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PREPARED BY IJAIN. NIKHIL.R. ,...~

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DEPARTMENT OF CIVIL ENGINEERING .Sardar VallabhbhaiRegionalCollege of 1

Engineering c" Technology i=I Surat-395007. [Gujarat) .=.~18I1IIJ.1I""""IIIIIIIIJ.~II111IIih.Ila8l11l1l111111bDml1odDballll"'CllldlllblldllllJb.

CIVIL ENQINEERING STUDIES

ENVIRONMENTAL ENGINEERING

iIi

PROJECT REPORT ON

",DESIGN OF

WATER TREATMENT PLANTJ

8

,~ACULTY ADVISOR

t.

iI

iI

Ii

Ii

I

I

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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 Plant",

hasbeenpreparedby $-,./A. IJC~~./;/. 71. Roll. No 26. 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.

DEEPAK V.M. (15)I"

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 components5.3 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 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

6.3 Storage tank

7.0 CONCLUSION

REFERENCES:

lUG-.=

(fr 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, Fire-

fighting, 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 micro-organisms, 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 21.61N, 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.

...

"

[I_(ir 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.

1. Name of the place

2. District

3. Location

(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

Description

- Mandvi

- Surat

(Table No. 2.2)

Sr.No. Design Considerations

1. Design period (years)

2. Average rate of water supply (Ipcd)

3. Industrial demand (MLD)

4. Quality of raw water

Values

30

135

0.6

I) Ph 7.5

..

3

II) Turbidity (mg/L) 50

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)

Year 1961 07Year 1971 12Year 1981 15Year 1991 22

6. I F.S.L. of river (R.L. in mts.) 27

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

a) Jack well site 28

b) Location of aeration unit 29

8. I Invert level of raw material gravity intake pipe

(R.L. in mts. ) 24-

9. I Length of raw water rising main (mts.) 200

10. I Source supply:

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

~-r::tr SALIENT FEATURESOF

WATER TREATMENT PLANT

3.1. General

~ 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 Collection Works

Intake Works

Intake Well

: 1

: 5.5

:4

: 24

: 28

:10

Penstock

~ No.of penstockwell

2. Dia. Of penstock (mm)

:2

: 400

Bell mouth strainer

01 No. of bell mouth strainer : 2

2. Dia. (m) : 0.9

4

No. of units

2. Dia. Of well (m)

3. Ht of intake well

. R.L. of bottom well (m)

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

... Detention time (min)

Gravity main

No. of units

'" Dia. (mm)

3 Invert level (m)

~ slope

Jack well

No. of units

Dia. (m)

3 Depth of water

. Detention time (min)

Rising main and pumping units

Rising :

~ Dia.(m)

2 Velocity of flow (m/s)

Pumping unit:

Capacity of eachpump(HP)

2. No.of pumps

Aeration unit

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

(Bottom)

2. Dia. Of top tray (m)

3. Dia. Of bottom tray (m)

4 Dia.of each tray decreasing by(m)

5. Rise of each tray (m)

6. Tread of each tray (m)

Dia.of central rising main pipe (m)

8 No. of trays

: 1

: 550

: 23.88

: 1:862

: 1

: 6.15

: 3.12

: 10

: 0.45

: 1

: 60

: 1

: 31.40

:29.40

: 1

:5

: 1

: 0.4

: 0.5

: 1.0

:5

5

- I

3.3 Treatment works

Chemical storage house

1. Length (m)

2. Breadth (m)

3. Height (m)

: 20

: 12

: 3.0

Chemical Dissolving Tank

1. No. of Tank

2. Length (m)

3. Breadth (m)

4. Depth (m)

: 1

:3

:2

: 1.5

Flash Mixer

Flocculator :

1. No. of units

2. Dia. (m)

3. Dia. of Inlet pipes (m)

4. Depth of water flow (m)

5. Velocity of flow (m/s)

: 1

: 10.16

:0.45

: 3.5

: 1.0

6

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

Disinfection House

1. ChlorinerequiredIday (kg)

2. CylinderrequiredIday (no.)

: 18.662

:2

3.4 Storage Units

Underground Reservoir1. No. of units

2. Length (m)

1

14-

7

.>

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

8

..;

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

lUG~

(ir POPULATION FORECASTING

4.1 Desian Period

.. ,'a:er supply 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

~"'1sideredas 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)

Arithmetical Increase Method

Using the relation

Po = Pn + nc

Where,

Po = Initial population;

Pn = Population in dh decade;

n = No. of decades;

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

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 = Percentage increase ( Ref. Table 4.1, col. 5 )

N = No. of decade

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

10

Sr. Year Population Increase Increase Increament DecreasNo. (thousand) (thousand) % al increase ein%

(thousand) increase1 2 3 4 5 6 71. 1961 7.48 - - - -2. 1971 12 4.52 60.45 - -3. 1981 15 03 25 -1.52 35.454. 1991 22 07 46.67 4.0 -21.67

Total 14.52 132.12 2.48 13.78Average 4.84 44.04 1.24 6.89

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 anydecade;

Pn = Populationin n decade;

P2031 = 40239.49+ ( 4840.33+ 1239.5)= 46319.32

Decrease Rate Of Growth Method

Year Expected population

22000 + 39.78/100 x 22000 = 30751

30751 + 32.39/100 x 30751 = 40865

40865 + 26/100 x 40865 = 51490

51490 + 19.11/100 x 51490 = 61330

2001

2011

2021

2031

4.3 Description Of The VariousMethodsArithmetic 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 unlimitedscope 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 giving

...,portanceto whole data.

12

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 OfDifferent 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

= 2 x average daily demand(iv) Lift pump

= 17.778 MLD

5.3 Phvsical And Chomical Standards Of Water

15

.. . . - . - .,

Sr. Characteristics Acceptable Cause forNo. Rejection1. 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

16

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.

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 MATERIALS20. 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 ACTIVITY28. GROSS Alpha Activity in pico Curie 3 3

(pCi/L)

29. Gross Beta Activity (pCi/L) 30 30

5.4 ComDarison Of Given Data And Standard Data

(Table No. 5.2)

17

Sr. Particulars Actual Standard Difference Means for

No. Treatment

1. pH 705 7 to 8.5 O.K. Not

necessary

2. Turbidity 50 2.5 47.5 Clarifier &

rapid sandfilter

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

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

2 I 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 Collection units

6.1.1 Design Of Intake Well

(a) Intake Well

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 theintakes.

19

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.

Location Of Intakes :

. The location of the best quality of water available.

. Currents that might threaten the safety of the intake structure.

. 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.

. Ice storm.

. Floods.

. Power availability and reliability.

. Accessibility.

. Distance from pumping station.

. Possibilities of damage by moving objects and hazards.

The intake structure used intake our design is wet-type.

20

(b) Design Criteria

(c) Design Assumptions

Given F.S.L.

Minimum R.L.

=27m

=28m

Given invert level of gravity main = 24 m

Detention time = 10 min.

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

Design Calculation

Flowof waterrequired

Volume of well

= 13.33 MLD 13600 x 24

= 0.1543 m3/sec.

= 0.1543 x 0 x 60

= 92.57 m3

= 92.57 14

= 23.14 m2

= ...J4x 23.14 In

= 5.42 < 10 m (O.K.)

provide 1 intake well of diameter 5.42 m ==5.5 m

Cross-sectional area of intake well

diameter of intake well (d)

(e) Summary

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

Diameter of each pen stock

Number of pen stock for each intake well

=0.6 t01.0 m/sec.

= lessthan 1 m

=2

21

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

.~

MANHOLE

., . - . ."..-. R. L. .2B MT

F.S.L..-I.-,.R.L.(J:N M1".--------.-------..---:0=-

. ..'

Lw.L. --

- )3MT

.. ,.-GRJ\VIIY MAIN (0..55)'17 MT

. . -.;----.."... . ...

.....

:NT!-\I-<C\VrLL

(c) Design Calculation

Number of intake well

Number of pen stocks at each level

Velocity

CIS area of each pen stock

Diameter

= 1

=2

= 0.75 m/sec. (assumed)

= 0.1543/0.75 x 2

= 0.1029 m2

= 0.3619 m ==0.4 m

(d) Summary

Design Of Bell Mouth Strainer:

(a) Design Criteria

Velocity of flow = 0.2 to 0.3 m/s

Hole diameter = 6 to 12 mm

Area of strainer = 2 x diameter of holes

(b) Assumptions

Velocity of flow

Hole diameter

= 0.25 m/s

= 10 mm

(c) Calculation

1t d2

Area of each hole = - = 0.7853cm24

Area of collection = Area of pen stock

0.1543= 0.7853 x N

0.25 x 2N = 3929.7

Area of Bell mouth strainer= 2 x area holes

22

1. Number of pen stock 1well 2 units

2. At each level 1 m

3. Diameter of pen stock 0.4 m

Diameter

= 1

=2

= 0.75 m/sec. (assumed)

=0.1543/0.75x2

= 0.1029 m2

= 0.3619 m ==0.4 m

(c) Design Calculation

Number of intake well

Number of pen stocks at each level

Velocity

C / S area of each pen stock

(d) Summary

Design Of Bell Mouth Strainer:

(a) Design Criteria

Velocity of flow

Hole diameter

= 0.2 to 0.3 m/s

= 6 to 12 mm

Area of strainer = 2 x diameter of holes

(b) Assumptions

Velocity of flow

Hole diameter

= 0.25 m/s

= 10 mm

(c) Calculation

1t d2

Area of each hole = - = 0.7853cm24

Area of collection = Area of pen stock

0.1543= 0.7853 x N

0.25 x 2

Area of Bell mouth strainer = 2 x area holes

22

1. Number of pen stock / well 2 units

2. At each level 1 m

3. Diameter of pen stock 0.4 m

(b) Design Criteria

Diameters of gravity main

Velocity of water

Number of gravity main = number of intake well

Assumption velocity

= 0.3 to 1 m

= 0.6 to 0.9 m/s

= 1

= 0.7 m/s

= 2 x 3929.7 x 0.7853

= 6171.98

Diameter of Bell-mouth strainer = 88.64

Provide diameter of 0.9 m for bell mouth strainer.

6.1.3 Design Of Gravity Main

(a) Gravity Main

The gravity main connects the intake well to the jack well and water flows

though it by gravity. To secure the greatest economy, the diameter of a

single pipe through which water flows by gravity should be such that all

the head available to cause flow is consumed by friction. The available fall

from the intake well to the jack well and the ground profile in between

should generally help to decide if a free flow conduit is feasible. Once this

is decided the material of the conduit is to be selected keeping in view the

local cost and the nature of the terrain to be traversed. Even when a fall is

available, a pumping or force main, independently or in combination with a

gravity main could also be considered. Gravity pipelines should be laid

below the hydraulic gradient.

(c) Design Calculation

R.C.C. Circular pipe is used.

Conduit velocity = 0.7 m/s (assumed)

Area of conduit required = 0.1543 I (0.7)

= 0.2204 m2

Diameter of the conduit = 0.5297 m ==0.55 m

23

Using Manning's formula,

1V = R 2138112-

n

n2V28 - -- -

R413

= 1.59 x 10-4

8 = 1 : 862

(0.013)2 X (0.7)2

(0.55/4)413

= 100 / 862

= 0.116

= 27 - 3

=24m

R.L. of gravity main at jack well = 24 - 0.116

Headloss

R.L. of gravity main

= 23.88 m

(d) Summary

6.1.4 Design Of Jack Well

(a) Jack Well

This structure serves as a collection of the sump well for the incoming

water from the intake well from where the water is pumped through the

rising main to the various treatment units.

This unit is more useful when number of intake wells are more than one.,

so that water is collected in one unit and then effected.

The jack well is generally located away from the shore line, so that the

installation of pumps, inspection maintenance is made easy.

24

1. Number of gravity intake 1 unit

2. Diameter of gravity intake 0.55m

3. Invert level at intake well 24m

4. Invert level at jack well 23.88 m

Design Criteria

Detentiontime = 0.5 x detention time of intake well.(3 to 15 min.}.

=0.5)( 10

=5min.

Suction head < 10m.

Diameter of well < 20m.

Design Calculation

Detention time =5m.

Assumingsuctionhead = 8 m.Bottomclearance = 1.0 m.

Top clearance = 0.5 m.

Maximumdepth of water that can be stored in condition when

water is minimumin rive

26 - 22.88Capacity of well

=3.12 m=0.1543x10x60

= 92.58 m3

= 92.58/3.12

= 29.67 m2

= 6.14 m

= 22.88 m

= 22.88 + 7

= 29.88 m

C / S area of well

Diameter of well

R.l. of bottom of jack well

R.l. of bottom of jack wellwhen full

Summary

Diameter of jack well

R.l. of bottom of jack well

R.l. top of jack well

Suction depth

Top clearance

Bottom clearance

6.15m

22.88 m

29.88 m

2.12m

O.5m

1m

.25

(b)

.

.

.

(c)

(d)

r:c-

3.4.

tE6.

-

-

REGULAI\NG'VALVE~

:'-1'. I ..:.-'Ii :: :: ~,.:;>-~-r'- _._l~:,,.._.to.._I_~"",I_J _ _'." _ 4'"_"_... :

" : _" I.. .. --

PIAn

,.~.:~ :'~~;

;I1l'. . . " ~...: .".: -", ..

~{

RISING MAIN ( 0- 45)_ "iT- . _. ,s R.L. ...0':~"',: .:., ','j: 4.2,q. €>BV" ,. ,', . , " ,." TI~ .

!iG ,co MT

R!:G ULATt"'GVALVE

GRAVITYMAt/'oJ

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

~. ~'L.'

li.iY~

cu\VrLL AND PUMPJ-JOU£f

/....k'..

.'I - ..--...

; I :0:J'I .....

I .I I'I. .

-

5.1.5 Design Of Pumping System

(a) Pumps

. in the water treatmentplant, pumpsare used to boost the water from

thejack well to theaerationunits.

. The followingpointsareto be stressedupon.

. The suction pumpingshould be as short and straight as possible. It

shouldnot be greaterthan 10m,for centrifugalpump. If head is more+han 10 m ..v... ter is converted in+n ""' po' 'r ~ +h, ,... in"'pite n~ , n at

.lngL I I, V g I , ILV yg U g, '''' LIIU,", I ''"' I VI LA v

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

. Positive displac.ementpumps

. Velocity adoptions pumps

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.

· Selecting the operating speed of the pump and suitable drive.

o The efficiency of the pumps and consequent influence on power

consumption and the running costs.

(b) Diameter Of Rising Main

Q = 0.1543m3/sec.

Economical diameter = 0.97 --.fato 1.22 --.fa

-

Provide D

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

=0.38 to 0.48 m

= 0.45 m

(c) . Design Criteria

Suction head should not be greater than 10m.

Velocityof flow length = 0.7 to 1.5 mts

Top clearance =0.5 mBottomclearance = 1 m

(d) Design Calculation

Frictional losses in rising main

Assumingvelocity = 0.9 mtsec.

F = 0.02

0.02 x -190x (0.9)2FPv2hf=-

2gd

=

Head loss

2 x 9.81 x 0.45= 0.348

=0.35

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 8.35W.H.P. = . = =17.17HP

75 75W.H.P. 17.17

S.H.P. = = - =22.90HPn 0.75

(e) Summary

: Provide 1 - 25 HP pump in parallel

, Diameter of pipe I0.45 m

2.7

--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 = 0.97Ja to 1.22.[0= 0.38 to 0.48 m

Provide diameter = 0.45 m

V = alA = 0.97 m/sec.

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 UnitAeration 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 = 2 m

Space requirement = 0.015 - 0.045 m2/m3/hr

Design Calculation

Qmax

Provide area at tray

Diameter of bottom most tray

Rise of each tray

Tread of each tray

= 0.1543 m3/sec.

= 17 m2

=5m

= 0.4 m

=50cm

31

CASCADE. i. (A. ~>

CA~CA[)E ~.Ct ~

CASC.AbE 3.

. (3qSJ,C-ASCADE ~

f4 .~)

~

<:'ASCI'obE

~(5#

, .

PIA M ETE-R Of:

CAse ADt; ~r<J MT5

1NLE'T =--

~

-.-1"R. L.{Jt.OO)

- R.'L(30t'c.:)

Rl SING MAIN (0..1.,;:)MT

G: I: I

AERA\IQ\J UN\-r

-R..L., :roe ~C.)

~"

R.l(,2(h8~ ,-,

R'L:(29; It 0)

2Cf -OD

,r

R..L. IN MTS

~

Summary

R.L. of ground at site = 29.00 m

Design Of Chemical House And Calculation Of Chemical Dose

The space for storing the chemicals required for the subsequent treatment

of water consists of determining space required for storing the most

commonly used coagulant alum, lime, chlorine, etc. for the minimum

period of three months and generally for six months.

The size of unit also depends upon the location, transport facilities,

weather conditions, distance of production units and availability of

chemicals. Chemical house should be designed to be free from moisture,

sap, etc. These should be sufficient space for handling and measuring

chemicals and other related operations.

It should be located near to the treatment plant and chemicals should be

stored in such size of bags that can be handled easily.

Alum Dose:

Coagulation

The terms coagulation and flocculation are used rather indiscriminately to

describe the process of removal of turbidity caused by fine suspension

colloids and organic colors.

32

Sr. Cascade Diameter R.L. (m)

No. of tray (m)

1. First 1 31.00

2. Second 2 30.60

3. Third 3 30.20

4. Fourth 4 29.80

5. Fifth 5 29.40

Coagulation describes the effect produced by the addition of a chemical to

a colloidal dispersion, resulting in particle destabilization. Operationally,

this is achieved by the addition of appropriate chemical and rapid intense

mixing for obtaining uniform dispersion of the chemical.

The coagulant dose in the field should be judiciously controlled in the light

of the jar test values. Alum is used as coagulant.

Design Criteria For Alum Dose

Alum required in particular season is given below:

Monsoon = 50 mg/L

Winter = 20 mg/L

Summer = 5 mg/L

Alum required

Let the average dose of alum required be 50 mg/L, 20mg/L, 5 mg/L in

monsoon, winter and summer, respectively.

Per day alum required for worst season for intermediate stage

= 50 x 10-6x 555.48 X 103x 24

= 666.58 kg/day

For six months (180 days) = 666.58 x 180

= 119984.40 kg

Number of bags whence 1 bag is containing 50 kg = 2400

If 15 days in each heap = 160 heaps

If area of one heap be 0.2 m2,then total area required = 80 m2.

Lime-Soda Process:

Softening

A water is said to be hard, when it does not form leather readily with soap.

The hardness of water is due to the presence of calcium and magnesium

ions in most of the cases. The method generally used are lime-soda

33

process. Softening with these chemicals is used particularly for water with

high initial hardness ( > 500 mg/L) and suitable for water containing

turbidity, color and iron salts. Lime-soda softening cannot, however,

reduce the hardness to values less then40 mg/L.

Design Criteria For Lime-Soda Process

It should be possible to remove 30 mg/L carbonate hardness and 200

mg/L total hardness by this process.

Lime And Soda Required

Lime required for alkalinity

Molecular weight of

CaC03 = 40 + 12+ 48= 100

= 40 + 16

= 56.

CaO

100 mg/L of CaC03alkalinity requires

110 mg/L of CaC03 requires

Lime Required For Magnesium

24 mg/L of magnesium requires

1 mg/L of magnesium requires

3.5 mg/L of magnesium requires

= 56 mg/L of CaO

= (56/100) x 110

= 61.6 mg/L of CaO

= 56 mg/L of CaO.

= 56/24 mg/L of CaO.

= (56/24) x 3.5

= 8.2 mg/L of CaO.

= 61.6 + 8.2

= 69.8 mg/L

Also 56 kg of pure lime (CaO) is equivalent to 74 kg of hydrated lime.

Hence, hydrated lime required = (69.8 x 74)/56

=92.23 mg/L.

Hence, the total pure lime required

Soda (Na2C03) :

Soda is required fir non-carbonate hardness, as follows.

3+

100 mg/L of NCH requires

161.6 mg/L of NCH requires

Total quantity of lime

= 106 mg/L of Na2C03

= ( 106/100) x 161.6

=65.59 mg/L of Na2C03

=(92.23 x 555.5 x 180 x 24 x 103)

=221329.86 kg

One bag contains 50 kg.

Number of bags required

If 15 bags in each heap, number of heaps

If area of one heap is 0.2 m2.

Total quantity of soda required

= 4426

= 295

= 295xO.2

= 59 m2

= 65.59x 10-6x 555.5x103x 24 x 180

= 157400.25 kg.

= 3148

= 209.86 heaps.

= 0.2 x 209.86

= 41.97 m2

= 80 + 59 + 41.97

= 180.97 m2

Add 30 % for chlorine storage, chlorine cylinders etc.

Total area = 235.26 m2

Number of bags

If 15 bags in each heap

Total area of heap

Total area for all chemicals

Provide room dimension = 20 x 12

= 240 m2

= 20mx 12mprovide dimension

Chemical Dissolving Tanks :

Total quantity of alum, lime and soda

Area required

Dimensions

= 119984.4 +221329.86 +157400

= 498714.26/180

=19394.44 day

=387 bags

=25.8 heaps

= 5.16 m2

= 3.0 m x 3.0 m

35

Chemical Solution tanks:

Total quantity of alum, lime and soda required per day

= 2770.63 kg/day

Hence solution required per day = 2770.63 x 20

=55412 Lit/day

= 38.48 Lit/min

Quantity of solution for 8 hours = 38.48 x 8 x 60= 18470 Lit

= 18.47 m3

Assuming depth of tank (1.2m) and 0.3m free board

Dimension of solution tank = 4.5 x 3.5 x 1.5

Summary

Design Of Mechanical Rapid Mix Unit

Flash Mixer

Rapid mixing is and operation by which the coagulant is rapidly and

uniformly dispersed throughout the volume of water to create a more or

less homogeneous single or multiphase system.

This helps in the formation of micro floes and results in proper utilization of

chemical coagulant preventing localization of connection and premature

formation of hydroxides which lead to less effective utilization of the

coagulant. The chemical coagulant is normally introduced at some point of

36

1. Per day alum required 666.58 k/j2. Hydrated lime required 92.23 mql3. Soda required 65.59 'M/A.-4. Size of chemical dissolving 3x3

tanks

5. Size of chemical solution tanks 4.5 x 3.5 x 1.5

.high .. ,..hu1ence "n +h" ..vater T he S" u"c" Of P"u,,,.. f".. ..~

pl.d mivl

'

ng toII U..l11.I I I LIIO Y' . II V 10 I vnol IVI IQ iliA

create the desired intense turbulence are gravitational and pneumatic.

T h" I' n+ens ~' "f I.vi n,.. is d" pendent UpO'" th e t" "

, m" an ""' OCi+u110 LILY VI III All ~ I 0 I I II LII vllll-'VIQ Iv I YOI ILY

gradient 'G'. This is defined as the rate of change of velocity per unit

distance normal to a section. The turbulence and resultant intensity of

mixingis based on the rate of power input to the water.

Flash mixture is one of the most popular methods in which the chemicals

are dispersed. They are mixed by the impeller rotating at high speeds.

Detention time =30 to 60 sec.

Design Criteria For Mechanical Rapid Mix Unit

Velocity of flow = 4 to 9 m/sec.

Depth

Power Required

Imeeller 8eeed. .

Loss of head

= 1 to 3 m

= 0.041 'r<J/vi"1000cu.m/day

=100 to 250 rpm

=O.4to;.O

Mixing device be capable of creating a velocity gradient

= 300m/sec/m depth

Ratio of impeller diameter to tank diameter

= 0.2 to 0.4 : 1D a+in nf tank hO !

.g t to rfi amo tor - -I +0 ':! . -II' uv VI .. I , "" I I \..II '"' ". - J" v. I

(C) Design Calculation

Design flow

Detention time

Ratio of tank height to diameter

Ratio of impeller diameter to tank diameter

Rotational speed of impeller

Assume temperature

= 13331.52 m3/day

= 30 sec.

= 1.5:1

= 0.3:1

= 120rem.=200

1. Dimension of tank:

Volume = 4.629 m3

D = 1.6m

Height = 2.37 + (0.23 m free board)

Total height of tank = 2.6 m

2. Power Requirement:

Power spend =5.47 KW

3. Dimensions of flat blade and impeller:

Diameterof impeller = 0.65m

Velocity of tip impeller = 4.08 m/sec.

Area of blade = As

Power spent =:h x CDx rox As x VR3

Let CD = 1.8 (Flat blade); VR = % XVT

5.47 x i 03 = % x 1.8 x i 000 XAs x % x 4.08

As = 1.99 m2

Provide 8 blades of 0.5 x 0.5 m = 2m2

Provide 4 numbers of length 1.5 m and projecting 0.2 m from the wall.

4. Provide inlet and outlet pipes of 250 mm diameter.

Summary

38

- ---

11.Detention Time 30 sec.

2. Speed of Impeller 120 rpm

3. IHeight of Tank (0.23 m free board) 2.6mI

4. PowerRequired 5.47 t<JN

5. Numberof Blade(0.5mx 0.5m) 8 I

16. Number of baffles (length 1.5 m) 4

7. Diameter of inlet and outlet 250

Design Of Clariflocculator

Clariflocculator

The coagulation and sedimentation processes are effectively incorporated

in a single unit in the clariflocculator. Sometimes clarifier and

clariflocculator are designed as separate units.

All these units consists of 2 or 4 flocculating paddles placed equidistantly.

These paddles rotate on their vertical axis. The flocculating paddles may

be of rotor-stator type. Rotating in opposite direction above the vertical

axis. The clarification unit outside the flocculation compartment is served

by inwardly raking rotating blades. The water mixed with chemical is fed in

the flocculator compartment fitted with paddles rotating at low speeds thus

forming floes.

The flocculated water passes out from the bottom of the flocculation tank

to the clarifying zone through a wide opening. The area of the opening

being large enough to maintain a very low velocity. Under quiescent

conditions, in the annular setting zone the floc embedding the suspended

particles settle to the bottom and the clear effluent overflows into the

peripheral launder.

(b) Design Criteria: (Flocculator)

Depth of tank = 3 to 4.5 m

Detention time = 30 to 60 min.

Velocity of flow = 0.2 to 0.8 m/sec.

Total area of paddles = 10 to 25 % of cis of tank

Range of peripheral velocities of blades = 0.2 to 0.6 m/s

Velocity gradient (G) = 10 to 75

Dimension less factor Gt = 104to 105

Power consumption

Outlet velocity

= 10 to 36 KW/mld

= 0.15 to 0.25 m/sec.

39

-- -

Design Criteria: (Clarifier)

Surface overflow rate =40 m3/m2/day

Depth of water = 3 to 4.5 m

Weir loading =300 m3/m2/day

Storage of sludge = 25 %

Floor slope = 1 in 12 or 8% for mechanically cleaned tank.

Slope for sludge hopper = 1.2:1 (v:h)

Scraper velocity = 1 revolution in 45 to 80 minutes

Velocity of water at outlet chamber = not more than 40 m/sec.

(c) Assumptions

Average outflow from clariflocculator

Water lost in desludging

Design average period

Detention period

Average value of velocity wadient

=2%

= 566.82 m3/hr

= 30 min.

= 30 S-1

Design Of Influent Pipe

Assuming V = 1 m/sec.

Dia = 0.447 m

Provide an influent pipes of 450 diameter.

Design Of Flocculator : wall

Volume of flocculator = 566.82 x 30 160

= 283.41 m3

Providing a water depth = 3.5 m

Plan area of flocculator = 283.41/3.5

= 80.97 m2

D = diameter of flocculator = 10.16m

Dp = diameter of inlet pipes = 0.45 m

D =10.2m

Provides a tank diameter of 10.2 m

40

Dimension Of Paddles:

= G2X !l v x vol

= 302x 0.89 x 10-3X (1tf4x 10.22x 3.5)

= 229.08

Power input = % (Cd x Px Ap X(V-U)3

Cd = 1.8

P = 995 kg/m3(25°c)

V = Velocity of tip of blade = 0.4 m/sec.

v = Velocity of water tip of blade = 0.25 x 0.4

= 0.1 m/sec.

= % x 1.8 x 995 x Ap x (0.4-0.1)3

= 9.47 m2

229.08

.. Ap

Ratio of paddles to cis of flocculator

[9.47/ P (10.2 - 0.75) 3.5] x 100

Provide Ap

= 9.11 % <10 to 25 %

= 10.5 m2

Ap = [10.5ht (10.2-0.75) 3.5] x 100 = 10.1% ok

Which is acceptable (within 10 to 25 %)

Provide 5 no of paddles of 3 m height and 0.7 m width

One shaft will support 5 paddles

The paddles will rotate at an rpm of 4

V = 2 x x x r x x/60

0.4 = 2 x x x r x 4/60

r = 0.96m ==1m

r = distance of paddle from C1. Of vertical shaft

Let velocity of water below the partition wall between the flocculator and

clarifier be 0.3 m/sec.

Area = 555.48/0.3 x 60 x 60 = 0.51m2

Depth below partition wall = 0.51/x x 10.2

= 0.016m

Provide 25% for storage of sludge = 0.25 x 35

= 0.875m

41

-----

Provide 8% slope for bottom

Total depth of tank at partition wall = 0.3 + 3.5 + 0.016 + 0.875

= 4.69m ==4.7m

Design Of Clarifier

Assuming a surface overflow rate of 40m3/m2/day

Surface of clariflocculator = 555.48 x 24/40

= 333.29m2

Oct= Dia. of Clariflocculator

P/4 [Oct2 - (10.2)2] = 333.29

Oct = 22.99m ==23m

Length of weir = 1tX Oct

= 1tx 23 = 72.26m

Weir loading = 555.48 x 24/72.26

= 184.49m3/day/m

According to manual of Govt. of India. If it is a well clarifier. It can exceed

upto 1500m3/day/m.

Summary (Clariflocculator)

1. Detention Period 30min

2. Diameter of influent pipes 450mm

3. Overall depth of flocculator 3.5m

4. Diameter of tank 10.2m

5. No. of paddles (3 m height and 0.7 m width) 5

6. Distance of shaft from C.L. of flocculator 1m

7. Paddles rotation (RPM) 4

8. Distance of paddle from C.L. of vertical shaft 1m

9. Slope of bottom (%) 8

10. Total depth of partition wall 4.7m

11. Diameter of clariflocculator 23m

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6.2.5 Design Of Rapid Gravity Filter

(a) Rapid Sand Filter

The rapid sand filter comprises of a bed of sand serving as a single

medium granular matrix supported on gravel overlying an under drainage

system, the distinctive features of rapiq sand filtration as compared to slow

sand filtration include careful pre-treatment of raw water to effective

flocculate the colloidal particles, use of higher filtration rates and coarser

but more uniform filter media to utilize greater depths of filter media to trap

influent solids without excessive head loss and back washing of filter bed

by reversing the flow direction to clear the entire depth of river.. .

The removal of particles within a deep granular medium filter such as

rapid sand filter, occurs primarily within the filter bed and is referred to as

depth filtration. Conceptually the removal of particles takes place in two

distinct slips as transport and as attachment step. In the first step the

impurity particles must be brought from the bulkof the liquid within the

pores close to the surface of the medium of the previously deposited

solids on the medium. Once the particles come closer to the surface an

attachment step is required to retain it on the surface instead of letting itflow down the filter.

The transport step may be accomplished by straining gravity, setting,

impaction interception, hydrodynamics and diffusion and it may be aided

by flocculation in the interstices of the filter.

(a) Design Criteria: (Rapid Sand Filter)

. Rate of filtration = 5 to 7.5m3/m2/hr

. Max surface area of one bed = 100m2

· Min. overall depth of filter unit including a free board of 0.5m = 2.6m

· Effective size of sand = 0.45 to 0.7

· Uniformityco-efficientfor sand = 1.3 to 1.7

43

. Ignition loss should not exceed 0.7 percent by weight

. Silica content should not be less than 90%

. Specific gravity = 2.55 to 2.65

. Wearing loss is not greater than 3%

. Minimum number of units = 2

. Depth of sand = 0.6 to 0.75

. Standing depth of water over the filter = 1 to 2m

. Free board is not less than 0.5m

(b) Problem Statement

Net filtered water

Quantity of backwash water used

Time lost during backwash

Design rate of filtration

Length - width ratio

Under drainage system

Size of perforations

(c) Design Calculation

Solution: required flow of water

Design flow for filter

Plan area for filter

Using 2 units,

Plan area

Length x width

L

= 555.48m3/hr

=2%

= 30min.

= 5m3/m2/hr

= 1.25 to 1.33:1

= central manifold with laterals.

= 13mm

= 555.48m3/hr

= 555.48 x (1 + 0.02) x 24/23.5

= 578.65m3/hr

= 578.65/5

= 115.73m2 ==116

= 58m2

= L x 1.25L

= 58

=6.8m

Provide 2 filter units, each with a dimension 8.6m x 6.8m.

44

Estimation Of Sand Depth :

It is checked against breakthrough of floc.

Using Hudson Formula:

Q x d x h/L = 8 x 293223 11

Where, Q, d, hand 1 are in m3/m2/hr,mm, m and m, respectively.

Assume, 8 = 4 X 10-4(poor response) < average degree of pre-treatment

h = 2.5m (terminal head loss)

Q = 5 x 2m3/m2/hr(assuming 100% overload of filter)

d = 0.6mm(meandia.)

10 x (0.6)3x 2.5/1 = 4 x 10-4x 293223

L>46m

provide depth of sand bed = 60cm

Estimation Of Gravel And Size Gradation:

Assuming size gradation of 2 mm at to 40 mm at bottom using empirical

formula :

P = 2.54 R (log d)

Where, R = 12 (10 to 14)

The units of Land dare cm and mm, respectively.

Provide 50 cm depth of gravel.

Design Of Under Drainage System :

Plan area of each filter = 8.6 x 6.8

= 58.48m2

Total area of perforation = 3 x 10-3 x 58.48

= 0.17544m2

= 1754.4cm2

45

J

Size 2 5 10 20 40

Depth(cm) 9.2 21.3 30.5 40 49

Increment 9.2 12.1 9.2 9.5 9

--

Total cross section area of laterals = 3 x area of perforation

= 3 x 1754.4

= 5263.2cm2

= 2 x area of lateral

= 2 x 5263.2

= 10526.4cm2

= ..J10526.4 x 4hc

= 115.76cm

Providing a commercially available diameter of 100 cm.

Assuming spacing for laterals = 20cm

Number of laterals = 8.6 x 100/20

Area of central manifold

Diameter of central manifold

= 43 on either side

D = ..J61.2 X 4ht

= 8.83cm ==90mm

Number of perforations /Iaterals = 86 units

Length of one lateral = % width of filter - % dia. of manifold

= %x6.8-%x 1

= 2.90 m

Let n be total no. of perforation of 13mm dia.

.. Total areaof perforation = n x 1t/4 x (1.3)2

= 1754.4

= 1321.76 ==1322

No. of perforation /Iateral = 1322/86

= 15.37 ==16

Spacing of perforations = 2.90x 100/1.6

= 181.25cm clc

.. n

Provide 16 perforations of 13 mm diameter at 180 cm clc.

46

-

Computation of wash water Troughs:

Wash water rate = 36m3/m2/hr

= 36 x 58.48

= 2105.28m3/hr

= 0.5848m3/sec.

Assuming a spacing of 1.8 m for wash water trough which will run parallel

to the longer dimension of the filter unit.

No. of trough = 6.8/1.8

=3.78=:4

discharge per unit trough = 0.5848/4

= 0.1462m3/sec.

Wash water discharge for one filter

For a width of 0.4 m the water depth at upper end is given by

Q = 1.376 b h312

0.1462 = 1.376 x 0.4(h)312

h = 0.41

Freeboard = 0.1m

Provide 4 troughs of 0.4 m wide x 0.5 deep in each filter.

Total Depth Of Filter Box:

Depth of filter box = depth of under drain + gravel + sand + water depth

+ free board

= 900 + 500 + 600 + 2200 + 300

= 4500mm

Design Of Filter Air Wash :

Assume rate at which air is supplied

Duration of air wash

= 1.5m3/m2/min.

=3min.

Total quantity of air required per unit bed = 1.5 x 3 x 8.6 x 6.8

= 263. 16m3

47

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(d) Summary

6.2.6 Disinfection Unit

(a) Chlorination

Treatment method such as aeration, plain sedimentation, coagulation,

sedimentation, filtration, would render the water chemically and

aesthetically acceptable with some reduction in the pathogenic bacterial

content. However, the foregoing treatment methods do not ensure 100%

removal of pathogenic bacteria, and hence it becomes necessary to

'disinfect' the water to kill the pathogenic bacteria.

Disinfection should not only remove the existing bacteria from water but

also ensure their immediate killing even afterwards, in the distribution

system. The chemical which is used as a disinfectant must, therefore be

able to give the "residual sterilising effect" for a long period, thus affording

some protection against recontamination. In addition to this, it should be

48

1. Number of units 2

2. Size of unit 8.6 x 6.8m

3. Depth of sand bed 60cm

4. Depth of gravel SOcm

5. Diameter of perforation 13mm

6. Diameter of central manifold 100cm

7. Spacing for laterals 20cm

8. Number of laterals 86

9. Diameter of laterals 90mm

10. Number of perforations 16

11. Number of troughs 4

12. Size of trough 0.4 x 0.5m

13. Total depth of filter box 4500mm

14. Duration of air wash 3min.

15. Total quantity of air required per unit bed 263. 16m;:!

- CHLORINE GAS

cI.oI--(~-~o..J1tJ

$\-IUT oP'f: YALVE

SC.HeCK VALliE~ ~

L.IQUID C1.1c. YLINCEP-

TO CI~TRI~IJTIONMAIN

WEIGHING.sCALE

Pl1~p

OVER r:/..f:)/N

To t:>AA/fIJ

..STRoNG CJ.,). SOLUTION

IWATeR 70 13€TflEAT EJ>

LINE DIAGRAM OF A. 'YPICAl .5oLUTION

FEED CHLORINA70R INSTALJ..ATloN

II

II

I

harmless, unobjectionable to taste,

simple tests. 'Chlorine' satisfies the

disinfectant and hence is widely used.

ecomomical and measurable by

above said more than any other

(b) Design Criteria (chlorination)

. Chlorine dose = 1.4mg/L (rainy season)

= 1mg/L (winter season)

= 0.6mg/L (summer season)

· Residual chlorine = 0.1 to 0.2 mg/L (minimum)

· Contact period = 20 to 30min.

(c) Design Caculations

Rate of chlorine required, to disinfect water be 2 p.p.m.

Chlorine required. Per day = 13.33 x 106x 1.4 x 10-6

= 18.662kg

= 18.662 x 180

= 3359.16kg

Number of cylinder (one cylinder contain 16 kg)

For 6 months

= 3359.16 x 2/16

= 419.895

Number of cylinders used per day =2 cylinders of 16kg

(d) Summary

6.3 Storaae Tank

General

Distribution reservoirs also called service reservoirs are the storage

"eservoirs which store the treated water for supplying the same during

emergencies and also help in absorbing the hourly fluctuations in water

demand. Depending upon their elevation with respect to the ground they

49

1 Chlorine required per day 18.662kg2 Number of cylinder required per day 2 of 16kg

-

are classified as under ground reservoir and elevated reservoir both of

these reservoirs designed for this project.

Storage Capacity

Ideally the total storage capacity of a distribution reservoir is the

summation of (i) balancing reserve (ii) breakdown reserve and (iii) fire

reserve. The balancing storage capacity of a reservoir can be worked out

from the data of hourly consumption of water for the town/city by either the

mass curve method or analytical method. In absence of availability of the

data of hourly demand of \AJaterthe capacity of reservoir is usually 114to 1/3

of the daily average supply.

Underground Storage Reservoir (U.S.R.) :

(a) General

The reservoir is used for storing the filtered water which is now fit for

drinking. From this, the water is pumped to E.S.R. normally the capacity of

this type of reservoir depends upon the capacity of the pumps and hours

of pumping during a day. If the pumps work for 24 minutes then the

capacity of this reservoir may be between 30 minutes to 1 hour.

(b) Design Criteria (U.S.R.)

(i) Detention time

(ii) Freeboard

(c) Design Calculations

Assuming that all pumps are working for.hours

Capacity of underground reservoir = 6hr capacity of average demand

= Qavg.x detentiontime= 18 MLD x 4 x 106x 10-3/24

= 4500 m3

= 1 to 4hr

= 0.4 to 0.6m

50

.........

-.

Assuming 6 compartments

Let depth = 4m

Area = 1125 m2

Area of each compartment = 190 m2

Dimension = 14 m x 14 mFree board = 0.5m

Provide 6 compartments of 14 m x 14 m x 4.5 m

(d) Summary

Elevated Service Reservoir (ESR) :

(a) General

Where the areas to be supplied with treated water are at higher elevations

than the treatment plant site, the pressure requirements of the distribution

system necessitates the construction of ESR. The treated water from the

underground reservoirs is pumped to the ESR and than supplied to the

consumers.

(b) Design Calculations

Assumingcapacityof ESR= 1/10 of underground storage

= 450 m3

Free board

Overall depth

Diameter

.. d

=0.3m

=4m

= "450x 4 In X4

= 11.96m

Provide 1 ESR of overall height = 4.3m and Diameter = 11.96m

51

1. Capacity of reservoir 4500 m;1

2. Total depth 4.5m

3. Compartments 6

4. Size 14 m x 14 m x 4.5 m

5. Detention time 4 hr

..

(b) Summary

52

1. Number of tanks 1

2. Depth of tank 4.3m

3. Diameter of tank 11.96m

_0_-

--d~~.:!=-~:?<

:1°'lC- fL.oWI

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.. .:" "..I I... - . . ..

OUT LeT ]!t.-'YA-LIIEPIPE

.

COLUMN BERMS

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(iF CONCLUSION

The designed project deals with the design of a conventional water

treatment plant having a perennial river as the source. The design has

been done for a predicated population of 61400 expected after 30 (2001 to

2031) years. Although this project and its data is totally hypothetical, this

exercise will help us when we may come across some such design infuture.

The above treatment of the water makes it possible to safe guard the

health of the people.

53

rJfr REFERENCES

1. A.G.Bhole.

2. Birdie J.S.

3. FairG.M.

4. Garg S.K.

5. Govt. of India.

6. Hudson H.E. Jr.

7. Steel E.W. &

Mcggee T.J.

TwartA.C.8.

"Low cost package water treatment plant

for rural areas"l.E. (I) Journal - EN 1995.

"Water supply and sanitary engineering",

Pub.: Dhanpat Rai & Sons, New Delhi, 1994.

"Water and waste water engineering"

(vol.1&2) john Wiley & sons, inc. New York,

1967.

"Water supply engineering" Khanna pub.,

New Delhi, 1994.

"Manual on Water Supply & Treatment",

Ministry of works & housing, New Delhi, 1984.

l'Water Clarification process: Practical

Design & Evaluation" Van Norstrand

Reinhold Co., New York, 1981.

l'Water Supply & Sewerage" McGraw Hill

Ltd., New York, 1981.

l'Water Supply" Arnold International Student

Edition (AISE), Great Britain, 1985.

54

pr

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