water supply and waste discharge

7/25/2019 water supply and waste discharge

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WATER SUPPLY ASSIGNMENT


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EFFORTS BY:

AAKANKSHA KHATRI

AAKASH DUA

DEEPSHI GUPTAGARIMA SHARMA

GUNJAN DOGRA

MOHD IRFAN

NIKITA ANEJA

NUPUR GARG

PRATEEK WASON

RISHABH VADERARUCHI BAKSHI

TANYA DHINGRA

TARANG MATIA

UMESH INDORIA


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The problem of estimating the quantity of water may be tackled by studying inthe following two factors:

Rate of demand

Population

Rate of demandIn order to arrive at a reasonable value of rate of demand for any particular

town, the demand of water for

various purposes is divided under the following five categories:

Domestic purposes

Civic or public purposes

Industrial purposes

Business or trade purposes

Loss and waste

1) Domestic purposes

The quantity of water required for domestic purposes can be sub-divided asfollows:

i. Drinking: The quantity of water which a man would require for drinkingdepends on various factors. But on the average and under normalconditions, it is about 2 liters per day.


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ii. Cooking: The amount of water required for cooking may be assumed as

about 5 liters per head per day.

iii. Bathing: For an Indian bath, this quantity may be assumed as about 30 to

40 liters head per day and for tub-bath, it may be taken as about 50 to 80

liters per head per day.iv. Washing hands, face etc.: The quantity of water required for this purpose

will depend on the habits of people and may roughly be taken as 5 to 10

liters per head per day.

v. household sanitary purposes: The water required for washing clothes ,

floors, utensils, etc. may be assumed to be about 50 to 60 liters per head

per day.

vi. Private gardening and irrigation: In case of developed cities, there will be

practcally no demand of water for this purpose. In case of underdeveloped

cities, the private wells are generally used to provide water for private

gardening and irrigation. It is therefore not essential to include he quantity

of water required for this purpose in case of public water supply project.vii. Domestic animals and private vehicles:


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2) Civic and public purposes: the quantity of water required for civic or

public purposes can be sub-divided as follows:

i. Road washing: On an average, the quantity of water required for this

purpose may be taken as about 5 liters/head/day.

ii. Sanitation purposes: The quantity of water required for this purpose will

depend on the growth of civilization and may be assumed to be about 2 to

3 litres per head per day.

iii. Ornamental purposes: In order to adorn the town with decorative features,

the fountains or lakes or ponds are sometimes are provided. As far asindian towns are concerned, the quantity of water required for this purpose

may be treated as quite negligible since in most of the towns, the quantity

of water available is enough even to meet with the most urgent needs of

the society.

iv. Fire demand: the fire hydrants are located in the mains at distances of not

more than 150 metres or so. When a fire occurs, the pumps installed ontrucks are immediately rushed to the site of fire occurrence and these

pumps, when connected to the fire hydrants, are capable of throwing

water with high pressure. The fire is thus brought under control.


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3) Business or trade purposes: some trades such as dairies, hotels,

laundries, motor garages, restaurants, stables, schools, hospitals, cinema

halls, theatres, etc. require a large quantity of water. The number of such

business centres will depend upon the population and for a moderate city, an

average value of about 15 to 25 litres of water per head per day may betaken as water requirement for this purpose.

4) Loss and waste: The quantity of water required under this catergory is

sometimes termed as the unaccounted requirement. It includes careless use

of water, leakage in mains, valves, other fittings, etc. for the purpose of

calculating the average rate of demand, it may be estimated to be about 30

to 40 per cent of per capita consumption.Factors affecting rate of demand:

1) Climatic conditions: the requirement of water in summer is ore than in

winter. In extreme cold, people may keep water taps open to freezing of

pipes. This may result in increased rate of consumption

2) Cost of water: the rate at which water is supplied to consumers may alsoaffect the rate of demand. The higher the cost, the lower will be the rate of

demand and vice versa.

3) Distribution pressure: the consumption of water increases with increase in

the distribution pressure. This is due to loss and waste of water at high

pressure.


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4) Habits of population: for high- value premises, the consumption rate ofwater will be more due to better standard of living of persons. For middle class premises, the consumption rate will be average while in case of slumareas, it will be much lower.

5) Industries: the presence or absence of industries in a city may also affect

its rate of demand. As there is no direct relation between the waterrequirement for industries and population, it is necessary to calculatecarefully present and future requirements of industries.

6) Policy of metering: the quantity of water supplied to a building isrecorded by a water meter and the consumer is then charged accordingly.The installation of meters reduces the rate of consumption. But the fact ofadopting policy of metering is disputable one as seen from the following

arguments which are advanced for and against it.7) Quantity of water: the improvement in quality of water may result in the

increase of rate of consumption.

8) Sewerage: the existence of sewerage system in a locality will lead to anincrease in use of water for civic or public purposes.

9) Size of city: generally, smaller the city , the lower is rate of demand. Butthe presence of a waterconsuming industry in a small town may resultin a higher rate of demand, even if the town is small.

10) System of supply: the supply of water may be continuous or intermittent.It is claimed that the intermittent supply of water will reduce the rate ofdemand.


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Measurement of water:1) Reasons to measure the quantity of water:

i. To ascertain the quantity of water to supplied free of charge.

ii. To determine the costs of treated water at different stages of operations.

iii. To give an idea of operation efficiencies of various units of the water supply

scheme.

iv. To maintain records for administrative purposes.

v. To measure the quantity of water to be sold either on retail basis to the

individuals or on wholesale basis to another supply.vi. To provide a control on operations of various units such as pumps, elevated

reservoirs, chemical feeding devices, etc.

2) Categories of meters to measure water:

i. Displacement type: such meters contain a vessel of known volume and the

number of times it is filled and emptied is automatically recorded. This type ofmeter is useful for small installations to measure relatively small quantity of

flow as in case of hotels, residential buildings, etc.


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ii. Velocity type: such meters are turbine or venturi type and they contain adevice by which a vane or propeller turns in direct ratio to the quantity of

flow passing through the propeller. This type of meter is

useful for big installations such as on pumps, water main lines, etc.

3) Points to select for any water meter: In any case, the following points

should be considered while making selection for any water meter:

i. accuracy of measurement

ii. Availability of spare parts

iii. Capacity with minimum head loss

iv. Cost

v. Durability

vi. Ease of repair

vii. Noise during working

viii. Quality of workmanship

ix. Registration with varying discharges

x. Self cleansing property etc


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Effects of variation on designThe water supply units are designed in accordance with the fluctuations or

variations in rate of demand .

i. the pumps and filters are generally designed for 1.50 times the averagerate of daily demand.

ii. If pumps are working in shifts, the abpve rate is still to be multiplied by the

ratio of 24 hours to pumping hours.

iii. The distribution mains are to be designed for the maximum hourly demand

on maximum day.iv. The other units of water supply scheme such as sedimentation tanks and

overhead tanks are designed for the average daily rate of demand only.


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water requirements for buildings other

than residences:

No. Type of buildings Waterrequirement

in litres per

day

1. Cinema and concert halls 15 per seat

2. Factories 50 Per worker3. Hospitals with less than

100 beds

340 per bed

4 Hospitals with more than

100 beds

450 per bed

5 Hostels 135 per head

6 hotels 180 per bed

7 Medical quarters 135 per head

8 offices 45 per head

9 restaurants 70 per head10 schools 45 per head


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Estimating populationThe term population is used to indiate the total number of human beings

residing in a certain area at any

particular time.

The future period for which various service units of water supply or sanitary

engineering are designed is known as the period of design.

Period of design for important components of water supply project

no. Component Period ofdesign in

years

1. Clear water service reservoirs 15

2. Conveying pipes for raw and clear

water

30

3. Distribution system 30

4 Electric motors and pumps 15

5. Infiltration works 30

6. storage reservoirs 50

7. Water treatment units 15


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The termpopulation densityis used to indicate the number of persons per unit

area and the distribution of population is well studied by finding out the

population densities of various parts of the city.

Methods of populationFollowing are the various methods of population forecasts or population

projections and the selection of method will naturally depend on the

available data:

i. Arithmetical increase methodii. Geometrical increase method

iii. Incremental increase method

iv. Graphical method

v. Comparative method

vi. Zoning methodvii. Ratio and correlation method

viii. Growth composition analysis method

ix. Logistic curve method


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Sources of water supply


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Surface runoff

The net quantity of water which remains on the surface after losses from

evaporation, percolation and transpiration is termed as surface runoff.

Seen in the form of various streams which ultimately join and form river

Harmful effects of surface runoff

Economic use requires costly reservoirs or land improvement schemes

Erosion

Loss of water

Occurrence of flood


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Factors affecting runoff coefficient Catchment area

Characteristics of catchment

Condition of ground at the time of rainfall

Intensity of rainfall

Interval between successive hours

Season of rainfall Yearly rainfall

NoteRunoff coefficient : ratio of surface runoff from an area to the total rainfall on that area

in a fixed interval of time.

Catchment area : upstream area contributing to the water of a river


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Precipitation

Water which returns to the surface of earth in forms like rain, snow etc.

Types of precipitation

Convective precipitation

Cyclonic precipitation

Orographic precipitation


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Measurement of rainfall

Measured by standard instruments known as rain gauges

Non recording type gauge

Recording or automatic gauge

Following points should be kept in mind while selecting site of rain gauge:

Location

Protection of side

obstruction


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Types of sources for water supply

schemes Surface sources

Underground sources

Factors affecting choice of source of water supply for a particular town or

city

Cost

Elevation

Location

Quality of water

Quantity of water


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Surface sources of water supply

Lakes and streams

Ponds

Rivers

Storage reservoirs


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Lakes and streams Lake- large body of water with impervious bed and may be used as a

source of water supply for nearby localities Streams-formed by surface runoff

Catchment area of lakes and streams is very small, hence low quantity of

water available.

Not considered as principal sources of water supply schemes for large

cities. Adopted for hilly areas and small towns

Ponds

Man made body of standing water smaller than lake Formed due to excessive digging of ground for the construction of roads,

houses etc.

Cant be adopted as a source of water supply and its water can only be

used for washing of clothes or for animal washing


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Rivers

Principal source of water supply schemes for many cities

Perennial rivers- snow fed , water flows in all seasons

Non-perennialdry in summers, heavily flooded in monsoon

Chief points to be considered in investigating a river supply of water are:

Adequacy of storage of purified water

Efficiency of subsequent stages of purification system adopted

General nature of river, rate of flow and the distance between the sources of

pollution and the intake of water

Relative proportions of the polluting matter and the flow of river when at its

minimum


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Storage reservoirs

An artificial lake formed of dam by the construction of dam across a valley

A storage reservoir essentially consists of the following 3 parts:

A dam to hold water

A spillway to allow the excess water to flow

A gate chamber containing necessary valves for regulating the flow of water


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Forms of Underground sources of

water supply

Infiltration galleries

Infiltration wells

Springs

wells


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Infiltration gallery

Horizontal or nearly horizontal tunnel which is constructed through water

bearing strata.

Useful source of water supply when ground water is available in sufficient

quantity just below ground level or so.

Usually constructed at depth of about 5-10m form the ground level.

Infiltration wells In order to obtain large quantities of water, infiltration wells are sunk in

series in the banks of river.


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Springs

When underground water appears at the surface for any reason, springs are

formed

Serve as a source of water supply for small towns, especially near hills or

bases of hills.

Hot springs (discharge hot water) cant be used to supply water for domestic

purposes.

Factors to be noted when a spring needs to be developed as a source of

water: should be easier, cheaper, and surer enough to develop the spring than to adopt

any other source of water supply for the locality

The flow of water should be adequate even in dry weather

should be adequately protected from the pollution sources

Should be located so as to have natural gravity flow

The water should be of good quality

Types of springs:

Artesian spring

Gravity spring

Surface spring


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Wells

Artificial hole or pit made in the ground for the purpose of tapping water

3 factors which form the basis of theory of wells are:

Geological conditions of the earths surface

Porosity of various layers

Quantity of water which is absorbed and stored in different layers

Types of wells

Shallow wells

Deep wells

Tube wells

Artesian wells


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No. Item Surface sources Underground sources

1. Forms in which

available

Lakes, streams, ponds, rivers,

storage reservoirs

Infiltration galleries,

infiltration wells, springs,

wells2. Quality of water Sometimes highly polluted

and unsafe to consume,

contain inorganic impurities,

organic impurities and

industrial wastes

Generally free from

impurities because of natural

filtration but may contain

large amounts of dissolved

salts, minerals and gases

3. Quantity of water Huge quantity of water is

available during monsoon,

but is considerably reduced

during summer

Quantity of water available is

generally limited

4. Treatment Suitably tested and a line of

treatment is to be decidedbefore they are adopted for

public use

Can be supplied to public

with no or minor treatmentonly

5. Use Useful for big towns and

cities, can be adopted for

irrigation facilities as well

Useful for small towns and

villages only


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QUALITY OF WATER


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PURE WATER

The impurities of water are to be removed so that it does not prove harmful

for public health.

Uses of water: domestic, civic(washing of roads, sewers),trade or business use

(laundry) , commercial or industrial use

Impurities in water: Physical impurities

Chemical impurities

Bacteriological impurities


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ANALYSIS OF WATER

Physical tests

Chemical tests

Bacteriological tests


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PHYSICAL TESTS

1. colour:

sources contributing colour to the water. Algae metabolism End products of degraded organic matter Discharge of untreated and partially treated waste water from various

industries Divalent species containing iron and manganese

Tintometer: instrument used to measure colour in water

Disadvantages of water possessing colour: Many colour bodies in nature are colloidal and behave as absorbents. Thus,

they exert toxicity to aquatic life. Coloured water in unsuitable for various industries like dairy production,laundry etc.

Coloured water retard photosynthetic reactions.


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2.taste and odour:

Odour is expressed as disagreeable, earthy, fishy, grassy, mouldy, peaty, sweetishetc.

Taste is expressed as blackish, saline, salty, etc.

3.temperature:

Multiplication of bacteria in water is more rapid at higher temperature than inwaters at lower temp.

4. turbidity:

The colloidal matter present in water interferes with passage of light and thusimpart turbidity to water.

Caused due to clay and silt particles, discharges of sewage, microorganisms, etc.

Instruments used to measure turbidity: turbidity rod, Jackson turbidimeter,

naphelometric turbidimeter.


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CHEMICAL TESTS

Tests are carried out to examine water for:

Chlorides

Dissolved gasses

Hardness

Hydrogen-ion concentration(pH value) Alkalinity

Acidity

Metals and other chemical substances

Nitrogen and its compounds

Total solids


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BACTERIOLOGICAL TESTS

Total count or agar plate count test

B-coli test:the combined group of pathogenic(harmful) and non-pathogenic(harmless) bacteria is designated by bacillus coil(bacterium &intestine) or b-coli test


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WATER-BORNE DISEASES

Diseases carried out by water : cholera,dysentery, typhoid, etc.

Caused by pathogenic bacteria.


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SEDIMENTATION TANKS

The first stage of treatment is PREFILTRATIONof water and it includes provision

of sedimentation tanks or settlement tanks or clarifiers.

They are designed to give complete rest to the flowing water or water is allowed to

flow at a very slow pace.

To make the process of sedimentation tans effective, the coagulants are added to

the water before it is brought to the sedimentation tanks.


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THEORY OF SEDIMENTATION

In water there are mainly two types of impurities :

1. Inorganic suspended solids ( heavier)

2. Organic suspended solids (lighter )

The phenomenon of settling down of particles at the bottom of the sedimentation

tanksis known as the HYDRAULIC SUBSIDENCE.

The process of settlement of particles is obstructed by three forces:

1. Velocity of flow

2. Size and shape of particle3. Viscosity of water


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TYPES OF SEDIMENTATION

TANKS1.FILL AND DRAW TYPE TANKS

The water is filled and then allowed to rest for some time.

The particles settle down at the bottom.

The clear water is then drawn off and the tank is cleaned and filled again.

Period of rest to cause settlement = 24 hours or so


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DISADVANTAGES

1. Labor and supervision - These tanks are to be filled ,emptied , washed,

cleaned everyday. These operations require manual labor and expert

supervision.

2. Loss of headIn this type of tank , the loss of head is equal to the heightof the silt zone takes place as outlet valve is situated above that zone.

3. Units of tanksThe minimum units of tanks required is three, which

makes it less economical.

4. Wastage of timeThere is considerable wastage of time in filling ,

emptying and cleaning the tank. In addition a clear water storage tank is

to be provided.


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2. CONTIONUOS FLOW TYPE TANKS

Principleif velocity of water is reduced , a large amount of suspended impurities

form water can be easily removed.

The water enters from one end, exits from the other. The velocity is broken or

reduced by means of baffle walls. These walls contain openings at different levels.

The velocity of flow from one end to other is more than the time for settlement of

impurities.

The silt is deposited at the bottom of the tank and when it accumulates in sufficient

quantity , the flush valve is opened and the tank is cleaned.

ADVANTAGES


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ADVANTAGES

1. Less labor and supervision - No manual labor is required except at the time of

cleaning . Only general supervision is required.

2. Little loss of headThe outlet is situated at the top of the tank and hence

there is practically very little loss of head.

3. Tanks in seriesThese are arranged in series and hence any one of them

maybe isolated for cleaning or washing purpose. The provision area for

standby units works out comparatively less.

4. Time of operationas the flow of water is continuos , there is no wastage oftome . No clean water storage tanks are required .

COAGULATION OF WATER


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COAGULATION OF WATER The water, even after sedimentation, is turbid and contains suspended impurities

like fine particles of clay and silt.

It also possesses color which is due to colloidal matter and dissolved organic

material.

All these impurities are in a finely divided state and it not possible to detain them

in plain sedimentation tanks.

So to remove these impurities, the size of the particles is increasedby adding

certain chemicals, known as the coagulants.

The coagulants react with the impurities and convert them into a settle able size.

The most common coagulants used for the process are:

Aluminium Sulphate, Chlorinated Copperus, Ferrous sulphate & lime,

Magnesium Carbonate, Polyelectrolytes, Sodium Aluminate

The process of coagulation assists the process of sedimentation and is followed by

the process of filtration.

The coagulants may be fed or allowed to enter water either in powder form (dryfeeding) or in solution form (wet feeding).

Devices used for this purpose are:

Centrifugal pumps, Compressed Air, Hydraulic Pump, Mixing Channel, Mixing

basins with baffle walls, Mixing basins with mechanical means


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DISINFECTION OF WATER

When water leaves the filter plant it is still found to contain some of the


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When water leaves the filter plant, it is still found to contain some of the

impurities, such as

Bacteria

Dissolved inorganic salts

Color , odor and taste

Iron and manganese

The water should be disinfected before it enters the distribution system.

The main purpose of disinfection is to prevent contamination of water during its

transit from the treatment plant to the place of its consumption.

The materials or substances which are used for disinfection are called the

disinfectants.

Requirements of a good disinfectant are:

Its dose should be such that some residual concentration is obtained to

grant protection against contamination in the water during its conveyance

and retention.

It should be effective in killing all the harmful pathogenic organisms from thewater and make it perfectly safe for consumption.

It should be harmless, unobjectionable, economical and easily available.

It should be of such nature that its strength or concentration in the treated

water can be quickly determined.

It should not require skilled labour and costly equipment for its application.

It should take only reasonable time in killing the harmful pathogenicorganisms at normal temperature.

METHODS OF DISINFECTION


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METHODS OF DISINFECTION

CHLORINATION

In this treatment for disinfection, the chlorine and its compounds are used

as the disinfecting material.

However chlorine is a poisonous gas which requires careful handling and it

may also give rise to the problem of taste and odor in water.

The action of chlorine is directly proportionate to the pH value of water.

At high pH value for e.g. above 8.50, the chlorine cannot be relied

upon and when pH value is below 7.00, disinfection by chlorine israpid.

As the action of chlorine is not instantaneous, an adequate contact time

must be allowed.

The contact time varies from one to four hours or more, and it mainly

depends on the impurities present in the water.

The temperature also has a noticeable effect on chlorination. The delay

occurs in cold in both germicidal and absorption of chlorine.

The water should be so prepared that chlorine can be properly, reliably and

efficiently applied

ADVANTAGES OF CHLORINATION :

It li h t b t i l ifi ti i i t th t


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It accomplishes greater bacterial purification in minutes than storage

achieves in an equal number of days, thus eliminating the need of costly

storage reservoirs.

It works better against water- borne diseases.

It serves as a convenient accessory to the process of filtration

FORMS OF CHLORINATION

Depending upon the stage of treatment at which chlorine is added and also the

expected results of chlorination, the various forms of chlorination comes into

existence. Plain chlorination

Pre- chlorination

Postchlorination

Double- chlorination

Break point chlorination

Super- chlorination Dechlorination

PLAIN CHLORINATION : when chlorine treatment is given to raw water to


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control the growth of algae , remove bacteria and color from the water, it is

called Plain Chlorination.

PRE- CHLORINATION : when chlorine is added to the raw water before

any treatment, it is known as Pre- Chlorination. A small dosage of chlorineis added to raw water before it enters to sedimentation tanks.

POST- CHLORINATION : the application of chlorine after all the treatments

of purification of water are completed is known as Post- Chlorination.

This is the standard treatment and chlorine is added to the water after it

leaves rapid sand filters and before it enters the distribution system.

DOUBLE CHLORINATION : when water is added to the raw water at more

than one point, it is known as the Double chlorination. When raw water is

highly contaminated and contains large amount of bacterial life, it becomes

important to adopt both pre- chlorination and postchlorination.

BREAK POINT CHLORINATION: this refers to the amount of chlorine required to treat

the water.

SUPER- CHLORINATION : the application of chlorine beyond the stage of break point

is known as super- chlorination. The excess chlorine can be added at any stage or

stages of the treatment , but usually it is added at the end of filtration.

DECHLORINATION th l f hl i f t i k


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DECHLORINATION : the removal of excess chlorine from water is known as

Dechlorination.

The dechlorination should be done in such a way that at the end of the

process, some residual chlorine remains in water. This residual chlorine

will disinfect water when it is flowing through the distribution system.

some dechlorinating agents are: sodium thiosulphate, sodium bisulphate,

activated carbon etc.

OTHER MINOR METHODS OF DISINFECTION

Boiling method

Excess lime treatment : the treatment of lime is given to the water for the

removal of dissolved salts. Lime also acts a disinfecting material when added

in excess in water.

Iodine and bromine treatment : the use of iodine and bromine is limited to

small water supplies such as private plants, swimming pools, etc.

Ozone treatment : the advantage of ozone treatment is that ozone is unstable

and it does not remain in the water when it reaches the consumer.

Ozonisation is however costly and complicated compared to chlorination

and it requires skilled labors.


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Potassium permanganate treatment : this disinfectant works as a powerful

oxidizing agent and is found to be effective in killing cholera bacteria.

Silver treatment

Ultra violet ray treatment : invisible light rays beyond the violet spectrum are

very effective in killing all types of bacteria.

The treatment doesnt develop any taste or color in the water because

no chemicals are used in the process and there is no danger of

overdose. But as the treatment is costly it is unsuitable for large scale treatment

plants .

It can however be adopted for water supply installations of private

institutions like pharmaceutical, food and beverage, chemical, drugs,

dairy and paint industry for processed water and waste water

USES OF UV- SYSTEM : For microbial reduction

For ozone destruction

In tertiary treatment


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Water softening


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Purpose

The water to be supplied to the public should not be very hard though there isfear of no health hazard, but is undesirable as it leads to several economic

disadvantages.

1. It affects the working of dyeing system and leads to the modification if some

colors.

2. It causes corrosion and incrustation of pipes and plumbing fixtures.

3. It causes more consumption of soap in laundry work and hence, proves to

be uneconomical for washing processes of textile industries.

4. It increases the fuel costs.

5. It makes the food tasteless, tough or rubbery.

6. It provides scale on the boilers and hot water heating system.


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Types of hardness

Temporary hardness Permanent hardness

Temporary hardness

Also known as carbonate hardness and it is mainly due to the presence ofbicarbonates of calcium and magnesium.

Removal of temporary hardness: temporary hardness can be easily removed by usingthe following method:

1. Boiling the water

2. Adding lime to the water


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Permanent Hardness

Also known as non-carbonate hardnessand it is mainly due to the presence ofsulphates, chlorides and nitrates of calcium and magnesium.

Removal of permanent hardness: the permanent hardness cannot be easily removedwith water. The special treatment, known as the water softening treatment, is to begiven to the water.

Methods adopted for water softening treatment:-

1. Lime soda process

2. Zeolite process

3. Demineralization

4. Reverse osmosis


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Lime-Soda process

Advantages of lime-soda process:

pH value of water is increased which results in decrease in the corrosion of the

distribution system

Less amount of coagulant is required

There is a likelihood of killing pathogenic bacteria. This process is economical

The process is easy and simple and can be accommodated in the existed filter

plant of any water suplly scheme.

In this process, the lime and sodium carbonate or soda ash are

used to remove permanent hardness from water.

Disadvantages of limesoda process

The large quantity of sludge formed during the process is to be disposed off bysome suitable method.

The process requires skilled supervision for its successful working

This process can only remove water hardness up to about 50mg/l. thus thewater of zero hardness cannot be produced by this process. But as water of zerohardness is not required for the public water supply, this disadvantage does notprove to be serious.


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Zeolite processThis process is also known as base exchange or ion exchange process. The

zeolites are the compound of aluminium, silica and soda.

Advantages of Zeolite process

No sludge is formed in this process. Hence the problem of sludge disposaldoesnt arise.

The zeolite unit is compact in design. And can be easily operated so it does notrequires any skilled supervision.

This process removes hardness of water to about zero. So it has got particularimportance for the water to be used in the boilers and certain textile industries.

Disadvantages of Zeo lite process

This process can not to be adopted for highly turbid water

This process is unsuitable for water containg iron and manganese. The zeolite unit should be carefully operated to avoid injury or damage to the

equipment or the quality of water.


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Demineralization process This process in also known as deionisationprocess. It is similar to zeolite process

but in this process, the hydrogen is exchanged for metallic ions. This process is mainly used for preparing water to be used for the industrial

purposes.

Reverse Osmosis process

Reverse osmosis, which is also known as hyperfiltration, is the finest filtrationknown. It works on the principle of diffusion.

Diffusion means movement of molecules from a region of higher concentrationto a region of lower concentration. And osmosis is a special case of diffusion inwhich movement of molecules occurs through a semi permeable membrane.

The most common use of reverse osmosis is in purifying water. It is used incommercial and residential water filtration to desaline water.


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MISCELLANEOUS METHODS

OF WATER TREATMENT1. Color, odor and taste removal

2. Iron and manganese removal3. Fluoridation


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Some Special Methods To Remove

Color, Odor And Taste

1. Aeration: The process aims at bringing water in intimate contact with air.

Methods of aeration:

Air diffusion: The perforated pipes are installed at the bottom of tanks and air isblown through them.

Cascades: a cascade is a waterfall and a simple cascade consists of a series of

three four steps.

Spray nozzles: water is sprinkled in fine jets through nozzles at a height of

about 2.5m.

Trickling beds: beds of coke and slag are prepared and water is allowed to

trickle down from the top to the bottom of the bed.


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2. Treatment by activated carbon: activated carbon is applied either as a filter

media or in a powder form.

3. Use of copper sulphate:

In distribution pipes, a solution of copper sulphate is prepared and is just

added at the entry of water distribution system.

In open reservoirs, powdered cuso4 may be sprinkled, or placed in open

bags which are attached behind moving boats, or a solution maybe simply

sprayed.


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Iron and manganese removal

When iron and manganese occur in water without combination with organicmatter, they can be removed by aeration followed by coagulation,

sedimentation and filtration.

When they occur in combination with organic matter, the bond between

them maybe broken by adding lime or adding chlorine or potassium

permanganate.


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Fluoridation

The fluoridation is aimed to improve the physical comfort with respect to thedental caries of the people drinking such water.

Usual fluoride compounds which are added to water are sodium fluoride, sodium

hexafluorosilicate and hexafluorosilic acid.

Defluoridation: To remove excess of fluoride. Can be done by adding activated

carbons, calcium phosphate, bone charcoal etc.


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Conveyance Of Water


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Conveyance of water is

Drawing of the water

from the sources knownas intake

Leading the water from

intakes to purification

and then to consumers


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Intake

It is a structure constructed around the water surface. It is watertight andmay be of stone, brick, RCC or concrete.

Considerations of location of intake are:

Controlling device

Cost

Navigation channels

Permanency of supply

Quality of water

situation


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Design of intakes

Consideration factors in the design of intakes are:

Factor of safety-so that it resists the external force caused by waves

and currents

Foundations- depth of foundation should be sufficient so that no

damage is done by currents.

Protection of sides Screens or strainers-it is provided at entry of intake which avoids the

entry of floating matter and fish

Self-weight-it should be of adequate self weight so that it doesnt wash

away. Broken stones should be added at the bottom.

Size and number of inlets


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Types of intakes

Canal intakes-it isconstructed in the canal

section River intakes

P t bl i t k i f


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Reservoirs or lake intakes- itconsists of intake well which is

placed near the dam.

Portable intakes-in case of

emergencies it becomes

necessary to draw water with

the help of movable intake. It

is a truck with a pumpingplant. The pump is placed on

site and the suction pipe is

immersed just above the bed

level of water.


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Intake tower

They are used for large projects where there are chances of

considerable fluctuations of water level. They are made of concrete.

They are of two types:

1. Dry intake tower-there isno water inside the tower

when gates are closed.

The water is drawn directly

into the outlet pipe through

gate controlled entry ports.

2. Wet intake tower- the

water enters from the

open entry port and then

enters the outlet pipe

through separate gate

controlled entry ports.


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Pipes

The pipe material is selected while keeping in view of the forces resisted byit- the stress due to water pressure, stress due to temperature, stress due to

change of direction etc.

Materials used for pipe are

Asbestos cement pipe

Cast iron pipes Cement concrete pipe

Copper pipe

Galvanised iron pipe

Lead pipe

Plastic pipe Steel pipe

Wood pipe

Wrought iron pipe

Pipe Advantage Disadvantage


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Asbestos cement pipe- it is

mixture of asbestos fibres

and cement

i. Inside surface is smooth

ii. Joining of pipes is good

and easy.

iii. Anti-corrosive and cheap

iv. Light weight

v. Suitable for distribution

pipes

i. Brittle and cant stand

impact forces

ii. Not durable

iii. Cant be laid in exposed

places

iv. Can be used for low

pressure

Cast iron pipe- it is made

from pig iron with surfaces

given corrosion treatment

i. Cost is moderate

ii. Easy to join

iii. Not subjected tocorrosion

iv. Strong and durable

v. Life span is 100 years or

so

i. Large breakages

ii. Carrying capacity

decreases with increasein life of pipe

iii. Not for

pressure>0.7N/sq.mm

iv. They become heavier

and uneconomical when

dia>1200mm.

Cement concrete pipes-

maybe plain,reinforced or

prestressed with dia varying

500mm to 2500mm or more.

i. Low maintenance cost

ii. Durable with 75 years

life span

iii. Can be casted at the site

iv. Heavy in weight and

hence can withstand

i. If no reinforcement then

no tensile strength and

thus cant withstand

pressure

ii. Heavy and difficult to

transport

Pi Ad t Di d t


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Pipe Advantages Disadvantages

Copper pipes i. Dont sag orbend due to

hot water

ii. Dont corrode

iii. Can be bent easily

i. Use is restricted for hot

water in buildings

ii. Costly

Galvanised iron pipe- dia

vary from 6mm to 75mm

i. Cheap, light in weight,

easy to handle and

transport

ii. Easy to join

i. Can be affected by acidic

or alkaline water

ii. Short life of pipe of 7 to

10 years

Lead pipes i. Can be easily bent andhence less number of

specials are required in

joinery.

ii. Adopted for apparatus

required for alum and

chlorine dosages.

i. Not used for watertransport

ii. If proper care is not

taken, can cause lead

poisioning

iii. Reacts with acidic water

iv. Sag or bend due to hot

water

Steel pipes i. Available in long lengths

hence less joints

ii. Cheap in first cost.

iii. Durable and can resisthi h internal water

i. Maintenance cost is high

ii. Likely to be rusted by

slightly acidic or alkaline

wateriii. Re uire more time for

Pipes Advantages Disadvantages


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Pipes Advantages Disadvantages

Plastic pipe- they are black in

colour and resistant to most

of the chemicals.

i. Freedom from damage

due to thawing and

freezing of waterii. Cheap

iii. Durable and enough

strength to resist impact,

sunlight etc

iv. Flexible and low

hydraulic resistancev. Free from corrosion

vi. Good electric insulators

vii. Light in weight and easy

to bend, join and install.

viii. Available in coils and

thus easy to transport.

i. Coefficient of expansion

is large

ii. Difficult to obtain theplastic pipe of uniform

composition.

iii. Less resistant to heat

iv. Some types of plastic

may impart taste to

water.

Wood pipes- they are planks

of wood held together by

steel bands

i. Light weight i. Alternate conditions of

dryness and wetness can

cause wet rot

ii. Cant bear high pressures

Wrought iron pipes i. Light weightii. Can be easil cut

i. Costlyii. Less durable

Pi i


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Pipe corrosion

Factors of pipe corrosion are:

Acidity

Alkalinity

Biological action

Chlorination

Electrical currents Mineral and organic constituents

Oxygen

Effects of pipe corrosion are:

Disintegration of pipe

May impart colour, taste or odourto water

May make water unfit for drinking

Prevention of pipe corrosion:

Cathodic protection

Proper pipe material


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RADIAL SYSTEM OF WATER

SUPPLY


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This is a zoned system.

Water is pumped to the distribution reservoirs.From the reservoirs it flows by gravity to the tree system of pipes

The pressure calculations are easy in this system.

Layout of roads need to be radial to eliminate loss of head in bends.

This is most economical system also if combined pumping and gravity flow is adopted.


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This system is not adopted in India, because for this system the roads should belaid out radial from the centre.

This system is the reverse of ring system.

The entire district is divided into various zones and one reservoir is provided for

each zone, which is placed in the centre of zone.


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PIPE APPURTANANCES

The distribution pipes are provided with various pipe appurtenances oraccessories so as to make the distribution of water easy and effective

Air valves

Bib cocks

Fire hydrants

Reflux valves

Relief valves

Scour valves

Sluice valves

Stop cocks

Water metres

1 Air Val es


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1. Air Valves

Also called air relief valves.

Some quantity of air is contained in the flowing water and this air tries to

accumulate at high points along the water pipes. In order to provide an

exit for such accumulated air, the air valves are provided at summits along

the water pipe.

The air valves should be located at points which are close to or above thehydraulic gradient. If air valves are not provided, there are chances for

pipes to be air-locked.

The effective area of flow and consequently the discharge through water

pipe are greatly reduced due to air-locking.

The provision of air valves along water pipe also helps in admitting airquickly when vacuum occurs in water pipe due to sudden breakdown of

water pipe at low points.

l f h b


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An air valve consists of a cast-iron chamber,

float, lever and poppet valve. The chamber

may be circular or rectangular in shape. TA

poppet valve is a valve that is lifted bodily. The

working of the air valve is as follows:o In the normal condition, the chamber is

full of water drawn from water pipe. The

float therefore touches the roof of

chamber and poppet valve is in a closed

position.

o

When air from water pipe enters thechamber, it starts accumulating just below

the roof of chamber. This accumulation of

air makes the lever to work and to bring

down the float.

o When air escapes, the water rises again in

the chamber and the lever works to raise

the float. It ultimately results in theclosing of poppet valve before escape of

water takes place through it.

o The action of air valve is then repeated.

2. Bib Cocks


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2. Bib Cocks

These are the water taps which are attached at the end of water pipes and

from which the consumers obtain water.

It is operated from a handle and when handle is turned, the opening from

which water comes out , gets increased or decreased in size.

The bib cocks may also be of push type and they operate automatically.

They open out when a slight push is given and close down as soon as the

push is removed or withdrawn.

3. Fire Hydrants


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A hydrant is an outlet provided in water pipe for tapping water mainly in case of

fire.

Location:

The number of fire hydrants in distribution system and their location depend on variousfactors such as utility of buildings, requirement of water for fire fighting, chances of fire

occurrence, population of area, etc.

the fire hydrants are placed at all street junctions and they are so located that if a circle

of about 60 to 90 metres is drawn from any hydrant, it will partly overlap that of the

adjoining hydrant

Requirement of a Fire Hydrant: Following are the requirements of a good firehydrant:

o It should be cheap.

o It should be easily detectable in case of a fire.

o It should be of such nature that it can be easily connected with the hose or motor

pump.

o It should function properly and should not go out of order during operation.

o It should permit undisturbed flow of water when being fully opened.

Types of Fire Hydrants

1.Flush Hydrant:


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y

A flush hydrant is provided below the footpath or street leveland it is protected or

covered by cast-iron box or brick masonry chamber.

The flush hydrant is more safely attached to the water pipe and cannot therefore be easily

dislocated. However it is not prominently seen and hence, some arrangement has to bemade to detect easily when a fire occurs. Usually a plate with letters F.H. (Fire Hydrant)

is attached on some nearby permanent structures, such as building, compound wall,

light-post, telephone-post, big tree, etc.

Working: When the nut is operated by a key, the valve goes up and it allows the water from

water pipe to rise and to fill the barrel. The water is then delivered from the outlet. The

diameter of outlet should correspond to the diameter of hose to be attached to it. The usual

diameter is about 60 mm or so.

2.Post Hydrant:

a post hydrant is provided projecting

above the road level and its heightabove road level is about 1 m to 2 m.

this type of hydrant is more prominent

and can be easily detected when a fire

occurs.

However it is liable to be damaged by

mischief or misuse.

4.Reflux Valves


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Also known as the check valves or non-return valves.

A reflux valve is an automatic device allows water to go in one direction only. The

swing type of reflux valve is widely used in practice.

When water moves in the direction of arrow, the valve swings or rotates aroundthe pivot and it is kept in an open position due to the pressure of water. When

flow of water in this direction ceases, the water tries to flow in a backward

direction. But in this case, the valve occupies its seat and it thus prevents the

passage of water in the reverse direction.

The reflux valve is invariably placed in water pipe which obtains water directly

from pump. When pump fails or stops , the water will not run back to the pump

and thus the pumping equipment will be saved from the damage. Similarly at

inter-connections between a polluted water system and a potable water system,

the provision of reflux valve will prevent the entry of polluted water into the pure

water.

5.Relief Valves


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These are also known as the automatic cut-off valves or safety valves.

The load on the spring is adjusted to the maximum pressure.

The relief valves are located at every point along the water pipe wherepressures is likely to be maximum.

When pressure of water exceeds a predetermined limit, the valve

operates automatically and it will save a particular section of water pipe

before bursting of pipe takes place.

6.Scour Valves


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These are also known as the blow-off valves or drain valves or washout

valves.

These are ordinary sluice points in mains.

They are operated to remove sand or silt deposited in the water pipe.

They are operated with hand and closed down as soon as clear water is

seen passing through them.

7 Sluice Valve


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7.Sluice Valve

These are also known as the gate valves or shut-off valves or stop valves.

These valves control the flow of water and are helpful is dividing the

water mains into suitable sections.

They are generally placed at a distance of about 150 m to 200 m and at

all junctions.

For long straight mains, the sluice valves can be installed at a distance of

about 1 km also to divide the pipe in different sections.

The raising or lowering of valve is carried out by rotating the handle from

top.

8 Stop Cocks


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8.Stop Cocks

These are small sized sluice valves and they are installed in service pipes

serving the bib cocks.

They operate on the same principle of sluice valve and they are usually

used upto sizes of about 50 mm.

They are placed on water pipe leading to flushing tanks, wash basins,

water tanks, etc.

9.Water Meters


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These are the devices which are installed on the pipes to measure the

quantity of water flowing at a particular point along the pipe.

The readings obtained from the metres help in working out the quantity ofwater supplied and thus the consumers can be charged accordingly.

The water meters are usually installed to supply water to industries,

hotels, big institutions, etc.

The water meters can be classified into the following two categories:

(1)Positive displacement type meters:

The positive displacement type meters record the number of times a container of

known volume is filled and emptied with water.


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(2)Velocity Meters:

The velocity meters work on the principle of velocity of entering water and

higher the velocity of water, more will be the discharge through meter. The

turbine meters and venturi meters come under this category.

Following are the requirements of a good water meter:

o It should accurately measure the discharge of water to the permissible

tolerance of about 2% and capable of registering even a small quantity of

flow of water.

o It should be easy to repair and to maintain in good working conditions.

o It should contain an arrangement in the from of a screen at the inlet do

that the entry of grit is prohibited.

o It should not offer any resistance or obstructions to the natural flow of

water and should be non-corrosive.


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Water Pollution And Water

Management

So rces of Water Poll tion


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Sources of Water Pollution

Domestic Sewage Industrial Waste

Catchment Area

Distribution System

Oily Wastes

Radioactive Wastes

Source of Water Supply

Storage Reservoir

Travel of Water


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Types of Water Pollution


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Types of Water Pollution

(1) Physical PollutionOccurs due to following factors :-

Color

Taste and Odour

Temperature

Turbidity

Suspended Matter

Radioactivity

Foam


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(2) Chemical PollutionPollution due to inorganic chemicals :-

Acids

Alkalies

Toxic Inorganic Compounds

Dissolved Inorganic Substances

Suspended Inorganic Substances

Types of organic pollution in water :-

Suspended organic substences

Dissolved organic substances


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(3) Bacteriological Pollution Occurs due to presence of pathogenic bacteria, viruses, parasitic worms,

etc.

Sources are :-

Domestic Sewage

Industrial Waste

Preventive Measures


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Preventive Measures

Administration Catchment Areas

Closed cycle operations for industrial plants

Conservation of forests

Design

Discharge into water sources

Economic use of water Funds

Joint responsibily

Legal provisions

Personnel

Planning of towns

Propaganda Regulations

Research

Re - use

Water Management


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Water Management

Some salient aspects are :- Hydrosphere

Hydrological Cycle

Water Exchange

Transport of water

Measures For ReShaping Local Water


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p g

Balance

Adequate and proper treatment of industrial waste. Adopting suitable measures for water pollution.

Construction of storage reservoirs.

Cultivation and preservation of productive forests.

Developing large scale underground water reservoir.

Improving characterstics of catchment area for rivers and strems.

Soil improvement techniques.

Conservation of Water Resources


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Conservation of Water Resources

New techniques should be found out for reducing water requirements ofindustries having high water demand.

Water per unit farm should be reduced.

Economical use of water should be encouraged.

Dumping of sewage into natural water resources should be avoided.

Industries must reduce their requirements for the water consumption. The water conservation should form a part of the water use.

The water use and conservation should be achieved through the multi

purpose projects.


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Radioactivity and Water

Supplies

Radioactive Sources


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Radioactive Sources

Atomic Reactors Nuclear Explosions

Soils and Rocks

Use of Radioactive Substances

Waste of Radioactive Substances

Disposal of Radioactive Waste


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Disposal of Radioactive Waste

Dilution (diluted with inert materials) Storage (waste are stored till they decayed and become harmless)

Reclamation (converted to usefull products)

Effect of Treatments of Water


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Effect of Treatments of Water

The coagulation is not effective in removing radioactive substances. The sand filters only remove colloidal matter held in suspension.

The limesoda softening process is fairly effective.

The zeolite or ion exchanging method is proving to be effective.

Recommended Methods


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Recommended Methods

Phosphate coagulation Electrodialysis

Adding clay materials

Adding metallic dusts

Distillation of water


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COLLECTION AND CONVEYANCE

OF REFUSE

COLLECTION AND CONVEYANCE OF REFUSE


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The solid and liquid waste are to be properly collected and conveyed at

suitable spot. The refuse formed should be rapidly , conveniently and safely carried to

disposal site to maintain clean environment.

METHODS OF CARRYING

WASTE REFUSAL

- Different types of refuse are collected separately andthen disposed off.

-The garbage of refuse is collected from roads andstreets and then carried to suitable places.

CONSERVANCY SYSTEM-In this system, water is used to convey the sewageto the point of treatment of water disposal.

-Garbage is collected similarly like conservancysystem . The storm water may be carried separatelyor may be allowed to flow with sewage

WATER CARRIAGE SYSTEM

SYSTEM OF SEWERAGE


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SYSTEM OF SEWERAGE

There are three methods of sewerage

1. Separate system

2. Combined system

3. Partially separate system

-Separate system - In this system , two sets of sewerage is laid. One for carrying

sewerage to treatment plan and in the other ,water is directly discharged into

natural outlet ( river or stream )

-Combines system - In this system , only one set of sewerage is laid which carries

both , sewerage and water waste

-Partially separate system - This system permit early washings by rain into sewers

by sewage. But , when the quantity of storm water exceeds a particular limit , it iscollected and conveyed in open drains to the natural river or streams.

TYPE OF SEWERAGES


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TYPE OF SEWERAGES

TYPE OF SEWERAGES

Dry weather flow

-Domestic orsanitary sewage - Industrial waste

Storm water


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CONSTRUCTION OF SEWERS

MATERIALS FOR SEWERS


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Factors to be considered while selecting materials for the sewers;

Cost : it should be moderate and reasonable

Durability : material should be durable to prevent frequentreplacements

Imperviousness : the material should be impervious in nature

Abrasion resistant

Corrosion resistant

Strength : sewers are generally laid underground hence subjected to

heavy external loads thus requires a strong construction material Weight : the material should possess moderate weight so as to make

handling and carrying of sewers easy

MATERIALS USED :

1. Asbestos cement sewers 6. Plastic sewers

2. Brick sewers 7. Steel sewers

3. Cast iron sewers 8. Stoneware sewers

4. Cement concrete sewers 9. Wood sewers

5. Corrugated iron sewers

ASBESTOS CEMENT SEWERS

these sewers are made from mixture of asbestos fibers and cement

il bl i i t 900 di t


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are available in sizes up to 900 mm diameter

Advantages :

Its easy to cut and join these sewers are durable against soil corrosion and offer good resistance to salts, acids

and other corrosive materials

inside surface is exceptionally smooth thus offering least resistance to

friction

light in weight thus easy to handle

Disadvantages :

These sewers are brittle and cannot stand impact forces during handling

processes

Structural strength of the material is poor thus cannot be laid to resist

heavy external loads

BRICK SEWERS

Earliest forms of sewers were made of brick

At present not favored mainly because of more labor involved their

construction

CAST-IRON SEWERS

Available in sizes varying from 150 mm diameter to 750 mm diameter

Th hi h t th


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They possess high strength

They are durable

Their surfaces should be coated with paint or cement concrete to resist the

action of acids in sewage They are watertight

They are adopted for special purposes, such as :

Danger of contamination : they are used where sewers are laid under or

over the water pipelines so as to prevent contamination of underground

water due to leakage in sewers

Expensive road surface : as they do not require frequent repairs they areused under costly road surfaces

Heavy external load : used in sewers under railway lines, foundation wall

as it could withstand heavy external loads

Pressure : for conveying sewage through pumping stations and treatment

works, cast iron sewers are adopted

Temperature : these are suitable for places which are subject to

considerable change in temperatures

Vibrations : these are proven to be advantageous where ground is likely

to be subjected to heavy monuments and vibrations

Wet ground : these sewers in wet ground results in considerable

reduction of the rate of infiltration

CORRUGATED IRON SEWERS


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mainly used for carrying storm water only

corrugations reduce the velocity of flow and hence for given diameter and slope

the carrying capacity of the sewer is also reduced

made in varying metal thicknesses and in diameters up to 4500 mm

these sewers should be protected from effects of corrosion by galvanization or by

bituminous coatings

PLASTIC SEWERS

use of plastic sewers still in elementary stage

More commonly used for carrying water than sewage

In cases of industrial wastes with corrosion problems, they are proven to be useful

They possess excellent flow characteristics which permit flatter ruling gradients,

economic excavation, faster laying, greater shock resistance, etc.

They are available in long lengths and permit cold negotiation of bends Strength of these sewers is reduced with increase in temperature

They are liable for stress cracking and ductile failure in vacuum

STEEL SEWERS

used mainly at places where imperviousness, lightness and resistance to high pressure


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y p p , g g p

is needed

these sewers are flexible and can absorb vibrations and shocks in a better way

generally used for main, outfall and trunk sewers having diameters exceeding 750 mm

These sewers are either riveted or welded

May be protected from corrosion by galvanization or by provision of bituminous coating

or by using special corrosion resistant steel in the manufacturing process

CEMENT CONCRETE SEWERS

they may be plain or reinforced

plain cement concrete sewers used up to 600 mm diameter

Reinforcing bars necessary beyond the limit of 600 mm diameter

Ways of placing reinforcements :


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Cement concrete sewers withsingle circular cage

reinforcement

Main circumferentialreinforcement is placed at a

distance of about 25 mmfrom inner surface

Such arrangement adoptedwhen sewer diameter is lessthan 800 mm and is subjectedto internal pressure only

Cement concrete sewer withdouble circular cage

reinforcement

Main circumferentialreinforcement placed in 2 sets

: first at distance 25 mm frominner surface and other 25from outer surface

Such arrangement is adoptedwhen sewer diameterexceeds 800 mm and itssubjected to internal as wellas external pressures

Cement concrete sewer withelliptical cage reinforcement

Main circumferentialreinforcements placed to form

elliptical rings Such arrangement adopted

for large diameters of sewersand its subjected to externalpressures only

STONEWARE SEWERS

also known as vitrified clay sewers or salt-glazed sewers as they are prepared

form ario s cla s and shale


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form various clays and shale

Manufactured in short lengths and diameters

Generally favored for house drainage connections

Advantages : If properly laid, these sewers are strong enough to take load of backfilling

and traffic

Interior surface is impervious and smooth

overall performance in carrying sewage is appreciable

These sewers are cheap and easily available

These sewers are durable and offer better resistance to corrosion fromacids and erosion due to grit and high velocity of flow

Disadvantages :

these sewers are brittle in nature and likely to be damaged during transport

of handling processes

Not strong enough to allow sewage to flow through them under pressure

These are bulky and heavy in weight thus making it difficult to handle,

transport and lay them

WOOD SEWERS

Life of wood sewers is short and are rarely adopted for conveyance of sewage

SHAPES OF SEWERS Circular shape


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Circular shape

Advantages :

It affords the least perimeter hence construction material required is

minimum, thus being the cheapest and most economical There are no corners hence chances of deposition of organic matter is

reduced to minimum

They are easy to manufacture or construct and handle

They possess excellent hydraulic properties

They prove to be advantageous when sewers are running at least half

full and discharge does not vary too much

Non-circular shape Advantages :

They bring down cost of construction

They improve velocity of flow when depth of sewage is low

They secure more structural strength

They simplify process of construction

They are made large enough for a man to enter for cleaning, repairing,

etc.

Types of non-circular shape sewers:

1. basket-handle section 6. rectangular or box-type section

2. Catenary shaped section 7. semi-circular section

3. Egg-shaped or ovoid section 8. semi-elliptical section

4. Horse-shoe section 9. U-shaped section

5. Parabolic section

BASKET-HANDLE SECTION

It carries the small discharges through the bottom narrow portion and during

monsoon the combined sewage is carried through the full section


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monsoon, the combined sewage is carried through the full section

This shape of sewer not generally used at present

CATENARY-SHAPED SECTION

This shape of sewer is suitable for tunneling work

EGG-SHAPED SECTION

This type of sewer is suitable for carrying combined flow. It gives a slightly higher velocity during low flow than a circular sewer of same

capacity

But its difficult to construct and less stable than circular section

HORSE-SHOE SECTION

This type of sewer is used for construction of large sewers with heavy discharges


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y g y g

such as trunk and outfall sewers

It is mostly used for constructing sewers in tunnels

PARABOLIC SECTION

It is suitable for carrying comparatively small quantities of sewage

Economic in construction

RECTANGULAR OR BOX-TYPE SECTION

It is sometimes used to work as a storage tank

It is easy to construct and stable

SEMICIRCULAR SECTION

It gives a wider base at the bottom hence becomes suitable for constructing large

sewers with less available headroom


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sewers with less available headroom

Rectangular section is preferred over them as it possesses better hydraulic

properties

SEMI-ELLIPTICAL SECTION

It is adopted for soft soil areas as it is more stable

This section is not suitable for carrying small quantity of sewage

Generally adopted for sewers having diameters greater than 1.80 m

This section possess good hydraulic properties except at low depths

U-SHAPED SECTION

Such an arrangement is adopted for combined sewers having predominant flow of

storm water

JOINTS IN SEWERS


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Requirements of a good sewer-joint :

construction should be such that tree roots cannot penetrate through it

It should be capable of resisting the effects acidic, alkaline or gaseous

actions of sewage

It should be cheap and economical

It should be easy to construct

It should be non-absorbent and durable

Types of joints :

Cement mortar joints : cement mortar of proportions 1:1 or 1:2 is used for fillingthe joint space

Collar joints : theses joints are used for sewers of large diameters

Flexible or bituminous joints : these joints are flexible are adopted at places

where there are chances of sewer settlement

Mechanical joints : mechanical devices such as flanged rings, bolts, etc. are used

to keep two ends of sewer together, and used for metallic sewers

Open joints : these are adopted when there is no objection to the infiltration and

when the sewer is passing through dry ground

LAYING AND TESTING OF SEWERS The borings or trial holes are dug along the proposed sewer line to ascertain the natur


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The borings or trial holes are dug along the proposed sewer line to ascertain the natur

of ground

From longitudinal section of sewer line, manhole positions are marked

The center line pegs of sewer line are driven at distance of every 7.5015 m Center line of the sewer should be properly maintained by:

Vertical post method :

It is adopted in all cases for taking the levels of invert of all proposed sewer

lines

Offset line method :

a parallel offset line is marked usually at a distance D which is about one-halfthe trench plus 600mm

Other side is used to dump the excavated material

This method is adopted for short duration of time, mainly to avoid

inconvenience to traffic

The modified levels of invert at each sight rail are given and these are marked on

the sight rail

The excavation of trench for laying the sewer line is started


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y g

The sewers are now laid in the trench or if they are to be constructed at site, the

process of construction of sewer is started.

Test for water tightness of joints is then carried out The refilling of trenches is started after the sewer line is properly laid in position.

Each layer should be well watered and rammed.

VENTILATION OF SEWERS


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Sewers should be properly and satisfactory ventilated for following reasons:

Continuous flow : the surface of sewage should remain in contact with free

air otherwise air-locks will be formed Disposal of sewer gases

METHODS OF VENTILATION :

Manholes with chemicals :

Chemicals are placed in manhole covers, these chemicals react with sewer gasesand make them harmless

This method is costly hence rarely adopted

Manholes with gratings :

Here manhole covers are provided with gratings or openings through which

sewer gases escape

This method causes pollution hence adopted in isolated places Proper construction of sewers

Proper design of sewers

Proper house drainage system

Providing Ventilating columns or shafts

CLEANING AND MAINTENANCE OF

SEWERS


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SEWERS

Cleaning of sewers is necessary

To check breakage of sewers

Check for clogging

Check and prevent odors

Methods for cleaning and maintenance of sewers

Cleaning and flushing Cleaning of large sewers is done manually

Cleaning of small manholes is effected by flushing

When flushing is inadequate, following methods are employed:

Flexible rod

Mechanical tools

Use of pills Cleaning of catch pits, etc.

Regular Inspection

Periodical repairs should be done

Proper connections : connections of lateral sewers with branch sewers

should be carried out by properly and made watertight

SURFACE DRAINS


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These are sometimes constructed to provide a cheap arrangement for collecting

sullage and storm water

But they are less hygienic as they are open and exposed to atmosphere

SHAPES OF SURFACE DRAINS

Rectangular surface drains

These drains are suitable for carrying heavy discharge. They do not develop the required velocity when depth of flow is small and

hence they get easily deposited.

Semi-circular surface drains These drains can be easily constructed

These drains are found to be suitable for small streets where the discharge to be

accommodated is of small quantity.


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accommodated is of small quantity.

U-shaped surface drains

These are easy to construct They combine the advantages of semi-circular drains and rectangular surface

drains

V-shaped surface drains

These drains possess better hydraulic properties but are difficult to construct

These drains are capable of producing a good velocity


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DESIGN OF SEWER

GENERAL APPROACH


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The general approach to design a sewer is same as that of water mains. Themain differences between the two are:

Size of particles

Pressure

MINIMUM AND MAXIMUM

VELOCITIES


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VELOCITIES

SELF CLEANSING VELOCITY The silting or deposition of particles of solid matter is undesirable in sewers

and hence, the sewers should be laid at such a gradient that a minimum

velocity which will prevent the silting of particles in sewers is developed over

a wide variation in discharge of sewerage. Such a minimum velocity is

known as the self cleansing velocity.

It should be developed at least once in a day; preferably twice. It dependson the nature of suspended matter in sewage and the size of sewer.


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NON-SCOURING VELOCITY If the velocity of the flow exceeds a certain limit the particles of solid matter

start to damage the inside smooth surface of sewers or a scouring action

takes place. The maximum permissible velocity at which no such scouring

action takes place is known as non-scouring velocity and it will mainly

depend on the material used in the construction of sewers.

The sewage flows in the sewers under gravitational force, which is obtainedby laying the sewers on slope. The velocity of flow depends directly on the

gradient of sewer and hydraulic mean depth of condition of the sewer with

respect to roughness. The optimum slope or grade is required to be

calculated to achieve the self-cleansing velocity.


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Following points should be noted in connection with the self cleansing andnon-scouring velocities:

1. Gradient of sewers are to be properly correlated to achieve desired

results.

2. In a flat country, the design of sewers should be such that the self-

cleansing velocity is developed at the time of maximum discharge.

3. In a rough country , the sewers are designed to achieve non scouring

velocity at the time of maximum discharge and self cleansing velocity at

the time of minimum discharge.

4. For combined sewers, it becomes difficult to achieve self-cleansing

velocity at the time of minimum discharge. For this purpose special forms

of sewers should be adopted.

FORMULAS FOR DESIGN OF

SEWAGE


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SEWAGE

The main factors which influence the flow of sewage in sewers are: Characteristics of sewage

Conditions of flow

Cross sectional area of sewer

Presence or absence of bends , obstructions etc.

Roughness of interior surface Slope of sewer etc.

Following are the common empirical formulas used in design of sewers:

chezy,s formula

Bazin,s formula

Mannings formula Kutters formula

Crimp and bruges formula

Hazen and williams formula

TIME OF CONCENTRATION


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This term is used in connection with the design of storm water drains. Asthe rain falls on the ground, all the area to be served by the sewer doesnot start to contribute immediately to the flow of sewer but the flow isbuilt up gradually as follows:

The area just near the sewer line will start contributing first and it will goon increasing as more and more area starts to contribute.

When the whole area is contributing to the flow of sewer maximum limitof flow will be reached and it will be equal to the rate of precipitation ofrain water.

The maximum flow continues until the storm stops. The flow thengradually falls down as the area near the ground line stops contributingfirstly, while flow continues to come for considerable time from the distantareas.

The importance of time of concentration in the design of storm watersewers lies in the fact that out of all the storms of equal frequency ofoccurrence, that storms which has duration equal to the time ofconcentration, produces the maximum flow in sewer.

DESIGN PROCEDURE


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1. FORMATION OF ZONES: the area to be served by drainage system is

divided into zones.

2. ARRANGEMENT OF SEWERS : the proposed arrangement for sewers

for different zones is worked out. Low lying areas are isolated and

pumping systems are installed for them. Various sewers like main sewers,

branch sewers, trunk sewers etc. are marked on map.

3. QUANTITY OF SEWAGE: after proper study of variations in rate ofsewage, a suitable multiplying factor is applied to the quantity of sewage

for which sewer is designed.

4. Velocity of flow: a suitable value for velocities of flow is then determined.

Thus value should fall between the minimum and maximum limits.

5. Section of sewer:Section of sewer=sectional area of sewer x velocity of flow

6. GRADIENT : slope of sewer line is worked out and longitudinal sections

of each are drawn to a suitable scale.


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Water appurtenances


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To make the process of construction easy and to have efficient working andmaintenance, the sewer system requires various other additional structures

known as sewer appurtenances

Important sewer appurtenances:-

Catch basins or catch pits

Clean-outs

Drop manholes

Flushing tanks

Grease and oil traps

Inlets

Inverted siphons

Lampholes Manholes

Sto

Date post:	28-Feb-2018
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