Design of Water Treatment Plant

r ~"'.~IIIIIIIItQIIP'''''''''llqliill1"mllftllllJl'l'*~''''IIIIJPP~IIIIIIfIP"IIIQDI.IIIIIIIIIIIJI"II~ CIVIL ENQINEERING

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STUDIES

ENVIRONMENTAL ENGINEERING

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Ii PROJECT REPORT ON

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DESIGN OF WATER TREATMENT PLANT

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~ACULTY ADVISOR

PREPARED BY

,

JAIN. NIKHIL.R.

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DEPARTMENT

OF CIVIL ENGINEERING

I .

Sardar VallabhbhaiRegionalCollege of Engineering c" Technology

I

Surat-395007. [Gujarat)

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DEPARTMENT OF CIVIL ENGINEERING

SARDAR VALLABHBHAI

REGIONAL COLLEGE

.OF ENGINEERING & TECHNOLOGY

SURAT

- 395007

CERTIFICA TE

This is to certify that the project,entitled "Design of Water Treatment has beenpreparedby $-,./A. IJC~~./;/. 71.

Roll. No

26.

Plant",

a final year student of

Civil Engineering, during the year 1998-99, as a partial fulfillment of the requirement for the

award

of

Bachelor

of

Engineering

Degree

in

Civil

Engineering

of

SOUTH GUJARAT UNIVERSITY, SURAT. His work has been found to be satisfactory.

.

GUIDED BY:

---------.

~~'-' .

of B. K. Samtani)

( Dr. B. K. K'atti)

Acknowledgment Right from the procurement of material to the cleaning of conceptual difficulties, we cannot withhold our sincerest thanks to Prof. B.K.Samtani, Civil Engineering department,

SVRCET,

Surat,

without

whose

invaluable

guidance

and

cooperation the project would not have been accomplished.

we would also like to thank Dr. B. K. Katti, Prof. and Head, Civil Engg. Department, whose support and encouragement are transparent in the work it self.

Lastly, we would like to thank Mr. SUNIL MISTRY (Navsari) for preparing the report.

I"

DEEPAK

V.M.

(15)

DESAI DHARMESHM.

(16)

DHAMI VIJAY M.

(17)

DINTYALA SRINADH

(18)

DIWANJI NIBHRVTA R.

(19)

G. CHANDRAMOHAN

(20)

GAJJAR TEJAL S.

(21)

GAlJRAV PARASHAR

(22)

GHADIYALI MINESH S.

(23)

GHOSH lITPAL

(24)

GOPALAKRISHNANR.

(25)

JAIN NIKHIL R.

(26)

JAJlJ PRADEEPR.

(27)

CONTENTS Sr.No.

Title

1.0

INTRODUCTION

2.0

BASIC DATA FOR THE DESIGN OF WATER SUPPLY SYSTEM

3.0

SALIENT FEATURES OF WATER TREATMENT PLANT

4.0

POPULATION FORECASTING

5.0

CALCULATION OF WATER DEMAND 5.1

Calculation of different drafts

5.2

Design capacity of various components

5.3

Physical and chemical standards of water

5.4

Comparison of given data and standard data

5.5

Suggested units of treatment plant

6.0

DESIGN OF UNITS 6.1

Collection units 6.1.1

Design of intake well

6.1.2

Design of pen stock

6.1.3

Design of gravity main

6.1.4

Design of jack well

6.1.5

Design of pumping system

6.1.6

Design of rising main

6.2

6.3 7.0

Treatment units 6.2.1

Design of aeration unit

6.2.2

Design of chemical house and calculation of chemical dose

6.2.3

Design of mechanical rapid mix unit

6.2.4

Design of cIarifiocculator

6.2.5

Design of rapid gravity filter

6.2.6

Disinfection unit Storage tank CONCLUSION REFERENCES:

-.=

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INTRODUCTION

Water, undubiously is a basic human need. Providing safe and adequate quantities of the same for all rural and urban communities, is perhaps one of the most important undertaking, for the public works Dept. Indeed, the well planned water supply scheme, is a prime and vital element of a country's social infrastructures as on this peg hangs the health and wellbeing of it's people. The population in India is likely to be Hundred crores by the turn of this century, with an estimated 40% of urban population. This goes on to say that a very large demand of water supply; for Domestic, Industrial, Firefighting, Public uses, etc.; will have to be in accordance with the rising population. Hence, identification of sources of water supply, there conservation and optimum utilization is of paramount importance. The water supplied should be 'Potable' and 'Wholesome'. Absolute pure water is never found in nature, but invariable contains certain suspended, colloidal, and dissolved impurities (organic and inorganic in nature, generally called solids), in varying degree of concentration depending. upon the source. Hence treatment of water to mitigate and lor absolute removal of these impurities (which could be; solids, pathogenic microorganisms, odour and taste generators, toxic substances, etc.) become indispensable. Untreated or improperly treated water, becomes unfit for intended use proves to be detrimental for life. The designed water treatment plant has a perennial river as the basic source of water the type of treatment to be given depends upon the given quality of water available and the quality of water to be served. However such an extensive survey being not possible in the designed water treatment plant. It is assumed that all kinds of treatment processors are necessary and an elaborate design. 1

The design of water treatment plant for Mandvi situated in district Surat of Gujarat has been done. Mandvi is located on the bank of river Tapti. The latitude and longitude of the town corresponding 21.61 N, 73.118E respectively. The population of the given year 2031 will be 61400. There are many industries like diamond industries and chemical industries in the town so, treated water supply for domestic and industrial uses are very essential.

...

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BASIC DATA FOR THE DESIGN

OF

WATER SUPPL V SVSTEEM The given problem includes the design of water treatment plant and distribution system and also the preparation of its Technical Report and Engg. Drawings showing the required details of collection and treatment units. The following Table gives the basic necessary data required for the design of water treatment plant. (Table No. 2.1) No.

Description

1.

Name of the place

2.

District

3.

Location

- Mandvi - Surat

(a) About 27 mile (43.2 kms) away from Kim railway station of western railway. (b) Nearest railway station is Mandvi station (9 mile, 14.4 kms) on Tapti valley railway (c) On the right bank of Tapti. 4.

Latitude (Lat.)

21.61 N

5.

Longitude (Lon)

73.18 E

(Table No. 2.2)

Design Considerations

Sr.No.

Values 30

1.

Design period (years)

2.

Average rate of water supply (Ipcd)

135

3.

Industrial demand (MLD)

0.6

4.

Quality of raw water I)

..

Ph

7.5

50

II)

Turbidity (mg/L)

III)

Total Hardness (mg/L) [as CaC03]

550

IV)

Chlorides (mg/L)

200

V)

Iron (mg/L)

2.5

VI)

Manganese (mg/L)

3.5

VII)

Carbonates (mg/L)

110

VIII)

M.P.N. (No.l100ml)

3.5

5.

I Population of past four decades (In thousand)

6.

Year 1961 Year 1971 Year 1981 Year 1991 I F.S.L. of river (R.L. in mts.)

7.

I Ground level at ; (R.L. in mts.)

8.

07 12 15 22 27

a)

Jack well site

28

b)

Location of aeration unit

29

I Invert level of raw material gravity intake pipe 24-

(R.L. in mts. ) 9.

I Length of raw water rising main (mts.)

10.

I Source supply:

200

A river with sufficient perennial flow to satisfy the required demand. 11.

I Highest G. L. in (m)

34

12.

I Lowest G. M. in (m)

28

13.

I Bed level of river (m)

I

22

14.

I H.F.L. of river (m)

I

32

3

~r::tr

SALIENT FEATURESOF

WATER TREATMENT PLANT 3.1. ~

Populationof the town (In thousand) Year 1991

:22

Year 2031

: 61.4

2. Average daily draft (M.L.D.)

: 8.89

Maximum daily draft (M.L.D.)

: 13.33

3. Design period (Years)

: 30

3.2 Intake Works Intake Well :1

No. of units 2. Dia. Of well (m)

: 5.5

3. Ht of intake well

:4 : 24

. R.L. of bottom well (m) 5

: 28

R. L. of top of well (m)

... Detention

:10

time (min)

Penstock ~

General

:2

No. of penstockwell

: 400

2. Dia. Of penstock (mm)

Bell mouth strainer 01 No. of bell mouth strainer

:2

2. Dia. (m)

: 0.9

4

Collection Works

-

Gravity main :1

No. of units '" Dia. (mm)

: 550

3 Invert level (m)

: 23.88

~ slope

: 1:862

Jack well No. of units

:1

Dia. (m)

: 6.15

3 Depth of water

: 3.12

.

: 10

Detention time (min)

Rising main and pumping units Rising : ~

: 0.45

Dia. (m)

:1

2 Velocity of flow (m/s)

Pumping unit: : 60

Capacity of eachpump(HP)

:1

2. No. of pumps

3.3 Aeration unit ~

: 31.40

R.L. of aeration unit (m) (top)

:29.40

(Bottom) 2. Dia. Of top tray (m)

:1

3. Dia. Of bottom tray (m)

:5

4 Dia.of each tray decreasing by(m)

:1

5. Rise of each tray (m)

: 0.4

6. Tread of each tray (m)

: 0.5

Dia.of central rising main pipe (m)

: 1.0 :5

8 No. of trays 5

Treatment works

I

Chemical storage house

1. Length (m)

: 20

2. Breadth (m)

: 12

3. Height (m)

: 3.0

Chemical Dissolving Tank

1. No. of Tank

:1

2. Length (m)

:3

3. Breadth (m)

:2

4. Depth (m)

: 1.5

Flash Mixer

1 No. of units

:1

2. Dia. (m)

: 1.6

3. Detention time (min)

: 0.5

4. Height (m)

: 2.6

5. Depth of water (m)

: 2.37

Clariflocculatoi

Flocculator :

1. No. of units

:1

2. Dia. (m)

: 10.16

3. Dia. of Inlet pipes (m)

:0.45

4. Depth of water flow (m)

: 3.5

5. Velocity of flow (m/s)

: 1.0 6

Clarifire : 1. No. of units

:1

2. Dia. (m)

: 23

3. Depth of water (m)

: 4.4

4. Overall depth of tank (m)

: 4.7

5. Slope of bottom

:8%

Rapid Sand Filter 1. No. of units

:2

2. Surface area (Sq. m)

:58.48

3. Dimension of unit (m x m)

: 8.6 x 6.8

4. Thickness of sand bed (m)

: 0.6

5. Thickness of gravel bed (m)

: 0.5

6. Dia. of manifold (m)

:1

7. Laterals: (a) No's

: 86

(b) Dia. (mm)

: 90

(c) Length (cm)

: 2.9

(d) Spacing (cm)

: 20

8. No. of orifices

:16

9. Dia. of orifice (mm)

: 13

10.Wash water tank

:1

Disinfection House 1. ChlorinerequiredIday (kg)

: 18.662

2. CylinderrequiredIday (no.)

:2

3.4

Underground Reservoir 1. No. of units

1

2. Length (m)

147

.>

Storage Units

3. Breadth (m)

-14

4. Depth (m)

: 4.5

Elevated Service Reservoir 1. No. of units

:1

2. Dia. (m)

: 12

3. Height (m)

: 4.3

4. Capacity (Cu. m)

: 450

8 ..;

~

(ir

POPULATION FORECASTING 4.1

.. ,'a:er supply

lUG

Desian Period

project may be designed normally to meet the requirements

.

: 6'" a 30 years period after there completion. The time lag between :esgn and completion should be also taken into account. It should not :'"C'1arily exceed 2 years and 5 years even in exceptional circumstances. -~e 30 years period may however be modified in regard to specific :C"'lponents of the project particularly the conveying mains and trunk ~a "'ISof the distribution system depending on their useful life or the facility ;::~carrying out extension when required, so that expenditure far ahead of _:. ty is avoided. However in our case the design period has been ~"'1sidered as 30 years per given data.

4.2

POlJulation Forecast

General Considerations ~e population to be served during such period will have to be estimated .,:..t.~due regard to all the factors governing the future growth and :e/elopment of the city in the industrial, commercial, educational, social a"d administrative spheres. Special factors causing sudden immigration or ~ux of population should also be foreseen to the extent possible.

9

Calculation Of Population With Different Methods (TableNO.4. 1) Sr. No.

Year

1 1.

2 1961

3 7.48

4

5

(thousand) 6

-

-

-

2.

1971

12

4.52

60.45

-

-

15 22

03 07 14.52 4.84

25 46.67 132.12 44.04

-1.52 4.0 2.48 1.24

35.45 -21.67 13.78 6.89

Population (thousand)

3. 4.

1981 1991 Total Average

Increase (thousand)

Increase Increament % al increase

Decreas ein% increase 7

-

Arithmetical Increase Method Using the relation Po

= Pn + nc

Po

= Initial population;

Pn

= Population in dh decade;

n

= No. of decades;

c

= Average increase (refer table 2.1, col. 4)

Where,

P2031

= 36521+ 4840.33 = 41361.33

Geometrical Increase Method Using the relation Where,

Pn

=Po(1+IG/100)n

Pn

= Population in the dh decade;

Pn

= Population any decade ;

IG N

= Percentage increase ( Ref. Table 4.1, col. 5 ) = No. of decade

P2031 = 65744.86 + ( 44.04 /100 x 65744.86) = 94698.17 10

Incremental Increase Method Using the relation

Where,

Pn

= Po + ( r + i )n

r

= Average rate of increase in population per decade (Ref. Table 4.1, Col. 5) ; = Average rate of incremental increase per decade (Ref. Table 4.1, Col. 6) ;

Po

= Populationin any decade;

Pn

= Populationin n decade;

P2031 = 40239.49+ ( 4840.33+ 1239.5)

= 46319.32 Decrease Rate Of Growth Method

Year

Expected population

2001

22000 + 39.78/100 x 22000

= 30751

2011

30751 + 32.39/100 x 30751

= 40865

2021

40865 + 26/100 x 40865

= 51490

2031

51490 + 19.11/100 x 51490

= 61330

4.3

Description Of The Various Methods

Arithmetic Increase Method ~'"'lSmethodis basedupon assumptionthat the populationincreasesat a ~stant

rate and rate of growth slowly decreases. In our case also

:;opulationis increasingat a constantrate with slight decreasein growth ~e_

-=-. so this method is more suitable for. very big and older cities whereas in =

case it is relatively smaller and new town.

S: results by this method is although good but not as accurate as desired.

11

... -

Geometrical Increase Method In this method the per decade growth rate is assumed to be constant and which is average of earlier growth rate. The forecasting is done on the basis that the percentage increases per decade willremain same. This method would apply to cities with unlimited scope for expansion. Incremental Increase Method This method is an improvement over the above two methods. The average increase in the population is determined by the arithmetical increase method and to this is added the average of the net incremental increase, once for each future decade. This method would apply to cities, likely to grow with a progressively i,creasing or decreasing rate rather than constant rate. Decreasing Rate Of Growth Method As in our case the city is reaching towards saturation as obvious from the graph and it can be seen that rate of growth is also decreasing. Thus this ."ethod which makes use of the decrease in the percentage increases is "lore suitable. This method consists of deduction of average decrease in percentage increase from the latest percentage increase. ""'lus this gives weightage to the previous data as well as the latest trends. Decrease

in percentage increase is worked out average thus

...,portanceto whole data.

12

giving

Logical Curve Method This is suitable in cases where the rate of increase of decrease of population with the time and the population growth is likely to reach a saturation limit ultimately because of special local factors.

The city shall grow as per the logistic curve, which will plot as a straight line on the arithmetic paper with the time intervals plotted against population in percentage of solution.

Simple Graphical Method Since the result obtained by this method is dependent upon

the

'1telligence of the designer, this method is of empirical nature and not "'luch reliable.

Also this method gives very approximate results. Thus this method is useful only to verify the data obtained by some other method.

Graphical Comparison Method ~is

involves the extension of the population time curve into the future

:)ased on a comparison of a similar curve for comparable cities and ~odified to the extent dictated by the factors governing such predictions.

13

Logical Curve Method This is suitable in cases where the rate of increase of decrease of population with the time and the population growth is likely to reach a saturation limit ultimately because of special local factors. The city shall grow as per the logistic curve, which will plot as a straight line on the arithmetic paper with the time intervals plotted against population in percentage of solution.

Simple Graphical Method Since the result obtained by this method is dependent upon

the

'r'1telligenceof the designer, this method is of empirical nature and not "'luch reliable.

Also this method gives very approximate results. Thus this method is ...sefulonly to verify the data obtained by some other method. Graphical Comparison Method ~is

involves the extension of the population time curve into the future

:)ased on a comparison of a similar curve for comparable cities and "'-'odifiedto the extent dictated by the factors governing such predictions.

13

...

-= lUe (jj=

CALCULATION OF WATER DEMAND 5.1

Calculation Of Different Drafts

Expected population after 30 years

= 61400

Average rate of water supply

= 135 LPCD

(Including domestic, commercial, public and wastes)

Water required for above purposes for whole town

= 61400 x 135 = 8.289 MLD

Industrial demand

= 0.6 MLD

Fire Requirement : It can be assumed that city is a residential town (low rise buildings) Water for fire

= 100 P x 10-3MLD = 100 61.4 X 10-3MLD = 0.78 MLD

(i)

Average daily draft

= 8.289 + 0.6 = 8.889

(ii)

Maximum daily draft

= 1.5 x 8.889 = 13.33

(iii)

Coincident draft

= maximum daily draft + fire demand = 13.33 + 0.78 = 14.11 MLD

(Coincident draft < maximum hourly draft)

14

....

5.2

Desian CaDacitv For Various ComDonents

(i)

Intake structure daily draft

= 13.33 MLD

(ii)

Pipe main = maximum daily draft = 13.33 MLD

(iii)

Filters and other units at treatment plant = 2 x Average daily demand =2x8.889 = 17.778 MLD

(iv)

= 2 x average daily demand

Lift pump

= 17.778 MLD

5.3

Phvsical And Chomical Standards Of Water

.

Sr.

.

.

. - .

- .,

Characteristics

Acceptable

No.

Cause for Rejection

1.

Turbidity (units on J.T.U. scale)

2.5

10

2.

Color (units on platinum cobalt scale)

5.0

25

3.

Taste and odour

Unobjection

Unobjection

able

able

4.

PH

7.0 to 8.5

6.5 to 9.2

5.

Total dissolved solids (mg/L)

500

1500

6.

Total hardness (mg/L as CaC03)

200

600

7.

Chlorides (mg/L as C1)

200

1000

8.

8ulphates (mg/L as 804)

200

400

9.

Fluorides (mg/L as F)

1.0

1.5

10.

Nitrates (mg/L as N03)

45

45

11.

Calcium (mg/L as Capacity)

75

200

12.

Magnesium (mg/L Mg)

30

150

13.

Iron (mg/L Fe)

0.1

1.0

14.

Manganese mg/L as MnO

0.05

0.5

15.

Copper (mg/L Cu)

0.05

1.5

16.

Zinc (mg/L as Zn)

5.0

15.0

15

17.

Phenolic Compounds (mg/L as phenol)

0.001

0.002

18.

Anionic Detergents (mg/L as MBAS)

0.2

1.0

19.

Mineral oil (mg/L)

0.01

0.3

TOXIC MATERIALS 20.

Arsenic (mg/L as As)

0.05

0.05

21.

Cadmium (mg/L as Cd)

0.01

0.01

22.

Chromium (mg/L as Hexavalent Cr)

0.05

0.05

23.

Cyanides (mg/L as Cn)

0.05

0.05

24.

Lead (mg/L as Pb)

0.1

0.1

25.

Selenium (mg/L as Se)

0.01

0.01

26.

Mercury (mg/L as Hg)

0.001

0.001

27.

Polynuclear

Aromatic

Hydrocarbons 0.2

0.2

(mg/L) RADIO ACTIVITY 28.

GROSS Alpha Activity in pico Curie 3

3

(pCi/L) 29.

30

Gross Beta Activity (pCi/L)

30

Notes :

.

The figures indicated under the column 'Acceptable' are the limits upon which water is generally acceptable to the consumers.

.

Figures in excess of those mentioned under 'Acceptable' render the water not acceptable, but still may be tolerated in the absence of alternative and better source upon the limits indicated under column 'Cause for Rejection' above which the supply will have to be rejected.

.

It is possible that some mine and spring waters may exceed these radioactivity limits and in such cases it is necessary to analyze the individual radio nuclides in order to assess the acceptability for public consumption.

16

5.4

ComDarison Of Given Data And Standard Data

(Table No. 5.2)

Sr.

Actual

Particulars

Standard Difference Means

Treatment

No. 1. 2.

for

7 to 8.5

705

pH

50

Turbidity

2.5

O.K.

Not

47.5

necessary Clarifier & rapid sand filter

3.

Total

Hardness 550

200

350

Softening

(mg/L) 4.

Chlorides(mg/L)

200

200

50

5.

Iron (mg/L)

2.5

0.1

2.4

Aeration

60

Manganese (mg/L)

3.5

0.05

3.45

Aeration

70

Carbonate (mg/L)

110

-

-

Softening

8.

MPN (no.100)

3.5

0.0

3.5

Chlorination

17

.... -.

5.5

Suaaested Units Of Treatment Plant

J ue to previous analysis following units are required to be designed for ,',Iatertreatment plant. ~)

Intake Structure : (a) Intake well (b) Gravity main (c) Jack well (d) Rising main (e) Pump

2I

Treatment unit: (a) Aeration unit (b) Coagulant dose (c) Lime soda dose (d) Chemical dissolving tank (e) Chemical house 'f) Flash mixer (g) Clariflocculator (h) Rapid sand filter (i) Chlorination unit

..

Storage unit: fa) Underground storage tank b) Elevated storage ,.:..

~ematic

diagram of each of the unit is shown.

18

-=lu0

DESIGN OF UNITS

~

6.1 6.1.1

Design Of Intake Well

(a)

Intake Well

Collection units

Intakes consists of the opening, strainer or grating through which the water enters, and the conduct conveying the water, usually by gravity to a well or sump. From the well, the water is pumped to the mains or treatment plants. Intakes should also be so located and designed that possibility of interference with the supply is minimized and where uncertainty of continuous serviceability exists,

intakes should be

duplicated. The following must be considered in designing and locating the intakes.

The source of supply, whether impounding reservoir, lake or river (including the possibility of wide fluctuation in water level). The character of the intake surrounding, depth of water, character of bottom, navigation requirements, the effect of currents, floods and storms upon the structure and in scouring the bottom.

The location with respect to the sources of pollution. The prevalence of floating materials, such as ice, logs and vegetation. Types of Intakes :

·

Wet Intakes: Water is up to source of supply.

· · ·

Dry Intakes: No water inside it other than in the intake pipe. Submerged Intakes: Entirely under the water. Movable and Floating Intakes: Used where wide variation in surface elevation with sloping blanks. 19

Location Of Intakes :

.

The location of the best quality of water available.

. . . . .

Currents that might threaten the safety of the intake structure.

.

Ice storm.

. . .

Floods.

Accessibility.

.

Distance from pumping station.

.

Possibilities of damage by moving objects and hazards.

Navigation channels should be avoided. Ice flows and other difficulties. Formation of shoals and bars. Fetch of the wing and other conditions affection the weight of waves.

Power availability and reliability.

The intake structure used intake our design is wet-type. (b)

Design Criteria

1.

Detention time

5 to 10 min.

2.

Diameter

5 to10 m(maximum 15m)

3.

Depth

4 to 10m

4.

Velocity of flow

0.6 to 0.9 m/s

5.

Number of units

1 to 3 (maximum 4)

6.

Free board

5m

(c)

Design Assumptions

Given F.S.L.

=27m

Minimum R.L.

=28m

Given invert level of gravity main = 24 m Detention time

= 10 min.

20

Design Calculation = 13.33 MLD 13600 x 24

Flowof water required

= 0.1543 m3/sec. = 0.1543 x 0 x 60

Volume of well

= 92.57 m3

Cross-sectional area of intake well

= 92.57 14 = 23.14 m2 = ...J4x 23.14 In

diameter of intake well (d)

= 5.42 < 10 m (O.K.) provide 1 intake well of diameter 5.42 m ==5.5 m

(e)

Summary

1.

Number of intake wells

1 unit

2.

Diameter of intake well

5.5m

3.

Height of well

4.0m

4.

R.L. of bottom of well

24m

6.1.2 Design Of Pen stock And Bell Mouth Strainer (a)

Pen stock

This are the pipes provided in intake well to allow water from water body to intake well. These pen stocks are provided at different levels, so as to take account of seasonal variation in water level (as H.F.L., W.L., L.W.L.). Trash racks of screens are provided to protect the entry sizeable things which can create trouble in the pen stock. At each level more than one pen stock is provided to take account of any obstruction during its operations. These pen stocks are regulated by valves provided at the top of intake wells. (b)

Design Criteria

Velocity through pen stock

= 0.6

Diameter of each pen stock

= less than 1 m

Number of pen stock for each intake well

=2

21

t01.0 m/sec.

.~

.,

F.S.L..-I.-,. R.L. (J:N .-------.-----..--:0=-

Lw.L.

.-

MANHOLE

.

."..-.

R. L. .2B M T

M1"

.'. .

--

3MT -

)

.. ,.-GRJ\VIIY

'17

..

.

-.;----..

"...

MAIN

(0..55) MT

. ..

.....

:NT!-\I--~-r'_._l~:,,.._. to.._I_~"",I_J _ _'." _ 4'"_"_... : " : .. .. --_" I

REGULAI\NG'

VALVE~

PIAn

_

...: .".: .

,.~.:~ ..

"

:'~~;~

-",

-

MAIN

.

R.L. ...

_.

,s

0':~"',: .:., ','j:

..

(

RISING

4.2,q.

"iT

€>B

V" ,. ,', . , " I~

;I1l' ~{

,."

!iG ,co

-

R!:G ULATt"'GVALVE GRAVITY MAt/'oJ

0- 45)

.

. ..' ~-:--;":1.

~.

.

~'L.'

li.iY~

cu\VrLL AND PUMPJ-JOU£f

MT

.T

5.1.5 Design Of Pumping System (a)

.

Pumps in the water treatmentplant, pumps are used to boost the water from thejack well to the aerationunits.

. .

The followingpointsare to be stressedupon. The suction pumpingshould be as short and straight as possible. It should not be greaterthan 10m,for centrifugalpump. If head is more . '' ~ +h, ,... i "' i n~ , n +han 10 m ..v... ter i s converted i n+n ""' L I I, V g I , ILV yg poU r g, '''' LIIU,", I n''"' pI te VI LA v atlng water head, vapour head is created and pump ceases to function.

.

The suction pipe should be of such size that the velocity should be about 2m / sec.

.

The delivery pipe should be of such size that the velocity should be about 2.5m./sec.

The fonowing four to/pes of pumps are generally used.

.

Buoyancy operated pumps

. .

impuise operated pumps

.

Velocity adoptions pumps

Positive displac.ementpumps

The following criteria govern pump selection.

.

Type of duty required.

·

Present and projected demand and pattern and change in demand.

. ·

The details of head and flow rate required.

o

The efficiency of the pumps and consequent influence on power

Selecting the operating speed of the pump and suitable drive.

consumption and the running costs.

(b)

Diameter Of Rising Main Q = 0.1543m3/sec. Economical diameter

= 0.97 --.fato 1.22 --.fa

= 0.97 "';0.1543to 1.22 .../0.1543

=0.38 to 0.48 m = 0.45 m

Provide D

(c) . Design Criteria Suction head should not be greater than 10m. Velocity of flow length

= 0.7 to 1.5 mts

Top clearance

=0.5 m

Bottomclearance

=1m

(d)

Design Calculation

Frictionallosses in rising main

Assumingvelocity = 0.9 mtsec. F = 0.02 FPv2

0.02 x -190x (0.9)2

=

hf=-

2 x 9.81 x 0.45 = 0.348

2gd

=0.35

Head loss

Total head of pumping = hs + hd + hf + minor losses = 2.12+4.88+.35+1 =8.35

Assuming two pumps in parallel W.O.H. 1000 x 0.1543 x 8.35 W.H.P.

=

S.H.P. =

(e) :

,

.

75 W.H.P.

n Summary

=

75 17.17

= -

0.75

=22.90HP

Provide 1 - 25 HP pump in parallel Diameter

of pipe

I0.45 m

2.7

=17.17HP

-y:

6.1.6 Design Of Rising Main (a)

General

These are the pressure pipes used to convey the water from the jack well to the treatment units.

The design of rising main is dependent on resistance to flow, available head, allowable velocities of flow, sediment transport, quality of water and relative cost.

Various types of pipes used are cast iron, steel, reinforced cement concrete, pre stressed concrete, asbestos cement, polyethylene rigid PVC, ductile iron fibre glass pipe, glass reinforced plastic, fibre reinforced plastic. The determination of the suitability in all respects of the pipe of joints for any work is a matter of decision by the engineer concerned on the basis of requirements for the scheme.

(b)

Design Criteria

Velocity =0.9 to 1.5 m/sec. Diameter < 0.9 m.

(c)

Design Calculation

Economical diameter, D

= 0.97J a to 1.22.[0 = 0.38 to 0.48 m

Provide diameter

= 0.45 m

V

= 0.97 m/sec.

= alA

Summary Diameter of pipe I 0.45 m

28

6.2

Treatment Units

The aim of water treatment is to produce and maintain water that is hygienically safe, aesthetically attractive and palatable; in an economical manner. Albeit the treatment of water would achieve the desired quality, the evaluation of its quality should not be confined to the end of the treatment facilities but should be extended to the point of consumer's use. The method of treatment to be employed depends on the characteristics of the raw water and the desired standards of water quality. The unit operations and unit processes in water treatment constitute aeration flocculation (rapid and slow mixing) and clarification, filtration, softening, defloridization, water conditioning and disinfection and may take many different combinations to suit the above requirements.

In the case of ground water and surface water storage which are well protected, where the water has turbidity below 10 JTU (Jackson Candle Turbidity Units) and is free from odour and color, only disinfection by chlorination is adopted before supply.

Where ground water contains excessive dissolved carbon dioxide and odorous gases, aeration followed by flocculation and sedimentation, rapid gravity or pressure filtration and chlorination may be necessary.

Conventional treatment including prechlorination, aeration, flocculation and sedimentation, rapid gravity filtration and postchlorination are adopted for highly polluted surface waters laden with algae or microscopic organisms.

Based on the data given in second chapter, the following treatment units and accessory units are designed to meet the quality and quantity requirement of the project:

29

-Aeration unit Coagulant dose Lime soda dose Chemical dissolving tank Chemical house Flash mixer Clariflocculator Rapid sand filter Chlorination unit The detail design of the above units are discussed in subsequent sections.

6.2.1 Design Of Aeration Unit Aeration Unit Aeration is necessary to promote the exchange of gases between the water and the atmosphere. In water treatment, aeration is practiced for three purposes : To add oxygen to water for imparting freshness,

e.g. water from

underground sources devoid of or deficient in oxygen. Expulsion of C02, H2S and other volatile substances causing taste and odour, e.g. water from deeper layers of an impounding reservoir. To precipitate impurities like iron and manganese, in certain forms, e.g. water from some underground sources. The limitation of aeration are that the water is rendered more corrosive after aeration when the dissolved oxygen contents is increased though in earlier circumstances it may otherwise due to removal of aggressive C02. Also for taste and odour removal, aeration is not largely effective but can be used in combination with chlorine or activated carbon to reduce their doses. 30

The concentration of gases in a liquid generally obeys Henry's Law which states that the concentration of each gas in water is directly proportional to the partial pressure, or concentration of gas in the atmosphere in contact with water. The saturation concentration of a gas decreases with temperature and dissolved salts in water. Aeration tends to accelerate the gas exchange. The three types of aerators are : Waterfall or multiple tray aerators. Cascade aerators. Diffused air aerators.

Design Criteria For Cascade Aerators Number of trays

= 4 to 9

Spacing of trays

= 0.3 to 0.75 m c/c

Height of the structure

=2m

Space requirement

= 0.015 - 0.045 m2/m3/hr

Design Calculation Qmax

= 0.1543 m3/sec.

Provide area at tray

= 17 m2

Diameter of bottom most tray

=5m

Rise of each tray

= 0.4 m

Tread of each tray

=50cm

31

CASCADE.

CA~CA[)E

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-

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.

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