chemney; dilutes itself with the atmosphere and
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get diffused and distributed. Thus the height, greater is the
reduction of concentration. The stacks serve as pollution
controllers for odourous gases or low concentrated pollutants
The diameter of the stack depends upon the exhaust gas
flow rate and exist velocity required. The exist velocity
required is taken as 1.5 times the maximum wind velocity. The
height of stack is atleast 2.5 times height of the surrounding
buildings.
10.3
AIR POLLUTION
VEGETATION
CONTROL
BY
STACKS
(II)
POLLUTION CONTROL BY VEGETATION:
AND
The Vegetation plays a great role in the control of air
pollution. Some pollutants may be essential for their growth and
others may be decremental whatever may be the effect of the
pollutants on them, the plants help us in the reduction and control
of air pollution. The role of vegetation in this regard may be
explained by the following points
1. The plants consume carbondioxide for the preparation of
required carbohydrates, by the process of photosynthesis and
releases oxygen into the atmosphere. Thus the carbondioxide
pollution of air is reduced and on the other hand the air is
reduced and on the other hand, the environment is freshened
by the contribution of oxygen by plants
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Environmental Engineering
2. The gaseous and liquid pollutions of air also obsorbed by the
plants during the process of respiration and thus the
concentration of those pollutants is reduced in the air
3. The dust particles and other particulate matter are intercepted
by plants and get deposited on the leaves and twigs. Thus the
plants acts as collectors of dust and particulate matter, and
from this the qualitative and quantitative measurement of air
pollution can be done. During the rain, these deposited
particles are removed by natural scrubbing
10.4
ENVIRONMENT:
The environment is defined as all the systems namely
atmosphere, lithosphere, hydrosphere (non-living components)
and biosphere (living components) surrounding us. It includes air,
water, food, shelter, the pollutants, waste materials and other
ecological problems which affect his life and health
Because recent developments like the deteriorating
quality of environment is actually deteriorating the quality of life
on this planet. And also by globality leads to the establishment of
organizations like
1. United nations environment programme (UNEP)
2. Global Environmental monitoring system (GEMS)
3. World commission on Environment and development
(WCED)
4. World conservation strategy (WCS)
5. World wide fund for nature (WWFN)
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6. Scientific Committee on problems of the environment
(SCOPE)
7. United nations conference in environment and development
(UNCED)
10.4.1 BIO SPHERE:
Biosphere is the life-supporting environment of planet
earth which consists of atmosphere, Hydrosphere and lithosphere
in which air, water and soil are the chief media
10.4.2 ATMOSPHERE:
The multi layered gaseous envelope surrounding the
planet earth is called atmosphere. The atmosphere is divided into
five distinct layers namely
1. Trosphere – 1)
extended 0 to 8km at poles and
extended 0 to 18km at equator
2) Temperature decreases at the rate of 1°C for 165m if ascent.
3) Contains dust particles & 90% of earth’s water vapour
4) All the important processes leading to the climatic and
weather conditions
2. Stratosphere-
1) extended upto 50km
2) Temperature remains constant upto
20km and increases upto the 50km
3) Contains ozone layer which absorbs
ultra violet rays
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3. Mesosphere:
1) Extended upto 80km
2) Temperature decreases with height reaching upto
minus 100°C at 80km
4. Ionosphere:
1) This layer located between 80 and 400km
2) Temperature increases with height due to radiation from sun
3) Contains electrically charged ions which reflect radio waves
back to the earth surface and enables wireless
communication
5. Exosphere:
1) Extended beyond 400km and merged with the outer space
10.4.3 ACID RAIN:
The urban and industrial air pollution increases the
concentration of sulphurdioxide (SO2) and oxides of nitrogen
(NO2) in the air. The industries like thermal power plants release
SO2 and automobiles release NO2 which combines with water
vapour to produce air borne sulphuric acid (H2SO4) 60 to 70%
and Nitric acid (HNO3) 30 to 40% results in acid rain. Acid rains
have assumed to be global ecological problem because these
oxides travel longer distances, during the journey, undergo
physical and chemical transformation to produce more hazardous
products
The affects of acid rain are
1. Effect on human health: Skin problems, harmful to the
lungs causes respiratory problems.
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2. Effect on Vegetation: Increases the acidity of soil, surface
water and thus affecting aquatic life, plants and productivity
3. Effect on material: By acid rains, corrodes the buildings,
monuments, statues, bridges, fences and railing etc.
10.4.4 GREEN HOUSE EFFECT:
The term green-house is used to mean a building made
mainly of glass with heat and humidity regulated for growing
plants. The atmosphere is like the glass in a green-house. The
increased concentration of CO2 from industries and automobiles
and chemicals like chloro-fluoro carbons (CFCs) present in the
atmosphere absorb the long wave radiation and radiate energy
back to the earth resulting the increase in the temperature of the
earth. This global warming phenomenon is known as green-house
effect
By green-house effect the following are the changes in the
climate of earth
1. By the rise in temperature would cause the polar ice caps to
melt resulting in the rise of sea level, which would submerge
the low laying regions.
2. The plants and animals will be affected resulting in
distruption in the eco system.
3. In temperate regions, the winter will be shorter and warmer,
and the summer will be longer and hotter.
4. The tropics may become wetter and sub-tropics which already
dry may become drier
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5. The rapid pace of industrilization with the drastic falling of
forests will create a layer of impenetrable gases on the earths
atmosphere converting the earth planet to a hot house.
10.4.5 OZONE LAYER DEPLETION:
The ozone layer is vital for the life on the earth because it
acts as an umbrella against the harmful ultraviolet radiation
reaching the earth. Certain chloro-fluro carbons (CFCs) get
accumulated in greater amounts at high altitudes releases chlorine
atoms under the influence of ultra violet radiation. These chlorine
atoms react with ozone converting ozone (O3) to Oxygen (O2).
Thus holes are formed in the ozone layer. This is dangerous in
the sense that ultra violet rays from the sun cannot be filtered and
rays reach the earth surface. The following are the affects of
ozone layer depletion.
1. Increase of skin cancers and eye ailments.
2. Effect crop yield especially that of timber.
3. Disturbance in ecosystem.
4. Damage of immune system.
5. Shorter life of paints and plastics.
10.5
ECOLOGY AND ECO SYSTEM:
Ecology indicates the study of inter-relationship of
organisms and their environment. Eco system is defined as any
unit that includes all the organisms (i.e.,) communities in a given
area, which interact among themselves and with the physical
environment so that a flow of energy leads to clearly defined
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tropic (nourishing) structure, biotic diversity and material cycle
(exchange of material) within the system. There exists nutritional
relationships (Food Links) among the organisms of such a
system. Keeping in this view, the earth can be considered as a
gaint ecosystem where non living and living components
constantly acting and reacting up on each other bringing
structural and functional changes in it.
Fig 10.5 shows diagrammatic representation of eco
system. For the sake of convenience, we generally study nature
by making its artificial sub divisions into of smaller ecosystems
such as terrestrial (forest), desert, grass land, aquatic man
engineered land etc. Thus the ecosystem may be as small as
pond, a crop land or as large as ocean, desert, forest. Through
these unit ecosystems are separated from each other with time
and space but functionally they are linked with each other
forming an integrated whole.
Fig 10.5 Diagrammatic Representation of Eco System
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The relationship between the plants, animals and environment:
The living organisms and their nonliving environment are
separated Inter related and interact with each other and thus
maintain a balance. The fig 10.6 shows the generalized scheme of
nutritionalships (Food Links) among the living organisms of such
system.
Fig 10.6 Generalised Scheme of Nutritional Relationships among
Different Biotech Components of an Eco-system
10.5.1 COMPONENTS OF ECOSYSTEM:
PRODUCERS:
These are photo autotrophic green plants and
photosynthetic bacteria and to lesser extent chemo synthetic
microbes, which fix light energy of sun and produce complex
organic substances with the help of minerals derived from water
and earth. The producers are mainly two types
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1. Macrophytes which included mainly the rooted large sized
plants.
2. Photoplanktons which are microscopic floating or suspended
lower plants (Algae)
CONSUMERS:
These are Heteotrophic components of the living
organisms. They consume the matter built up by producers. The
consumption of matter by the consumers is done by the activities
of utilization, rearrangement and decomposition of complex
organic materials. The consumers are further categorized into the
following.
1. Macro Consumers:
The macro consumers depends for their neutrition on the
organic food manufactured by producers. Macro consumers are
further divided into the following types
1. Herbivores or primary consumers:
These animals feed directly in living plants or plant
remains.
2. Carnivores order-I or secondary consumers:
These carnivores feed on the herbivores and include
chiefly insects, fish and frogs.
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3. Carnivores order-2 or tertiary consumers:
These are large fish as the game fish, which feed on the
smaller fish. They also include other animals, which feed
on her bivoles and consumers.
2. Micro Consumers or Decomposers
They absorb only fraction of the decomposed organic
matter. They bring about the decomposition of dead organic
matter of both plants and animals to simple forms and help in
returning of mineral elements to the original; medium of mineral
elements to the original medium.
10.5.2 Flow of Energy in an Eco System:
In an ecosystem one can observe the energy flow or transfer of
energy from one trophic level to other in succession. The primary
producers trap radiant energy of sun and transfer that to chemical or
potential energy of organic compounds such as carbohydrates, proteins
and fats. The energy flow is a universal phenomenon and is due to
operation of laws of thermodynamics.
1. Energy is transformed from one type into another but is neither
created nor destroyed
2. No process involving an energy transformation will occur unless
there is a degradation of energy from a concentrated form into a
disposed from because some energy is always disposed into
unavailable heat energy; no spontaneous transformation (as light
to food for example) can be 100 percent efficient
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The interaction of energy and materials in the ecosystem
is the primary concern to ecologist. Infact, the one way flow of
energy and circulation of materials are the two great principles of
general ecology. The sequence of energy flow including further
transfers to animals and man as shown in fig no. 10.7
Fig10.7 Energy Flow Diagram
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SYNOPYSIS
1. Air pollution is defined as the presence of one or more
contaminants in the atmosphere or ambient air; of such quantity
and duration as may be injurious to human, plant and animals.
2. The normal air consists of nitrogen, oxygen, carbondioxide and
others in the percent respectively are 78.08, 20.95, 0.03 & 0.94.
3. The sources of air pollution are
1) Natural sources are electrical storms, volcanic eruptions,
desert winds, forest fires, radio activity of earth, natural
chemical reactions bio-chemical reactions etc
2) Manmade sources are combustion of fuels, automobile
pollution, pollution due to industries etc.
4. The effects of air pollutions are
a) Effects on human health.
b) Effects on physical properties of atmosphere.
c) Effects on plants and animals.
d) Effects on materials and properties.
5. The control of air pollution may be by
a) Zoning.
b) Air pollution prevention at source.
c) Air pollution control by controlling device and
equipment
d) Air pollution by stacks and vegetation.
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6. The term environment is defined as all the systems namely
atmosphere, Lithosphere, hydrosphere and biosphere surrounding
us and includes air, water, food, shelter, pollutants, waste
materials and other ecological problems which affect his life and
health.
13. Ecology is the term indicates the study of inter relationship of
organisms and their environment.
7. Biosphere is the life supporting environment of the planet earth
which consists of air, water and soil.
8. The atmosphere is multilayered gaseous envelope surrounding
the planet earth is called atmosphere.
9. The atmosphere consists of
a) Troposphere (0 to 18 km)
b) Stratosphere(18 to 50km)
c) Mesosphere (50 to 80km)
d) Ionosphere (80 to 400km)
e) Exosphere(beyond 400km)
10. Acid rain is due to the increase of the pollutants of SO2 and NO2
due to urban or industrial may produce acid rain which causes
health effects, effect on materials and effect on crop production
11. By the increase of concentrations of CO2 and other gases causes
increases in temperature of earth, which in turn causes as Green
house effect. By this rise of sea level, which may submerge the
low laying areas of world map.
12. Certain chloro-floro-carbons get accumulated in greater amounts
at high altitudes and releases chlorine atoms under the influence
of ultra violet radiation and the chlorine atmos react with ozone
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Environmental Engineering
and changes to oxygen. Thus holes are formed in the ozone layer
through which the rays of the sun are directly comes on to the
earth results increases of radiation, skin cancers and effect on
plants.
13. Eco system is defined as any unit that includes all the organisms
which interact among themselves, and with the physical
environment, so that the flow of energy leads to clearly defined
trophic structure, biotic diversity and material cycle within the
system.
14. The components of ecosystem are producers and consumers.
15. The energy flow is a universal phenomenon and is due to
operation of laws of thermodynamics.
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SHORT ANSWER TYPE QUESTIONS
1. Define air pollution.
2. Name the main type of air pollution.
3. What are the main sources of natural air pollutions?
4. Name any four chemical pollutants.
What are the effects of following pollutants
5. Hydrocarbons
6. CO2
7. SO2
8. NO2
9. Name the methods of control of air pollution.
10. Name any four control equipment used in control of air pollution.
11. What is meant by zoing?
12. Define environment.
13. What is Biosphere?
14. Define atmosphere.
15. Name the different layers of atmosphere.
16. What are the effects of acid rain?
17. Define Ecology.
18. What are the components of Ecosystem?
19. Define producers and consumers.
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Environmental Engineering
ESSAY TYPE QUESTIONS
1. Explain various sources of air pollution.
2. Explain the effects of air pollution.
3. What is green house effect? What are its adverse effects?
4. What is meant by ozone layer depletion and what are the effects?
5. What is meant by acid rain? Explain the effects.
6. Explain gravity settling chamber with neat sketch.
7. Explain the working of cyclone with the help of neat sketch.
8. Explain fabric filters.
9. Explain the electrostatic precipitator.
10. Explain air pollution control by stacks and vegetation.
11. Explain air pollution control by zoing.
12. What is meant by Ecosystem and explain with the help of sketch.
13. Explain briefly with the help of diagram the concept of energy
flow.
REFERENCE BOOKS
1.
Water Supply & Sanitary Engineering by G.S. Birdie.
2.
Water Supply & Sanitary Engineering by Rangawala.
3.
Waste Water Treatment & Disposal by Medcaff & Graw.
4.
Solid Waste Management by Shivaji Rao.
5.
Environmental Lab Manual by Shivaji Rao.
6.
Environmental Engineering by M.Ramachandraiah.
7.
Environment Engineering by Balijeet Kapoor.
8.
Sewage Disposal
S.K.Garg.
9.
Water supply Engineering by Santhosh Kumar Garg.
and
Air
Pollution
Engineering
by
10. Water Treatment and Sanitation- Simple Methods for Rural
Areas by H.P.Mann and D.Willianson.
11. Water Supply & Sewerage by E.W.Steel.
12. Water Supply & Waste Water Disposal by W.A.Hardenbergh
& E.R.Rodie.
13. Water Supply & Waste Water Disposal by G.M.Fair,
J.C.Geyar & Oken.
14. Water Supply & Sanitary Engineering by V.N.Vazirani.
15. Water supply and Sanitary Engineering by Duggal.
16. IS 1172-1993 code of practice for water supply in buildings
by BIS.
17. IS12183:1987 code practice for plumbing in multi storeyed
buildings by BIS.
18. Plumbing Designs & Practice by S.G.Deolalikar.
19. SP 35(S&T) 1987 – Hand Book on water supply and
drainage with special emphasis on plumbing by BIS.
MODEL PAPER
SUB: ENVIRONMENTAL ENGINEERING
II YEAR WS & SE
TIME : 3 HRS
MAX MARKS : 50
SECTION – A
Note: 1) Attempt all questions
2) Each question carries 2 marks
1. Define sewage and sewerage.
2. What is meant by dry weather flow?
3. Name any four sewer materials.
4. What is the purpose of manhole?
5. What is meant by strength of sewage?
6. Define B.O.D.
7. What is the use of grit chamber?
8. What is meant by composting?
9. Define air pollution.
10. What are the effects of acid rains?
SECTION – B
Note: 1) Attempt any five of the following
2) Each question carries 6 marks
11. Explain systems of sewage disposal.
12. Explain the significance of the following tests.
a) solids
b)B.O.D
13. Draw the neat sketch of JANATA model biogas plant and
explain the operation.
14. Explain the disposal methods of solid waste by
a. Sanitary land fill.
b. Incineration.
15. Explain the testing and maintenance of sanitary fittings.
16. Explain the following briefly.
a. Disinfection of wells.
b. Effects of air pollution.
17. Draw the neat sketch of cyclone and explain the operation.
18. Explain the following briefly.
a. Ozone layer defletion.
b. Industrial waste treatment – equalization.
*
*
*
CONTENTS
Chapter
No.
Name of the chapter
No. of
periods
1.
Introduction
05
1
2.
Quantity of Sewage
15
16
3.
Sewerage Systems
15
28
4.
Sewer Appurtenances
15
49
5.
Sewage Characteristics
10
76
6.
Sewage treatment and
disposal
35
90
7.
Solid waste disposal
20
132
8.
Drainage and Sanitation in
15
141
Sanitation
10
165
Air pollution and Ecology
20
183
Buildings
9.
10.
Pg. No.
Rural Water Supply and
TOTAL PERIODS
MODEL PAPER…..…….….
REFERENCE BOOKS…….
INDEX ……….………….….
160
INDEX
A
E
Acid rains
Action of activated sludge
Activated sludge process
Aerosols
Air pollutants
Air pollution
Analysis of sewage
Aqua privies
Ecology
Effects of air pollution
Environment
Environmental health
hazard
B
Bio-gas
Bore-hole prives
C
Catch basins
Catch pits
Cesspools
Cleaning and maintenance
of sewers
Composition of air
Construction of sewers
Control of air pollution
D
Drainage plans of buildings
Drop manholes
Dry weather flow
Dust
F
Fertilizers
Flushing cisterns
Flushing tanks
Fog
G
Garbage collection and
removal
Garbage disposal
Green-house effect
Grit chambers
H
House drainage
I
Importance of air pollution
M
Manholes
Materials for sewers
Methods of sludge disposal
Micro-organisms
O
Oxidation ponds
Ozone layer
P
Pit privies
Primary clarifiers
Primary
treatment
of
sewage
Principles
of
house
drainage
Properties of sewage
Pumping of sewage
Purpose of sanitation
Q
Quality of sewage
Quantity of sewage
Quantity of sludge
R
Refuse
Rural sanitation
S
Sanitary fittings
Sanitary protection of wells
Screens
Secondary clarifiers
Secondary treatment
Septic tanks
Sewage as fertilizer
Sewer
Sewer appurtenances
Sewerage
Shapes of sewers
Sizes of sewers
Skimming tanks
Sludge digestion
Sludge digestion tanks
Sludge disposal
Smoke
Sources of air pollution
Surface drains
Systems of sewerage
T
Testing of drains and pipes
Trickling filters
U
Urban air pollution
V
Ventilation of sewers
W
Wash basins
Water-borne diseases
Water closets