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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.

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SECOND YEAR

ENVIRONMENTALENGINEERING

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

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).

Introduction Page 3

Tab

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1.1 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 water-courses 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


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.


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 Page 9

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.

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.


1.5 TYPES OF SEWERAGE SYSTEM AND THEIR SUITABILITY:

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.


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.


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.


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


SHORT ANSWER TYPE QUESTIONS

1. Define the terms

(a) Sewage (b) Sewerage (c) Sewer (d) Sullage

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.


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


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) Rational method

(ii) Empirical formulae method

(i) RATIONAL METHOD:

In this method , the storm water quantity is determined by the rational formula

C.i.A

Q = --------- where Q=quantity o storm water in m3/sec

360 C=Coefficient of runoff from table

I=intensity of rainfall in mm/hour


A=drainage area in hectares

* The runoff coefficient ‘C’ is calculated (overall)

A1C1 + A2C2 + ---------+ AnCn ∑AC

= -------------------------------------- = ------------

A1 + A2 + --------------+ An ∑A

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)

C.I.A 4√S

Q = ---------------- -----

141.58 A

(B) Mc.Math Formula (used in U.S.A)

C.i.A 5√S

Q = ---------- -----

148.35 A

(C) Fuller’s Formula


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


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


1. 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.


2.4 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.


Fig 2.2 Nomogram


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


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



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?


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


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


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 semi-circular with sides vertical or inclined as shown in 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 3.3

Fig 3.4


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.

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 3.5

Fig 3.6


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.


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


(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


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.


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.


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.


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 sewer-line 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


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.


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 cast-in-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.


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.


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 best-quality 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.


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


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.


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


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



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 non-

circular type of sewers?

10. Draw the neat sketch of egg-shaped sewer.


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 Page 49

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.


(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


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.

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


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.


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


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.


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.


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


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

2300 2500 3000

1500 1800 2300

1300 1500 2000

500 800 1000

0.0050

0.0075

0.0100

0.0200

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


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


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.


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.


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


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.


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


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


(ii) 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.


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


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.


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.


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


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.


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


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



1. What is the necessity of providing following sewer appurtenances?

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


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.


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

Sewage Characteristics 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


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


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.

Environmental Engineering 5.2 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


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


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.


5.3 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


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


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

Environmental Engineering 5.3.6 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.


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 - solids, other chemical substances, gases

(iii) Biological characteristics – aerobic, anaerobic or fraculative

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


(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



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.


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 Page 91

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

5. Trickling filter (High rate) proceeded and followed by plain sedimentation

65 to 92 80 to 95 70 to 95

6. Activated sludge process followed by plain sedimentation (ordinary)

85 to 90 90 to 98 75 to 96

7. Activated sludge process followed by plain sedimentation (high rate)

65 to 96 95 to 96 65 to 96


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


Impurity Process used for removal

1. Bulky floating and suspended matters

Racks and screens

2. Oils and greese Floating tanks (skimming tanks)

3. Heavy and coarse suspended matter

Grit chamber, detritus tanks and sedimentation tanks

4. Non-settlable suspended and some dissolved solids

Chemical flocculation

5. Colloids and dissolved organic matter

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


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


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


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.


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


(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


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.


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.


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%.


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.


a. 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.


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


(3) 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.


(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.


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.


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


(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.


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.


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.


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

Trickling filter

High rate trickling

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 of aeration

Less flexible and requires less skilled supervision

More flexible and requires more skilled supervision


6. Quality of secondary sludge

It is black and highly oxidized with slight fine particles

It is brown and not fully oxidized with fine particles

7. Rate of filter loading

I) Kg of B.O.D per hectare meter per day

ii) Kg of B.O.D per day per 100m3 of filter media

iii) Million litres per hectare of surface area per day

1000 to 2000

15 to 50

25 to 40

8000 to 14000

above 45

100 to 300

8. Effluent The effluent is highly nitrified and stabilized

The effluent is nitrified upto nitrite stage only and hence it is of inferior quality

9. Recirculation system

It is generally not included but it can be adopted

It always included However, in some types it may be used daring periods of low & low only

10. Size of filter media

30mm to 80mm 30mm to 60mm


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


(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


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


6.3.4 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.


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


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


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,


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.


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.


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.


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.


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


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.


2. 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) Oxidation-reduction (d) Sun light. This phenomenon of automatic purification of natural water in due course is called self-purification.

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


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.


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%.


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



1. What is the purpose of screens? 2. What is the use of skimming tanks? 3. What are the objects of primary treatment? 4. What are the treatment methods in the secondary treatment? 5. What are the advantages of oxidation pond? 6. What is the purpose of soak pit? 7. What are methods of sewage disposal? 8. What is the purpose of grit chamber? 9. What is the use of plain sedimentation?


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


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, cows, goats, birds etc collected from municipalities

Solid Waste Disposal Page 133

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


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


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


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


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.


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... compost is prepared by aeration in 3 to 5 days.


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.



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?


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?

Drainage & Sanitation in Buildings Page 141

CHAPTER 8

DRAINAGE AND SANITATION IN BUILDINGS


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.


8.2 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


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.


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


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


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 IS1742-1972.

Fig 8.2 Layout of Drainage System in Multistoreyed Building


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 anti-siphonage.

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.


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.


b. Q-trap.

c. S-trap.

Fig 8.3 Traps according to shapes

2. Classification according to use as shown in fig 8.4.


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


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


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


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


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.


8.2.6 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


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.


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.


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


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.


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


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.


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.



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.


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.


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.

Rural Water Supply & Sanitation Page 165

CHAPTER 9

RURAL WATER SUPPLY AND SANITATION


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


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


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


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


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


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


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


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.


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


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.


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.


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.


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


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 3m3 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.


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


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.


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.


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.


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?


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 following 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 ----------


10.1.3 SOURCES OF AIR POLLUTION:

Following are the main sources of air pollution

(i) Natural sources

(ii) Man made sources

(i) 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,


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


(i) 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.


(ii) EFFECT ON PHYSICAL PROPERTIES OF ATMOSPHERE

a. 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 hydro-carbons 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


(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.


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


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 BY CONTROL DEVICES AND EQUIPMENT

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.


1. Characteristics of the gas like pressure, humidity, temperature density, dew point, viscosity etc.

2. Operational factors like space required, corrosion, service requirements.

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.


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.


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.


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


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.


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.


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


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


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 CONTROL BY STACKS AND VEGETATION

(II) POLLUTION CONTROL BY VEGETATION:

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


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)


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


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.


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


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


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


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


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.


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


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


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.


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


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.



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.



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 and Air Pollution Engineering by S.K.Garg.

9. Water supply Engineering by Santhosh Kumar Garg.

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 Name of the chapter No. of Pg. No. No. 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 Buildings 15 141 9. Rural Water Supply and Sanitation 10 165 10. Air pollution and Ecology 20 183

TOTAL PERIODS 160

MODEL PAPER…..…….…. REFERENCE BOOKS……. INDEX ……….………….….

INDEX A

Acid rains Action of activated sludge Activated sludge process Aerosols Air pollutants Air pollution Analysis of sewage Aqua privies

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

E

Ecology Effects of air pollution Environment Environmental health hazard

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

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