CV-603 environmental engineering & pollution control

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Subject name : environmental engineering
and pollution control
Course code : cv-603, semester : 6th
(civil)
Prepared & uploaded by :
Kamal Chandra kataki
Lecturer (selection grade)
Civil engineering department
Assam engineering institute
Guwahati
&
Nibedita gupta
Lecturer (selection grade)
Civil engineering department
Silchar polytechnic
meherpur

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Subject Name : Environmental Engineering & Pollution Control
Course Code : CV – 603, Semester : 6th
(Civil)
1 : Introduction
2 : Water Supply
Objectives of public water supply :
1. To supply safe and wholesome water to consumers.
2. To supply water in adequate quantity.
3. To make water easily available to consumers so as to encourage personal and
household cleanliness.
Wholesome water : A wholesome water is usually one which is unpolluted, free from
toxic substances as well as excessive amount of mineral and organic matter that may
impair the quality of water.
2.1 : Quantity of water
Demands of Water
Estimating requirements :
1. The probable population at the end of the design period.
2. Rate of water supply per capita per day
Design period : This is the period into the future for which the estimate is to be made.
It is generally varying from 20 to 30 years.
Per capita consumption : If Q is the total quantity of water in litres required by a
community per year having ‘P’ as its population then per capita consumption per day
lpcd =
365P
Q
Factors affecting rate of demand
1. Climate
2. Class of consumer
3. Industries and commerce
4. Quality of water

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5. Pressure in the distribution system
6. Extent of metering system
7. Sewage facilities
8. System of supply
9. Number of inhabitants
Consumption for various uses :
1. Domestic use : 135 litres
2. Industrial and commercial use 20 to 25 %
3. Public use 10%
4. Loss and waste (15%)
Fire demand : It is the quantity of water required for fire fighting purposes. Generally
5-10 % of total consumption is required.
Kuichling formula
PQ 3182
Where Q is the fire demand in litres/min and P is the population in thousand.
Forecasting of Population :
The following methods are used for forecasting of population.
(i) Annual rate of increase method : In this method rate of increase per annum is
first determined and the population predicted from there by
Pn = P(1+i)n
Pn is the population at the end of n years
P= Present population
i= Annual rate of increase of population
1
1

P
Pn
n
i
(ii) Arithmetical Progression Method (AP) : In this method a constant increase
in the growth of population is added periodically. The population may be determined
by the following formula.
Pn = P+ni
P is the present population

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i= per year or decade increase of population.
This method is good for old cities or small town.
(iii) G.P. (Geometrical Progression Method) :
In this method a constant percentage growth is assumed for equal period of time.
Mathematically
ni
PPn )
100
1( 
This method gives erroneously high results
(iv) Incremental increase method : In this method the average of increase in
population is found out as per AP method and to that is added the average of
incremental increase once for every future decade.
(v) Changing rate of increase method or Decreasing rate of method : This is
similar to the geometrical progression method except that a changing rate rather than a
constant rate of increase is assumed .
(vi) Graphical Method
(vii) Comparative Graphical Method
(viii) The Master plan method
(ix) Logistic Curve Method
(x) The Apportionment method
2.2 : Sources of Water
Classification
a) Surface source
Ex. : Rivers, lakes, impounding reservoirs.
b) Ground Waters
Ex : Springs, infiltration galleries and wells.
Impounding reservoir :
An impounding reservoir may be defined as an artificial lake created by the
construction of a dam across a valley containing a water course.

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Springs :
Springs may be regarded as out crops of ground water which appear as small water
holes at the foot of hills or along river banks.
Springs are of two types :
i) Gravity spring : The gravity spring may result either from the out-cropping
of an impervious stratum below the water bearing formation or from the
overflow of water table by the continuous rise in the water table into the
sides of the valley.
ii) Artesian spring : It is one resulting from the water bearing stratum being under
pressure above and below by impervious strata. Water flows to surface through the
weaker spots in the upper impervious layer through some faults in the rock. The
yield of artesian spring is more uniform and almost constant throughout the year.
Wells : Well is a vertical cylindrical opening which extends from the surface of
the ground down into the water bearing formation. The water bearing formation is
called aquifer.
Classification :
a) Wells according to the aquifer tapped
(i) Shallow well (ii) Deep well
A shallow well is one which is constructed by tapping the upper most water bearing
stratum. If deeper and more extensive aquifers have to be tapped in order to get larger
and more reliable supplies of water, then it is called deep well. A shallow well may be
sometimes be deeper than a deep well. The distinction lies mainly how water is
tapped. But, from the practical point of view the depth of shallow well is generally
less than 30m in length and 3 to 9m in diameter. If the length is more than 30 m,
diameter is between 0.6 to 0.9 m or more it is termed as deep well.
Comparison :
(i) The quantity of water available from the well per unit time is uncertain, due
to the large variation in the ground water level throughout the year in case
of shallow well. But yield of a deep well is large and uniform since there
are no quick fluctuations in the water level.

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(ii) Quality of water from shallow well is poor since the upper most
underground stratum is tapped, the well water may be open to the risk of
contamination due to surface wash or close existence of septic tanks etc.
On the other hand, water from the deep well is more reliable since most of
the pollution is removed by longer travel of water and the straining action
provided by the intervening porous strata.
(b) Wells according to the condition of flow :
(i) Gravity well : A gravity well is one in which the surface of water in the
aquifer outside of and surrounding the well is at atmospheric pressure.
(ii) Pressure well : It is also called artesian well, the acquifer is confined or
sandwitched between two impervious strata one above or other below, so
that water flows under pressure into the well, which is greater than
atmospheric. In some cases the pressure is so high that the water flows from
the well automatically.
(c) Wells according to the type of construction
(i) Dug well : It is a shallow well having masonry walls and excavated from
the ground surface. Such wells are quite popular in small towns and rural
areas because of their relative cheapness and ease of construction.
(ii) Driven well : It is a shallow well constructed by driving a casing pipe 25-
100 mm dia, the lower end of which is closed and pointed forming a well
point.
(iii) Tube wells : A tube well is constructed by taking a boring into the ground
and driving with auger or bit by hand or machinery. Tube wells are suitable
both for deep as well as shallow wells. Their sizes ranages from 25-900 mm
in diameter.
Various methods used for construction tube wells –
(a) Percussion drilling
(b) Core drilling
(c) Rotary drilling

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Ground water recharging :
This is a term used to describe methods of recharging or increasing the capacity
of the well. As a new well is pumped, the fine sand grains in the vicinity of the
strainer will move towards it and pass through along with water in large amount so as
to form bridging over the strainer opening. This reduces the capacity of the well.
Developing is achieved by the following methods.
(i) Back water : Water is forced outwards from the well through the strainer
by air pressure. The material around the well is agitated, fine sand particles
around the strainer are subjected to rapid movement and drawn into the
well. These are later removed by pumping.
(ii) Surging : A plunger is raised and lowered in the well subjecting sand in the
neighbourhood to severe agitation. The down stroke forces water outwards
through the strainer. In this process the sand particles are carried in to the
well and later removed.
(iii) Gravel packing : Developing can also be done by placing gravel 13mm-
50mm in size around the strainers, there by enlarging the effective diameter
of the well, decreasing the velocity of flow of sand carrying water and
increasing the yield of the well. Such wells are called gravel packed well.
Well interference : Two or more wells are said to interfere with one another when
their circle of influence overlap.
The net effect of this interference is to reduce the yield of each well.
Causes :
1. Close spacing of wells
2. Heavy rate of pumping
Infiltration wells :
These are infact shallow wells with closed tops constructed along the banks of
rivers in sandy soil with the object of tapping water from them. Radial pipes having
strainers are placed horizontally from the interior of the well into the aquifer tapping
water from all directions.

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Infiltration Galleries :
These are wells constructed to a horizontal position along the river banks or
other seepage areas from where water can be tapped across the line of flow. These
wells which are generally located 15m or more from the river bank constructed in
open cut 7.5m to 9m below the ground level. The trench is carried below the
minimum level of the water table and a gallery or pipe with numerous small openings
are constructed. The openings are than back-filled with graded gravel to prevent the
entry of fine material into the gallery. It is a simple means of obtaining naturally
filtered water.
Intake Structures
The intakes or intake work comprise a structure placed in a surface water
source to permit the withdrawal of water from this source and then discharged into
an intake conduit through which it will flow to the water works system. Intake
consists of
(i) A conduit with protective works
(ii) Screens at open ends.
(iii) Gates and valves to regulate the flow.
Types of intake :
(i) Reservoir intakes
(ii) River intakes
(iii) Canal intakes
(i) Reservoir intakes : This intake is usually located either along the up-
stream toe or within the body of a masonry dam. There are a no of inlets
protected by screens and at different level, since water level fluctuates from
time to time. This enables to draw water from near the surface.

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(ii) River intake : When the intake structure is constructed along the banks of a
river to draw water it is called river intake.
Different types of river intake
(a) Cross weir intake
(b) Side weir intake
(c) Floating Pontoon intake
(d) Piled crib intake
(iii) Canal intake : Canal intake is comparatively a simpler arrangement
consisting of brick masonry chamber built partially in the canal bank. It has
side opening fitted with coarse screens which exclude heavier matter, silt
etc from entering the conduit. The entry of water in to the conduit is
controlled by gate valves which can be operated from the top.
For transportation of water two types of conduits are used :
(i) Gravity conduits
(ii) Pressure conduits.
(i) Gravity conduits : Gravity conduits are those in which water
surface is free and the water flows by gravity.
(ii) Pressure conduits : Pressure conduits are those in which water
flows under hydraulic pressure.
Pipe joints:
(i) Poured joints : In this joint common materials used are lead, cement,
sulphur and sand compounds.
(ii) Spigot and socket joint : This joint is commonly used in case of cast
iron pipes.
(iii) Flanged joint.
(iv) Mechanical joints.
(v) Joints for concrete and asbestos cement pipes.
(vi) Screwed and socketed joint.
(vii) Special joints.

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Pipe laying :
Steps to be followed :
(i) Preparing detailed maps of roads and streets.
(ii) Locating the proposed alignment on the ground.
(iii) Excavating trenches.
(iv) Bottoming up of the trench excavated
(v) Lowering of pipes into the trench.
(vi) Laying of pipes.
(vii) Jointing of pipes
(viii) Anchoring of pipes
(ix) Back filling.
Pumps and Pumping
Necessity of pumping :
(i) When the elevation of the source of water supply is such that the water will
not flow into the mains by gravity.
(ii) When it is required to increase or boost up pressure in the mains.
(iii) When water has to be lifted from one level to another.
Pump classification :
(i) According to the class of service
(a) Deep well pump
(b) Booster pump
(c) Pump for fire service
(d) Stand by pump
(ii) Pumps according to the form of motive power
(a) Electrically driven pump
(b) Diesel pump
(c) Gasolin engine

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(d) Steam engine
(iii) Pumps according to the mechanical principle of operation
(a) Displacement pump
Reciprocating pump
Single Acting Reciprocating pump Double acting reciprocating pump
(b) Centrifugal pump
(c) Airlift pump
(d) Rotary pump
Centrifugal pump : In this type of pump water entering into the pump casing is
revolved by a wheel called impeller which discharges it in a direction at right angle to
its original direction of flow.
Advantages :
(i) Low initial cost.
(ii) Simple mechanism, simple operation and repair.
(iii) Stability of flow.
(iv) Safe against high pressure.
(v) Adaptability to high heads.
(vi) Small space requirements.
(vii) Good durability.
Disadvantages :
(i) Limited suction lift (4.5m)
(ii) Absence of self priming arrangements.
(iii) Necessity of employing speed regulating gears for adjusting speed.
(iv) Low efficiency.
Priming of centrifugal pump :
Priming requires that all the air must be removed from the pump so that it is
completely filled up with water.

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Method of priming :
(i) Flooded suction i.e. Admitting water into the suction side of the pump until
all the air is displaced and the suction pipe and pumps are filled full.
(ii) Exhausting air from the suction pipe and pump by the use of vacuum pump
or ejector.
(iv)Pumps according to position of shaft
(a) Horizontal shaft pump
(b) Vertical shaft pump
(c) Well pumps
(i) Deep well turbine pumps
(ii) Submersible pumps.
2.3 : Quality of water
Impurities in water.
(i) Physical Impurities.
(ii) Chemical Impurities.
(iii) Bacteriological Impurities.
(i) Physical Impurities : Physical Impurities give taste, odours, colour and
turbidity. Taste and odour may be caused due to presence in water of
organic matter dissolved in it. Turbidity is caused due to the presence in
water of suspended and colloidal matter, while colour may be due to the
presence of mineralogical compounds such as iron-oxide etc. Physical
Impurities do not have direct relationship with health but produce many
indirect consequences. A turbid water may protect pathogens from the
effects of chlorination and it may contain mineral matters that irritate
stomach linning.

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(ii) Chemical Impurities: Chemical Impurities may be either organic or
inorganic
Impurities Causes Effects
A. Inorganic
Or
Mineral
(i) Suspended
(ii) Dissolved
Particles of silt and clay
Carbonates and bicarbonates of
Ca and Mg
Turbidity
Hardness and alkalinity
Sulphates and chlorides of Ca
and Mg
Hardness and corrosion
of boilers
Carbonates and bi-carbonates of
Na
Alkalinity and softness
Nitrates Causes blue babies
Chlorides of Na Salty taste
Fluorides of Na Excess causes teeth to
be stained.
Iron oxide Taste, colour, hardness
Maganese Taste and brown colour
B. Organic
(a) Suspended
(i) Vegetable
(ii) Animal
(b) Dissolved
(i) Vegetable
(ii) Animal
Decayed leaves, algae, fungi
etc.
Dead animals, hair, insects etc.
Large quantities of albuminoid
nitrogen with a little free
Ammonia and Chlorides
Large quantities of albuminoid
nitrogen with large quantities of
free ammonia and chlorides
Acidity, Taste and
change of colour, water
suspicious.
Bacteria,water
contaminated and
dangerous for health.
Bacteria, water
suspicious.
Disease producing
bacteria, pollution due
to sewage, water
dangerous.

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(iii) Bacteriological Impurities :
They are caused by the presence in water of Pathogenic or disease producing
type of bacteria, making water dangerous for human consumption and
health. From the public health point of view, therefore bacteriological
impurities are the most important.
Physical analysis :
(1) Turbidity : Turbidity is expressed by the amount of suspended matter present in
water parts per million (ppm) or mg/l as ascertained by optical observations. Turbidity
is determined by an instrument called turbidimeter. Common types of turbidimeters-
(i) Jackson Turbidimeter
(ii) Hellige Turbidimeter
(iii) Baylis Turbidimeter
The permissible turbidity for drinking water is between 5 to 10 mg/l
(2) Colour : Colour in water is harmless but objectionable on grounds of
appearance. The unit of colour is that produced by 1 Mg of platinum in a litre
of water. The maximum permissible colour for domestic water or drinking
water is 50 mg/l on Platinum cobalt scale.
(3) Taste and odour : Taste and odour are closely related. Taste may be sweet,
bitter and salty as well as irritating, hot and cold. For drinking water there
should be no objectionable taste and odour.
Chemical analysis : This involves tests for determination of total solids, hardness, pH
value, chlorides, residual chlorine, iron and manganese, fluorides, organic matter etc.
(1) Total solids : It is the sum of dissolved and suspended solids in water. Upto
500 mg/l is acceptable for domestic use.
(2) Hardness : Hardness in water is that characteristics which prevents the lathering
of soap. This is due to the presence in water of certain salts of calcium and magnesium
dissolved in it. If carbonates and bi-carbonates of calcium and magnesium are present
then it is called carbonate hardness, but if sulphates and chlorides of calcium and
magnesium are present then it is called non-carbonate hardness. Total hardness is the
sum of carbonate hardness and non-carbonate hardness. It is objectionable as apart

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wasteful consumption of soap, it modifies colour if used in dyeing work and also
produces boiler scale. Hardness is usually expressed in ppm or mg/l
Scale : 0 to 50 mg/l – Soft
50 to 100 mg/l – Moderately soft
100 to 150 mg/l – Slightly hard.
150 to 250 mg/l – Moderately hard
Over 250 mg/l – Hard
Upto 200 mg/l is acceptable for using domestic purpose.
Hardness may be determined by soap test and EDTA method. In EDTA
Method the total hardness is measured by titrating against –EDTA, so as to form
stable complex ions with the Ca++
and Mg++
ions in water.










 
Mg
EDTACaEDTA
Mg
Ca Complex
Hardness =
sampleofml
usedEDTAofml 1000
= mg/l Hardness
(3) Alkanity and Acidity : Alkalinity in natural water is due to the presence of salts
of weak acids. Acidity in natural water is due to the dissolution of carbon-dioxide in
water. Both acidity and alkalinity are measured on calcium carbonate scale. Alkanity
or acidity itself is not harmful to human beings. Drinking water with moderate
amounts of alkalinity or acidity can be consumed without adverse health effects.
Determination of acidity and alkalinity along with PH
value is helpful in controlling
the water treatment process. Determination of acidity is significant as it leads to
corrosion in pipes.
pH value or hydrogen ion concentration : It is a measure of acidity or alkalinity of
a substance. When a substance is dissolved in water, the solution ionizes, i.e. splits up
into electrically charged hydrogen ion (+H) and hydroxyl (-OH) ions. Acidity is

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caused if hydrogen ion is excess over hydroxyl ion and alkalinity is caused when
reverse takes place, i.e.
   )OHH 
  )( OHH 
In a neutral solution there number is equal
   OHH 
Mathematically PH
value is expressed as
PH
value = log 



H
I
For a neutral solution, PH
value is 7. The solution is acidic, if PH
value is less
than 7, the solution having PH
value 1 being strongest acidic. The solution is alkaline
if the PH
value is greater than 7. The solution having PH
value 14 becomes strongest
alkaline.
For drinking water PH
value should be 7 to 8.5
(4) Chlorides : Chlorides are usually present in water in the form of ‘NaCl’ which
gives a salty taste to water. Upto 200 mg/l of chlorides is acceptable in water.
(5) Sulphates : Sulphates is an important constituent of hardness with Ca and Mg. In
public water supply upto 400mg/l is acceptable.
(6) Residual Chlorine : It is the free chlorine remaining in water after about 15 to 30
mints of contact between the water and the chlorine dose. The residual chlorine may
be present in free form or combined form.
Total Residual chlorine = Combined residual Cl + free residual Cl.
The amount of total residual Cl in practice varies between a trace to 0.20mg/l
produced by an applied Cl-dose of 1 mg/l
(7) Iron and Manganese : These are normally occur together in water and are not so
objectionable if present less than 1.5 mg/l. When more, water may produce rust spots
on fabrics and plumbing fixtures.
(8) Organic matter : The organic matter in water is due to decaying vegetable or
plant matter and waste products of animals and human origin.
The organic waste of human origin may contain pathogenic germs and may cause
dangerous contamination.

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(9) Phosphorus : Higher concentration is indicative of pollution.
(10) Fluorides : Fluorides are normally considered beneficial in water when present
upto 1mg/l in water. But if it is more than 1.5mg/l, it causes a teeth related disease
called fluorosis.
(11) Heavy metals : Arsenic, Lead, Copper, Zinc, Cadmium , Mercury, Selenium,
Cyanide. These are toxic even at very low concentrations.
Bacteria in water :
Bacteria are minute single cell organism which are commonly found in natural
water.
Classification
According to shape :
(a) Cocci (b) Bacilli (c) Spirilla (d) Tricho bacteria.
According to the way they live :
(a) Saprophytes - which live on dead or decaying organic matter, they are
harmless.
(b) Parasites - which live in the bodies of humans and animals.
According to the manner of deriving oxygen :
(a) Aerobic – Which live on the free oxygen.
(b) Anaerobic – Which live in the absence of free oxygen.
(c) Facultative bacteria - which live either with or without oxygen.
Resistance type bacteria : Which developed under unfavourable conditions, are not
easily destroyed, called spores.
Bacteriological analysis : This analysis is done primarily to determine the potability
of drinking water. As many diseases of intestinal origin such as typhoid, dysentery etc.
have been known to be transmitted to human through polluted water, the
bacteriological analysis helps to indicate the degree of pollution in water. It involves
two tests.
(a) Total count of bacteria also called standard plate count. It provides an
estimate of the total no of bacteria in a water sample which will grow and

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develop in a particular culture medium at a temperature 370
C for a period of
24 hours under laboratory condition.
(b) E-coli Test : It includes three tests
(i) Presumptive test.
(ii) Confirmed test.
(iii) Completed test.
Coliform index : The coliform index is a measure of the concentration of coliform
organisms or E-coli in a water sample.
MPN is defined as that bacterial density which if it had been actually present in the
sample under examination would more frequently than any other have given the
observed analytical results.
2.4 : Purification of Water
Object : (a) Removal of all pathogenic germs contained in untreated water.
(b) Freedom from unpleasant taste and odour.
(c) Freedom from objectionable colour and having good appearance.
(d) Suitability for domestic purposes such as cooking, washing and industrial
purposes.
(e) Reduction of corrosive and tuberculating properties of water.
Methods :
1. Methods for the removal of suspended impurities i.e. plain sedimentation and
filtration.
2. Methods for the removal of dissolved impurities. i.e. sedimentation with
coagulation, filtration, aeration.
Sedimentation : This is the process of causing heavier solid particles in suspension
both organic and inorganic to settle by retaining water in a basin. When the process is

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carried without taking help of any chemicals it is called plain sedimentation and when
it is done with chemicals that is coagulants, it is called sedimentation with
coagulation.
Plain sedimentation : Many of the impurities suspended in water have specific
gravity greater than one and are held in suspension by virtue of the turbulence or
currents maintain in the water. When these currents are retarded the suspended matter
generally settles to the bottom of the body of water. This is the principle involved in
sedimentation process.
Detention period : The detention period of settling basin is the theoretical time, water
is detained in it. Sedimentation Basin are generally designed for a detention period of
3 to 4 hours.
Sedimentation with coagulation : The removal of very fine and light colloidal
impurities from water such as clay particles, gels, emulsions is difficult to achieve in
practice by the process of plain sedimentation. This can be easily done by the addition
to water certain chemical compound which when thoroughly mixed form wooly
masses of flocculate precipitate become heavier and finally settle out. This substances
are called coagulants and process is called coagulation.
Common types of coagulants are
[Al2(So4)3], Fe So4, Lime etc.
Dosages of coagulants per litre of water varies from 0.3 to 0.13 gm or may be
more in practice.
Jar test is the laboratory method to determine the dosage of coagulant.

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Mixing Basin : Tanks in which water and coagulant are mixed together called Mixing
Basin.
There are two types :
(i) Baffle type (ii) Mechanically agitated type.
Sedimentation tank or clarifier : In a sedimentation tank also called settling tank or
clarifier, the operation involved is either to detain unflocculated water containing
heavier and suspended impurities and thereby caused them to settle out or to let the
flocculated water flow in from the mixing basin and allow the flocculent precipitate to
settle out of suspension.
Filtration : Filtration in its commonest form consist in allowing water to pass through
a thick layer of sand or other filtering media. It is observed that by doing so, the
suspended and colloidal matter in water are removed, the chemical characteristics of
water are changed and the number of bacteria are also reduced.
There are three types of filter.
1. Slow sand filter
2. Rapid sand filter
3. Pressure filter
1. Slow sand filter : It consist of a water tight tank 2.5-3.5 m in depth having a
sand bed of 0.6-0.9m thick supported on a bed of gravel 0.3-0.45m thick laid in
5-6 layers of gravel with different sizes below which the under drainage system
is laid over a concrete bed sloping towards a central longitudinal drain. The
under drainage system consist of open jointed drains of baked clay or concrete
pipe in length of 30 to 40 cm with a maximum spacing of lateral of 2m. The
raw water is led gently on the filter bed and percolating downwards passes
through the underdrains into an outlet chamber.
2. Rapid sand filter : It consists of an open water tight tank 3-3.5, deep of
masonary or concrete with a concrete floor, having coarse sand 0.6 to 0.7 m
thick laid on the top with a layer of graded gravel 0.45 m thick supporting
below. The gravel is underlain by an under drainage system consisting of a cast

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iron central longitudinal conduit or manifold with strainers mounted on top and
pipes of smaller diameter called laterals branching off at right angles to the
manifold. The laterals are fixed 15 to 20 cm centres and carry perforations on
sides and bottom. About 1.7 to 2.5m water depth may be allowed on the filter
bed.
Comparison between Slow Sand Filter & Rapid Sand Filter
Sl.
No.
Characteristics SSF RSF
1
2
3
4
5
6
7
8
9
Area
Size of sand
Rate of filtration
Loss of head
Supervision
Coagulation
Method of
cleaning
Period of cleaning
Efficiency
Requires more area
Sand grains are finer. Size
lies between 0.3 to 0.35 mm.
Uniformity co-efficient is 2
Low, 100 to 200 litres per
meter square per hour
It is very small, only 0.6 to
0.9m
Simple to operate, does not
require skill operators
Does not require coagulation
Washing is done by scraping
a thin layer of sand from the
surface
Once every 2-3 mouths
Removes bacteria almost
completely, because the rate
Requires less area
Sand grains are slightly
coarser, effective size 0.35
to 0.5 mm. Uniformity co-
efficient is 1.6
High, 2000 to 6000 litres
per meter square per hour
It is more 2.5-3m.
Requires skilled operators
Requires coagulation
Washing is done by
reversing the flow of
water with the help of
compressed air and a high
pressure of wash water. It
is done within 15-30
minutes.
Every 24 to 48 hours.
Removes bacteria
partially. It is efficient in

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10
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Operating cost
Maintenance
of filtration is slow
Operating cost per 1000 litres
of water is less
It is very small
the removal of colour
Operating cost is more
It is more, because of
maintenance of pumps for
pumping up wash water
and a compressor unit for
obtaining compressed air
3. Pressure filter :
A pressure filter is a rapid gravity sand filter enclosed in an air tight cylindrical
steel container. The sand bed is 45-90cm thick and lies upon graded layers at the base
of which are perforated connecting pipes for collecting the filtered water.
The water admitted into the filter is coagulated, it then passes through sand and
gravel and finally emerges at a pressure usually sufficient to allow distribution without
additional pumping.
Because the cylindrical shell is airtight it is possible for water to pass through
the filter and emerge at a pressure greater than atmospheric. The rate of filtration is
high, 100 to 250 litres/m2
/mint. Pressure filters are commonly used on relatively small
public supply, swimming pool water. So far the quality of water is concerned, results
are less satisfactory than those obtained from rapid gravity sand filter.
Disinfection of Water : The treatment of water with chemicals to kill bacteria is
termed disinfection of water.
Methods : Chlorination – It is the application to water small quantities of chlorine or
chlorine compounds. The dose applied is generally less than 1mg/L so as to produce
residual chlorine of quantity varying from a trace to 0.05 and upto 0.2 mg/l
The amount of chlorine so required to be added depends upon the chlorine
demand of water, which is the difference between the amount of chlorine added and
the amount of chlorine remaining at the end of a contact period of 10-20 min. Chlorine
may be applied by the following methods.

24
1. As dry chlorine gas
2. As chlorine solution
3. In powder form as bleaching powder
 2)(OClCa
Or
Sodium Hypochlorite (Na OCl).
Special Methods :
1. Prechlorination
2. Double chlorination
3. Super Chlorination
4. Break Point Chlorination : It is also termed as free residual chlorination
involves the addition of sufficient chlorine so as to oxidize all the organic
matter, reducing substances and free ammonia in raw water leaving behind
mainly free available chlorine which possesses strong disinfecting action
against pathogens.
Stage A : Destruction of Cl by reducing compounds
Stage B : Formation chloro-organic compounds and chloramines.
Stage C : Destruction of chloro-organic compounds and chloramines.
Stage D : Formation of free available chlorine. The addition of chlorine at the break
or dip is termed as break point chlorination.
This indicates the point at which free residual chlorine begin to appear.

25
Other methods of Disinfection :
(a) Ozonization method
(b) Ulrta-violet ray method
(c) Excess lime method
(d) Silver
(e) Iodine and bromine
(f) Potassium Permanganate
Special Methods :
Aeration : This is the process of bringing water into intimate contact with air with the
object of driving out objectionable dissolved gases and oxidizing other soluble
compounds present in the ground waters or in stagnant waters of pools and reservoirs.
Aeration is effected in many ways :
(i) By causing water to flow over weirs and water falls called cascade aerators.
(ii) By droping water through perforated plates.
(iii) By forcing it through spray nozzels.
(iv) By filtering through perforated trays, coke beds.
(v) Through special devices.
The spray nozzle is the most effective aerator. Aeration is effective in removing
75% of odours. Removal of carbon dioxide is equally high.
Miscellaneous water treatment methods :
Water softening Process :
There are 3 methods used for water softening :
1. Lime process : Lime process reduces only carbonate hardness.
This process is known as clark process.
2. Lime and soda ash process : Lime has no effect on sulphates of Ca and Mg,
which are responsible for causing most of the non-carbonate hardness.
However by the use of Soda Ash the non carbonate hardness can be removed.
3. Base exchange process : In this process, hard water is passed through a bed of
Zeolite sand where by it exchanges Ca and Mg for the Sodium (Na) in the
Zeolite until Na becomes exhausted. The sodium is then re-stored by
regenerating the zeolite with a solution of common salt.

26
4. Defluoridation Techniques : Defluoridation is defined as, „the downward
adjustment of level of fluoride in drinking water to the optimal level.
2.5 : Conveyance and Distribution of Water :
There are three types :
1. Gravity system : A gravity system is adopted where the source of supply is
such as a lake or an impounding reservoir is at a sufficient elevation with
respect to the city in order to produce adequate pressure for distribution. This
method is the safest and most reliable.
2. System with direct pumping : In this method water is directly pumped into
the mains. Consumption is the only outlet. This method is not reliable, a failure
in the power supply means break down of the system.
3. System with pumping and storage : This is also called the direct-indirect or
dual system. In this system, when the demand rate exceeds the rate of pumping,
the flow into the distribution system is both from pumping system as well as
elevated reservoir.
Methods of Supply :
1. Continuous supply : When water flows to the consumer 24 hours.
2. Intermittent supply : Water comes to the consumer from time to time in a day.
A continuous method of supply is always better than the intermittent supply.
1. When the supply of water is only for a few fixed hours of the day, consumers
are compelled to store water for use during the non supply hours. The domestic
storage tank may suffer for want of proper maintenance for a longtime,
resulting in a possible contamination.
2. The unused water of storage tank is most likely to be thrown out to be replaced,
during the supply hours by fresh supply of water, This is a wasteful use of
water.
3. In case of fire breaks out during non supply hours, considerable damage may
result.

27
4. During the non-supply hours pressure in the distribution mains may fall below
atmospheric causing partial vacuum, sucking polluted air and harmful gases
from seweres running close to the pipes which may result in contamination.
Classification of reservoir :
1. Balancing and equalizing tank
2. Elevated reservoirs
a. Stand pipe
b. Elevated tank
The Pipe system : Layout of distribution system-
1. Dead end system
2. Grid Iron system
3. Circle or ring system
4. Radial system

28
Advantages and Disadvantages :
1. Dead End System : It is suitable for old towns and cities having no definite
pattern of roads. Disadvantages. Due to many dead ends, stagnation of water
occurs in pipes.
2. Grid Iron System : It is suitable for cities with rectangular layout, where the
water mains and branches are laid in rectangles. Advantages: Water is kept in
good circulation due to the absence of dead ends.
3. Circle or ring system : The supply main is laid all along the peripheral roads
and sub mains branch out from the mains. Thus, this system also follows
the grid iron system with the flow pattern similar in character
to that of dead end system. So, determination of the size
of pipes is easy. Water can be supplied to any point from at least two
directions.
1. Radial system : The area is divided into different zones. The water is pumped
into the distribution reservoir kept in the middle of each zone and the supply
pipes are laid radially ending towards the periphery. It gives quick service and
calculation of pipe sizes is easy.
Appurtenances in the distribution system :
1. Sluice valves or shut off valves
2. Check valves
3. Air valves
4. Drains valves
5. Hydrants
6. Water Meters
3 : Domestic Sewage
3.1 : Introduction
Importance and necessity of sanitation, necessity to treat domestic sewage.
Sanitation is the prevention of sporadic outbreak of diseases dangerous for the
general health of public. This can be achieved by either controlling or eliminating

29
such environmental factors as contribute in some form or the other to the transmission
of the diseases.
Recycling and reuse of domestic waste : Recycling involves the collection of used
and discarded materials processing these materials and making them into new
products. It reduces the amount of waste that is thrown into the community dustbins
thereby making the environment cleaner and the air more fresh to breathe.
Sewage : Sewage may be defined as the used water or liquid waste of a community
which includes human and house hold wastes together with street washings, industrial
wastes and such ground and storm water as may be mixed with it.
Sewer : It is an underground conduit used for the removal of sewage.
Sewerage It is the general process of removing sewage. The entire system of conduits
and appurtenances involved is called sewerage system or sewer system.
Sullage : The waste water from kitchens and bath rooms etc are called sullage.
3.2 : Buildings Sanitation
Principles Governing design of water supply to buildings
There should be absolutely no risk involved in the contamination of supply for
domestic purposes. For this following 3 things to be taken into consideration
1. (a) There should not be any cross connection between pipe containing drinking
water and a pipe containing polluted water.
(b) There should be no back flow from any cistern or appliances towards the
source of supply.
(c) The water supply and drainage supply should not be laid very close to each
other.
2. The pipe and fittings should be throughly water tighted in order to the protect the
building against possible damage due to leakage.
3. The pipe work should be protected against any possible drainage.
4. Water supply pipe should carry inside building under adequate pressure in the water
main.

30
TRAPS
Trap is a fittings constructed with a water seal show that when place in a drainage pipe
it prevents the passes of foul gasses through the drainage pipe.
Classification of traps:
According to shape:
1. P- trap
2. Q - Trap
3. S- Trap
According to their particular use
(i) Floor traps
(ii) Gully traps : These are used for the reception of sullage
From bathrooms and wash basins as well as rain water from house tops or
back yards
(iii) Intercepting traps : This are used at the junction of the house drain and
house sewer with the primary object of preventing the foul gasses in the
public sewer from entering the house drainage system.
Soil Pipe (SP) : It is pipe through which liquid waste carrying human excreta can
flow.
Waste pipe (SP) : It carries liquid waste that don’t include human excreta.
Vent pipe (VP) : It is a pipe line install to provide flow of air to or from a drainage
system in order to protect the water seal or traps against syphonage or back pressure.
1. Ventilating pipe: It enables the foul gasses of sewer to safely discharge into
the atmosphere.
Water Closet : It may be defined as a water flushed plumbing fixture designed to
receive human excreta directly from the user.

31
There are two types:
1. Squatting or Indian type 2. Pedestrian or European type.
Plumbing system of drainage :
There are 3 system (i) Single stack system- In this system waste matter from
bathroom, kitchen and sink as well as foul matter or night soil from water process are
discharge into a single pipe are called soil pipe which also acts as ventilation pipe.
(ii) One pipe system : In this system a separate vent pipe is added or all the
traps of e.c., basin, bathroom etc are connected to this vent pipe.
(iii) Two pipe system : In this syotem water crosset… and urinals are connected
to a vertical soil pipe where as all waste appliances i,e bathroom wash
basin, sink etc are connected to another set of pipe called waste pipe
therefore two sets of vertical pipe the soil pipe, waste pipe its having
separate vent pipe.
3.3 : System of Sewerage :
Methods of collection of sewage :
(i) Dry or conservancy system
(ii) The water carriage or water borne system
Dry System
It is the earlier method and even now it is going on in unsewered areas. It
consists in the accumulation of night soil or human excreta collected in latrines and its
subsequent removal manually and transportation in vehicles to the points of ultimate
disposal.

32
Water carriage/ borne system
In this system, the night soil gets mixed up with sufficient quantity of waste water
forming sewage and is collected in a system of pipes and transported for subsequent
treatment and disposal in a harmless manner without any nuisance.
Comparison:
The dry system has a no. of disadvantages :
(a) Unhygienic aspect involved in the manual removal of human excreta.
(b) Nuisance due to bad smell resulting from decomposition of the accumulated
night soil.
(c) Insanitation caused by the transportation of night soil through streets or other
crowded localities.
(d) Risk of epidemics due to improper or careless disposal of night soil.
(e) Uneconomical from financial point of view being very slow and dependent
upon manual labour at various stages.
Water carriage/borne system has the following advantages :
(a) The removal of sewage in covered conduits is an efficient method without any
nuisance value. It ensures hygienic condition, better health and well-being of
the sewered community.
(b) Risk of out break of epidemics is reduced to the minimum.
(c) The properly treated sewage results in an economical saving because of the
manifold ways to dispose of the final products.
The main disadvantage of the water borne system is its high initial cost of pipes
and other sewer appurtenanees and maintenance cost. But, because of the hygienic
aspects, this system is widely used.
Types of sewers/pipes
(i) Sanitary sewer
(ii) Separate sewer
(iii) Combined sewer
(iv) House sewer

33
(v) Lateral sewer
(vi) Sub-main sewer
(vii) Main sewer
(viii) Intercepting sewer
(ix) Outfall sewer
Classification of sewerage system :
(i) Combined system :
In a combined system, the same sewer is used to carry both the domestic
sewage, industrial wastes as well as the surface and the storm water flow.
(ii) Separate system :
In a separate system, the domestic sewage and industrial wastes are carried
in one set of sewers whereas, the storm and surface waters are carried in
another set of sewers.
(iii) Partially separate system :
It is a modification of the separate system in which the separate sewer
discharging domestic and industrial wastes also contains a portion of
surface water drained from back paved yards and roofs of houses.
Situations for adoption :
A separate system will be suitable for use under the following situations :
(i) When rainfall is uneven.
(ii) Sanitary sewage is to have one outlet and other outlets for storm or surface
water are available.
(iii) Sanitary sewage is to be pumped
(iv) Separate sewer must be placed deeper and the storm water drains nearer the
surface to economize excavation.
(v) The drainage area is steep, water to run off quickly.
(vi) Sewers are to be constructed in rocky strata. The larger combined sewers
would then be more expensive.

34
(vii) Finance available are small.
Combined system will be useful under the following circumstances :
(i) Where rainfall is even throughout the year.
(ii) Both the sanitary sewage and storm water has to be pumped.
(iii) The area to be sewered is heavily built-up and space for laying pipes is not
enough.
(iv) Effective or quicker flows have to be provided.
Considering all the advantages or disadvantages of combined as well as separate
system, for Indian conditions partially separate system is always preferable. The
advantages offered by partially combined system are -
(i) It simplifies the drainage of the houses.
(ii) It provides reasonable sizes of sewers and is economical.
(iii) The rain water provides some safeguard against silting in sewers.
Disadvantages :
(i) Low velocity during the dry period.
(ii) Storm overflows may be found necessary.
Underground drainage and sewerage
Dry weather flow (DWF)
DWF is the total average discharge of sanitary sewage and is the normal flow
in a sewer during the dry weather.
It is expressed in liters per capita per day.
It depends upon the following factors :
(i) Population
(ii) Type of area served
(iii) Rate of water supply
(iv) Ground water infiltration.

35
Forms of sewers:
(i) Circular sewer
(ii) Non-circular sewer
(a) Egg shaped sewer
(b) Semi-elliptical sewer
(c) Rectangular sewer
Velocity in sewers:
(i) In general, a mean velocity of 0.3m/sec is sufficient to prevent deposition of
sewage solid.
(ii) Minimum velocity : A minimum velocity of 0.6m/sec should be maintained
in case of separate sewers and permissible upto 0.9m/sec which is very
acceptable.
In case of combined sewer, the velocity should not be less than 0.75 m/sec
(iii) Maximum velocity : The maximum velocity is limited to about 3m/sec and
it should be preferably maximum 2.25 m/sec
(iv) Self cleansing velocity : The minimum velocity at which no solids get
deposited in the invert of the sewer is called self cleansing velocity.
Ventilation of sewers :
Sewers are ventilated for the following purposes :
(i) To prevent the accumulation of explosive, corrosive or poisonous gases or
vapours such as CH4, H2S, petrol vapour etc.
(ii) To prevent concentration of unpleasant odours causing nuisance.
(iii) To relieve air pressures above or below atmospheric caused by sudden rise
or fall of sewage. This is done to permit free flow of sewage. Ventilation is
done by the following methods -
(i) Ventilation columns
(ii) Manhole covers
(iii) Exhaust fans
(iv) House vent and soil pipes.

36
Sewer materials:
(i) Salt glazed stoneware pipes.
(ii) Cast Iron pipes.
(iii) Cement Concrete pipes.
(iv) Asbestos Cement pipes.
Construction of sewer:
Steps :
1. Setting out
2. Alignment and gradient
3. Excavation of trenches
4. Laying and joining of pipes
5. Timbering of trenches
6. Dewatering of trenches
7. Testing of pipe
8. Back filling
3.4 : Sewer Appurtenances:
Manholes : These are openings constructed on lines of sewer or drains in order to
enable man to enter or leave the sewer. The objects are inspection, cleaning and other
maintenance operation in connection with sewers. The man holes are fitted with a
cover called Manhole cover. Man holes are provided at every change of alignment,
gradient, or diameter of sewer, at junction of sewers and at street intersections. The
maximum distance between manholes varies from 45-90 meter. Sewers are laid in
straight between manholes called sewer reach.
Components parts :
(i) Manhole cover resting on a heavy frame
(ii) Access shaft
(iii) Working chamber

37
The manhole cover and frame are made of cast iron may be of light, medium and
heavy types. The size of the opening should be such as to allow a man go inside and
come out easily. Generally 50-55cm diameter is maintained. The access shaft provides
an access to the working chamber below. The working chamber provides a working
space for man to stand inside and carry out the requisite work of cleaning or
inspection. It is constructed in brick masonry and is either rectangular or circular in
plan. Minimum diameter should be 1.2m for circular and 0.9-1.2m for rectangular
type. The man hole is built on a concrete bed 15cm to 30cm thick with a slope 1 in 6
towards the centre.
Drop Manhole : Where the inlet and outlet pipe sewers have to be connected at
different levels and where it is desired to drop the levels of invert of the incoming
sewer 0.9m or above that of the man hole, the connection is made by constructing a
vertical pipe outside the manhole.
This is done to avoid chances of sewage splashing on a man working inside the
manhole Chamber.
Lamp hole : These are openings usually of small size, made on lines of sewer to
permit the insertion of a lamp into the sewer with the object of viewing the lamp light
from the adjacent manhole up stream and downstream and detecting any obstruction
inside the sewers.
Street inlets : It is an opening in the gutter or street kerb in order to intercept the
storm water or surface wash and convey it into a storm or combineed sewer. Inlets are
located usually at street intersections near low places so as not to flood the cross walks
or cause interference to the traffic.
There are two types of inlets :
(i) Kerb inlets : When fixed vertically
(ii) Gutter inlets : When fixed horizontally.
Catch basin : A catch basin is an inlet which allows grit, sand or debris to settle out
and are thus prevented from entering into the sewer.
Flushing Tanks : These are devices to hold water used in flushing sewers. These
prevent clogging in sewers and permit the adoption of flatter grades than is otherwise
permissible. The location should be at the dead end or at head of the sewers.

38
3.5 : Analysis of Sewage :
Characteristics of sewage:
(i) Physical (ii) Chemical (iii) Bacteriological
(i) Physical characteristics are odour, colour, turbidity and temperature. Fresh
sewage is odourless, has an earthy or grey colour. In 3-4 hours it becomes
stale with all the oxygen present in the sewage being practically exhausted.
It then starts emitting offensive odour and the colour becomes dark. When
all the oxygen has disappeared, the sewage becomes septic.
(ii) Chemical characteristics indicates the state of sewage decomposition, its
strength and type of treatment required. Fresh sewage is alkaline and good
for bacterial action. Stale or septic sewage is acidic and difficult to be
efficiently treated. An average sewage contains around 1000 mg/l in
solution and suspension and this is about 99.9% of pure water. This means
sewage contains about 0.1% solid matter by weight. Solids present may be
in any of the four forms- suspended, dissolved, colloidal and settleable.
Besides solids and liquids, sewage also contains gasses obtained from
atmosphere and due to the action of bacteria on compounds in solution and
suspension. These gasses are mostly H2S, CO2 and CH4
Bacteriological : These are due to the presence in sewage of micro organisms which
include bacteria, fungi, algae, protozoa, rotifers etc.
Decomposition of Sewage : Fresh sewage usually contains some dissolved oxygen2-
5 mg/l. The organic matter present in the sewage is therefore, acted upon by the
aerobic and facultative bacteria. The available oxygen is soon used up, whereupon, the
anaerobic and facultative bacteria are brought into action. They split up the complex
organic compounds. Gasses like CO2, NH3, CH4 are also given off. This process is
termed as putrefaction and is the 1st
step of decomposition of sewage. The liberated
elements Nitrogen, Carbon and Sulphur are soon acted upon by the aerobic bacteria,
transforming them into stable and un-objectionable compounds of nitrates,

39
carbohydrates and sulphates, thus completing the second step of decomposition which
is termed as oxidation.
On putrefaction, alone are based on the following units of sewage treatment :
(i) Septic tank
(ii) Imhoff tank
(iii) Sludge digestion tank
Based on oxidation following units of treatments are used –
(i) Trickling filter
(ii) Diffused air system
(iii) Mechanical aeration.
Cycles of decomposition :
Nitrogen cycle
(i) Putrefactive stage sets in on the death of plants and animals.
(ii) Nitrification stage is brought about through the agency of the aerobic
bacteria by the oxidation of the ammonia in sewage to first as nitrites and
then nitrates.
(iii) Plant life : The nitrates are taken up by the plant roots and converted into
plant protein.
(iv) Animal life : It is the highest stage of cycle in which vegetable proteins and
carbohydrates form part of living animal substance. On the death of animal
the cycle is repeated.
Analysis of sewage :
Object of analysis :
(i) To ascertain various substances present in the sewage.
(ii) To determine their physical, chemical and biological characteristics in order
to know the type and degree of treatment required.
(iii) To obtain such information and the result as are necessary for the operation
and maintenance for the sewage treatment works.
Physical analysis : This includes test for temperature, turbidity, colour and odour.

40
Chemical analysis :
(i) Tests for determine total solids.
(ii) Tests for oxygen consumed, dissolved oxygen, bio-chemical oxygen
demand.
(iii) Tests for Nitrogen-albuminoid and free ammonia, Nitrite and Nitrate.
(iv) Tests for pH value
(v) Tests for chlorides and residual chlorine.
(vi) Tests for fats and grease.
Oxygen consumed : This is the Oxygen taken up in the oxidation of the readily
oxidizable carbonaceous matter. It involves chemical digestion using boiling
potassium dichromate and concentrated sulphuric acid and as such is termed as
Chemical Oxygen Demand (COD).
Dissolved oxygen : This is the amount of oxygen dissolved in a sewage.
Biochemical oxygen demand :
It is the amount of oxygen required for the biological decomposition of organic
matter under aerobic conditions. This test is most important in sewage analysis as it
indicates the amount of decomposible organic matter in the sewage, the larger the
concentration, greater the bio-chemical oxygen demand and consequently more of the
nuisance potential or strength of sewage. This test enables to determine the degree of
pollution in a stream at any time.
The test for BOD are usually made at a temperature 200
C and for a period of 5
days. 200
C is more or less mediun value as per as natural bodies of water are
concerned, while 5 days period is sufficient to satisfy 70-80% of the total BOD in case
of domestic and industrial wastes.
COD :

41
3.6 : Treatment of Sewage
Sewage Treatment Methods :
(i) Preliminary Process
(ii) Settlement Process
(iii) Biological Process
1. Preliminary Process: It is carried out by (1) Screens (2) Grit Chamber (3)
Skimming tanks and grease traps.
Objects of Screens:
(i) To Prevent the formation of unsightly sucms in settling and aeration tank
(ii) To prevent Clogging of sprinkler nozzles or the surface of trickling filter.
(iii) To protect pumping parts of different machineries from damage
(iv) To prevent formation of sludge banks or unsightly floating matter in the
receiving bodies of water.
Grit chamber: Grit chambers are long narrow tanks that are designed to slow
down the flow so that solids such as sand, coffee grounds, and eggshells will settle
out of the water.
Skimming Tanks : It is a chamber show arranged that the floating matter like oil,
fat, grease etc. rise and remain on the surface of the waste water until removed, while
liquid flows out continuously under partitions or baffles.
Grease Traps : A grease traps is a plumbing device designed to intercept most
greases and solids before they enter wastewater disposal system.
Settlement Process:
Comprises of following units of treatments
(i) Septic tank
(ii) Imhoff tank
(iii) Sludge digestion tank
2. Septic tank: It is a horizontal continuous flow sedimentation tank in which
sewage moves very slowly so as to retain it for a period sufficient to permit 60-
70% of suspended matter to settle down in form of sludge at the bottom of the
tank.

42
3. Sludge digestion tank: It is a R.C.C. tank of cylindrical shape with hopper
bottom and is covered with a floating type of roof. The Maw sludge is pump
into the tank where it is seeded with digested sludge. The digested sludge
which settle down to the bottom of the tank is removed under hydrostatic
pressure.
Sludge disposal Method:
(i) Burial or dumping into the sea
(ii) Shallow Burial into the ground
(iii) Mechanical dewatering of sludge
(iv) Drying on beds
Sludge drying Bed:
This is the most important method of sludge disposal. The wet sludge
from the digestion tank is run into specially prepared sand beds on which it
dries in the openly part of water evaporates and remaining percolates through
the sand to the under drains and return to the primary tank for treatment. A
sludge drying bed is made up of 15-30cm of coarse sand underlain by 7.5 cm
fine sand, 22.5cm of graded gravel at the top open jointed drain 10 cm diametre
laid in coarse gravel are provided at interval of abolet 3-6m. The side wall is
projected 1.6m above the sand surface. The Top of the beds generally kept
open or if necessary may be covered.
Biological process:
The biological process of sewage is secondary treatment involving
removing, stabilizing and rendering harmless very fine suspended matters,
colloids and dissolved solid of sewage that issue from the sedimentation tank
where most of the matter in suspension has been removed.

43
Sewage filters:
The sewage filters used to accomplish this action are
(i) Intermittent sand filter
(ii) The contact beds
(iii) Percolating or Trickling filter
Trickling filter: It is also called percolating filter which is similar to contact
beds in construction but allow constant aeration and the action is continuous. A
trickling filter consists of a bed of crushed stone or other material like granite, lime
stone etc 25 to 75 cm in size with a filter depth 2-3m. The longer stone 8-10cm in size
are placed in a layer of 15-20 cm thick at the bottom of the bed while the smaller size
stone make up the filter bed. Inside wall of brick masonry may be honey combed and
provide with air inlets which provide oxygen circulation. The sewage from sediment
ion tank is applied either intermittently through fixed sprays on continuously through
rotary distributor. The floor of trickling filter is made of concrete laid to a slope 1 in
200 with an under drainage system. The underdrainage system keeps the filter self
cleansing and also assist in the ventilation of beds.

44
Merits and demerits:
Advantages:
(i) They are self cleansing and rate of filter loading is much higher.
(ii) No diminishing capacity
(iii) They are cheap and simple in operation
(iv) Mechanical wear and tear is very small
Dis-advantages:
(i) High head loss
(ii) Cdour and fly nuisance
(iii) Harge area is required i,e cost of construction is relatively higher.
(iv) Their required preliminary treatment and therefore cannot treat row sewage.
Recirculation : Recirculation is sewage is and important feature of high rate filter.
This consists in pumping back part of the filter effluent to the primary settling tank
and thus letting the flow again pass through it and filter as a single stahe
recirculation process.
Activated sludge process: Activated sludge is defined as the sludge settle out of
sewage previously agitated in the prence of abundant oxugen. Activated sludge
process is an operation where by a portion of the activated sludge from secondary
clarifier is returned to be added to the effluent from primary clarifier which is
subsequently arerated and from which the activated sludge is removed in the
secondary clarifier in which both aerobic and an aerobic action takes place.

45
Oxidation Pond
Oxidation pond can successfully treat either raw sewage or the settled sewage.
Oxidation pond are suitable in case of small cities where land area are easily and
cheaply available. Main-advantage are-low cost, quickness of construction, easy
maintenance and high efficiency of BOD removal. Only disadvantage are-nuisance
due to mosteque breeding and odours.
It is also called stabilization pond is an artificial pond in which sewage can be
retained for a sufficient time to satisfy bio-chemical oxygen demand (BOD) and
thereby make the sewage non putresible. The purifying action is an oxidation pond
can be explained because of a unique relationship between bacteria and algae in
shallow pond. The bacteria metabolize organic matter releasing neutrients like
nitrogen, P, Co2. Algae uses this compound along with energy sunlight for synthesis
releasing oxygen into solution. Oxygen released by algae is taken up by bacteria. Thus
closing the cycle. This relationship between bacteria and algae is called symbiosis.
Because of the shallow depth less than generally 2m the oxidation pond acts as
facultative pond.
Oxidation Ditch : It is a modified activated sludge biological treatment process that
uses long solids retention time to remove biodegradable organic. The typical oxidation
ditch is equipped with aeration rotors or brushes that provide aeration and circulation.
Sewage disposal
Object:
1. To render sewage inoffensive without causing nuisance or odour.
2. To reduce or eliminate the danger to the public health by possible contamination of
water supplies etc, in case sewage is improperly treated.
3. To prevent the destruction of fish or other aquatic life by letting raw or untreated
sewage discharge into the bodies of water.

46
Sewage disposal Methods :
1. Dilution or disposal of sewage in water
2. Irrigation or disposal of sewage on land.
(a) Broad irrigation or sewage farming
(b) Sub-surface irrigation or land infiltration
Disposal by dilution:
It is the process where by treated sewage or the effluent from treatment plants
is discharged into the bodies of water or water courses.
Conditions for dilution :
1. Where sewage is completely fresh.
2. Where sewage has been mostly removed of the floating and settelable solids
3. Where it is possible to throughly mixed or diffused sewage through diluting
water
4. Where diluting water high in dissolved oxygen content is available.
5. Where currents are favourable causing no deposition, nuisance or destruction
of aquatic life.
Oxygen sag :
As sewage is discharged into a body of water, there is at first a depletion of the
dissolved oxygen of the diluting water in order to meet the biological
requirement of the organic sewage. This is termed as oxygen sag.
Disposal by irrigation:
1. Broad irrigation : In this process sewage is caused to flow over cultivated
lands from which a part of the sewage evaporates and through which the
remainder percolates ultimately to escape into surface drainage channels.
As sewage waters the land and adds to its fertilizing value, because of the
presence in it of nitrogen, phosphate, potash etc. crops like cotton, sugar-
cane, potatoes etc. can be profitably grown. This is called sewage farming.

47
Sewage Application Methods
i) Flooding: In this methods sewage is distributed over a ploughed
and level area enclosed by dykes.
ii) Surface irrigation: In this method, sewage is allowed to
overflow from channels or ridges over the surface or land.
iii) Ridge and furrow method : In this method, ploughing a field
into ridges and furrows, filling the furrows with sewage while
crop grown on or between the ridges.
2. Sub-Surface irrigation: It is also called land infiltration which is the
application of sewage into the land through a system of open jointed pipe or
drains laid near the surface of the ground allowing sewage to percolate into
the surrounding soil.
Condition for sub-surface irrigation:
(i) Where dilution water is not available
(ii) Where climate is dry
(iii) Hand is cheap
(iv) Sub-surface strata are porous
(v) Rainfall is uneven and demand of irrigation water is heavy
(vi) Sub-soil is water is law.
4. INDUSTRIAL WASTE
The waste from different industries are not the same. It differs from industry to
industry. This present days complex situation all wastes can no longer be treated in
same way. It is, therefore, necessary to identify the methods of treatment depending
on the types of industrial waste.

48
Characteristics of sugar mill wastes:
The waste from sugar mill is normally organic in nature with high BOD, high volatile
solids and low pH. Odour from sugar mill waste creates an objectionable environment.
Suggestive treatment:
The organic load of sugar mill waste could be brought down by proper operational
control.
The sugar mill waste is amenable to biological treatment with conventional activated
sludge process and trickling filters. Anaerobic treatment using both digesters and
lagoons may be more effective and economical if sufficient land is available.
Characteristics of Diary waste:
The diary waste though biodegradable is very strong in nature. Diary effluent contains
soluble organics, suspended solids, trace organics. Diary wastes are white in colour
and usually slightly alkaline in nature and become acidic quite rapidly due to the
fermentation of milk sugar to lactic acid. The characteristics of diary effluent contain
temperature, colour, pH(6.5-8.0), DO, BOD, COD, dissolved solids, suspended solids,
chlorides, sulphate, oil & grease .
Treatment process of Dairy Waste:
The waste generated in a diary is intermittent in nature. Before starting of any
biological treatment, it should be allowed to stand in equilisation tank with or without
aeration. Provision of grease trap is also necessary to remove fat and other greasy
substances. Both high rate trickling filters and activated sludge plant may be
employed to treat the waste biologically. For low cost treatment, oxidation ditch,
aerated lagoons, waste stabilization pond are the answers to the waste problem from
diary industry.
Characteristics of waste from Distillery:
The waste from breweries and distilleries characteristics are of high BOD and
damaging to the environment if discharge without any treatment. This waste originates
from bio- chemical process of fermentation of yeast, using carbohydrates as raw
materials and contains ethyl alcohol in different proportions.
For distilleries, two stage biological treatment is necessary –
a) Anaerobic treatment through anaerobic digestion or open anaerobic lagoon.
b) Followed by aerobic treatment in aerated lagoon or in oxidation ditch.

49
Characteristics of wastes from Paper and Pulp mill:
The wastes from the paper and pulp industry contains very high C.O.D. and colour.
Lignin which is predominantly present in the waste derived from the raw cellulose
materials and not easily biodegradable, makes C.O.D./B.O.D. ratio very high.
The treatment of waste consist of all or some of the treatment process stated below-
a) Recovery by destroying lignin.
b) Chemical treatment for colour removal.
c) Activated carbon for colour removal.
d) Physical treatment for clarification with mechanically cleaned circular clarifier.
e) Biological treatment through stabilisation ponds or aerated lagoon.
f) Land treatment method or disposal by irrigation.
Characteristics of wastes from Oil industry:
Large quantity of water used in refinery processes comes out as waste after getting
polluted by oil and other toxic substances. The waste water also contains emulsified
oil, spent up caustic and acid solutions, impurities of petroleum products and spent up
catalysts. The characteristics of waste may vary with the size of refinery, type of crude
oil used, nature of processing etc.
Generally the treatment process of refinery waste work in three phases –
1. Physical separation of free oil through gravity separators based on fundamental
principle of sedimentation.
2. Chemical treatment with chemical coagulation of emulsified oil with the help of
coagulants.
3. Biological treatment for the removal of BOD, phenol and other toxic materials in
biological reactors like waste stabilisation pond, aerated lagoons, trickling filters and
activated sludge process.
Characteristics of Textile industry :
Wastewater of textile industry contains a high degree of pollutants with high TDS and
suspended solids. The wastewater is highly coloured and viscous due to dyestuff and
suspended solids respectively. Sodium is only major cation due to high consumption
of sodium salts in processing units. Chloride is major anion found in the wastewater.
The wastewater also have high BOD and COD.

50
The treatment system consists of an electrochemical method, chemical coagulation
and ion exchange. The electrochemical method and chemical coagulation are intended
primarily to remove colour, turbidity and COD concentration of the waste water
effluent while ion exchange is employed to further lower the COD concentration and
reduce Fe ion concentration, conductivity and total hardness of the wastewater.
5 . Environmental Pollution
5.1 Air pollution
When due to some natural processes or human activities the amount of solid wastes
and concentration of gases other than oxygen increases in the air, which normally has
constant percentage of different gases in it, then the air is said to be polluted and this
phenomenon is referred to as air pollution.
Sources
The principal sources of air pollution are :
a) Volcanic eruptions, forest fire and other natural disasters – Forest fires and volcanic
eruptions release huge amounts of smoke and dust, sulphur compounds and nitrogen
compounds in to the air which are distributed over large areas by winds and air
currents resulting in air pollution.
b) Burning of coal and solid wastes – Gaseous pollutants such as carbon monoxide,
carbon-dioxide, hydrogen sulphide and sulphur dioxide are released. These gases
pollute the air when solid wastes are burnt in urban areas and also when fossil fuels
are burnt.
c) Automobile emissions – Automobiles and engines which run on petrol and diesel,
release pollutants like oxides of nitrogen and lead compounds into the air. This results
in air pollution in urban areas.
d) Industrial emissions – The rate of industrialisation is increasing along with the
increasing population. The gaseous hydrocarbons, nitrogen oxides, sulphurous and
other gases which are emitted by oil refineries and coal burning thermal power plants
cause air pollution in areas near these industries.
e) Nuclear testing and atomic research establishments – The radiation emitted by the
waste products of nuclear establishments causes air pollution. These radiations are
emitted by radioactive elements and radioactive wastes.

51
Effect
a) Effect on materials – Air pollutants affect certain materials in the following ways
and cause economic losses :
 Abrasion
 Corrosion
 Deposition and removal
 Direct chemical attack
 Indirect chemical attack
b) Effect on human health – The inhalation of undesirable gases from the atmosphere
has effect on human health. The emissions from industries and factories affect the
respiratory organs of people living in and around these areas. Radioactive substances
present in the atmosphere have harmful effects on the health of both plants and
animals.
c) Effect on vegetation – Even at low concentration of ozone, nitrogen dioxide and
sulphur dioxide gas may severely damage the sensitive vegetation. The air pollution
caused by forest fires and volcanic eruptions may affect crop production and may also
lead to destruction of certain plants. Industrial emissions also affect the photosynthetic
process in plants thereby hampering their growth.
d) Effect on physical features of atmosphere – Burning of fossil fuels releases huge
amount of carbon dioxide into the atmosphere which results in the rise in ambient
temperature. Decrease in visibility is another indication of air pollution.
Control
It is not possible to remove pollutants from the air. It is therefore desirable that air
pollution be controlled at the sources. Some of the measures which can be taken are
outlined below:
a) Emission from vehicles – Vehicles moving on the road should give out exhaust
constituents within prescribed limits. The design of the vehicles should be such that
complete combustion takes place inside the engine only.
b) Replacement – Causes of air pollution can be replaced by new technological
processes which does not contribute any pollution. Increased use of electricity and
natural gas in place of coal is an example of replacement.
c) Planting of trees – Planting of trees is helpful in reducing air pollution.

52
d) Legislation – Many countries has adopted legislation for control of air pollution. In
India, there is a Smoke Nuisance Act effective in few cities.
Noise pollution
Noise pollution means an unwanted or undesirable sound that leads to physical and
mental problems. Noise pollution is caused by any extremely loud, continuous and
unnecessary noise.
Sources
 Transportation systems are the main source of noise pollution in urban areas
 Construction of buildings, highways and streets cause a lot of noise due to the
usage of air compressors, bulldozers, loaders, dump trucks and pavement
breakers
 Industrial noise also adds to the already unfavourable state of noise pollution
 Loud speakers, plumbing, generators, air conditioners and vacuum cleaners add
to the existing noise pollution
Effects
 Noise pollution may cause temporary or permanent hearing impairment. Many
times, extreme noise ruptures the ear drums.
 Mental and physical equilibrium of people are affected.
 The blood vessels may be affected resulting in lowered blood pressure. Blood
circulation may also be affected leading to weakness.
 Noise pollution has extremely harmful effects on other organisms and
vegetation.
 Due to excessive noise, there is a decrease in the production of digestive juices.
Control
 Planting trees along the roadside reduces the intensity of noise pollution.
 Dense tree cover is very useful in the prevention of noise pollution. Such trees
help in absorbing high sound waves as well as deflecting them into the
atmosphere.
 Industries should be located in areas away from human habitation.

53
 Silencers i.e. noise reducing systems should be fitted in machines which
produce shrill noises.
 People should be educated about the ill effects of noise pollution. This
awareness will result in bringing down noise volumes.
Global warming
Heat and light reach the earth’s surface in the form of solar radiation. The earth
absorbs about 48% of this radiation. Atmospheric gases such as carbon dioxide,
methane, nitrous oxide, ozone and water vapour absorb about 21%. This gases act like
an umbrella over the earth, reflecting some of the heat back to the earth and releasing
the rest to the space. Thus, the temperature of the earth’s surface is maintained at an
equilibrium level. This is called the Greenhouse effect and the gases responsible for
these effect are called greenhouse gases.
Human activities around the globe has lead to an increase in the
proportion of green house gases in the atmosphere. As a result of this increase most of
the radiation from the earth’s surface is reflected back by these gases resulting in
rising temperatures on the earth. This phenomena is called ‘global warming’.
Acid Rain
The air in and around industrial areas contains large amounts of carbon dioxide,
sulphur dioxide, nitrogen dioxide and other acidic gases. These gases dissolve in the
water vapour
present in air to form sulphuric acid, nitric acid etc. These acids are washed down by
rain water. This is known as acid rain.
Ozone hole
The ozone is produced from the oxygen high up in the atmosphere and it is also
broken down by natural forces. It is thus constantly created and destroyed maintaining
an optimum concentration for effective filtration of the excess ultraviolet radiation
reaching the earth. When chemical pollutants such as chlorofluorocarbon(CFC)
emitted from refrigeration and other industrial operations, nitrous oxide and gases
containing halogens pollute the atmosphere, some of the ozone is broken down. Large
scale destruction of ozone causes holes in the ozone layer called ozone holes. These
holes allow the passage of amounts of ultraviolet radiation which causes skin diseases,
including skin cancer.

54
6. Solid Wastes from Society
6.1 Solid Waste Management
Definitions
Refuse: This is all the putrescible and non-putrescible solid wastes except body waste.
This includes all such materials as rubbish and garbage.
Rubbish : This refers to that portion of the refuse which is non-putrescible solid waste
constituents and includes such items as paper, pins, glass, wood etc.
Garbage: This refers to that portion of the refuse which is the waste or rejected food
constituents which have been produced during preparation, cooking or storage of
meat, fruits, vegetables etc.
Ashes: The powdery residue left after the burning of a substance.
Constituents of solid wastes
The solid wastes consist of –
 Residential or household waste consisting of leaves, food wastes,
paper, glass etc.
 Industrial waste including food-processing residue, ash, plastic,
packaging wastes etc.
 Building construction wastes such as bricks, sand, stones etc.
 Hospital wastes composed of blood, limbs, parts of human body etc.
 Bulky waste including trees, furniture, telephone poles etc.
 Hazardous wastes comprising of explosives, radioactive materials,
toxic materials etc.
Sources of solid wastes
Source Types of solid wastes
Residential Food waste, paper, card board, plastics, textiles, leather, glass,
metals, ashes, special wastes ( e.g. bulky items, consumer
electronics, batteries, oil) and house hold hazardous wastes.
Industrial Housekeeping wastes, packaging, food-wastes, construction and
demolition materials, hazardous wastes, ashes, special wastes.

55
Commercial Paper, cardboard, plastics, wood, food wastes, glass, metals,
special wastes, hazardous wastes.
Institutional Same as commercial.
Construction and
demolition
Wood, steel, concrete, dirt etc.
Agriculture Agricultural wastes, spoiled food, pesticide containers and other
hazardous materials.
Bio medical Syringes, bandages, used gloves, drugs, paper, plastics and
chemicals etc.
Collection of solid wastes
Waste collection is the collection of solid wastes from the point of production
(residential, industrial, commercial, institutional ) to the point of treatment or disposal.
Municipal solid waste is collected in various ways –
a) House to house : Waste collectors visit each individual house to collect garbage.
The user generally pays a fee for this service.
b) Community bins : Users bring their garbage to community bins that are placed at
fixed points in a neighbourhood or locality which is then picked up by the
municipality.
c) Curbside pick up: Users leave their garbage directly outside their homes according
to a garbage pick up schedule set with the local authorities.
d) Self delivered: Generators deliver the waste directly to disposal sites or transfer
stations or hire third party operators.
Methods of treatment and disposal of solid waste
Different methods of solid waste disposal are –
1) Open Dumping – In this method, the solid waste collected from the town is
deposited in low-lying land, generally on the outskirts of the town. Since the open
dumps are uncovered, these attract flies, insects etc. and produce odour. This method
is unscientific. It causes health and pollution hazards.
2) Sanitary Landfill – This is a modified form of open dumping. Waste is deposited in
0.9 – 4.5 m thick layers in depression and then compacted and covered atleast once a
day by earth. The process is completely sanitary. It converts low-lying, marshy
wasteland into useful area.

56
3) Incineration – In this method, the refuse is burnt off the volume is much reduced
and the refuse containing harmful micro organisms will be turned quite harmless. Air
has to be supplied to carry away the gaseous products and smoke treatment is
necessary to keep pollution hazards under control.
4) Composting – Composting is the biological decomposition of organic solid waste
in which the waste is converted into a stable, humas like end product which has a high
fertilizing value. This method is popular in developing countries.
Hazardous Waste
Introduction : Any solid waste, other than radioactive wastes, which by reasons of
physical or chemical or reactive or other characteristics causing danger or likely to
cause danger to health or environment are known as hazardous wastes. All toxic
substances are hazardous by definition.
Types and characteristics of hazardous wastes ;
i) Ignitable : Wastes which spontaneously ignite in dry or moist air at or below 600
C.
ii) Corrosive : Waste which have pH< 2.0 or >12.0 or which corrodes steel at a rate
greater than 6.35 mm per year at 550
C.
iii) Reactive : Wastes which are unstable and spontaneously react with water or air,
generate toxic gases explode due to shock or heat.
Treatment of hazardous waste :
The various treatment procedures can be classified as :
1) Physical Treatment : Physical treatment of hazardous waste includes a number of
separation processes commonly used in industry. It is of first importance where waste
containing liquids and solids are separated to reduce cost.
2) Chemical Treatment : These procedures involve the use of chemical reactions with
the help of various chemicals to convert hazardous waste into less hazardous
substances. The chemical treatment produces useful by-products and sometimes
residual effluent that are environmentally acceptable. Chemical reactions either reduce
the volume of the waste or convert the waste to a less hazardous form.
3)Biological Treatment : Biological treatment is an effective, efficient and cost-
effective way to treat & remove hazardous substances from wastewater through
biological agents. Hazardous waste materials are toxic to some of the microorganism.
But a substance which is toxic to one group of organism may act as valuable source of
food for another group. Biological systems can lower the cost of downstream

57
processes by reducing organic load if they are supplemented by other physical or
chemical treatment steps.
Disposal of hazardous waste :
Depending upon the characteristics of the wastes, two types of disposal methods can
be used for hazardous wastes –
1) Landfill.
2) Incineration.
7. Environmental Sanitation
13. Necessity and importance
The sanitary conditions in the rural areas are very poor. The sullage water from
kitchens, baths, etc. is let into the street and offers breading place for flies and
mosquitoes. Children defecate in front of houses as latrines are not provided. As
pathogenic bacteria thrive on faecal matter, this may lead to epidemics and cause
hazard to the health of the people.
In rural areas as well as in the outskirts of the urban areas, large scale sewerage
system with treatment works is not possible because the population is not
concentrated. People live far apart and the limited population make the scheme
prohibitive in cost. Hence it is essential that satisfactory cheap techniques are adopted
in rural areas in individual houses which should satisfy the following conditions
-The neighbourhood wells are not polluted.
-Odours are not produced.
-Flies and vermin have no access to the faecal matter.
14. Rural sanitation
Rural sanitation can be carried out in villages under the following heads-
a) To provide safe and clear water for domestic use- Village water sources are mainly
rivers, lakes, ponds and wells. A river can be accepted as a source of water if it has not
been polluted upstream. Lakes and ponds can also be sources of water provided the
catchment areas of these lakes and ponds are not contaminated by daily defecation by
people or animals. Wells are the best source of water for rural areas.

58
b) Disposal of dry refuse- Dry refuse consists of all source of dry wastes except
excretal waste from latrines. They can be disposed of any of the following methods-
 Dumping in low level areas for land reclamation
 If dry refuse is of organic nature, it may be disposed off by incineration
 The organic dry refuse, specially animal dung, can be disposed off by the
method of composting
c) Collection and disposal of waste water- Waste water consists of water used for
domestic purposes. It does not contain any excretal refuse, therefore is not very
dangerous. It can be disposed off by anyone of the following methods-
 May be used for watering the trees or kitchen gardens in the house
 It may be lead to the composting pit to help easy decomposition of compost
material
 May be carried outside the village by open drains and admitted into natural
water course
d) Disposal of excretal waste- The excretal waste from houses is collected and
disposed of suitably. This system is called conservancy system of disposal which
includes night soil and urine from latrines.
Types of privies
Aqua privy
This type consists of three underground masonry chambers, the first two filled with
water. Latrine pans enclosed in compartments are fixed on top of the masonry tank.
The water closet pipe is extended to 100 mm below the water level to maintain water-
seal. The organic matter in the first chamber is decomposed by anaerobic bacteria.
The gases produced escape through the vent pipe. In the second chamber, the organic
matter is decomposed by aerobic bacteria. The sludge collects at the bottom and is
cleared once in two years. The effluent is discharged into the third chamber which is
filled with clinker by means of a long bent pipe. As the effluent rises, it is purified.
The water collected can be lead to a nearby water course or used for gardening.

59
Bore-hole
In this type, a hole of 400 mm diameter is drilled. The depth of the bore should be 1 m
above the ground water table to prevent the ground water being polluted. A hole is
drilled outside the compartment. A trap is provided which reduces fly nuisance and
odours. When the hole is filled, it is covered with a thick layer of earth and another
hole is dug nearby. After two or three years, the contents could be used as manure.
This method is useful when-
 The water table is low
 No surface drainage is admitted into pit
 No well is located within 30 m

61
Reference Books :
Name of the Authors Titles of the Book Name of the Publisher
K.N.Duggal Elements of Public
Health Engineering
S. Chand & Company
Ltd. Ram Nagar, New
Delhi
G.S. Birdie
J.S. Birdie
Water Supply and
Sanitary Engineering
Dhanpat Rai Publishing
Company (p) Ltd., New
Delhi
A. Kamala
D.L.Kanth Rao
Environmental
Engineering
Tata Mc Graw-Hill
Publishing Company
Ltd., New Delhi

CV-603 environmental engineering & pollution control

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