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

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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-
(c)

Design Calculation

Number of intake well

=1

Number of pen stocks at each level

=2

Velocity

= 0.75 m/sec. (assumed)

CIS area of each pen stock

= 0.1543/0.75 x 2 = 0.1029 m2

Diameter

= 0.3619 m ==0.4 m

(d)

Summary

1.

Number of pen stock 1well

2 units

2.

At each level

1m

3.

Diameter of pen stock

0.4 m

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

= 0.25 m/s

Hole diameter

= 10 mm

(c)

Calculation 1t d2

Area of each hole

= -

Area of collection

4 = Area of pen stock

= 0.7853cm2

0.1543 = 0.7853 x N 0.25 x 2 N

= 3929.7

Area of Bell mouth strainer= 2 x area holes 22

(c)

Design Calculation

Number of intake well

=1

Number of pen stocks at each level

=2

Velocity

= 0.75 m/sec. (assumed)

C / S area of each pen stock

=0.1543/0.75x2 = 0.1029 m2 = 0.3619 m ==0.4 m

Diameter

(d)

Summary

1.

Number of pen stock / well

2 units

2.

At each level

1m

3.

Diameter of pen stock

0.4 m

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

= 0.25 m/s

Hole diameter

= 10 mm

(c)

Calculation 1t d2

Area of each hole

= -

Area of collection

4 = Area of pen stock

= 0.7853cm2

0.1543 = 0.7853 x N 0.25 x 2 Area of Bell mouth strainer = 2 x area holes 22

= 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.

(b)

Design Criteria

Diameters of gravity main

= 0.3 to 1 m

Velocity of water

= 0.6 to 0.9 m/s

Number of gravity main = number of intake well

=1

Assumption velocity

= 0.7 m/s

(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, 1 V=

R 2138112n 8 --

n2V2

--

(0.013)2 X (0.7)2

R413

(0.55/4)413

= 1.59 x 10-4 8 = 1 : 862

Headloss

= 100 / 862 = 0.116

R.L. of gravity main

= 27 - 3 =24m

R.L. of gravity main at jack well

(d)

= 24 - 0.116 = 23.88 m

Summary

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

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

Design Criteria

(b)

.

Detentiontime = 0.5 x detention time of intake well.(3 to 15 min.}. =0.5)( 10 =5min.

. .

Suction head < 10m. Diameter of well < 20m.

(c)

Design Calculation Detention time

=5m.

Assumingsuctionhead Bottomclearance

=

Top clearance

= 0.5 m.

8 m.

= 1.0 m.

Maximum depth of water that can be stored in condition when water is minimumin rive 26 -

=3.12 m

22.88

=0.1543x10x60

Capacity of well

= 92.58 m3 = 92.58/3.12

C / S area of well

= 29.67 m2

Diameter of well

= 6.14 m

R.l. of bottom of jack well

= 22.88 m

R.l. of bottom of jack well when full

= 22.88 + 7 = 29.88 m

(d)

r:c-

Summary Diameter of jack well

6.15m

R.l. of bottom of jack well

3.

R.l. top of jack well

22.88 m 29.88 m

4.

Suction depth

2.12m

Top clearance Bottom clearance

O.5m 1m

tE 6.

.25

/.... k'..

.'

--... J'

-

I

; I

I I.

I I

-0:.. :..... .I'

.

:'-1' . I .. :.-'Ii :: :: ~,.: ;>-~-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

i. (A.

~.Ct ~

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

~>

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

-

CASC.AbE 3.

.

~

,C-ASCADE

f4

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

(3qSJ R.l(,2(h8~

,-,

.~) R'L:(29;

It 0)

<:'ASCI'obE

~

~(5#

,

.

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

1N LE'T =-PIA M ETE-R CAse ADt;

Of: ~r<J MT5

2Cf -OD

"~ ,r

G : I

:

I

R..L.

AE RA\IQ\J UN\-r

~

IN

MTS

Summary

Sr.

Cascade

Diameter

R.L. (m)

1.

First

of tray (m) 1

31.00

2.

Second

2

30.60

3.

Third

3

30.20

4.

Fourth

4

29.80

5.

Fifth

5

29.40

No.

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

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

CaO

= 40 + 16 = 56.

100 mg/L of CaC03alkalinity requires

= 56 mg/L of CaO

110 mg/L of CaC03 requires

= (56/100) x 110 = 61.6 mg/L of CaO

Lime Required For Magnesium 24 mg/L of magnesium requires

= 56 mg/L of CaO.

1 mg/L of magnesium requires

= 56/24 mg/L of CaO.

3.5 mg/L of magnesium requires

= (56/24) x 3.5 = 8.2 mg/L of CaO.

Hence, the total pure lime required

= 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. Soda (Na2C03) : Soda is required fir non-carbonate hardness, as follows.

3+

100 mg/L of NCH requires

= 106 mg/L of Na2C03

161.6 mg/L of NCH requires

= ( 106/100) x 161.6 =65.59 mg/L of Na2C03

Total quantity of lime

=(92.23 x 555.5 x 180 x 24 x 103) =221329.86 kg

One bag contains 50 kg. Number of bags required

= 4426

If 15 bags in each heap, number of heaps

= 295

If area of one heap is 0.2 m2.

= 295xO.2 = 59 m2

Total quantity of soda required

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

Number of bags

= 157400.25 kg. = 3148

If 15 bags in each heap

= 209.86 heaps.

Total area of heap

= 0.2 x 209.86 = 41.97 m2

Total area for all chemicals

= 80 + 59 + 41.97 = 180.97 m2

Add 30 % for chlorine storage, chlorine cylinders etc. Total area

= 235.26 m2

Provide room dimension

= 20 x 12 = 240 m2

provide dimension

= 20mx 12m

Chemical Dissolving Tanks : Total quantity of alum, lime and soda

= 119984.4 +221329.86 +157400 = 498714.26/180 =19394.44 day =387 bags =25.8 heaps

Area required

= 5.16 m2

Dimensions

= 3.0 m

35

x 3.0 m

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

1.

Per day alum required

2.

Hydrated lime required

3.

Soda required

4.

666.58 k/j 92.23 mql

65.59 'M/A.Size of chemical dissolving 3x3

tanks

5.

Size of chemical solution tanks 4.5 x 3.5 x 1.5

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

. ,..h u1Ience "nI +h" ..Y'vater. hIIi gh ..U..l11.I LIIO

T

II

he SV" u"10c "

vnol P"u,,,..

OfI

. f".. ..~ iv ' IVI IQ pl d m iliA lng to

create the desired intense turbulence are gravitational and pneumatic. T " 110

h

'

ens ~' In+LILY

"f VI

.vi I III All

i " n,.. ~ Is d0 pendent I I

UpO'"II

th LII

" " e tvllll-'VIQ

,

mIv" anI

""' OCi+u 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. Design Criteria For Mechanical Rapid Mix Unit Detention time =30 to 60 sec. Velocity of flow

= 4 to 9 m/sec.

Depth

= 1 to 3 m

Power Required Imeeller 8eeed . .

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

Loss of head

=O.4to;.O

= 100

to 250 rpm

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 : 1 D I'

a +in uv

(C)

nf t

.

ank h""!g I It to rfi\..IIamo'"'tor".

VI .. I ,

O

-

J"+0 ':! v.

-I

.

-I

I

Design Calculation

Design flow

= 13331.52 m3/day

Detention time

=

Ratio of tank height to diameter

= 1.5:1

Ratio of impeller diameter to tank diameter

= 0.3:1

Rotational speed of impeller

= 120 rem .

Assume temperature

=200

30 sec.

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:

=5.47

Power spend

3.

KW

Dimensions of flat blade and impeller:

Diameterof impeller

= 0.65 m

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 11. 2. 3.

Detention Time

30 sec.

Speed of Impeller

120 rpm

I Height of Tank (0.23 m free board)

2.6m I

4.

PowerRequired

5.47 t<JN

5.

Numberof Blade(0.5mx 0.5m)

8

16.

Number of baffles (length 1.5 m)

4

Diameter of inlet and outlet

250

7.

I

38

- ---

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

= 10 to 36 KW/mld

Outlet velocity

= 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) = 1 revolution in 45 to 80 minutes

Scraper velocity

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

(c)

Assumptions

Average outflow from clariflocculator Water lost in desludging

=2%

Design average period

= 566.82 m3/hr

Detention period

= 30 min. = 30 S-1

Average value of velocity wadient 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 Provides

=10.2m 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 P x 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. 229.08

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

..

= 9.47 m2

Ap

Ratio of paddles to cis of flocculator [9.47/ P (10.2 - 0.75) 3.5] x 100

= 9.11 % <10 to 25 %

Provide Ap

= 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. = 0.51m2

Area = 555.48/0.3 x 60 x 60

Depth below partition wall = 0.51/x x 10.2 = 0.016m = 0.25 x 35

Provide 25% for storage of sludge

= 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

= 1t X Oct

= 1tx 23 Weir loading

= 72.26m

= 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 it flow 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

. . .

Wearing loss is not greater than 3%

. .

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

(b)

Silica content should not be less than 90% Specific gravity

= 2.55 to 2.65

Minimum number of units

=2

Depth of sand

= 0.6 to 0.75

Free board is not less than 0.5m

Problem Statement

Net filtered water

= 555.48m3/hr

Quantity of backwash water used

=2%

Time lost during backwash

= 30min.

Design rate of filtration

= 5m3/m2/hr

Length - width ratio

= 1.25 to 1.33:1

Under drainage system

= central manifold with laterals.

Size of perforations

= 13mm

(c)

Design Calculation

Solution: required flow of water

= 555.48m3/hr

Design flow for filter

= 555.48 x (1 + 0.02) x 24/23.5 = 578.65m3/hr

Plan area for filter

= 578.65/5 = 115.73m2 ==116

Using 2 units, Plan area

= 58m2

Length x width

= L x 1.25L = 58

L

=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)3 x 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. 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

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

--

Total cross section area of laterals

= 3 x area of perforation = 3 x 1754.4 = 5263.2cm2

Area of central manifold

= 2 x area of lateral = 2 x 5263.2 = 10526.4cm2

Diameter of central manifold

= ..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 = 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

= %x6.8-%x

-

% dia. of manifold

1

= 2.90 m Let n be total no. of perforation of 13mm dia.

..

Total area of perforation = n x 1t/4 x (1.3)2 = 1754.4

..

n

= 1321.76 ==1322

No. of perforation /Iateral = 1322/86 = 15.37 ==16

Spacing of perforations

= 2.90 x 100/1.6 = 181.25cm clc

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

46

Computation of wash water Troughs: Wash water rate

= 36m3/m2/hr

Wash water discharge for one filter

= 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. 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

= 1.5m3/m2/min.

Duration of air wash

=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

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 12. Size of trough

4

13. Total depth of filter box

4500mm

14. Duration of air wash

3min.

15. Total quantity of air required per unit bed

263. 16m;:!

6.2.6

Disinfection

(a)

Chlorination

0.4 x 0.5m

Unit

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

-

CHLORINE

GAS

TO

L.IQUID C1.1 c. YLINCEP-

CI~TRI~IJTION MAIN

WEIGHING .sCALE

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WATeR 70 13€

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DIAGRAM OF A. 'YPICAl CHLORINA70R

.5oLUTION

INSTALJ..ATloN I I II I

harmless, unobjectionable to taste, ecomomical and measurable by simple tests. 'Chlorine' satisfies the above said more than any other disinfectant and hence is widely used. (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 For 6 months

= 18.662 x 180 = 3359.16kg

Number of cylinder (one cylinder contain 16 kg)

= 3359.16 x 2/16 = 419.895

Number of cylinders used per day (d)

=2 cylinders of 16kg

Summary

1

Chlorine required per day

18.662kg

2

Number of cylinder required per day

2 of 16kg

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

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 114 to 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)

(c)

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

Detention time

= 1 to 4hr

(ii)

Freeboard

= 0.4 to 0.6m

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

50

.........

-.

Assuming 6 compartments Let depth

= 4m

Area

=

1125 m2

Area of each compartment

= 190 m2

Dimension Free board

= 14 m x 14 m = 0.5m

Provide 6 compartments of 14 m x 14 m x 4.5 m (d)

Summary

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

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

=0.3m

Overall depth

=4m

Diameter

= "450 x 4 In X4

..

d

= 11.96m

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

51

..

(b)

Summary

1.

Number of tanks

1

2.

Depth of tank

4.3m

3.

Diameter of tank

11.96m

52

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I' .,

4.3

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

I.. h-

:1°'lC - fL.oWI PIPe

PIPe M,. I r--j. 1/"'fT f_

.. .:"

"..I I.. OUT LeT PIPE

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COLUMN

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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 in future.

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

53

rJfr

1.

A.G.Bhole.

REFERENCES

"Low cost package water treatment plant for rural areas"l.E. (I) Journal - EN 1995.

2.

Birdie J.S.

"Water supply and sanitary engineering", Pub.: Dhanpat Rai & Sons, New Delhi, 1994.

3.

Fair G.M.

"Water and waste water engineering" (vol.1&2) john Wiley & sons, inc. New York, 1967.

4.

Garg S.K.

"Water supply engineering" Khanna pub., New Delhi, 1994.

5.

Govt. of India.

"Manual on Water Supply & Treatment", Ministry of works & housing, New Delhi, 1984.

6.

Hudson H.E. Jr.

l'Water Clarification process: Practical Design

&

Evaluation"

Van

Norstrand

Reinhold Co., New York, 1981. 7.

8.

Steel E.W. &

l'Water Supply & Sewerage" McGraw Hill

Mcggee T.J.

Ltd., New York, 1981.

TwartA.C.

l'Water Supply" Arnold International Student Edition (AISE), Great Britain, 1985.

54

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