Tube Settling Thailand

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ÎNTERNATIONAL REFERENCE'.'CENTRE

FORCOMMUNITY WATER SUPPLY. AND

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APPLICATION OF INCLINED TUBE SETTLERS IN URBAN WATER SUPPLY

s

by

Sow, Kim Leng

A T

. UBRARV

A thesis submitted in partial fulfillment of the requirements for the

degree of Master of Engineering.

Examination Committee:

Prof.

N.C. Thanh

Dr.

B.N. Lohani

Dr. S. Vigneswaran

(Chairman)

Sow, Kim Leng

Nationality

Previous Degree

Scholarship Donor

Malaysia

B.Sc. Engineering, University of Aberdeen,

Aberdeen, Scotland.

The King's (Royal Thai Government)

Asian Institute of Technology

' Bangkok, Thailand

:_.SRARY. iNi

_r<:V,'-.;.^:v,.'_ ixL_, u-U^.v^— , ^ _

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^ 1983

CENTRE FOR CDI.-inUX'iTV WATSR SL;?:'

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ABSTRACT

A study of a pilot scale Inclined tube settler was conducted at the

Bang Khen Water Treatment Plant, Bangkok, Thailand, ,in an attempt to verify

the applicability and the role that the tube settler can play in the modern

water treatment plant. The experimental results concluded optimistically

that the tube settler can provide comparable performance as that of the

conventional sedimentation tank. In addition, it possesses the advantages

of short detention time of only 14 minutes and that the construction costs

of the tube settler is 3/4 that of the conventional sedimentation tank. As

for the land requirement, tube settler needs only 1/4 the land necessary

for the construction of sedimentation tank.

The performance of the tube settler was evaluated using natural floc

culated water at various turbidity ranges and flow rates. Experimental

results reviewed that addition of polyelectrolytes does not impart signi

ficant effect upon the settling efficiency. If 80% of removal efficiency

is acceptable as the design criteria, then the overflow rates of 12.75 m

3

/m d

and 18.50 m

3

/m

2

d can be used for raw water turbidity of 25-37 NTU and 36-45

NTU,

respectively. To cater for the stringent effluent quality of 5 NTU,

overflow rate of 8.75 m

3

/m

2

d is satisfactory for raw water turbidities of

25-37 NTU if the system is working under optimum alum dose. For 'economic'

alum dose, overflow rate of 8 m

3

/m

2

d can be used to satisfy the effluent

requirement.

The present study also confirmed that column settling analysis can be

used to provide the correlation for the scale-up of the pilot plant tube

settler. For natural flocculated water, a safety factor of 2 can be used

for tube settler design.

Plenum forms an important component of the tube settler system. Em

pirical formulae were developed in this research to take into account of

the sludge scouring and the turbulent effect and at the same time to cater

for the period needed for desludging.

(iii)



LIST OF SYMBOLS

Cross sectional area of entrance

Cross sectional area of distance x

Longitudinal width of plenum

Unit adjustment constant

Adjusted integration constant

Integration constant

Diameter

Floe size at entrance

Floe size at distance x

Efficiency

A frictional factor

Acceleration due to gravity

Settling column depth

Depth of plenum at entrance (h

Q

= h = 0 )

Depth of plenum at entrance

Depth of plenum at entrance x = L

0 Depth of settled sludge at entrance

L Depth of settled sludge at distance x •= L.

Total plenum depth at entrance

Total plenum depth at distance x = L

A constant with magnitude close to S„

Relative length

Total longitudinal length of plenum

A constant

Flow at entrance section

Flow

at

distance x

Removal efficiency (%)

Reynold'.s Number

Shape factor or critical shape factor

Specific gravity of the floe particle

Time at t

Settling time

(iv)



LIST OF SYMBOLS (CONT'D)

U Velocity in x direction

V^ Displacement velocity

V

Q

Overflow rate

V

s

Settling velocity

V Velocity of particle in x direction

Vpy Velocity of particle in y direction

V

s c

Critical overflow rate

x x coordinate

X Distance across the plenum length

s

y y coordinate

Greek Symbols

8 Angle of inclination to horizontal

O

(v)



TABLE OF CONTENTS

CHAPTER TITLE PAGE

Title Page i

Acknowledgements il

Abstract iii

List of Symbols iv

Table of Contents vi

I INTRODUCTION 1

1.1 General 1

1.2 Sedimentation 2

1.3 Objectives of the Research 2

1.4 Scope of Study 3

II LITERATURE REVIEW 6

2.1 Historical Development of the Tube Settler 6

2.2 Parameters Affecting Tube-Settler Performance 7

2.3 Practical Applications of Tube Settlers 9

2.3.1 Primary Treatment of Sewage Effluent 9

2.3.2 Upgrading Humus Tank 10

2.3.3 Secondary Treatment of Sewage Effluent 10

2.3.4 Tertiary Treatment of Sewage Effluent 11

2.3.5 Raw Water Clarification 11

2.3.6 Other Applications 13

2.4 Column Settling 13

III SOME THEORETICAL CONSIDERATIONS ABOUT TUBE SETTLERS,

COLUMN SETTLING AND PLENUM DESIGN 16

3.1 High Rate Sedimentation 16

3.2 Column Settling 19

3.3 Plenum Design 19

IV EXPERIMENTAL INVESTIGATION 22

4.1 Background i 22

4.2 Raw Water Source 22

4.3 Experimental Apparatus and Materials 22

4.4 Clarifier . y 25

4.5 Methodology 25

4.5.1 Preliminary Analyses 25

4.5.2 Pilot Scale Investigation 25

4.5.3 Column Settling Analysis 26

(vi)



o

TABLE OF CONTENTS (CONT'D)

CHAPTER TITLE PAGE

V PRESENTATION AND DISCUSSION OF RESULTS

5.1 Preliminary Analytical Results

5.2 Overflow Rate Versus Efficiency

5.3 Effect of Turbidity on Efficiency

5.4 Effect of Flow Velocity on Efficiency

5.5 Experimental Results of Plenum Design

5.6 Column Settling Results

5.7 Practical Problem Encountered

5.8 Recommended Design Criteria and Numerical Example

VI ECONOMIC ANALYSIS

6.1 Introduction

6.2 Need of Cost Estimation

6.3 Design Assumptions

6.4 Design of Sedimentation Tank and Its Cost Estimation

6.5 Design of Tube Settler and Its Cost Estimation

6.6 Summary

VII CONCLUSIONS

VIII RECOMMENDATION FOR FUTURE WORK

REFERENCES

JAR TEST EXPERIMENTATION

TUBE SETTLER PERFORMANCE

COLUMN SETTLING ANALYSIS

PLENUM DESIGN

APPENDIX A

APPENDIX B

APPENDIX C

APPENDIX D

APPENDIX E LEAST SQUARE METHOD OF ANALYSIS

28

28

28

33

33

33

42

46

47

52

52

52

52

53

54

56

57

59

60

64

68

83

90

97

(vii)

O



- 1 -

I INTRODUCTION

1 . 1 G e n e r a l

The thirst of civilized man is unsatisfiable. The more sophisticated

he becomes the thirstier he seems to be. In the so-called developing coun

tries as little as 12 litres of fresh water sometimes suffices as the daily

supply for each person, while in the developed countries, the daily demand

in urban areas surpasses 150 to 200 litres per head. Yet this it only part

of the story; as for man becomes more advanced he nueds more and more water

for commerce,, industry, public institutions, power stations, and many other

uses.

Adding to this unremitting increase in demand, the ceaseless growth

in the world's population and the yearn of achieving higher standard of liv

ing enable man to have a glimpse of the extent of the problem it presents,

a problem that today seems to be happening in more and more areas around the

world.

Apart from water supply, the quality of supplied water should be safe

to drink, such demand imposes stress upon the engineers to provide water

which is free from organisms and from chemical substances that may be ha

zardous to health. In addition, coolness, absence of turbidity, colour and

disagreeable taste or smell are of prime concern.

In 1981, WHO estimated that approximately three out of five persons

in the developing countries do not have access to safe drinking-water (see

Table 1.1). For the urban areas, about 75% of the population having some

form of water supply through house connections or standpipes while only 29%

have equivalent water supply in rural areas.

TABLE 1.1

E s t i m a t e d S e r v i c e C o v e r a g e f o r D r i n i c i n g - W a t e r S u p p ly

i n D e v e l o p i n g C o u n t r i e s , 1 9 7 0 - 1 9 8 0 *

i 1 1 1 1

J Y e a r | 1 9 7 U | 1 9 7 5 | 1 9 8 0 |

I 1 1 1 1 1 1 1

j |Population|Percentage|Population

j

Percentage|Populati on(Percentage|

| |Served (in|ol To ta l |Served (in|of To ta l |Serv ed (in|of To ta l \

| |aillion) |Popul ation| iailno n) |Popula tion million ) |Popu latio n|

1 I 1 1 1 1 V

| 0 r o a n | 316 | 67 | 450 | 77 | 52b | 7b |

I 1 1 1 1 1 1 1-

| a u r a i | 182 | lu | 313 | 22 | Ub9 ( 29 |

I 1 1

-\ i

1 1 J-

| T o t a l | 4 9 b | 2 9 | 7 6 3 | 3 8 | 9 9 5 | 4 3 |

i

L —

1 1 » 1 1 _ i

»WH0 ( 19 8 1) l U n i t e u N a t i o n s D o c u m e n t A / 3 5 / 1 5 0 )

F i g u r e s d o n o t i n c l u d e t h e P e o p l e ' s R e p u o l i c of C h i n a .



- 2 -

To combat the above situations, the decade from 1981 to 1990 has been

designated an International Drinking Water Supply and Sanitation Decade.

It represents a concerted effort by the entire international community to

extend and improve water supply and sanitation worldwide. The decade's

targets were first formulated at the 1976 United Nations Conference on Human

Settlements in Vancouver. There, a resolution was passed urging the adop

tion of programs for urban and rural areas that would lead "if possible" to

safe water supply and hygienic waste disposal by 1990 for all human settle

ments.

1.2 Sedimentation

In tropical regions, high turbidity is one of the main characteristics

of the surface water. Pretreatment is therefore often necessary for water

^treatment plants using surface sources taken from the streams. Chemical coa

gulation followed by flocculation and sedimentation i,s normally the process

used in the conventional filtration plants,.

'^Sedimentation is one of the most widely used unit operation for removal

of turbidity and to concentrate solids in many diversified fields. It is

the most commonly used process in the field of water and sewage treatment.

The investments for settling in this aspect are probably about one third of

the total capital investment for treatment. Despite the importance of the

process, its basic design criteria have remained without significant change

for well over 50 years.y

In late 1960's tube settler was developed and has now been considered

as an accepted process for water treatment in most parts of the world. It

provides a breakthrough in the old practice and a newtool for increasing the

efficiency of sedimentation and reducing the cost of settling. In 1904,

HAZEN undertook the first realistic approach of the tube settling system

which was later explored extensively by CAMP in 1946. These units have small

size tubes of various shapes and operate at detention times of not more than

15 minutes (YAO,

1973).

The system accomplishes almost ideal condition of

settling i.e. laminar flow conditions, shallow depth, absence of thermal

currents and elimination of short circuiting.

To-day, two basic shallow depth settling systems are commercially

available, there are the essentially horizontal tube settler (with 5-degree

of inclination to the horizontal) and the steeply inclined tube settler

(with angle of inclination to the horizontal in the range of 45-degree to

60-degree) . The former tube system installed prior to the filter units and

the cleaning is accomplished by backwash water from the filters. For steeply

inclined tube settler, the sludge is removed by mean of gravity.

1.3 Objectives of the Research

Tube-settlers are compact and can provide the benefits of significant

cost savings in construction and land costs. They can also be used for up

grading an existing overloaded conventional sedimentation tank and still

provide comparable or better settling efficiencies normally obtained in

conventional settling tanks. The various other advantages offered by the



- 3 -

tube settler make it essential to develop design criteria for the clarifi

cation of tropical turbid waters.

In the developing countries where resources are scarce, therefore seek

ing toward appropriate technology which could lead to a cost-effective system,

for water treatment is of prime importance. In Asian Institute of Technolo

gy, many research studies were conducted in the past ten years to investigate

the effects of various factors and parameters which affect the performance

of the tube settler efficiency. Tube length, tube size, flow rate, overflow

rate,

raw water turbidity, angle of inclination and shapes of tubes were

among the factors and parameters considered in the researches (see Table

1.2).

The aims of this study are devoted mainly to the application of tube

settler design based upon the findings from AMIN

(1974),

BINH

(1975),

LIENGCHARERNSIT (1975), VASANADELOKLERT (1978), CHEN (1979) and PANNEERSEL-

VAM (1982). The other principal objectives of the present research are as

follows:

(i) To evaluate the role of the tube settler in the water treatment

systems and to investigate the performance of the tube settler

at various overflow rates, flow velocities and influent raw water

turbidities.

(ii) To conduct an in-depth study of the plenum design and to arrive

at empirical formulae which give the optimum design of the plenum.

i

(iii) To investigate the use of settling column and jar test techniques

to provide a correlation for the scale-up of the plant size tube

settler. ^

(iv) To determine the effect of settling depths upon the correlation

factors obtained from objective (iii).

(v) To look into the effect of residual current upon the performance

of the settling column.

(iv) To evaluate the creditability of the tube settler by estimating /

and: comparing the costs of the tube settler with the conventional /

sedimentation tank.

1.4 Scope of Study

The research was carried, out on pilot scale tube settler inclined at

60 degrees to the horizontal with relative length L=18. The experiment

was conducted in the Bang Khen Water Treatment Plant and it consisted of

three phases:

Phase 1: The effect of the operational variables upon the efficiency

of turbidity removal was studied. The operational variables

investigated were: overflow rate (2.0 to 30

m

3

/m

2

-d);



- 4 -

Past Researches oa Incline d Tube Settler Underta ken

at The Asian institute of Tecnnoiogy, BangKO/c, Tnailand.

• i

Att

_. ., ,

Descr iptio n or Resea rch |

Aia:

To evalu ate tne perfo rmanc e |

of horizontal tuDe settler;

Source: A. I. T. jclong's w at er ;

T u mi d it y : JO - yS wTU. |

Aim: App lica tio n of oano uo and |

corrugated asbestos

AS

tune

settlers;

|

S ou rc e: A .I . T . k l o n u ^ w a t e r ;

T u mi d it y: 10u - 140 NTU .

Aim: Practical a ppli cati on or

baa»boo tu be se tt le r in |

water treatment plant;

Source: Cnao Enya iiiver;

Tu mi di ty : 60 - 72 WTO. j

Aiiu: Deve lope d aes ign cri ter ia

for incli ned tune s ett ler

and plenua;

Source:

Synthetic wat er;

T u m i d i t y : 2 0 - 1 O U N T U .

Aim:

To

study tne performance

of inclined tuoe set tle r,

relative lenytn of lb ana

b = t>0 degrees;

Source: Syntnetic water;

[T um id it y: 50 - IbU N TU .

1. i

i

- - - • - - «

Con clu sio ns of rese arcn I

Effective in the turbidity |

removal and con tin uou s I

sludge removal is ach iev ed. |

Tube settler gave comparaolel

efficiency wnen compared to |

upflow con tac t bas in but it I

has shorter detention ti me . |

80

%

effic ienc y acnieved I

with len gt h of 120 ca and |

Vsc or 8 m

3

/iB* d. An gl e |

of inclin ation of 60 de g. |

was tae be st . Corrugated I

aso est os tune sett ler gave |

better perf orma nce tnan |

baoiboo se tt le r but it co st |

more.

[

i

r

Re&ovai etficiency of 93 .8 % I

was acnieved with tube |

length 12ocui, d i a . 6.3 cm , |

Vsc of 2.5 a V n

i

d at |

9=45 de g. . Cost of bam boo |

settler was 1/2 the cost of |

settling tank and land used |

was 1/J of the sedimentation|

basin.

|

Relative length of 14.9 was |

tne econom ical value tor |

square t u D e . ttatheaatical |

formulatio ns were developed |

tor tne etfi cien cy or the |

tune syst em and tne ple nua |

design was inves tigate d. |

r

Recounnended ove rtl ow ra te |

and flow velo city of 4 |

m-Via* d and 4 n

J

/ u

i

h |

respec tively . Column |

settling can provid e sc al e- |

[ up for tne p n o t s cale tube |

settler sys tem . A safety |

tactor of 2 was applicable. |

| Plenum desi gn was als o |

investigated. |

A J 7



o

- 5 -

influent raw turbidity (25 NTU to 45 NTU); flow velocities

(2 m

3

/ra

2

-h to 8 m

3

/m

2

-h).

Experiment was carried out first to determine the desirable

plenum bundle (of depth 0.2 m; 0.3 m; 0.6

m ) .

For the spe

cific plenum bundle, the depths of the accumulated sludge at

the different points across the plenum length (XI =0 . 0 cm;

X2 = 8.0 cm; X3 *= 16.0 cm; X4 = 24.0 cm and X5 = 32.0 cm)

were measured for different flow velocities.

In the column settling analysis, single level sampling was

used. Percentage of the turbidity removal at different

settling column depths (10 cm; 30 cm; 50 cm; 70 cm and 100 cm)

and at different time intervals were recorded. The effect

of residual current upon the performance was also determined

by using the conventional jar test technique and the revised

jar test technique using square tank.

O



- 6 -

II LITERATURE REVIEW

2.1 Historical Development of the Tube Settler

HAZEN (1904) recognised that the proportion of sediment removed in a

settling basin is primary a function of the surface area of the basin and

it is independent of the detention time. He pointed out that doubling the

surface area by inserting one horizontal tray would double the capacity of

the basin.

BRAHAM et al. (1956) reported one of the first attempts on practical

application of tray-settling principle which was patented in 1915. Several

shallow settling compartments were formed by a series of conical, circular

trays placed one above the other. The solids collected on each tray were

scraped to a centrally located sludge collection tube which then transports

the sludge to the bottom of the tank.

FREI (1941) inserted three circular, steel, radial-flow trays to an

existing primary sewage clarifier. He reported the efficiency of the

sus

pended solids removal increased from 41 to 61 per cent even though the

flow through the tank, was tripled following the addition of the trays.

CAMP (1946) assumed a uniform velocity profile of the tank and thus

the particles followed a straight trajectory in passing through the tank.

He then presented a design for a settling basin with horizontal trays spaced

at 12.24 cm (6 in) which he left the minimum distance for mechanical sludge

removal. The basin had a detention time of 10.8 min, a velocity of 168

m /m

2

-h, and overflow rate of 27 m

3

/m

2

-d. Outlet orifices were used to

distribute the flow over the width of the trays.

SCHMITT and VOIGT (1949) mentioned the use of a two-storey settling

basin in a water treatment plant. The trays were arranged in series and

spaced at 4.75 m (15 ft) and were cleaned by draining and hand-hosing.

DRESSER (1951) reported a similar use of series of trays in the Cambridge,

Mass., water treatment plant. The trays were spaced at 1.524 cm (5 ft)

and sludge removed by gravity with nozzles mounted at the end.

All attempts in 1940's and 1950's at the applications of shallow depth

sedimentation met with limited success due to two major problems:

(1) the difficulties encountered in proper distribution of flow to

a large number of trays,

(2) sludge removed from closely spaced trays.

To maintain proper hydraulic conditions for efficient sediments,

FISCHERSTROM (1955) felt that a Reynolds number of 500 (limit of laminar

flow at 32°F) in the settling would be most beneficial to the settling

process.

He pointed out that the Reynolds number could be lower to the

laminar flow range by increasing the wetted perimeter, or inserting longi

tudinal,

horizontal or vertical baffles in the basin.



- 7 -

HAZEN and CULP (1967) reported that longitudinal flow through the tubes

with diameter of few inches offered theoretically optimum hydraulic condi

tions for sedimentation. Such tubes often provide very low Reynolds number.

This show that even with largest tube and highest flow rate the Reynolds

number was only 96 which is far below the upper limit of laminar flow of

500.

w

CULP et al. (1968) described the two basic tube settler systems, namely

the essentially horizontal tube settler and the steeply inclined tube settler,

where both of them are now commercially available. He concluded that for

tube inclined at an angle of 60 degrees to the horizontal, continuous sludge

removal is possible.

HANSEN et al. (1969) observed that if the tube is inclined at an angle

of greater than 45 degrees, then the sediments accumulated on the surface of

the tube begins to move down after reaching a certain depth. This counter-

current flow of the solids aids in the agglomeration of particles into larger,

heaver floes which are able to settle against the upwardly flowing liquid.

v

YAO (1970) developed a mathematical model for the tube settlers with

the assumptions that the flow is laminar and one-dimensional and that the

suspended particles are discrete. He formulated a formula describing the

relationships between the shape of the tube, relative length and the angle

of inclination upon the settling efficiency.

YAO

(1973),

based on his previous model and coordinates system, arrived

at

an important equation of overflow rate against the shape factor, relative

length and the angle of inclination. He also pointed out that the higher

the raw water turbidity, the higher the removal efficiency for all overflow

rates.

AMIN (1974) investigated the performance of the essentially horizontal

tube settler and the steeply inclined tube settler. He found that the steeply

inclined tube settler performs beter than the essentially horizontal tube

settler in terms of higher flow rate (10 m

3

/m

2

-h compared with 2.45

m

3

/m

2

-h).

shorter detention time (5.5 min compared with 20

min),

and higher efficiency

(80%

compared with

60-70%).

CHEN (1979) developed a model based upon the hydraulic conditions in

the tube and eventually arrived at a formular which is similar to the equa

tion for overflow rate developed by YAO in 1973. From CHEN model, he recom

mended that the relative length of 14.9 and the flow rate should keep below

10.7 m

3

/m

2

-h.

\ .2.2 Parameters Affecting Tube-Settler Performance

YAO (1970) based on his model derived an expression for the critical

particle fall velocity for a given high rate settling system:

V

SC

/V

Q

=

S

c

/(Sin6

+ LCosO)

(2.1)



- 8 -

where L is the relative length,

V

s c

is the overflow rate,((^

A

'

V

0

is the average flow velocity,

S

c

is the shape factor,

6 is the angle of inclination

From this expression, he concluded that tube shape has an effect upon

the value of S

c

which in turn affects the efficiency of the tube settler.

For the circular tube, parallel plates, square conduits and shallow open

trays, he calculated the value of S

c

for each case to be 4/3, 1, 11/8, and

1, respectively. Therefore, in chosing the tube shape, the following cri

teria should satisfy:

(1) the tube height should be as short as possible to minimize the

settling distance,

(2) uniform settling distance is desirable so that most particles

have the same settling time,

(3) tube shape should permit nesting so that there is no wasted

space between tubes in the unit,

(4) as far as possible, the shape should promote sludge compaction

and flow.

• BEACH (1972) concluded that chevron shape is tfaj best design fulfill

ing all the above conditions and for 1 in chevron configuration, it has the

higher perimeter of any common shape of the same area.

CULP et al. (1968) investigated the influence of tube inclination on

the settler:performance. They concluded that the efficiency increases as

the angle of inclination increases to 35-45 degrees and then begins to

decrease as;the angle of inclination increases further. But as the angle

of inclination increases beyond 45 degrees, promotion of self desludging

by gravity becomes significant. 1973, YAO stated that it is necessary to

sacrify the

1

system efficiency so as to achieve self cleaning action at an

angle of inclination of 60 degrees.

In 1975, a different situation was encountered by BINH. For veloci

ties of 12.5 cm/min and 16.7 cm/min, the tube settler inclined at 40 degrees

gave slightly better performance than the one inclined at 60 degrees while

the third inclined at 50 degrees gave the lowest efficiency. In addition,

at higher flow velocity (20.8

cm/min),

the removal efficiency was not

affected significantly by the variation of angle of inclination, which agree

well with the remark made by YAO in 1973.

Raw water turbidity imparts a significant effect upon the settling

performance of the tube settler. YAO (1973) and PANNEERSELVAM

(1982),

both

claimed that the higher the raw water turbidity, the better the removal

efficiency for all flow rates. The reasons for such improvement could be

due to better flocculation before settling at higher turbidity.



- » -

A,T

- Lm

nA

RV

Tube diameter can also plays an important role in the tube settler

system. As the tube diameter increases, the turbidity removal efficiency

decreases and the effect is much more significant at higher flow rate than

that at lower flow rate. Small diameter offer lower Reynolds number thus

promote laminar flow which facilitates better settling performance.

Polyelectrolyte addition has positive and negative effect on the set

tling performance and its consequence depends very much upon the characteris

tics of raw water. HAZEN et al. (1967) concluded that addition of 0.2 mg/A

to 0.5 mg/it of polyelectrolyte could achieve better settling performance

while AMIN (1974) reported that addition of polyelectrolyte does not enhance

settling.

HANSEN (1967) and others reported that the turbidity removal efficiency

decreases as the overflow rate increases. In 1973, YAO concluded that if

the overflow rate criteria for the conventional sedimentation tank design

is used for designing high rate settlers, the later should provide better

performance within the practical range of overflow rate. He also stated

that if 80% removal efficiency is acceptable, then overflow rate of 61 m

3

/m

2

-d

can be used. WILLIS (1978) specified the maximum overflow rate value has

varied from 3.6 m

3

/m

2

-d to 16 m

3

/m

2

-d based upon the tube end area. AMIN

(1974) recommended that the overflow rate should not exceed 13 ra

3

/m

2

-d while

PANNEERSELVAM (1982) concluded that the overflow rate of 4 m

3

/m

2

-d is the

best.

The above variation of overflow rate could be due to the difference

in tube settler design, size, different raw water used, and different experi

mental conditions.

2.3 Practical Applications of Tube Settlers

2.3.1 Primary Treatment of Sewage Effluent

SLECHTA and CONLEY conducted a plant scale installation of

settling tubes in a primary clarifier at Philomath, Ore. In 1968

and concluded that settling tubes can be used to improve the quality

and possible increase the capacities of those installations where

a serious carry-over of solids exists. In those installations where

a good primary effluent is being obtained, an increased in the capa

city is possible provided the hydraulic limitations of the basin are

not exceeded. They found that for the same solid removal efficiency,

a three-fold increase in the flow-rate is possible for tubes loaded

at 6-10 m

3

/m -h based on the end area of the cubes. They also noted

that no improvement in the primary effluent quality can be achieved

through the use of settling tubes alone in a basin already providing

essentially complete settleable solids removal and 40-60 per cent

suspended solids removal. During the first few months of operation,

no maintenance problems have developed but after 6 months of operation,

a mat of 0.1 m thick had formed on the top of the tube and floating

septic sludge was observed. The problem was overcome by installing

a submerged water jet and agitating the module on weekly basis.



I

- 10 -

2.3.2 I Upgrading Humus Tank

In 1975, Water Research Centre carried out a full-scale module

of slopping tubes installed in one of two humus tanks in a small works

serving a village in the United Kingdom. Results indicated that the

solid removal efficiency depends upon the nature of the influent solids

and the upward-flow velocity calculated from the total plan area of the

inclined plates. For influent suspended solids concentration of 100

mg/i

(in

Winter),

the rate of flow can be increased to three times in

the modified tank for the same effluent quality. For influent suspended

solids concentration of 150 mgjI (late Spring), the flow-rate could be

increased to only 60 percent, while for 50 mg/ I (Summer) of influent

suspended solids, no appearent benifit was gained from installing the

module. In the course of the experimentation, no denitrification occured

and the module was cleaned every two weeks to prevent the growth of

slimes.

2.3.3 Secondary Treatment of Sewage Effluent

Inclined tubes had been Installed in the final settling tanks

at a number of full-scale activated sludge plants in U.S.A. The first

field installation was made at the Wickam Sewage Treatment Plant, Pen-

nyslvania (Fig. 2.1). Initial results were promising but experience

over a long period showed that there was periodic discharged of solids

and fouling of module. Fouling can be prevented by provision of sub

merged water

jets,

module agitation or air scrubber. It was recommended

that the loading should not exceed 3 m /m

2

-h based on the tube end area

and provision for removal of floating sludge must be ensured.

DICK (1970) pointed out that the final tank in the activated

sludge process has a thickening role as well as a clarification role,

and there is little advantage in upgrading such a tank if increase in

the clarification capacity of a settling tank accomplished at the expense

of thickening. This implies added cost of handling larger volumes of

more dilute sludge or provision of separate sludge thickeners.

In Sweden, "three major works were installed with self-contained

modules of sloping plates designed to achieve a rapid return of sludge

to the aeration tanks. Many problems were encountered such as bad dis

tribution of suspension under the tube and rapid growth of algae during

Summer time.

, Tubes have also been used for secondary clarification in trick

ling filter plant, for example in the Philomath, Oregon Sewage Treat

ment Plant. Prior to the tube installation, the secondary clarifier

effluent contained 60 mg/i to 80 mg/Jl of suspended solids but after the

installation, the effluent quality has been excellent with suspended

solids routinely less than 20 mg/i at an average daily flow of 0.7 mgd.

Another advantage as in the case of activated

s'4udge

plant, the capacity

of an existing trickling filter plant secondary clarifier can be readily

increased by installing tube modules over all or only a portion of the

basin.; No operational or maintenance problems have developed in the

several months of operation.



- 11 -

2.3.A Tertiary Treatment of Sewage Effluent O

CULP et al. (1969) showed that the general system as shown in

Figure 2.2 can be employed for the phosphate removal from the secondary

effluent by chemical coagulation. A report issued by FWPCA on Shagawa

Lake Project indicated that the secondary effluent phosphorus concentra

tion can be reduced from 5-6 mg/£. to

0.3-0.7

mg/£. In another instance,

MERCER reported the tube clarifier mixed media filter package plant

could reduced the secondary effluent turbidity from 10-12 to

0.3-0.7

(turbidity unit) and the phosphates from 26-28.5 mg/H to less than 0.5

mg/X..

Alum addition is 240 mg/£.

From SWEDEN successful used of inclined plates modules for the

separation of aluminium floe formed in the treatment of the secondary

effluent, has been achieved. Loadings as high as 30 m

3

/m

2

-h were reported.

Another tertiary system designed for BOD and suspended solids

removal utilizing the tube clarifier is illustrated in Fig. 2.3. This

system is designed to polish the occasional discharge of high suspended

solids .concentration from the secondary plant. Direct application of

these secondary effluent to the filter would result in expensive short

filter run, thus the purpose of the tube clarifier is to provide supple

ment solids separation so that the filter may continue to operate

effi

ciently even during severe upset of secondary plant. Data published

show that such system continuous to operate efficiently even with secon

dary effluent suspended solids concentration as high as 2000 mg/ii..

BINH (1975) reported that the inclined tube settler and the

anthracite sand filter system can generally removed all aluminium

resulted from the utilization of alum during the flocculation process.

VAN VLIET (1977) described the series of full scale experiments

in which both inclined plate and tube module were used to uprate the

conventional circular raked primary clarifiers of high lime clarifica

tion process. It was reported that the removal efficiency of both

modules were comparable and a 60 percent turbidity removal was general

attained within the modules.

2.3.5 Raw Water Clarification

The conventional plant at Buffalo Pond Plant, Saskatchewan was

faced with the requirement of additional treatment capacity, thus the

existing rapid sand filters were converted to mixed media beds and

operate at higher filtration rates while steeply inclined tube settlers

were used to cater for the increase in settling capacity. For 6 months

of operation, the tube installation has operated at over 2.5 times de

signed rate of the parallel conventional units, while producing an

average effluent of 0.5 unit. The installation of tubes in the conven

tional units permits a more than doubling of the clarifier capacity.



- 12 -

•ftssayt*.

Fig. 2.1 - Installation of Steeply

o

Inclined Tubes at the

W.ickam, Pennsylvania Sewage Treatment .Plant.

Fig. 2.2 - Flow Schematic, Basic System Employing Essentially

Horizontal Tubes.



- 13 -

Another example of increasing the capacity of water treatment

plant by utilizing tube clarifier and mixed media is the Georgia-

Pacific's Pulp and Paper Mill at Crosselt, Arkansas U.S.A. It was

reported that by installing angle tube modules over only a portion of

the clarifier surface, the capacity was increased from 56,775 m

3

/d to

170,325 m

3

/d. From the test conducted, it reviews that for overflow

rate of 4 m /m -h effective clarification observed even under cold

water conditions.

The flow diagram as shown in Figure 2.3 has also been applied

in many water treatment plants in U.S.A. with capacity varies from

0.0757 m

3

/min to 7.57 m

3

/min. For example at Emporia, Virginia, for

raw water turbidity of 20 standard units, a effluent quality of 3 units

can be achieved using alum concentration of 35 mg/£ and operate at

overflow rate of 193 m /m

2

-d with corresponding detention time of 10

minutes. Another plant located at Louisville, Mississippi with plant

capacity of 7.57 m /min can provide an effluent quality of approximately

2 units using the same system as described above.

2.3.6 Other Applications i

One of the most interesting applications now being evaluated

is the,use of steeply inclined tube directly injthe aeration basins

of an activated sludge plant. With proper baffling, it appears possi

ble to achieve activated sludge solids separation and return without

a secondary clarifier structure, therefore the economic implications

in secondary plant construction are indeed significant.

2.4 Column Settling

i

In the;world of limited resources, seeking toward economical techniques

to predict plant scale performance or to derive design criteria for plant

scale processes is of utmost importance.

i

YAO

(1979),

using column settling to predict the design overflow rate

of the tube settler system. He reported that a safety factor of 2 was needed

for uncoagulated synthetic water and natural unflocculated raw water. Table

2.1 shows the turbidity range involved and the experimental conditions.

PANNEERSELVAM (1982) concluded that for coagulated synthetic water of

turbidity greater than 180 NTU, then the results obtained from the column

settling tests can be used directly for designing the tube settler. For

turbidity of 120 NTU and 80 NTU or

less,

a safety factor of 1.4 and 2 were

respectively observed.

HUDSON (1981) claimed that the revised standard procedure of using

square jar test (see Fig. 2.6) can be used to established the design over

flow rate for tube settler system of plant size.



- 14 -

******

M ^ W M w

Fig. 2.3 - Schematic of Effluent Polishing System

for BOD and Suspended Solids Removal.

. > * * <

Fig. 2.4 - Revised Standard Jar Test (Hudson, 1981)



- 15 -

TABLE 2-1

Design Safety Factor for Overflow Rate Provided

by Colutan Settling to tne Tuoe settler System

, p - , -, ,

I A u t h o r | N a t u r e o f W a t e r | haw V i at e r T u r o i d i t y | D e p t h | S a f e t y F a c t e

I I 1 (NTU) | (cm) |

| YAO | N a t u r a l Baw | 100 - 28 0 | 7b | 2 . 0

| ( 1 9 7 y ) | H a t e r | ( M a y - S e p t ) | |

| | I 14 - 70 | 7 8 | 2 . 0

I 1 1 ( S e p t - N o v ) I |

| | U n c o a g u l a t e d | I |

| | S y n t h e t x c | 1 0 0 - 2 8 0 | 7 8 | 2 . 0

| | Haw M a t e r | | |

IPANNEEH-j S y n t n e t x c | IbO | 106 | 1 .0

ISELVAM | F l o c c u l a t e d | 120 | 106 | 1 .4

1 (1 98 2) | K a te r | 80 | 106 | 2 . 0

o

I



- 16 -

III SOME THEORETICAL CONSIDERATIONS ALOUT TUBE SETTLERS,

, COLUMN SETTLING AND PLENUM DESIGN

i

3.1 High Rate Sedimentation

High irate sedimentation is the use of shallow gravitational settlers

with detention period of not more than 15 minutes to achieve comparable or

even better settling efficiencies normally attained in the conventional

sedimentation tanks having detention time of usually more than 2 hours.

The above idea was originally suggested by HAZEN (1904) who claimed

that the removal is a function of the overflow rate and for a given

dis

charge, it is independent of the detention time. CAMP explored the above

concept extensively in 1946.

YAO (1970) conducted a theoretical research on high rate tube settlers

of various shapes and arrived at a design equation based on the parameter

"overflow rate", which is widely used in water and wastewater treatment

process design.

He assumed that the flow is laminar and one dimensional and the

sus

pended particles are discrete which do not aggregate. Ignoring the initial

effect,

the velocity components of the particles on the x and y directions

based on the coordinates system as shown in Fig. 3.1 are:

^ = Vpx = U - Vs x Sin 6 (3.1)

jl . = v

P

y = -Vs x Cos 6 (3.2)

Combining equations

(3.1),

and (3.2)

dy_

=

Vs x Cos 9

dx

=

~ U - Vs x Sin 8

(3.3)

Integrating equation

(3.3),

JV-dy -

Vs -y Sin 8 + Vs x Cos 8 = C (3.4)

where

<-'' C' is the integral constant

Dividing equation (3.4) with V o, the average flow velocity, and d, the

depth of the flow measured normal to the direction of flow.

v b

dy

•

I f

Y

*

sia

H

x

Cos 9 l (3

'

5)



- 17 -

Where CI is the adjusted integration constant, Y = y/d and X = x/d and

equation (3.5) is the general equation of a particle trajectory in the given

high rate settling system.

Each particle follows its own trajectory inside the tube settler (Fig.

3.2). Fl, F2 , F3 , indicate the trajectories of particles removed by the

settler because all three trajectories end at the invert of the settler.

The trajectory, Fl , represents a limiting case. All particles with the same

Vs of the particle following this trajectory would be completely removed by

the tube settler. This particular Vs is defined as the critical settling

velocity, Vsc.

For the limiting trajectory with Vs = Vsc, there are two boundary con

ditions,

X - L; Y = 0 (3.6)

i

X = p; Y - L (3.7)

i

in which L

=•

1/d, the relative length; and 1 = the length of the settler.

Therefore'by substituting equations

(3.6),

(3.7) into

(3.5),

Vsc

CI = ^~ • L • Cos 8

Vo

Since the flow velocity vanishes at the settler wall (Y = 0 ) , there

results:

(/ ~~ ' dy) = 0 (3.8)

Vo y=o

Substituting Cl and the second boundary condition, equation

(3.7),

into

equation

(3.5),

the following general equation is obtained:

Vsc

—•

• (Sin 6 + L • Cos 8) = Sc (3.9)

Sc » ( / £ •

d y )

y = 1

(3.10)

in which Sc is a factor with its magnitude depending on the shape of the

tube.

The values of Sc for circular, parallel plate, square, and shallow

open tray stellers are respectively 4/3, 1, 11/8, 1. For overflow rate, it

can easily be seen that is exactly the same as the critical settling velo

city, then,

Vo

4:.C • Overflow rate = C S c

S i n fl + L

.

C o 8 9

(3.11)

where C is a unit adjustment constant. For Vo(cm/min) and overflow rate

(m

3

/m

2

-d),

then C - 14.4.



- 18 -

e . ANGLE OF INCLINATION

OF HIGH -RATE SETTLER

Fig. 3. 1 - Coordinate System for Theoretical Study

6

*\i»'

Fig. 3.2 - Sketch of Particle Trajectories in High-Rate

Settler.



- 19 -

3.2 Column Settling

The clarification of dilute suspensions of flocculating particles is

not only a function of settling properties of the particles but also of the

flocculating characteristics of the suspension. During sedimentation, coa

lescence or flocculatin occurs, thus the mass of the particle increases and

it settles faster. The extent to which flocculation occurs is dependent on

the opportunity for contact, which varies with the overflow rate, the depth

of the basin, the velocity gradients in the system, the concentration of

the particles and the range of the particle sizes (RICH 1973; BARNES 1978;

and TCHOBANOGLOUS

1979).

Since 1940's, overflow rate has been extensively used as a parameter

for the design of the conventional settling tank. Besides, overflow rate

can easily be.obtained from the batch process of column settling tests and

could be used to predict the performance of the conventional settling tank

operated on a continuous basis. For these reasons, this study proposed to

adopt overflow rate as the key design parameter to predict the performance

of the tube settling system. For column settling, the overflow rate can

easily be calculated as follows:

If he(cm) is the distance between the water level and the sampling

port and ts is the settling time

(h) ,

then the overflow rate,

Vs = hc/ts (cm/h)

Vs - 0.24 x hc/ts (m/d) ' (3.12)

TCHOBANOGLOUS (1979) and RICH (1973) stressed upon the influence of

depth on the clarification process, the higher the settling depth (i.e.

larger the detention

time),

the better the efficiency of removal for certain

overflow rates. HUDSON (1981) pointed out the important of controlling the

depth of sampling such that the settled water quality data have much relation

to reality.. Therefore, it is the aim of this study also to verify the appli

cability of column settling and jar test to provide a scale-up correlation

with the plant scale tube settler for natural flocculated water and at the

same time to investigate the effect of depth upon the design safety factor.

3.3 Plenum Design

Plenum forms one of the important components of the tube settler system

and its design is of considerable importance. In proper design of the plenum

will severely affect the removal efficiency of the tube settler. If the

plenum depth is too shallow, and if the horizontal velocity is high, then

scouring of the settled sludge and turbulent condition will occur.

In 1968, FAIR et al. arrived at the following equation for scouring

velocity:

Vd - {(8K/f).g-(Sg - I)}*

4

• d*

5

(3.13)



- 20 -

where Vd = displacement velocity

f = a frictional factor

K = a constant with a magnitude close to S

g =» the gravitational constant

Sg = the specific gravity of the floe particle

d = the diameter of the floe

CHEN (1979) assumed that K, f, g, Sc are approximately constant and

Qx = (Lp - x)Qo/Lp.

Ax

a

(Lp - x) ,do.^

Ao Lp '

{

dx

}

(3.14)

where Qo = the treated water flowing through entrance section

Qx = the treated water flowing through a section at a distance x

Lp = the total longitudinal length of plenum

v Ao = cross sectional area at entrance

\ Ax = cross sectional area at a distance x

do = average floe size at entrance

dx *» average floe size at a distance x

Fig.

3.3 shows the graphical representation of the plenum. CHEN also

pointed out that the floe particle size varies in each section such that

dx = do

» - 1 ?> "

(3.15)

Substituting equation (3.15) into

(3.14),

thus

l-n/2

]« „ (1 _ JL)

ho

v

Lp'

(3.16)

If the plenum is rectangular, then the width of the plenum at entrance

is equal to the width of plenum at any distance x from the entrance, i.e.

Bo = Bx, : ^

hx

ho

i Lp

l-n/2

(3.17)

where

Bo = jwidth of plenum at entrance

i

Bx = width of plenum at a distance x from the entrance

i

hx » depth of plenum at a distance x from the entrance



o

- 21 -

ho = depth of plenum at entrance

n = a constant

M T

- UB*.

ARY

For practical operation, CHEN recommended that ho should be maintained

equal to Co«Qo in which Co = 3.1 s/m

2

and Q is in terms of m

3

and thus the

unit of hx will be in meter.

Let hs, x = 0 be the sludge depth at the entrance and hs, x = Lp, the

sludge depth at a distance

:

x » Lp from the entrance, then

where

Hx =• 0 (cm) = hx = 0 + hs, x = 0

HX = Lp (cm) = hx = Lp + hs, x = Lp

Ho = total minimum depth at entrance

Hx = total minimum depth at a distance x from the entrance

hx = o = ho

(3.18)

(3.19)

hx •* o

hs, x - 0

_i

Plenum

Sludge Profile

SBSJJSJ S* ?

Settled Sludge at Time t (h)

hx » L

hs, x =» L

Fig. 3.3 - Sectional View of Plenum

O



- 22 -

IV EXPERIMENTAL INVESTIGATION

4.1 Background

; O

In 1970, a master plan was prepared by the Metropolitan Water Works

Authority (MWWA) of Thailand in response to the increase in water require

ments of expanding communities, commercial development and industrial water

demands. For these reasons Bang Khen Water Treatment Plant was constructed

to serve as the center of,water production. In Stage I of Phase I, the

plant is designed to provide a capacity of 800,000 m

3

/d and by the year of

2000, the production will escalate to 4,800,000 m

3

/d.

In this study, all the experiments were conducted in the Bang Khen

Water Treatment Plant for the following reasons:

(i) To observe the applicability of the tube-settler in the modern

water treatment plant.

(ii) To compare the efficiency of the tube settler system with the

s,olid

contact, slurry return type of clarifier at Bang Khen

/

Water Treatment Plant and also to compare the cost-effective

ness of both the systems.

4.2 Raw Water Source

Raw water for the treatment plant is obtained from the Chao Phraya

River at Sam Lae Pump Station which is located at tambol Sam Lae, Muang

District of Changwat Prathum Thani, about 18 km North of Bang Khen Water

Treatment Plant. The raw water is then conveyed by Klong Prapa before

the influent conduit to the clarifiers. For this experiment, natural raw

water was tapped from the conduit at Clarifier No. 6 and the turbidity of

the raw water during the experiment was observed to vary from 25 NTU to

45 NTU. Table 4.1 indicates the raw water characteristics for the month

of December and January when the experiment was in progress.

4.3 Experimental Apparatus and Materials

Fig.

4.1 presents a schematic sketch of the experimental set up of

the tube settler system. The raw water is obtained from the raw water

conduit of the treatment plant. It is then flow by gravity to the constant

head tank via a rotameter. The rotameter is employed to ensure a constant

flow rate while the constant head tank which has a detention period of 3

minutes provides the necessary hydraulic mixing of the raw water with the

alum. This chemically mixed .water in then admitted into the flocculator

which is equiped with a motor of 1/20 Hp and a speed of 12 rpm.

^ The steeply inclined tube settler used in this experiment was designed

by PANNEERSELVAM (1982). It has a relative length of 18 and an angle of

inclination of 60 degrees to the horizontal. The settling unit is made of

steel and the tube has dimensions of 5 cm x 5 cm x 90 cm and is made of

marine plywood. The total end area of the tubes is 1,500 cm

2

. Figure .-42 l/i

gives the detailed dimensions of the unit.

• •

•: l - i



- 23

TABLE

4. 1

Haw wat er Qu a l i t y of Bang Khen Water T r e a t s e n t P l a n t

( L/ecemoer 1982 to J anuary 1983 )

,,_ ... _. .__ . .,

1

...,

| . Parameter , | Range of value (ppnt) I

i i i

ITurbidity (NTD) | 17- 60 |

IpH | 7 - 0- 7 . 5 |

ITotal AlKalinity | <J4 - 90 |

ITotal Solid | 170 - 185 |

(Dissolved Solid • | 100 - 120 |

ISuspenaed, Solid | b - 69 1

ITotal Hardness as CaCo3 | 84- 90 |

|Chloride las Chlorine | 12- 14 |

|Free Ain onia - N | 0.074 - 0.207 |

|Nitrate - N | tfIL |

laitrite j - N | 0.000b - 0.0043 |

|Iron | 0.29 - 0.3b (

(Manganese I 0.01 - G.26J |

Irtagnesiua | 5.7b - 7.2 |

IDissolved oxygen | 2.J - 5.5 |

|B0D5 I 1.4 - 2.0 |

(Standard Plate Count./100 m. | 790 - 1590 |



- 24 -

w

\

a

E E

o> tf> u>

_

2

- J

«> j>

• " F

c

UJ

l

h-

UJ

W O

_>

<

I -

z .

l l i

2

cc

UJ

Q.

X

UJ

a.

I

u .



- 25 -

The tank has an inlet chamber at one end and outlet chamber at other

end. Both chambers are of 55 cm wide and coupled with triangular weir at

the effluent end to facilitate good hydraulic condition at the outlet zone.

The bottom of the tube settler is designed with flange joint to faci

litate ease of replacing the plenum bundle of different settling depths.

The plenum bundle is provided with a clear PVC window to facilitate measure

ment of the accumulated sludge depths. A drain pipe was also included for

sludge draining.

For column settling' analysis, a single sampling level settling column

was designed with an internal diameter of 15 cm so as to minimise the wall

effect. The column is made of opaque PVC column with a strip of transparent

perspex window running from the top of the column to the bottom. A sampling

port is located at 5.5 cm from the bottom of the column which is arranged

in such a way that samples can be withdrawn from the center of the column.

4.4 Clarifier

In the Bang Khen Water Treatment Plant, the clarifiers are of solid-

contact with slurry-recirculation type. Each clarifier has an internal

diameter of 58 m and with side water depth just under 5 m . A total deten

tion time is about 100 minutes with approximately 13 minutes detention time

provided under the recirculation cone. The loading rate is about 95 m /m

2

-d.

Because of the size of the tanks a center-drive mechanical sludge-scraping

equipment is specified. Collected sludge is discharged periodically through

alternate sludge blow off lines.

4.5 Methodology

Turbidity was used as the main indicator of the settling performance.

HACH Laboratory Turbidity meter of Model 2100A was used for turbidity mea

surements and the results were then expressed in Nephelometric Turbidity

Units (NTUs) which is equivalent of the Formazin Turbidity Units (FTUs) or

the Jackson Turbidity Units (JTUs).

j

4.5.1: Preliminary Analyses

; In the preliminary analyses, the optlm&it alum concentration for

each turbidity range was determined using conventional jar test appa

ratus:.

The optimum concentrations of alum will be later used in the

evaluation of the tube settler performance. Also, the effect of poly-

electrolyte addition upon the settling performance was being tested.

Several different types of polyelectrolytes such as CAT-FLOC T (cationic),

SUPERFLOC

(anionic),

and Poly Aluminum Chloride (PAC) were used.

4.5.2: Pilot Scale Investigation

i

In the tube settling experiment, the tube settling tank was

first:

filled to the overflow level with tap water. Raw water was then

admitted into the constant head tank, simultaneously desirable alum

concentration was injected. Rapid mixing due to flow agitation was



- 26 -

accomplished after the point of chemical injection. The coagulated

raw water was then admitted to the flocculator where further coagula

tion and flocculation take place. The flocculated water was then in

troduced to the tube settler for sedimentation.

Raw water, flocculated water and clarified water were then

sampled in hourly intervals. For each run, the experiment was ter

minated once the effluent turbidity reached an approximate constant

value.

During the experiment, the following flows were used: 2

&/min,

5 Jl/min, 10 £/min, 15 £/min, 20 l/min.. In the case of the plenum design,

the settled sludge depths across the plenum length (i.e. XI = 0 cm,

X2 = 8 cm, X3 = 16 cm, X4 = 24 cm, X5

a

32 cm) were measured for each

flow velocity. Also, the efficiency of the tube settler for each flow

rate was recorded.

4.5.3 Column Settling Analysis

The experimental study was conducted in a form of quiescent

settling on a batch basis. Natural flocculated water was used for the ex

periment and the raw water turbidity ranges from 25 NTU to 45 NTU during

the period of experiment. The experiment was carried out with the following

assumption:

(a) Temperature variation was between a small range of 27 C to 33 C,

thus the effect of thermal current upon the percent of removal

was considered to be negligible.

(b) The distribution of the flocculated particles is homogeneous

within the settling column at the start of the experiment.

(c) All particles begin to settle as soon as the process start.

For each experimental run, the settling column was first filled

with raw water to the marked desired level from the sampling port. The

sample in the column was then thoroughly mixed to obtain a uniform suspen

sion.

For such size of column, an air diffuser located at the bottom of

the column is necessary to provide effective mixing. Optimum alum dose was

then added before flocculation took place and allowed to settle in quiescent

condition. Zero time was set as soon as flocculation was completed. Sample

were then withdrawn through the sampling port at time intervals of: 15 min,

30 min, 45 min, 1 h, 2 h, 3 h, 4 h, 5 h, and 6 h. The turbidity of each

sample was measured and the p.ercent turbidity removal was then computed.

U

i



- 27 -

inlet Pipe

• 32

Inlet

2c«

- 4 6

Sludge Oroin

Pipe

PLAN

ft*

[—15—f-15—

Outlet

2o i e

A

I

32a

5 5

Outlet

Pipe

| - . 5 - | - . 5 - j

ITO

ELEVATION < SECTION A-A J

5

T

• 55

T

33

1

I

TUBE MOOULE (SECTION C-C)

Net Tube End Arco • 1500 cm

2

— I S J-

<

— 55

EFTLUENT LAUNDER

(SECTION B-B)

NOT

TO

SCALE

ALL DIMENSIONS

ARE IN cm

F I G . 4 . 2 - DETAILS OF INCLINED TUBE SET TLER .



Al

-T. LlBR

ARY

V PRESENTATION AND DISCUSSION OF RESULTS

The data obtained from all experiments are presented In Appendices A,

B,

C, and D. This section will devote mostly to the presentation and

dis

cussion of the analysed results.

5.1 Preliminary Analytical Results

To determine the optimum alum concentration and to find out the effect

of polyelectrolytes upon the flocculation process, jar test technique which

was proposed by AMIN (1976) was used. The modified procedure consists of

fast mixing at 100 rpm for 1 minute followed by slowQnixing at 12 rpm for

30 minutes and 10 minutes for flocculation and sedimentation. This procedure

was devlced to match the pilot scale flocculator used In the experiment.

For all experiments, no pH adjustment was necessary since the pH of the

raw water was within the neutrality range (i.e. 7-8). Table Al-1, Al-2, Al-3,

(see Appendix A) show the optimum alum concentration of 28

mg/£.,

28

mg/Jl,

and 34 mg/i, for raw water turbidities of 25 NTU, 40 NTU and 56 NTU, respec

tively. Table Al-1 also illustrates that if the flocculation and sedimenta

tion time of the pilot scale flocculator could be increased from 10 minutes

to 30 minutes, then better percent turbidity removal could be accomplished.

Figure 5.1 shows the typical plot of residual turbidity against the alum con

centration for raw water turbidity of 25 NTU.

Currently, many authors claim that addition of polyelectrolyte could

enhance settling performance. On the other hand many researches concluded

that addition of polyelectrolyte does not improve the process. From this

study, the results show that polyelectrolytes either of cationic or annionic

in nature do not significantly improve the settling performance. Table A2-1

(Appendix A) indicates that addition of CAT-FLOC T at optimum alum dose could

only bring the residual turbidity down from 3.0 NTU to 2.6 NTU. Table A2-2

(Appendix A) also confirms that anionic polyelectrolyte such as SUPERFLOC

has no significant effect upon the residual turbidity.

Poly Aluminum Chloride (PAC), was also used in the experiment and

although PAC could achieve the same residual turbidity at lower dosage than

the alum, but due to the high cost of PAC which is four times that of alum,

make it unattractive to most treatment plants.

5.2 Overflow Rate Versus Efficiency

It is universally accepted that the design of a conventional settling

tank for water and wastewater treatment is based on the overflow rate, which

is expressed as the rate of flow per unit surface area. The same concept is

being adopted in high rate sedimentation.

Figure 5.2 presents the results of all experimental

runs,

showing the

turbidity removal efficiency at various computed overflow rates. As expected,

the removal efficiency decreases with the increase of overflow rate. It

appears that higher raw water turbidity tends to provide better removal

effi

ciency than those of lower turbidity.



- 29 -

3

1 -

<£.

lO

CM

y

T l

u

0>

E

F

o>

c

t

c/>

c:

E

o

to

o

CM

to

O

to

03

CM

CO

CM

CM

CM

CM

O

CM

CO

CD

-

T

E

<u

o>

o

n

o

Q

E

<

co to ^r

(O I N ) A i j p s q j n i l o n p i s a y

CM

CM



- 30 -

100

9 0 -

^ 8 0 -

> »

u

c

.2?

*o

£ 7 0

UJ

6 0 -

5 0

-

-

"•• 1 1 1

^ * * ^ o > v

2 5 - 3 7 NTU

o 2 5 - 3 7 NTU

A 3 6 - 4 5 NTU

i i i

i

, i . .

1 — I I

-

-

^ O

5 5 5 1

^ ^ ^ ^ ; ^ ^ ^

1 1 1

5 10 15 2 0 25

Overflow Rate , (m

3

/m

2

- d)

Fig; 5 . 2 - Effect of Overflow Rate on Efficiency

3 0

3 5

Table 5.1 gives the comparison of results obtained by several other

researchers and the present study. Although in each individual case,

different experimental conditions exist, yet the results of the present

study are in close agreement with the findings of previous works.

Fig. i5.3 indicates the effluent quality of the calrified water versus

the overflow rates. Three curves having alum concentrations of 22 mg/£,

28 mg/S, and 32 mg/£ were observed. In the Bang Khen Water Treatment Plant,

the Authority insists upon the clarified water that should be equal to or

less than

;

5 NTU before it is allowed to enter the filter system. This

cri

teria is to safeguard the filter system from overloading. From the graph,

at optimum alum dose of 28

mg/Jl,

overflow rate of 8.75 m

3

/m

2

-d will provide

water effiuent of 5 NTU. In Bang Khen Water Treatment Plant, "economic"

alum dose of 22 mg/& is used (during the course of study) to provide effluent

quality of 5 NTU. Therefore to cater for such situation, alum concentration

of 22 mg/ I was also used to perform tube settler experimental

runs.

Fig.

5.3 shows that at 22

mg/Ji,

of alum dose, overflow rate of 8.0 m

3

/m

2

-d will

provide effluent quality of 5 NTU. The above experimental comparison is

essential in the later section where comparison of costs between the conveiy-

tional sedimentation tank and the tube settler system needs to be analysed.



-

31 -

TAbLE 5.1

CoQpanson

of Percent Turoidity Removal for Various

Overflow Hates Investiyatea by Soae Autnors

•

i I i I

--I—

• i

( O v e r f l o w

;|Kaw

w a t e r

| KAO |

Vk^kUAD-

|

CHhN |PA Nt l r . i iE-

|

P r e s e n t

| fiate ( T u r o m x t y

| |

l L G K L £r . T

|

| S £ L V a tt ( S t u d y

| ( a

J

/ m ^ a) i (tj'rii") | ( l y 7 j ) | ( ly V b ) | ( i y / y ) | ( l y d ^ j | ( 1 y a 3 )

i > I I | | |

| M a t u r e of rtater l a . K . r t . ( l i . t t . w . | S . R . W . | S . a . n . I t l . R - W .

1

i 1 1 1 - {- •• —. . . . j

1 ( ^0 | b 5 . 0 u * > | - | d 3 . 5 0 * | - i -

I I 30 | - | ( - | | a 2 . 2 S * .

h 13 | HO | - | - | y l . 0 0 ; o | | -

| | 50 | y 0 . 0 0 * ( - | - | b 4 . 4 0 % | b a .5 0

L

A

1

| bo | - |

oy.OO'A

| - | - | -

1 1 20 | - | | 7 y . 0 0 ; » | - |

I 20 | 30 | d 2 . 5 0 r i | - | | - | 7 4 . 2 5 *

I | 40 | - | ( d b . O O * | - | -

1 | 50 J b b . 0 0 / . | - ( 6 0 . bO * | - I 7 y . 0 0 *

M.B.W. = Natural tdw fater

S.H.W. = Synthetic aaw Water

10

8

3

z

f 6

3

c

0)

3

UJ

1 r

*

Alum Dosage

*28mg/l

0

n^ 25 NTU -

37

NTU

A—A

36 NTU -

45 NTU

' I L

0

10

15

20 25 30

3 2

Overflow Rate, (m /m d

35

Figi 5.3 - Effluent Turbidity vs Overflow Rate



- 32 -

U

If

80

removal efficiency

is

acceptable, then

a

design overflow rate

of 12.75 m

3

/m

2

-d for raw water turbidity of 25-37 NTU and 18.5 m

3

/m

2

-d for

raw water turbidity of 36-47 NTU can be used within the limits of experi

mental conditions.

If effluent quality

of 5 NTU is

insisted, then

the

overflow rate

of

8.75 m

3

/m

2

i-d

and 8.5

m

3

/m

2

-d

for raw

water turbidity

of

25-37

NTU and

36-45

NTU, respectively under the optimum alum dosage. For "economical" alum

dose, overflow rate of 8.0 m /m

2

-d is recommended for raw water turbidity

range

of

25-37

NTU.

Table; 5.2 shows the practical operational overflow rates for most ex

perimental conditions.

TABLE 5.2

The Perrormance of the In cl in ed Tu be b'ettier at

Various overflow Ka te s, Alua Dos e,

ana Raw

Water

Turbidity

T 1

Effluent |

yuaiity

J

(MTU)

J

|Haw Water

ITu mid i ty

| (NTO)

£ J . U I U

D o s e

( 31U / 1 )

uverilow fiate

(la^/m* a)

Eff ic iency

A

| 2 5 - 3 7

I

J

| 3 b - 4 5

2 ^

2b

b

.00

d

.OU

b.75

ti3 . 0 0

b4

.30

b J .b0

5 . 0

4 . 8

5 . 0

I

I

1 2 5 - 3 7

I

a

.i>0

b b

. 50

5 . 0

no

12 .75

oO .00

7 . 9

J 3 6 - 4 5

3 2

la .50

dO

.0u

d . d

Since the removal ef fi ciency is a function of overflow rate (for a l l

other parameters are fixed) , a regression analysis was used to produce fo r

mulations which f i t best for the experimental data obtained for removal

eff iciency and overflow ra te .

For raw water turbidi ty of 25-37 NTU,

In E - 4.52993 - 0.0114(1 x Vsc (5.1)

Correlation factor

for

this relationship

was

found

to be

97.65%.

For raw water turbidity of 36-45 NTU,

In

E -

4.55008

-

0.00873

x Vsc (5.2)



- 33 -

Correlation factor for this relationship was found to be 98.30%.

Fig.

5.4 shows the regressed values for both the turbidity range and

Table B5-1 and B5-2 (Appendix B) show the mathematical calculations using

the Least Squares Method to arrive at the formulations.

i

5.3 Effect of Turbidity on Efficiency

Fig.

5.2 shows the removal efficiency curves fon raw water turbidity

of 25-37 NTU and 36-45 NTU. The figure demonstrates that the removal effi

ciency increases with the increase of raw water turbidity for all overflow

rates. The reasons for this improvement in efficiency could be due to

better flocculation before sedimentation, or better aggregation during set

tling. Both of these result in the formation of heavier or larger floe

particles.

However, it is important to note that higher removal efficiency

at higher influent turbidity does not automatically mean a lower effluent

turbidity as provided in the case of lower influent turbidity. Fig. 5.2

confirms such important observation.

i

5.4 Effect iof Flow Velocity on Efficiency

In this research, flow velocity of 0.8 m

3

/m

2

-h, 2 m

3

/m

2

-h, 4 m

3

/m

2

-h,

6 m

3

/m

2

-h, and 8 m

3

/m

2

-h were used as shown in Table B6-1 (Appendix B ) .

Fig.

5.5 shows that as the flow velocity increases, the percent turbidity

removal decreases, this high flow velocity causes resuspension of settled

particles and also scouring of the settled sludge surface.

Table 5.3 shows the comparison of present study with the works done

by PANNEERSELVAM (1982), the results of both the studies concluded that

synthetic raw water does provided better settling performance than the

natural raw water. This could be due to natural raw water contains more

colloidal particles than that of synthetic raw water. The table also re

views that for the same flow velocity, high efficiency could be achieved

for higher raw water turbidity.

As mentioned in section 5.2, if 80% turbidity removal is acceptable,

then the flow velocity of 3.87 m /m

2

-h and 5.43 m

3

/m

2

-h are recommended for

raw water turbidity of 25-37 NTU and 36-45 NTU, respectively under the op

timum alum dose. If to comply with the effluent requirement of 5 NTU, the

flow velocity of 2.67 m

3

/m

2

-h and 2.55 m

3

/m

2

-h should be resorted to for

raw water turbidity of 25-37 NTU and 36-45 NTU, respectively.

5.5 Experimental Results of Plenum Design

Preliminary experiment confirmed that plenum bundle of 20 cm depth

could be used to provide data which is necessary for the derivation of em

pirical formulae for the plenum design.

Appendix D includes Table Dl-1 to Table Dl-3. Each table contains

the data of the operation of tube settler at certain flow velocity and the

percent turbidity removal and the sludge depth across the plenum length

at XI = 0.0 cm, X2 = 8 cm, X3 = 16 cm, X4 => 24 cm, and X5 = 32 cm were



100

9 0 -

£ 8 0

o

UJ

£ 7 0 -

6 0 -

50

-

-

1 1 1

^^"^^0 ^^''^'fc*.

o 2 5 - 3 7 NTU

A 3 6 - 4 5 NTU

i i

- 34 -

1 1

i

A

1

1

1

o^"** * * *

1

1

-

-

1 ._ .

0

I 2 3 4 5 6 7

Row Veloci ty,(m /h) ^

Fig. 5 .4 " Effect of Flow Velocity on Efficiency

8 10

4.6

-I 1 1—

o Regressed Value

A

2 5 - 3 7 NTU

o 3 6 - 4 5 NTU •

4.5

4 4

u

| 4 . 3

"3

i t

4.2

4 .1 -

0,

o In E = 4.5 50 08 - 0.008 73 V,

sc

A In E = 4 . 5 2 9 9 3 - 0 . 0 1 1 4 0 V,

sc

D 5 10 15 2 0 25

Flow Veloci ty,(m/h)

Fig. 5 .5

—

In ( Efficiency) vs Overflow Rote

30 35



- 35 -

TAESLE

5-J

i

J

r<ri <=iit.

; t u u y r t j . t i i t - ii ji .i £ ,2 .i < Jc iL 7. i i.J

1

•

| V e l o c i t y

|P< i t f N £L S i i

1 ( 1 ^ ^ ^ )

| SO »J *

1 ( i y b 3 )

I 3 i

j

/

L L

'/ /i

i *

•

;

l

r<)

I l i i r i u e i i t

I T u r D i d i t j

| r s r c - n t '

| : , t J i O « ' d i

| I . l t X l K - a t

| t ' f c t C i i l l t

|

. . c i O ' J d l

| l e t l u e i i t

I T u r o i a i . t j '

|

t^nceiir.

| . - v t a O V a l

U

. fi

—

—

O

3 . 0

-

1

| z .Li

| cw

1

^ u

1

z b

1

| b t» . 7

Jt>

I

| b b . o

»

1

i

1

1

1

1

•

alU

1

1

rtTi)

1

1

•

d.

t o

—

t o

-

1

| 4 . L >

1

1

| bo

~ 1

1

| b 5

itl

1

1 / ' j . < .

4 b ;< '

1

I ~

._ ,..

i *^

U

1

I

u

I

1

. 6

7 z

b J

—

-

r • -

I fa.O

| -

| —

1

1 7 o .

1

| b O .

— i

. d

. 4

r •

d . U

b b

7 y

l

| ob

I

| 7 4

1

i

1

i

1

1

1

1

1

. J

» * • •

*£0W

ojnt.attic Ca« Wfitct was used

recorded. The hourly samplings proceeded until the efficiency of turbidity

removal deviates drastically from the approximate constant value.

Figure 5.6 summarises all informations regarding the percent turbidity

removal and the operation time. From the curves, it is obvious that at 21

hours, 11 hours, and 8 hours of operation at flow velocity of 3.2 m

3

/m

2

-h,

6 m

3

/m

2

-h and 8 m

3

/m

2

-h, respectively, the effluent turbidity begins to

deteriorate, hence the efficiency of the tube settler starts to decrease.

These phenomenon could be due to the occurrence of turbulent flow in the

tube settler plenum or could be the consequence of sludge scouring at the

plenum.

Table :5.4 indicates the sludge depths at various distance Xs across

the plenum width after 8 hours of operation. The settled sludge profile

for each flow velocity is as shown in Figure 5.7. Higher the flow velocity,

faster the settled sludge depth reaches it critical plenum depth. This

implies that if operated at higher flow velocity, deeper plenum blundle

should be provided for the same number of operation hours as for those with

low flow velocity.

Figure 5.8 reviews the relationships between flow velocity against the

depth of settled sludge at the entrance and at the exit of the plenum bundle,

Due to the I importance of predicting the sludge depth, regression analysis

'Least Squares Method', was used to derive empirical formulae for sludge



100

50.

- 36 -

Scouring

V = 3 . 2 m / h

V = 8 m/h

V = 6 m / h

8 242 16 20

Operation Tim e,(h ou r)

Fig. 5.6 - Efficiency vs Operation Time for Plenum Design

2 8

12

A Velocity 8.0 m /h

D Velocity 6.0 m /h

o Velocity 3.2 m /h

2 -

8 12 16 2 0 2 4

Distance across the Plenum Length ( c m )

28 32

Fig.

5.7 T Sludge Profile after 8 Hours of Operation



o

TABLE 5.4 .

- 37 -

S e t t l e d S i m i l e D e p tn A t t t r o r i o u r s o f C o t t t i n u o u s

u p e r a t i o n a t V a r i o u s V e l o c i t i e s

1 • — i

Siu uge Deptn Alter b Hours of Operati on

(est)

| P l o w | F lo w V e l o c i t y

I ( 1 / m i a ) |

(

J

/ia^

a )

X I X 2

X3 X4

X 5

| 8 . 0 0

I

3 . 2

2 . b 5

2 . b U 3 . 0 U 3 . 5 5

5 . 6 5

| 1 5 . 0

6 . U

4 . 3 0 a . 6 5

7 . 9 0 9 . 2 0

| 2 0 . 0

8 . 0

4 . o 5

5 . 1 0

5 . y o 8 . 9 0

1 0 . 4 5

d e p th a s a f u n c t i o n of t im e a nd t h e f lo w v e l o c i t y . F i g . 5 . 9 i l l u s t r a t e s

t h e r e g r e s s e d v a l u e s o f I n ( S l u d g e D e p t h ) v e r s u s I n ( V e l o c i t y ) .

F o r 8 h o u r s o f o p e r a t i o n a nd f o r t u r b i d i t y r a n g e o f 3 6 - 4 0 NTU,

h s ,

x = 0 (cm) = 1.28499 x

V

0 i 5 8 9 1 7

0 . 6 8 8 0 8

h s , x = 32 (cm) = 2.57 14 7 x V

w h e r e h s , x = 0 i s t h e s e t t l e d s l u d g e d e p t h a t x = 0 c m,

h s , x = 32 i s t h e s e t t l e d s l u d g e d e p t h a t x = 3 2 cm .

F o r t h o u r o f o p e r a t i o n , T a b l e E l - 2 ( A p p e n d i x E) c o n f i r m s t h a t

0 .63917 , , „ .

h s ,

x = 0 (cm) = 1.28499 x V ( t / 8 )

0 .68808 , , „

x

h s , x = 32 (cm) = 2 .5 71 47 x V ( t / 8 )

(5.3)

(5.4)

(5.5)

(5.6)

In order to have general formulations, it is necessary to take into

account of the length of the plenum and the vertical thickness of the tube

blundle. According to Figure D2 (Appendix

D ) ,

equations (5.5) and (5.6)

can be replaced by

hs, x = 0 (cm) = 1.28499 x V •'

hs, x - Lp (cm) - 2.57147 x V

(t/8)(32/Lp)(a/33)

(t/8)(32/Lp)(a/33)

(5.7)

(5.8)

where Lp = length of the plenum

a = vertical distance of the tube bundle.-

In this study, the formula derived by CHEN (1979) can not be verified

due to the fact that for X = 1 which is the critical condition, the formula

(equation 3.17) derived by him cannot take this into consideration. Table

O



3 4 5

Flow Velocity , (m/h)

Fig. 5.8 - Sludge Depth vs Flow Velocity

8



- 39 -

5.5 shows the critical plenum depth at various flow velocities that were

obtained from the experiment. Figure 5.10 illustrates the plot of flow

velocity versus the critical plenum depth for X *= 0 cm and X = 32 cm.

Least Squares Method was used to fix the curves, which give:

hx = 0 (cm) = 14.92354 x V

hx = 32 (cm) = 4.29316 x V

0.1357i»

0.57992

(5.9)

(5.10)

Correlation factor of

99.08%

for both cases and V is in terms of m/h.

Therefore, for time t, flow velocity V, the total minimum depth at entrance

and at plenum exit (i.e. X •= 1 cm), ^j

.0.63917

Hx = 0 (cm) = 1.28499 x V (t/8)(32/Lp)(a/33)

0.13574

+ 14.9235 x V

Hx = 32 (cm) = 2.57147 x

V

° *

6 8 8 0 8

(t/8)(32/Lp)(a/33)

+ 4.29316 x V

-57992

(5.11)

(5.11)

(5.12)

Appendix E shows the details calculations of all functions involving

Least Squares Method of analysis in this section.

TASLE 5.5

C r i t i c a l P l en um D e p t n A c r o s s t n e P ie uu iu W i dt n

t o r V a r i o u s F lo w V e l o c i t y

Raw W a t e r ' 1 ' y r o i a i t y

t l t u u i u b u n a i e l l £ £ u

Aiuai Dost;

3t>-45 rtTCJ

20 cai

28 iftg/i

1

IFiOV

j (i/min)

1

1

|8.00

i

|15.0

i

I

J20.0

i.

r

-

1

1

i

i

1

i

l

1

i

1

1

--L.

f lOJ Velc ci

/ * * • u )

3.2

0 -U

6

.U

t-Y

r

... ...

1

1 xi

I

1 7 . J 5

I lb.yS

Critical

X2

I 17.10

I 17.*5

I ly.us

i

i

Plenum

XJ

15.bu

lo.b5

18.o0

Depttt

X M

11 .55

13.15

15.60

i

i

1

1

—L.

X5

8.350

12.SO

1U.05

1

1

1

1

1

r

i

i

Table 5.6 shows the comparison of the total plenum depths obtained by

PANNEERSELVAM (1982) and the present study by assuming appropriate values

for all necessary parameters. The frequency of desludging is assumed to be

2

days.

The results from the table review that the values obtained in accor

dance to PANNEERSELVAM findings yield lower magnitude than the results of

the present study for the total plenum depths. There are several reasons



- 40 -

2 0 -

E 16

o

"5.

< u

Q

e

3

C

. 2 ?

Q .

12-

S 8

o

4 -

1 1

Q

Regressed Value

^ —

-

i

^^*^

i

i

i

i i

i i i r i

h = 14 .92354 V °

, 3 5 7 4

6 ^

^ ^ ^ \ , < A .

2 9 3 . 6 V

0 5 7

"

2

^ X

(

= 0 cm

o X

5

= 32 cm

i i i i i

-

-

-

-

0 3 4 5

Flow Velocity , (m/h)

Fig.

5; 10 - Critical Plenum Depth vs Flow Velocity



- 41 -

AJ-T.

LIBRARY

TABLE 5 . 6

C o m p a r i s o n o r tr ie T o t a i t i e n u m D e p tn u o u i n e a oy

PArJ;jKc;iii;iiLVi»i*. a n a t n e t - L e s e n t S t u a y

P a r a m e t e r

~t 1 ~»

| ^ t-AKNESftSLLVaa C P r f e s e a t St u d y

C a p a c i t y ( : n V a )

1000

1000

F low V e l o c i t y ( u - V ^ a)

a ( W iti tn i n ca )

3 2 0

3 2 0

Lp ( p l e n um l e n c t i i i u CM )

l o o 1 0 0

t ( f r e q u en cy o r ae s iu a< jf c )

2 d a y s

2 d a y s

H

T o t a l p l e n u m d e p t n a t e n t r a n c e (cm ) |

37.o» 76.043

Total plenum deutn at x = l (ci)

7

a .

0 2

^

1 3 3 . d 7 *

»Hx=0 (ca ) = 0 - b 7 7 x v

0

-

0 7

^ ( t : / 1 0 ) ( 3 2 / L p ) ( a / 3 3 ) + h o

2Hx=Lp (cm) = 0 .9 7 9 x V * .

o j r

* ( t / 1 0 ) ( 3 ^ / L p ) ( a / 3 3

• 0 i = O ( 1 - X / L p ) ° '

J

*Hx =0 (cm) = 1.26499 x V ° -

6 i 4 1 ?

( t / o j ( 3 2 /L p ) ( a / J j )

+

1 4 . 9 2 . I S

x V ° - »

; i S , /

*

•tfx=Lp

{coil -

2 . 5 7 1 4 7 x v o . o a a o a ( t / t i ) ( 3 2/ L p ) ( a / j 3 )

+ 4 .2 9 3 1 o x l f ° - s ^ ^

5

S y n t n « t i c «aw w a t e r # a s U s eu

•" N a t u r a l n d v w a te r «4as Use a

which c o n tr ib u te d to the above d i f fe r e n c e s . F i r s t l y , PANNEERSELVAM co n

ducted the exper iment based on 10 hou rs o f op er a t io n , and du r ing th a t 10

h o u r s p e r io d , t h r ee d i f f e r en t f lo w v e lo c i t i e s were u sed and toward th e

t r a n s i t i o n a l p o i n t f o r e ac h v e l o c i t y , t h e s e t t l e d sl u d g e d e p t h s a t e n t r a n c e

and at x = 3/4 I a long the p lenum le ng th were measured . But the f i n a l

e q u a t i o n s a r r i v e d a t by h im f o r t h e s e t t l e d s l u d g e d e a t h s , i . e .

hx = 0 : (cm) - 0.8 77 0 x V '

&?2

( t / 1 0 ) ( 3 2 / L p ) ( a / 3 3 ) ( 5 .1 3 )

hx - Lp

1

(cm) - 0.9 79 2 x y

1

*

0 7 2

( t / 1 0 ) ( 3 2 / L p ) ( a / 3 3 )

(5.14)

These equations are based on only single flow velocity for the 10 hours of

operation period, thus contradict the experimental conditions. Other sub-

sidary reasons which contribute to the differences are:

I

(1) the value of hx = 0 = CoQo postulated by CHEN (1979) is low as

compared to the findings of the present study.

(2) in the derivation of the critical plenum depth equations, i.e.

0.1

hx = 0 = ho(l - x/Lp) = ho

h* = 1 = ho(l - x/Lp)

0

'

1

(PANNEERSELVAM, 1982)

(5.15)

(5.16)

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I

- 42 -

the value of n was chosen based on only one flow velocity (optimum velocity),

thus the value of 0.1 for the equations above does not represent the actual

situation.

5.6 Column Settling Results

Appendix C presents the results obtained in batch column settling of

the natural raw water. Each table in the Appendix C contains informations

regarding the column height, sampling time, the effective height of the

flocculated water and the effluent turbidity. These data were then

pro

cessed and transformed into the respective overflow rate and percent of

turbidity removal. For all the experimental runs, optimum alum concentra

tion of 28 mg/I was used.

Fig.

5.11 shows the plot of percent turbidity removal versus the over

flow rate for the settling column of depths 10 cm, 30 cm, 50 cm, 70 cm,

and 100 cm. The graph also includes the curve of percent turbidity removal

against the overflow rate for the tube settler system which can be used as

the basis of comparison.

From Fig. 5.11, it is obvious that the general trend of the column

settling results obtained from shallow settling column of depths 10 cm to

50 cm follow very closely to that of the tube settler system. This

indi

cates that the parameter overflow rate computed by YA0 (1973) for tube

settler has similar characteristic to that of the column settling. But as

the depth of the settling column increases, the deviation of results from

the tube settler performance seems to be significant. This graph also

reviews that flocculation and sedimentation of the flocculation natural

water does depend upon the settling depth and selection of appropriate

settling depth for column analysis to provide the required correlation

factor is of great importance.

Correlation factor is the safety factor (S.F.) obtained from the com

parison of the results obtained from the column settling and the tube set

tler.

This factor can be used directly for tube settler design. For example

if a S.F. of 2 is accepted for practical design, this implies for the same

efficiency to be achieved by the tube settler, the overflow rate obtained

from the column settling tests which provides the same efficiency should be

halved.

Table fj.7 contains all the correlation factors for various depths of

settling columns.

A Least Squares Method was used to derive a general formula such as,

S.F. =2.7014 - 0.0277 x he (5.17)

6

Correlation factor for the method is 90.84% and he is the depth of the

settling column. Figure. 5.12 shows the plot of equation (5.17).

Table 5.8 shows the comparison of the results of present study with

some other past researches. YA0 (1979) recommended that the safety factor



»3

-

(o

/o

) * fouapwB



T A E L L 3 . 7

TAOLL 5 . 6

- 44 -

E t r e c t o r i t r t t i i n o L»tv.-T.ii U p o n

U pon t i u C o f . r e x u n o : ; F a c t o r

i 1 — 1

| ; i c t t i i n o D rfp ta | C o r r e l a t i o n i ' a c t c c

I (C JIJ |

10 .U

jO.O

5 2 . 0

7 2 . u

l u u . u

2 , b

C*b

1 . i i

0 . 5

u . 1 7 5

UfcSio.'i l i a t b t y F a c t o r r o c o v i n i a * a u t c r - t o v i a e a

c y C o iu .u n S « t t l i r . y t o t , i

c

T t iu e s s t t i e r S y s t e m

I 1 . , . . . . , . , , . _ ,

| A U t a O C I 3 d U C : oZ . i r . r. e r | :X arf ( i c t c l I 'U X ii-LQA t / | D e D t a ( i a r t t y F a C t O t ' l

I I 1 i:;TU ) I (c .a j | |

| YAO | : i. . t a r u i :•;.». w j l uO - i b u | / o | 2 . 0 |

| ( 1 ^ 7 ^ ) | •.•iutdC | l a ^ y - o t u t ) | | |

| | | m - 70 | 7 c | 2.0 |

I I 1 i ^ e p t - r . o v ) I | |

| I J n c : ) n i _ ; u i ^ t ' . - u | I I I

| | i ' / t a a e t i c . j 10u - 2csu | ' / c | ^ . 0 (

| | i f i j i ( . j t = r 1 i I I

J P A^ M lL L-t-| i ; n t ; i c t i c I l e u | l u o | 1 . 0 J

|

S^LVJî

| i i o c c u i c a j a I 1<.0 | lO o | 1 .4 |

| ( V . ' u ; ) | t a t . e e 1 o u | l o o | 2 . 0 |

| | . in t a r ux | | ID | z . y |

|i>uw 1 r ' l o c c i u n t c j j <-- - J O | izi | ^ . 0 |

| ( l

l

J b i ) I , i " t . - r I | J O l 1 .5 |

| 1 1 1 3 ^ . ^ 1 1 .2 |

I 1 1 | / ^ 1 0 . 5 |

| 1 1 J 1 0 0 | 0 . 1 7 5 |

http://tat.ee/

http://tat.ee/

http://tat.ee/



3.0

- 45 -

U .

o

a

o

0

I i

o Experimental Value

SF = 2.7014 - 0 .0 27 7 h„

I

A Regressed Value

D 20 4 0 6 0 8 0 100

Settling Column Depth,(h

c

= cm)

F ig .

5 .12 - Sa fe t y Fac to r vs Se t t l ing Co lum n De p th

120

140

X 90

>»

o

c

a>

o

UJ

8 5 -

8 0

1 1

; V \ O

i i

l I

*-C^^-ô

i i

I 1

Column

o 10 cm Square

o 10 cm Circular

o

I .. i

-

-

0 4 8 12 16 2 0 2 4 2 8

Overflow Rate, (m

3

/m ^ d )



- 46 -

of 2 should be applied for natural unflocculated water and synthetic un-

flocculated water using settling column of 78 cm. PANNEERSELVAM (1982)

also concluded that a safety factor of 2 was adequate for synthetic floc

culated water using settling column of depth 106 cm. From this study, to

provide a safety factor of 2, a column of settling depth of 25 cm can be

employed.

Settling depth imparts a great influence upon the flocculation and

clarification process of the natural flocculated water. Therefore, when

selecting the settling column depth, one needs to realise that the over

flow rate can be provided by various combinations of settling depth and

detention time, for example:

Vsc = 1 m/h for he = 1 cm and time = 1 h,

Vsc =» 1 m/h for he = 10 cm and time = 0.1 h = 6 min

Configuration of column does have effect upon the settling process.

Fig.

5.13 shows the comparison of the results for settling column of 10 cm

deep with circular and square type. Evidentally, square configuration does

provides less residual current and as expected, it provides higher settling

performance than that of the circular column. Thus, when specifying the

design safety factor, one should also indicates the settling column depth

and its configuration.

5.7 Practical Problem Encountered

From the experiment, it was observed that after 30 hours of continuous

operation, the floes start to clinge on to the tube surface and after 50 hours,

the sludge begin to discharge to the effluent chamber and deteriorate the

clarified water. In practice, several methods are available to overcome

such circumstances. One method of removing this accumulation is by occa

sionally dropping the water level of the basin ben'fthth the top of the tubes.

The floe particles are then dislodged and fall to the bottom of the basin.

This method of cleaning besets with practical problem since it is impossi

ble in some cases to remove the basin from service in order to drop the level.

Another cleaning technique involves the installation of a grid of diffused

air headers beneath the tubes. To use this system, the influent is stopped

and the air turned on and allowed to rise through the tubes, scrubbing any

attached floe from the tubes. A quiescent period of 15-25 minutes follows

before the basin is placed back in service. Such system demands a separate

air supply system and thus discourage its wide application. Apart from the

above mentioned methods, installation of a submerged water jet headers di

rectly on;top of the tubes appears to be the most attractive technique. In

this system, sufficient turbulence is created on the edge of the tubes by

the jet, thus loosen all the deposited material adhered to the top of the

tubes.



- 47 -

5.8 Recommended Design Criteria and Numerical Example

To illustrate the applicability of the results obtained from the present

study, the following design criteria and procedures are recommended and a

numerical example is presented to aid in the understanding and use of the

results.

Table 5.9 shows the recommended design values for overflow rate and

flow velocity for various probable effluent qualities. If the effluent

quality of 5 NTU is insisted, then the overflow rate of 8.0 m

3

/m

2

-d or flow

velocity of 2.43 m

3

/m

2

-h can be used.

TABLE 5 . 9

D e s i g n T d D i e I n d i c a t e s t n e a ec od iif le nd eu V a l u e s t o r O v e r f l o w

H a te a nd f l o w V e l o c i t y a nd I t s P r o b a o l e E f f l u e n t T u r b i d i t y

r - • — • • - i

|3aw dater

(Turbidity

| (NTU)

| 2 5 - 3 7

| 3o - 45

| 2 5 - 3 7

r i

A lu m

Dose

(ag/l)

2b

32

| 22

.. .. . .... _. ,

Etficiency

<%)

90.00

85. 00

au.oo

bO.uo

75.00

9O.0O

89.dO

b5.00

ao.oo

75.0U

90.00

b5.00

bj.00

bU.OO

| 75.00

r - • l

u v ^ m o w

Kate

(ai-V** d) |

2.Jb

7.3b

b.75

12.75

1y .00

7.0o

b.3b

12.3b

Id. 50

2b.25

1.75

o.75

b .ou

12.13

| 18.50

Flow

Vexoci

(aV^

0.72

2.24

2.04

J.b7

5.77

2.13

2.55

3.7o

5.43

7.97

0.53

2.04

| 2.43

3.ob

5.62

i

ty

4 )

r

Probable

Etfluent

Turbidity

(NTU)

2.5

4.6

5.0

t>-1

7.5

4.6

5.0

6.3

7.9

9.o

2.2

| 4.6

5.0

b.7

| y.O

r

i

r

Table 5 .10 and Table 5 .11 a re th e de s ig n t ab le which can be used to

ca lc u l a t e the t o ta l number o f tubes r equ i re d fo r flow v e l o c i ty a t 2 .43

m

3

/m

2

-h and 3.87 m

3

/m

2

-h r e sp e c t i v e ly . Tab le 5 .12 aAvl Tab le 5 .13 in d ic a te

the to ta l plenum dep ths needed fo r va r io us f r eque nc ies o f des ludg ing and

p lenum leng ths .

EXAMPLE; A tub e se t t l e r syste m i s to be de sign ed to se rv e a po pu la ti on of

10,000 people wi th per capi ta consumption of water amount to

100 X./c»d. The i n f l u e n t t u r b i d i t y i s a round 25 NTU to 40 NTU and

i t i s p r e f e r a b l e t h a t t h e c l a r i f i e d w a t e r sh o u l d n o t b e m ore th a n

5 NTU.



- 48 -

O

TABLE 5.10'

Design Table f o r T n e Total Nuaioer of Tunes Required

Flow Velocity

Probaole Efflueat

Haw Hater Turbidity

Temperature

Operation period

= 2.4 3 m-»/ia

2

h

= 5 . 0 KTD

='25 - 4 5 NTU

= 27 - jJ °C

= 24 Hours

Alum Dose

Angle

TuDe lengtn

Tune Size

22-32mg/l

60°

0.9 a

0.5cm x 0.5ca

Population

Per Capita tfater Consumption (1/c.ci)

T 1

50

T

1U0 150 200

250

10,000

3,440

o ,6oo 10,290 U,720

17,150

20,000

o , 6 D 0

13,720 20,560

27,440

34,300

30,000

10,290

20,570

30,870

41,160 51,440

40,000

U,720 27,4 40

41,

160 54,870

66,590

50,000 17,150 J4,J00 51,440 b6,5y0 65,740

60,000

20,560 41

,

1 o \j 61,730

62,J10

102,b60

70,000

24,020

4a,0^0

72,020

9b,030 120,030

80,000

:7,440

5n,ti70

62,310

10^,740

137,160

90,000

JO,S70

o 1 , / J 0

92,b00

12J,460

154,J30

100,000

34,300

oo,5y0

102,b90

137, 160

171,470

O



- 49 -

TABLE 5.11

D e s i g n T a o l e r o c T h e T o t a l N u m oe r o f T u n e s H e q u i r e d

F l o w V e l o c i t y

P r o b a o l e E i r i u a n t

Raw H a t e r T u r o i i i t y

T e m p e r a t u r e

O p e r a t i o n p e n o a

3 . 8 7 a - y ^ a

o . 1 - b . 7 NTU

2 5 - 4 5 MTU

27 - 33 °C

2 4 H o u r s

Alum Oose

Angle

Tuoe iengtn

Tune Size

2 2 - j 2 a g / l

o 0 °

0 . 9 in

0.5ca

x

0.5cra

i

•

I P o p u l a t i o n

| 1 0 , 0 0 0 :

| 2 0 , 0 U 0 ;

•

l

| 3 0 , 0 0 0

1 , 4 0 , 0 0 0 ;

I 5o ,uoo :

| 6 0 , 0 u 0 |

| 7 0 , 0 0 0

| b 0 , O U O

I y o , u u O

1 1 0 0 , o u o

" -

P e r

5 0

*. ,

1 6 0

4 , 3 1 0

b , 4 b 0

b , o 2 0

1 0 , 7 7 0

1z I , :>2U

1 5 , 0 f c 0

1 7 , / 3 0

1 y , J t i O

^ 1 , 5 ^ 0

C a p i t a Wo

l u O

4 , 3 1 0

b , t > / 0

1 2 , 9 2 0

1 7 , i J U

2 1 , 5 4 0

^ 5 , d 4 0

J 0

, 1 5 0

_>4 , 4 b U

J b , 7 o 0

4 j , o 7 0

i t e r C o n s u m e

I

i

i

1t>0

b , 4 b 0

1 2 , ^ 2 0

i y , 3 b 0

2 5 , « 4 0

3 2 , 3 0 0

3 d , 7 o 0

4 5 , ^ 2 0

5 l , o o 0

5 b ,

1 4 0

b 5 , b 0 0

) t i o n ( 1 / c .

i

2 0 0 |

d , b 2 0

1 7 , 2 3 0

2 5 , 8 4 U

3 4 , 4 6 0

4 3 , 0 7 0

5 l , b o 0

b o , 3 0 0

b d , 9 0

7 7 , 5 2 0

b o , 1 4 0

. d )

2 5 0

1 0 ,

/ 7 o

2 1 , 5 4 0

3 2 , 3 0 0

4 3 , 0 7 0

b J , f a 4 0

D 4 , o 0 0

7 5 , 3 7 0

b o ,

1 4 0

9 o , 9 0 0

1 0 7 , 6 7 0

i

•

1

i

I



- 50 -

TABLE 5.12

D e s i g n T a b l e f o r t n e T o t a l P l e n u m D e p t h s

P low V e l o c i t y = 2 . 4 3 m

3

/

i n £

n

P r o b a b i e H f i l u e n t = 5 . 0 NTU

Haw W a t e r T u r o i d i t y = 2 5 - 4 5 NTU

T e a p e r a t u i e = 27 - J 3 °C

Tu be W ia th (a) = 4 in

Alum D o s e = 2 2 - 3 2 m g / l

A n g l e = 6 0 °

Tune length = O.y ui

Tuoe Size =

0.5C31

x 0.5ca

1 1

I L o n g i t u a x n a i c 'l â u ui L e n g t h ( L p (m) ) |

i i 1 i i i i 1

I F r e g u e n c y o f | S J J I D O I i 1 I i I 1

( O p e r a t i o n | I 0 . 5 | 1 . 0 | 1 . 5 | 2 . 0 | 3 . 0 I

1 (d ay ) I 1 1 1 1 1 1

| 1 | Mlx

= 0

I 0 . 7 0 | 0 . 4 3 | 0 . 3 4 | 0 . 3 0 l 0 . 2 b |

| , | *HX=Lp | l . l b | 0 .b 2 | 0 .4 4 | 0 . 3 5 | 0 .2 b |

1

i i i I i t i

1

1 1 1 1 1 1 I

| 2 | | dx= u | 1 .2 3 | 0 .7 0 J 0 .5 2 | 0 . 4 4 | 0 . 3 5 j

| | Hx=Lp | 2 .2 8 | 1 .1b | O .b l l 0 . 6 2 | 0 . 4 4 |

| 3 ' | Ux=0 | 1 .75 | 0 .9 o | 0 .7 0 | 0 . 5 7 | 0 . 4 3 |

| I | Hx = Lp | J . J b | 1 . 7 3 | 1 . 1 1 | 0 . •JO | 0 . 6 J

i i l I I I i i

| l 1 1 1 1 1 1

| 4 | tix = U | * . z b | 1 . 2 J 1 U . b b | 0 . 7 0 | 0 . 5 2 |

| | Hx = Lp | 4 . 4 * | 2 . 2 b | 1 . 5 5 | l . l b J 0 . B 1 J

i ' i i i i i < i

*rix = 0 \:a) - t o t a l p le nu m a e p c n a t e n t r a n c e

2 h x = L ; ( m )

t o t a i p ie nu ni a e p t n a t a i n s t a n c e x = Lp



- 51 -

TA.ELE 5 . 1 3

D e s i g n T a b l e t o e t n e 1 ocdi P l en u m U c p t n s

F l o w V e l o c i t y

P r o b a o l e E f f l u e n t

Raw W a t e r T u r o i u i t y


T u b e H i a t a ( a)

3 . 6 / i V i

2

h

6 . 1 - b . 7 K U

25 - 45 STU

27 - J j °C

4 ai

Alum Dose

ai iylfe

Tube ienyta

TuDe Size

22-32ag/l

60°

o . y m

0.5ca» x u.Sca

, 1

I L o n g i t u d i n a l P l e nu n i L e n q t n ( Lp (m) ) I

i i 1 i i i i

| F r e q u e n c /

ot

| Sy m bo l I 1 1 I I

| O p e r a t i o n I | 0 . 5 | 1 . 0 I 1 . 5 | 2 . 0 | 3 . 0

1 (a a y ) | | | l | |

I 1 |

1

r i x = 0 | O . d y | 0 . 5 3 | 0 . 4 ^ | 0 . 3 6 | 0 . 3 0 '

J |

2

H x = L ? | l . o l | 0 . 6 5 | O . bO | 0 . 4 7 | 0 . 3 5

| 2 | Hx=U J 1 . 60 | 0 . 8 9 J 0 . 6 5 | 0 - 5 3 | 0 . 4 2

| | Hx=Lp | 3 . 1 4 | 1 . 62 | 1 . 1 1 | 0 . 7 6 | 0 . 5 1

| 3 1 H x =0 | 2 . 3 1 | 1 . 2 5 l 0 . 0 9 | 0 . 7 1 | 0 . 5 3

| | Hx=Lp 1 4 . 6 5 | 2 . 3 7 | 1 . 6 2 | 1 . 2 4 | 0 . 8 5

| 4 | Hx=0 | 3 . 0 2 1 1 . 6 0 | 1 . 13 | 0 . 8 9 | 0 . 6 5

| | Hx = Lp | b . 1 7 | 3 . 1 J j i 2 . 1 2 | 1 . o2 | 1 . 1 0

i ; 1 1 1 1 — ' 1

_ L

»Hx = 0 ( )

*tix = Lp (a.)

t o t a l p le nu m d e p t h a t e n t r a n c e

t o t a l p le nu m d e p t n a t a a i s ^ n c e x = Lp

SOLUTION: From Ta ble 5. 9 , flow v e l o c i t y of 2.4 3 m

3

/m

2

-h w i l l p rov id e an

ef f l u en t q u a l i t y of 5 NTU. F or t h i s f low v e lo c i t y , Tab l e 5 .10

g i v e s th e t o t a l nu mber o f t u b e s r e q u i r e d , i . e . 6 ,8 6 0 ( t u b e d i

m en sio ns : 5 cm x 5 cm x 90 c m ).

i

j Say, if daily desludging is feasible and a plenum length of 1 m

i can be allocated, then the total plenum depth of 1 m (see Table

; 5.12) is adequate with a safety factor of 38%.



- 52 -

VI ECONOMIC ANALYSIS

6.1 Introduction

Many developing countries are at present trying to achieve fast social

and economic development with the problem of limited available resources.

Since these resources are scarce and at any moment their availability is

limited in the sense that if a resource is used for one purpose, it is denied

to another which therefore will be forgone. Such situation demands the

determination of design alternatives which could provide the desirable cost

effective system. Economic analysis therefore can be used as a tool to

assess the creditability of each alternative.

6.2 Need of Cost Estimation

Sedimentation is one of the most commonly used process in the field of

water and wastewater treatment. It was estimated that about 1/3 of the total

capital investment is spent on this unit operation, for this reason, econo

mical alternatives should be considered in the modern water and wastewater

treatment systems.

Many authors claimed that tube settler could provide same or even better

performance than that of the conventional sedimentation tank with relatively

low cost, therefore this section will be devoted to the cost estimation of

both the systems and to compare their cost-effectiveness.

6.3 Design Assumptions

In designing the conventional sedimentation tank and the tube settler,

the following assumptions will be used:

(1

(2

(3

(4

(5

(6

(7

(8

(9

(10

Population served = 10,000

Daily water demand = 150 £/cd

Plant operation period = 24 h/d

Check list presented in Table 6.1 is applicable

For tube settler, 80% efficiency is acceptable

Cost of form work includes

nail,

wood etc,

Cost of equipments is not included '

Cost of excavation is not included

Operation and maintenance costs are excluded

Expected life-span for the sedimentation unit, tube settler and

the plywood tube is 15 years, 15 years and 5 years, respectively.

Plant capacity

10,000 x 150/(24 x

1,000)

(m

3

/h)

62.5 m

3

/h

I



o

- 53 -

TASL£ 6.;1 ChecK Li st (1yd2 - lybJ ba ng Ko k' s Ma rk et Pric e)

1 _ , - . . - . . . . , .__. . . — — . _ . _ — ,

I I tt to i j C o s t ( T n a i b a n t ) j

| C o n c r e t e [ 1 ,0 2 5 b a n t / a

3

[

| For'is WOEK | 2 5 B a h t / . s

<

[

J Ply wo od (u mm) | y o b a h t / a ^ |

| S t e e l | y b a h t / K v j |

6.4 Design of Sedimentation Tank and Its Cost Estimation

The detention time for the clarifier at Bang Khen Water Treatment Plant

is 113 minutes. GLUMRB Standards recommended that the detention time for

suspended solid contact clarifier should be greater than or equal to 2 hours.

Let choose the detention time of 2 hours for the design.

Detention time

Horizontal velocity

Volume of the tank

= 2 h

* 10 m/h

= 62.5 x 2

= 125 m

3

= 4 m + 1 m (free board)

= 125/4

= 31.25 m

2

Depth x W x flow velocity = Plant capacity

4 x W x 10

Let the depth

Surface area of tank

Say

Length of the tank

Say

- 62.5 m

3

/h

W = 1.56 m

2

W = 1.6 m

2

- 31.25/1.6

= 19.53 m

L =» 20 m

Actual surface area of the tank = 20 x 1.6 = 32 m , which is greater

than 31.25 m

2

, the design is acceptable.

Let the wail of the reinforcement concrete be 0.2 m thick,

Volume of concrete required = (20 x 0.2 x 5) x 2 + (1.6 x 0.2 x 5) x 2

+ (20 x 1.6 x 0.2)

= 49.6 m

3

Unit cost of concrete + labour =» 1,025 Baht/m

3

Total cost of concrete + labour = 50,840 Baht ,

Steel reinforcement = 50 kg/m

3

of concrete

I U



- 54 -

Total steel required

Unit cost of steel + labour

Total cost of steel + labour

Area required for form work

Unit cost of form work + labour

Total cost of form work + labour

i

Total cost of sedimentation tank

(excluding pipe, equipments)

Amortized cost

where erf is the capital recovery factor.

erf - 10% - 15 years - 0.131474 (GITTINGER, 1979)

Amortized cost » 83,960 x 0.131474

- 11,039 Baht (say)

C on t ig en cy 10% =« 8 ,3 96 Ba ht

• 2 ,480 kg

= 9 B a h t / k g I

= 22 ,32 0 B ah t

= (20 x 5) x ^ + (1 .6 x 5) x 4

- 432 m

2

= 2 5 B a h t / j i

2

1 0 , 8 0 0 B a h t

= 5 0 , 8 4 0 + 2 2 , 3 2 0 + 1 0 , 8 0 0 ( B a h t )

= 83 ,96 0 B ah t

= P ( c r f ) (HARBOLD, 198 0)

Final total cost

103,395 Baht

6.5 Design of Tube Settler and Its Cost Estimation

From the experimental result, for 80% efficiency the recommended flow

rate is 3.87 m/h.

Plant capacity

Flow velocity

Required tube settler area

= 62.5 m

3

/n.

= 3.87 m/h

= 62.5/3.87 (m

2

)

- 16.15 m

2

Let choose square tube of 5 cm x 5 cm x 90 cm and assuming 80 tubes

per column,

No.

of tube required

(see Table 5.11)

No. of column of tubes

Actual total No. of tubes

Length of column

= (16.15/25) x (100)

2

=

6,460

= 6,460/80

- 81 (say)

- 80 x 81

= 6,480 (acceptable)

- 81 x 0.05 m



- 55 -

Let the inlet and the outlet chamber total to 1 m width, and the fre

quency of desludging is 1 day. Therefore, from Table 5.13 the plenum depth

of 1 m is adequate.

Surface area occupied by the tube settler = 1.9 x 4.05

«= 7.695 m

2

Volume of concrete = A.05 x 0.2 x 5 + 4.05 x 0.2 x 4 + 0.5 x 0.2 x 4

x 2 + 0.5 x 0.2 x 5 x 2 + 0.5 x 0.2 x 4.05 x 2

+ 4.05 x 1 x 0.2 + 4.05 x 0.9 x 0.2

- 11.44 m

3

,

1

Total cost of concrete + labour = 1025 x 11.4

= 11,726 Baht (dJy)

Total steel required = 572 kg

Total cost of steel + labour = 5,148 Baht (say)

Area required for form work = 4.05 x 5 x 2 + 4.05 x 4 x 2

i + 0.5 x 5 x 4 + 0.5 x 4 x 2

= 87 m

2

(say)

Total cost of form work + labour =2 ,175 Baht

Subtotal cost = 11,726 + 5,148 + 2,175

=

19,04 9

Baht

erf - 10% - 15 years = 0.131474

Amortized cost = 19,049 x 0.131474

=

2,505

(say)

Unit cost of plywood = 90 Baht/(2.5 m x 2.5 m x 4 mm)

Effective No. of tube = (2.5/0.05 x 2) x 2

in one sheet = 50

No.

of sheet needed = 130

Total cost of plywood = 130 x 90

= 11,700 Baht

Let the design period be 15 years and the life-span of the plywood be

5 years. The rate of interest is 10% and the inflation rate is 13%, there

fore according to THUESEN et al. (1977):

Present cost of plywood = 11,700 Baht

Cost of plywood in 5 years time

(at inflation rate of 13%) = 21,557 Baht

Present worth of plywood = 13,387 Baht

(at 10% interest rate)



- 56 -

Cost of plywood in 10 years time = 35,147 Bant

(at inflation rate of 13%)

Present worth of plywood

(at 10% interest rate)

Total present worth of plywood

erf - 10% - 5 years

Amortized cost

Total cost of tube settler

(excluding amortized cost)

Contigency 10%

Final total cost

13,567 Baht

38,654 Baht

0.263797

38,654 x 0.263797

101,976 Baht (say)

57,703 Baht

5,770

Baht

76,175 Baht

6.6 Summary

From the cost estimation, it is clear that the tube settler system

only required 1/4 of the land needed for the construction of the conven

tional sedimentation tank. As for the construction cost, the tube settler

can provide a saving of 1/4 of the total cost involves in the construction

of the conventional sedimentation.

O



- 57 -

A

-JT. LIBRARY

VII CONCLUSIONS

Tube settler can play an important role in the modern water treatment

Its applicability in urban water supply can be validated by the

wing conclusions:

(1) From the jar test experiment, the optimum alum dose for raw water

turbidity of 25-45 NTU was 28 mg/X. to 32 mg/A. Addition of poly-

electrolytes, whether they are cationic or anionic have no signi

ficant effect upon their settling performance.

(2) In Bang Khen Water Treatment Plant, the Authority has imposed a

stringent criteria such that the clarified water should not exceed

5 NTU so as to ensure no overloading of the filter system. The

tube settler used in the present study does in fact satisfy the

above requirement. For raw water turbidity in the range of 25 NTU

to 37 NTU and working under the optimum alum concentration, maxi

mum overflow rate of 8.75 m

3

/m

2

-d can be used

to

provide effluent

quality of equal or less than 5 NTU. For economic reasons, usually

the "economic" alum dose is used, thus if the tube settler is per

forming at the 'economic' alum" dose and at 8 m /m

2

-d, then it

can provide a effluent satisfying the requirement of 5 NTU.

(3) If 80% efficiency is accepted for practical design, overflow rates

of 12.75 m

3

/m

2

-d and 18.5 m

3

/m

2

-d for raw water turbidity of 25-37

NTU and 36-45 NTU can be used, respectively. But it is important

to note that higher percent removal does not automatically implies

the effluent could comply with the required standard.

(4) For practical application, the following formulations can be used

to predict the overflow rate (Vsc) by specifying the required ef

ficiency (E) : |

In E - 4.52993 - 0.01140 x Vsc for 25-37 NTU

In E = 4.55008 - 0.00873 x Vsc for 36<>5 NTU

(5) The recommended overflow rate from this study is 8 m

3

/m

2

-d which

is double the recommended overflow rate concluded by PANNEERSELVAM.

(6) Plenum forms an important component of tube settling system. From

the sludge profile, it is clear that the point immediately below

the tube is the most critical due to th>i fact that the sludge accu

mulated at it maximum rate.

i

(7) For practical plenum design, it is necessary to consider the

height of the settled sludge operate at t hours and the critical

plenum depth for certain flow velocity. If the tube settler has

a plenum of length Lp (cm) and tube thickness of a (cm) and operate

for t hours at velocity V

(m

3

/m

2

-h),

then the following equations

can be used to calculate the total depth needed immediately below

the tube and at entrance;



- 58 -

Hx = 0 (cm) = hs, x = 0 + h x = 0

Hx = Lp (cm) = hs , x = Lp + hx = Lp

where Ho = total depth at the entrance

Hx = Lp = total depth immediately below the tube

hs, x = 0 = depth of settled sludge at entrance

hs, x = Lp = depth of settled sludge at distance x = Lp

hx = 0 rz critical depth of plenum at entrance

hx = Lp = critical depth of plenum at distance x = Lp

Therefore,

Ho = 1.28499V

0,63917

(t/8) (32/Lp) (a/33) + 14.92354V° *

1357l<

Hx = Lp = 2.57147V ' (t/8)(32/Lp)(a/33) + 4.29316V '

(8) From the experiment, for 80% turbidity removal, the recommended

flow velocity for raw water turbidity of 25-37 NTU and 36-45 NTU

is 3.87 m /m -h and 5.43 m

3

/m

2

-h, respectively. To comply with

the effluent requirement of 5 NTU working under optimum alum dose,

then velocity of 2.67 m

3

/m

2

-h should be used for raw water tur

bidity of 25-37 NTU.

(9) From the experimental observation, it is recommended that sub

merged water jet system should be installed and daily jetting

is necessary to prevent the sludge from adhering to the surface

of the tubes.

(10) Column settling results indicate that the trend of overflow rate

versus the percent turbidity removal ressemble very closely to

those computed from the tube settler results. Thus column settling

analysis could be used to provide correlation for the scale-up of

the tube settler system.

(11) The following general formulation can be used to provide the

require depth of the settling column for specified safety factor

(S.F.),

S.F. =

2.7014

- 0.0277 he

where he is the height of the settling column of circular type.

i

For safety factor of 2, the recommended depth of settling column

of circular type is 25 cm.

O

(12) From the cost analysis, the cost of installing the tube settler

system is 3/4 that of the conventional sedimentation system.

Land requirement for the tube settler system is 1/4 that of the

conventional one.



- 59 -

VIII RECOMMENDATION FOR FUTURE WORK

1. One of the most Interesting applications now being evaluated is the use

of steeply inclined tube settler directly in the aeration basin of an

activated sludge plant. With proper design and allocation of the baf

fles, it appears possible to achieve activated sludge solids separation

and return without a secondary clarifier structure, therefore the econo

mic implications in secondary plant construction are indeed significant.

i '

2. With the present knowledge about the characteristics of the raw water

in Bang Khen Water Treatment Plant and also the operation parameters of

the tube settler system. Further work can be pursued by installing the

tube into the contact solid clarifier and to evaluate.the creditibility

of upgrading the overloaded clarifier.

3. From this research, it was observed that sludge deposited on the surface

of the tubes after 30 hours of continuous operation. Therefore, it is

recommended, that submerged water headers should be installed directly

above the tubes so as to create sufficient turbulence to dislodge the

deposited sludge. As for the frequency of cleaning, daily jetting is

necessary but YAO (1971) recommended that weekly cleaning is sufficient,

eventhough he understood that weekly cleaning does momentarily deterio

rate the effluent quality while cleaning on daily basis does not sub

stantially deteriorate the effluent quality. To justify the above recom

mendation, further work can be pursued to determine the design criteria

for the submerged water jet headers and also to find out the frequency

of cleaning that could provide the best result.



- 60 -

REFERENCES

ADAM, C.E., FORD, D.L. and ECKENFELDER, W.W. (1981), Development of Design

and Operation Criteria for Wastewater Treatment, C.B.I. Publication,

91.

AMIN, M.M., (1974), Performance of Tube Settlers in Clarification of Turbid

Tropical Surface Waters, Master's Thesis No. 636, Asian Institute of

Technology, Bangkok, Thailand.

ARIES, R.S. (1955), Chemical Engineering Cost Estimation, McGraw-Hill Book

Co.

BARNES, D. et al. (1978), Chemistry and Unit Operations in Sewage Treatment,

Applied Science Publications Limited, London, 115.

BEACH, W.A. (1972), Fundamentals of Tube Settler Design, 27' Ind. Waste

Conf.i Purdue Univ. Engg. Extn. Series No. 141, 67.

BINH,

N.C.j (1975), Optimization of the Inclined Tube Settlers and Anthra

cite-Sand Filter, Master's Thesis No. 834, Asian Institute of Techno

logy,' Bangkok, Thailand.

BRAHAM, W.L., MATHERNE, J.L. and KELLER, A.G. (1956), Clarification, Sedi

mentation and Thickening Equipment, A Patent Review, Bulletin No..54,

Eng. Experimental Station, Louisiana State Univ. (Baton, Rouge, La).

CAMP,

T.R. (1946), Sedimentation and the Design of Settling Tank, Trans.

ASCE.,

3, 895.

CAMP, T.R. (1953), Studies of Sedimentation Basin Design, Sew. Ind. Waste,

25, 1.

CHEN, Y.R. (1979), Design Criteria for Inclined Tube Settlers, Master's

Thesis No. EV-79-29, Asian Institute of Technology, Bangkok, Thailand.

CULP, G.L., et al. (1968), High Rate Sedimentation in Water Works, J. AWWA.

60, 691.

CULP,

G.L., HSIUNG, K.Y. and CONLEY, W.R. (1969), Tube Clarification Process,

Operating Experiences, J. Sanit. Eng. Div. Proc. ASCE. 9 5, 829.

CULP, G.L. and CULP, R.L. (1970), New Concepts in Water Purification, Van.

Nostrand Reinhold.

DANIEL,

C. and WOOD, F.S.

(1971),

Fitting Equations to Data, Computer Analy

sis of Multifactor Data for Scientists and Engineers, Wiley-Interscience

Publication.

DICK, R.I. (1970), Tube Clarification Process, Operating Experiences, J.

Sanit. Eng. Div., ASCE, 96, 1009.



- 61 -

DRESSER, H.G. (1951), Trays, Nearly Tripple Settling Tank Capacity, Eng.

News Record, V147, No. 29, 32.

ECKENFILDER, W.W. (1966), Industrial Water Pollution and Control, McGraw-

Hill Book Co., 28.

FAIR, G.M. et al. (1968), Water Purification and Wastewater Treatment and

Disposal-Volume 2, John Wiley and Sons Inc., New York.

FISHCHERSTROM, C.N.H. (1955), Sedimentation in Rectangular Basin, Proc.

ASCE., J. Sanit. Eng. Div.

FREI, J.K. (1941), Multiple-Tray Clarification at a Modern Treatment Plant,

J. Sew. Eng. Div., 12, 423.

GITTINGER, J.P.

(1979),

Compounding and Discounting Tables for Project

Evaluation, EDI, Teaching Materials Series Number 1, Johns Hopkins

University Press, London.

i

HANSEN, S.P. et al.

(1967),

Applying Shallow Depth Sedimentation Theory,

J. AWWA., 1134.

(^ i)

HANSEN, S.P. et al.

(1969),

Some Recent Advances in Water Treatment Tech

nology, Chemical Engineering Progress Symposium Series, 65, 97, 207.

HARBOLD, HIS.

(1980),

Sanitary Engineering Problems and Calculations for

the Professional Engineers, Ann Arbor Science, 227.

HAZEN, A.

(1904),

On Sedimentation, Trans. ASCE., 53, 45.

HAZEN, S.Pi and CULP, G.L. (1967), Applying Shallow Depth Sedimentation

Theory, J. AWWA, 59, 1134.

HERBERT,

E.H., Jr. (1981), Water Clarification Processes, Practical Design

and Evaluation, Van Nostrand, Env. Eng. Series, 146.

HOPKINS,

J. (1979), Compounding and Discounting Tables for Project Evalua

tion,, A. World Bank Publication, EDI Teaching Materials Series, Number 1

HUDSON, H.E. and WAGNER, E.G.

(1981),

Conduct and Uses of Jar Tests, J.

AWWA., V73, No. 4, 218.

i

LIENGCHARERNSIT, W.

(1975),

Use of Bamboos and Corrugated Asbestos as Local

Materials for Tube Settler, Master's Thesis, Asian Institute of Tech

nology, Bangkok, Thailand.

MORAN, W.D. and CHEYER, T.F. (1975), Bang Khen-Bangkok's Response to a Cri

tical Water Shortage, J. AWWA., V 67, No. 6, 302.

MOSTELLER, F. and TUKEY, J.W. (1977), Data Analysis and Regression, 2°

Edition, Addison-Wesley Publishing Company.



- 62 -

O'CONNOR, J.T. (1975), Environmental Engineering Unit Operations and Unit

Processes, Laboratory Manual, 2

n d

Edition, Association of Environmental

Engineering Professors, University of Texas.

PANNEERSELVAM, K.N. (1982), Use of Tube Settlers for Tropical Surface Water

Treatment, Master's Thesis, Asian Institute of Technology, Bangkok,

Thailand.

PEURIFOY, R.L. (1975), Estimating Construction Costs, 3

r

Edition, McGraw-

Hill Inc.

RICH, L.G. (1973), Environmental Systems Engineering, McGraw-Hill Book Co.,

336.

SCHMITT,

E.A. and VOIGT, O.D.

(1949),

Two Storey Flocculation Sedimentation

Basins for the Washington Aqueduct, J. AWWA., V. 41, No. 9, 837.

SLECHTA, A.F. and CONLEY, W.R., (19 ) , Recent Experience in Plant Scale

Application of the Settling Tube Concept, J. WPCF., 43, 1724.

TARIQ, M.N. (1976), A Laboratory Study on Tube Settling, Ins. of Public

Health Eng. and Research, Univ. of Eng. and Technology, Pakistan.

TCHOBANOGLOUS, G. (1979), Wastewater Engineering : Treatment Disposal and

, Reuse, Metcalf and Eddy Inc., McGraw-Hill Pub., 201.

y THANH, N.C., CHEN, Y.R. and LOHANI, B.N. (1979), Practical Design Criteria

for Inclined Tube Settlers, 2

n d

Regional Conf. on Water Supply, Taipei,

Environmental Eng. Div., Asian Institute of Technology, Bangkok,

Thailand. I

THUESEN, H.G. (1977), Engineering Economic, Prentice Hall Inc., 123.

VAN VLIET, B.M.

(1977),

The Efficiency of Inclined Tube and Plate Modules

in a High Rate Clarification Process, Water Research, V 11.

VASANADILOKLERT, P. (1978), Use of Inclined Tube-Settlers in Water Treat

ment System, Master's Thesis No. 1403, Asian Institute of Technology,

Bangkok, Thailand.

WALPOLE, R.E. and MYERS, R.H. (1978), Probability and Statistics for

Engineers and Scientists, 2nd Edition, Collier Macmillan International

Editions, 280.

^ W I L L I S ,

R.M.

(1978),

Tubular Settlers - A Technical Review, J. AWWA., 331.

YAO, K.M. (1970), Theoretical Study of High Rate Sedimentation, J. Wat.

Pollut. Cont. Fed., 72, 218.

YAO,

K.M.

(1973),

Design of High Rate Settlers, J. Env. Eng. Div., Proc.

ASCE, 621.



- 63 -

YAO, K.M. (1975), Extended Plain Sedimentation, Proc. ASCE., Env. Eng.,

Div. 101, 413.

YAO, K.M. (1976), Theoretical Study of High Rate Sedimentation, J. WPCF,

72,

218.

YAO, K.M. (1979), Colume Settling Test and Tube Settling, J. AWWA, 71, 109.

"Bang Khen Water Treatment Plant", Jan. 1981, Metropolitan Water Works

Authority, Bangkok, Thailand.

"Drinking Water and Sanitation, 1981-1990, A Way To Health", WHO, Switzer

land.

"The Application of Inclined Tubes or Plates to Sedimentation Tanks in

Wastewater Treatment", 1975, Water Research Centre, No. 68.

"Tube Settlers Up Clarifier Throughput", April 1972, Env. Sc. and Techno

logy, V 6, 312.

6

i



o

-

64 -

APPENDIX A

JAR TEST EXPERIMENTATION

o



- 65 -

TABLE A 1-1

Determination

of

Optimua Alua Concentration

Haw Water Turbidity : 25 HTD

Optimum Alum Concentration : 28 »g/l

O

Jar Number 1 4 1 5

-i

i

22.0 |2b.U |28.0

lum Concentration (mg/i))

14.0

18.0

30.0

+

Besidual | 10 sin Settling

Turbidity | 30 a m Settling

(NT0)

|

7.4

6.0

5.1

4.6

3.9 |

3 3

| 3.0

3.1 I 2.b | 2.2

i

I

i i

3.1

2.3

TABLE A1-2

Determination of Optiiaua Alum Concentration

Haw Water Turbidity : 40 STU

Optimum Alu» Concentration : 28 mg/1 is sufficient

T

I

-\

T

I 6

Jar Number

•

I 1

h

+

I 2

H

I 3

I 5

+

I

+

-i

lAlua Con cent ra ti on (ag/1) J 14.0 |18-0 | 22. 0 J26.0 |2d.O | 3 0 . 0 |

1 1 1 I 1 1 1

IBesidual Turbidity («TU) | 2.0 J 1.2 | 1.1 |0.86 10.82

{0.70|

i

1 » 1 1 1 •

TABLE

A1-3

Determination of Optimum Alum Concentration

Saw Water Turbidi ty : 56 NT0

Optiiaua Alum Co nc en trat ion : 34 »g / l

| J a r Nuaoer

I 1 1 2

h

+

+

I 1

_,

I 5

+

I

<> I

+

H

|Alua Concen trat ion (a g/ i) |1 8. 0 | 22-0

28.0

|32-0 |3b.O

|40.0|

l-

+ +

+

+

4

|Residual Turbidity (MTU) | 7.5 | 6.0

t. . 1 1

4.5 | 3.3 [ 3.3 | 3.61

i

1 i i



- 66 -

TABLE A2-1

To Determine the Effect of Cationic Polyelectrolyte

OpoQ the Hesiduai Turbidity

Raw water Turbidity : 25 NTO

Optimum Alum Concentratioa : 28 mg/1

Polyelectrolyte : CA-T-PLOC T

r

1 I

h

r

3 I

J a r N u m b e r

I

2 I

H

+

4 I

h

I

+

| P o l y e l e c t r o l y t e ( a g / 1 )

I

0 0 d I . 0 0 6 | . 0 U 4 | . 0 0 2 ( . 0 0 1 5 | . 0 0 1 0 1 . 0 0 0 5 I - 0 00 31

+

+ + + +

+ +

•i

IBesidual Turbidity (NT0)

6.9| 4.b| 2-8| 2.6| 2.8 | 3.0 | 3.2 | 3.3 |

i i i i t i i i

TABLE A2-2

O

To Determine the Effect of Anionic Polyelectrolyte

Opon the Hesiduai Turbidity

Haw Water Turbidity : 30 NTQ"

Polyelectrolyte : SOPEfiPLuC

|Jar Number

I

I I

1

J — 1-

20.0 | 22.0 | 24.0 |

1 1 1

4.6 | 4.3 | 3.1 |

| Alum Concentration (mg/1)

I

14.0 | lb.0 | 18.0

1 1

(Residual Turoidity (MTO)

7.1 | b.O | 5-6

i i

|Jar dumber

I

;

|Alum Concentration (mg/1)

j

20.0 |

0.0 20.0 20.0 20.0 20.0

I

|Polyelectrolyte (ag/1)

J

,080 I

000

.050 .060 .0b5

,070

|

IBesidual Turbidity (NT0)

i . .

1

5.1 I

.7 5.5 4.9 4.7

5.1

|Jar number

H —

|Alum Concentration (mg/1)

I

»

22.0 |

2.0 22.0

22.0 22.0

22.0

I

| Polyelectrolyte (mg/1) .000 .050 .060 .065 ,070 .080 |

I

(Hesiduai Turbidity (NT0)

4.5

4.5

4.2

4.5

4.6 *.5 |



- 67 -

T a b l e & 3 - 1

T o E v a l u a t e t h e A p p i i c a o i l i t y o r PAC o n C o a g u l a t i o n

a nd . P l o c c u l a t i o n P r o c e s s

Raw M a t e r T u r b i d i t y

: 31 NTO

I . - .

| J a r H u n b e r

•

i

| A 1 U I B

C o n c e n t r a t i o n

i

1

I f i e s i d u a l T u m i d i t y

•

|P A C C o n c e n t r a t i o n

i

I H e s i d u a l T u r b i d i t y

- — 1

( u i g / 1 )

(NTU)

( a g / 1 )

(MTU)

.. ., _ ,

1

1 4 - 0

fa.7

6 . 0

8 . 1

i .. 1

i

2

1 6 . 0

5 . o

b .O

5 . 8

L _ . , _ . .

3

1 8 . 0

4 . 8

; 1 0 . 0

4 . 2

t

• i

1 **

| 2 0 . 0

I 3 . 6

J 1 2 . 0

I 3 . 5

•

1 5

i

l

1 2 2 . 0

| 3 . 4

•

1

| 1 4 . 0

1

1 3 . 1

i

I fa

| 2 4 . 0

| 3 . 0

| 1 6 . 0

| 2 . 7

-r

1

1

i

* PAC = P o l y A l u m m u * C h l o r i d e

<L>



- 68 -

APPENDIX B

TUBE SETTLER PERFORMANCE

i)



- 69 -

TABLE

B1-1

Percoriance

of the

inclined Tube Settler

for Baw

rfater

Tumidity of 25 NTU to 37 NTO

Flow

: 2

1/min

,

Average Effluent Tu mi di ty :

2.8 NTO

Flow Telocity : 0.8 n/h Average Efficiency : 69.63 *

Overflow Hate

:

2.68 a^/a*

d

Aluat Concentration

: 2B ag/i

r • • . — ,

(Operatxng |

|

Tiaie

J

1 («) i

1".

1

I

I 2

I 3

| 4

I

5

I

b

I

1

1 B

1 9

1 10

1 11

I 12

— , . ,

Raw

Water

Turoidity \

(NTU)

29 i

2 9

2 9

2 9

2 9

3 3

3 5

2 7

2 b

2 B

I 2b

1 27

. . . . _,

Floc c ula ted

Hater |

(N TO)

1 9

1 b

1 7

I d

I B

1 7

l b

1 6

1 b

1 7

1 17

I 13

i

Etixuent

j

Tumidxty

|

(NTU) |

6.5 |

7 . 5

6 . 7

5 - 5

5 . 0

4 - 2

^-d

3 . 4

3 - 0

3 . 0

•- '

2-7

| 2 .6

iiffxciency

70.69

74 . 1 4

7 b . 90

B1-04

62.14

B7.2 7

89-14

67.41

Bd.50

89.29

90.3b

I

90.37

i i

Temperature|

32 |

32

|

32 |

33 |

33 |

33 I

30

|

30 |

30 |

30 |

1 30 |

1 30 |

u



TABLE B1-2

- 70 -

U

Performance of the Inclined Tube Settler for Baw Hater

Turbidity of 25 MTU to 37 NTO

Plow :|5 l/«in Average Effluent Tumid ity: 4.5 NTU

Flow Velocity : 2 . 0 u/ii Average Eifxcxency : 86.72 %

Overflow Rate : 6.70 IB

3

/"* d Alua Concentration : 2d ag/1

1

' • ' •" 1

l O p e r a t i n g

| T i a e

1 (A) |

| 1

i 2

I 3

I t

| 5

I 6

I 1

1 &

1 9

r

_ ., , ..

n

Raw ; W a t e r

T u r b i d x t y

(NTO)

3 2

3 2

2 9

3 7

3 3

3 6

3 6

3 2

3 7

f l o c c u l a t e s

W a t e r

(tfTU)

1 7

1 b

2 0

2 1

2 0

2 1

2 1

l

l b

1 7

• • • — 1

E f f l u e n t |

T u r b i d x t y

(NTO)

3 . 4

7 . 3

6 . 3

5 . 0

5 . 1

4 . B

5 . 0

l

4 . 1

4 - 3

L'f f i c i e u c y

*

6 9 . 3 9

7 7 . 1 9

7 8 .

2 8

8 4 . 3 2

8 4 . 5 5

8 6 . 6 7

8 6 . 1 1

8 7 . 1 9

8 8 . 3 8

T "

I T ea

^ > e r a t u r e |

°C |

28 |

28 1

28 |

28 |

29 |

30 |

31 I

32 |

33 |

10 | 31 I 17 I 3.9 | 67.42 | 33



TABLE B1-3

- 71 -

Performance of the Inclined Tube Settler for Raw water

Turoidity of 25 NTU to 37 HTO

\

Flow : 10 1/ain Average Effluent Turbidity: 6.5 NTO

Plow Telocity \: 4.0 m/h Average Efficiencyo : 79.21 %

overflow Hate :13.3b a

3

/ia^ d Alua Concentration : 28 og/1

1 1 •;•- - t i , . . . . . . „ _ . , ,

|Operating

|

aaw Water JPlocculatea [E ifluent |Efficiency JTeaperature|

| Time | Turbidity | Water | Tu mid ity | |

I (h) | (NTU) | (UTU) | (NTO) |

%

| °C |

| 1 | 31 | 22 | 4.0 | 87.10 | 30 |

I 2 I i 31 | 22 | 6.6 | 7b.7b | 29 |

| 3 | 29 | 24 | 7.2 | 75.17 | 29 |

| 4 | 25 | 20 | 4.2 I 83.20 | 29 |

| 5 | . 2 7 | 21 | 5.6 | 79.26 | 29 |

| 6 I : 33 | 23 | 7.8 I 76.3b | 28 |

| 7 | 31 | 24 | 8.2 I 73.55 | 2b |

| 8 1 34 | 23 | 8.5 | 75.00 J 27 |

| 9 | 30 | 22 | 4.2 | 8b.00 | 27 |

10 I 32 | 23 | 4.5 | 85.94 | 27



- 72 -

TABLE B1-4

Perrormance of tne Inclined Tuoe Settler for Haw Mater

Turbxdity of 25 NTO to 37 NTU

Flow

: 15 i/»xn Averaye Effluent Tum id ity : 7.3 NTO

Flow

Velocity : b.O a/n Average Efficxency : 76.75 %

Overflow Bate

:

20.07 o V »

2

d Aiua Concentration : 28 ag/1

•

l O p e r a t x n g

i T i a e

1 < M

| 1

I 2

i 3

I t

| 5

I 6

I 7

I

8

•

R a w R a t e r

T u r b i d i t y

(NTU)

33

3 3

2 9

2 9

3

2

1 37

',

3 0

:

J 2

i

F l o c c u l a t e d

W a t e r

(MTO)

2 7

3 0

1 9

1 9 . 5

2 0

2 2

2 1

2 8

i

f i f f iuent

T u r o i a x t y

(MTU)

4 . 9

1 2 . 0

1 1 . 0

7 . 2

7 . 5

7 . 0

7 . 6

7 . 2

— r

i i

« |

I

. . . . . ,

E f f i c i e n c y

%

6 5 . 1 5

6 3 . 6 4

6 2 . 0 7

7 5 . 1 7

7 6 .

5 o

8 1 . 0 6

7 4 . 6 7

7 7 . 5 0

T e m p e r a t u r t

2 7

2 7

2 b

2 8

2

b

2 9

2 9

2 9

9 { 29 | 2b | 7.1 | 75.52 I 30



- 73 -

A.I.T. LIBRARY

TABLE B1-5

Perioraiance . ot toe Inclined Tuue Settler for Raw tfater

Turbxdxty of 25 NTU to 37 NTO

Flow : 20 l/»xa Average Effxuent Turoiaity: 8.9 NTU

Plow Velocity : 8.0 a/a Average Efficxency : 68.33

%

Overflow ftate :2fa.7b m-*/m* d Axuai Conceotratxon ; 2b ag/l

• • , . . . . , • • i — — T • r

( O p e r a t i n g Jfiaw w a t e r J F i o c c u x a t e r i ( A f f l u e n t | £ f f x c x e n c y | T e a p e r a t u r e |

| T x a e J ' f u r o x d x t y | W a t e r I T u r o i d x t y | J j

I (h ) | (NTO) | (MTU) | (dTO ) |

%

| °C |

i i i i l l 1

| 1 | 2 7 | 1 3 I 7 . 2 | 7 3 . 3 3 J 3 0 |

1 1 1 1 I i I

| 2 1 2 b | 2 1 | . 7 . 1 | 7 2 . 7 0 | 3 0 |

i i i I I t 1

I 3 l 28

| 1 9 < a . 9 | b d . 2 1 J 3 0 |

i l l I I i i

| 4 | 2 7 | 2 5 | b . 7 | b 7 . 7 8 | 3 0 j

I I I I I i 1

| 5 | , 3 0 | 2 b | y . O | 7 0 . 0 0 |

30

|

i l l i i i l

1 -

• —

1 I I i l 1

1 6 1 2 8 t 2 0 | o . 9 | b 8 . 2 l | 2 9 f

t 7 J 2 8 | 2 0 t 9 . 0 | | 6 8 . 8 b | 2 9 |

I I I | i 1 i

| 8 | j 2 7 | 2 5 | b . b | O b 7 . 4 l | 2 8 |

•

I I i i

I l

I - •

i

l I

l i t

| 9 | : 2 8 | 2 3 | 9 . 0 I 6 7 . 8 b | 2 6 I

» « ' 1 _ A . . . . _ _ . . . . . . . . . . . . 1



- 74 -

TABLE B2-1

P e r f o r m a n c e o f t n e Tur>e S e t t l e r a t E c o n o a x c a l

A l u a d o s e

F lo w : fa.O 1 / i i D A v e r a g e E f f l u e n t T u r D x ' d i t y : 4 . 8 5 NTU

F lo w V e l o c i t y : 2 - 4 a / a A v e r a g e E f f i c i e n c y : 8 7 . 1 9

i

O v e r f l o w B a t e : 8 . 0 3 i nV

f f l 2

d A l u a C o n c e n t r a t i o n : 22 « g / l

r • • • • - • • '

( O p e r a t i n g

| T x a e

( 1

1 2

1 3

1

4

| 5

1

b

| 7

1 8

1 9

i 10

. . . . . ,

Baw Water

T u r o i d x t y

(NTO)

3 5

3 4

32

3 6

3 d

3 o

3 b

3 7

1 37

|

t

Jb

l— " 1


M a t e r

H

TO)

1 5

l b

l b

1 9

1 4

1 4

1 7

2 2

i 23

1 21

• i

E f f l u e n t |

T u m i d i t y

(NTU)

5 . 5 |

b . 7

b . 7 i

5 . 8

5 . 1

4 . 2

4 . b

5 . Q

1 4 . 7

| 4 . b

• • • • • — • — • • -j

E f f i c i e n c y |

*

8 4 . 2 9 ,

6 0 . 2 9

7 9 . O o |

8 4 . 7 4

6 o . 5 b

6 6 . J 3

6 7 . 2 2

8 6 . 4 9

8 7 . 3 0

6 7 . 2 2

i — -


° C

3 0

3 0

J l

3 1

3 2

S2

32

32

3 2

3 1

o



- 75 -

O

TABLE B2-2

P e r f b r a a n c e o f t& e T u be S e t t l e r a t E c o n o i a xc a l

Alum dose

P lo w : 8 . 0 1 / a i n A v e r a g e E f f l u e n t T u r b i a L x t y : 6 . 4 0 NTO

F lo w V e l o c i t y : 3 . 2 a / a A v e r a g e E f f i c i e n c y : 8 1 . 4 5 %

O v e r f l o w S a t e : 1 0 . 7 0 I D

3

/ * * & A l u a C o n c e n t r a t i o n : 22 t ag /1

f J 1 1 I . . . . . .

r

. . . . _ ,

( O p e r a t i n g | Raw W a te r | F l o c c u l a t e d | E f f l u e n t | E f f i c i e n c y | T e m p e r a t u r e

I

| T i a e I T u r o i a i t y | W a t e r f l u r o i d i t y | 1 |

| (h ) | (NTU) | (MTU) i (fil'fU) I * | °C |

| 1 | 37 | 27 | 6 . 4 | 8 2 . 7 0 | 30 |

| 2 | 36 | 2 5 | 6 . b | 8 1 . 6 7 | 3 1

\

| 3 | 3 7 . 5 | 24 I 0 . 8 | 8 1 . 6 7 | 31 |

| 4 | 33 | 29 | 7 . 5 | 7 7 . 2 7 | 3 1 |

| 5 | 35 | 31 | 7 . 1 | 7 9 . 7 1 | 32 |

| 6 I 34 | 29 | 7 . 5 | 7 7 . 9 4 | 32 |

| 7 | 3u ( 2 6 | o . 6 | 8 0 . 4 3 | 3 2 |

1 . 8 1 3 5 | 2 7 ( 6 . 2 | 8 2 . 4 1 J 33 |

| 9 | 34 | 25 | b - 3 | 8 1 . 5 0 | 33 |



- 76 -

TABLE B2-3 <j

Performance of the Tube Settler at Economical

Alum

dose

Flow :12.0 l/»in Average Eftluent Turbidity: 8.20 NTU

Flow Velocity :;4.8 a/a Average Efficiency : 7b.b9 %

Overflow Rate :16.0b a

3

/ a

2

d Alua Concentration : 22 ag/1

r - . . . . , _ . - r

-

• • i i •• • - • • r ••• • I

( O p e r a t i n g |Hawi w a t e r ( F l o c c u l a t e d ( E f i i u e u t ( E f f i c i e n c y j T e m p e r a t u r e

( T i a e I T u r b i d i t y | W a t e r ( T u r o i d i t y | | (

| (Q) I (NTU) ( (MTO) ( (NTU) I % | °C |

| 1 | 35 I 20 I 7 . 2 | 7 9 . 4 3 | 31 |

| 2 . | 34 | 22 | 9 . 0 J 7 3 . 5 3 | 31 J

( 3 | 3 b | 2 5 I 9 . 2 I 7 4 . 4 4 I 3 0 |

( 4 I 3 5 ( 1 8 | b . 9 | 7 4 . 5 7 I 3 0 |

( 5 | 3 4 | 2 3 | 8 . 7 | 7 4 . 4 1 | 3 0 |

| 6 I 3 5 [ 2 0 | 6 . 3 I 7 b . 2 1 |

30

|

| 7 | 3b | 29 | b . 2 | 7 7 . 2 2 ( 2y |

B | 35 ( 23 | 6.2 | 7b.57 | 29



TABLE B3-1

- 77 -

Performance of the Inclined Tur>e Settler for Haw Water

Turbidity of 36 MTU to 45 WTO

Flow : 8.0 1/mxn Avrerage Effluent Turoidxty: 5.8 NTU

Flow Velocity : 3.2 s/h Average Efficxency : 85.78 %

Overflow Bate : 10.70 m*/** a Alum Concentration : 32 ag/l

,_ ,

J O p e r a t x n g |

| T x a e

I ( M |

I 0 |

I 1 I

I 2 |

I 3 |

I 4 I

I 5 |

( 6 I

I

~1 \

< 8 i

1 9 |

1 10 |

I 11

1 12

I 13

I 14

I 15

I 1t>

I 17

1 1 "

I 19

1 20

1 21

i

Raw W a t e r |

T u r b x d i t y

(N T 0 ) |

37 |

13 |

:

4 1

bO |

4

1

|

, 3 8 |

; 3 7 |

: 3 9 |

| 4 2 ,

3 b

i

3b

J 9

4 0

4 2

4 5

i 4U

; 36

4 0

4 0

1 41

I

a

3

I 42

F l o c c u l a t e d |

W a t e r i

(UTO)

, 2 6 |

28 |

29 I

28 |

2 7 |

29 |

30 |

2y |

28 |

2 6

2 7

2 6

2 y

2 9

2 5

2 9

2 4

2 9

Z 3

2 4

1 28

| 20

— i

E f f l u e n t j

T u r o x d x t y

(Z4TD)

7 . 0 |

5 . 4 |

5 . 6 |

5 . 0

5 . 4 ,

5 . 5

5 . 0

b . O

5 . 5

b . 2

b . O

O . I

b . O

b . 3

b . O

b . 2

O . I

o . O

i b .O

5 . 2

| o .O

| . . .

| o .O

•

E f f i c i e n c y |

8 1 . 0 8

8 7 . 4 4 j

6 b . 3 4

9 1 . 6 7

6 6 . 8 3

8 5 . 5 3

11)

6 0 . 4 9 |

8 4 . 6 2

8 6 . 9 1

8 3 . b o

8 4 . 2 1

6 4 . 3 o

8 5 . 0 0

8 5 . 0 0

8 b . 6 7

8 4 . 5 0

8 3 . 0 6

6 5 . 0 0

1 8 5 . 0 0

i 8 7 . 3 2

| 8 b . 0 5

I 6 5 . 7 1

1


1

°C |

33 |

33 |

33 |

32 |

32 J

3 1 |

3 1 1

30 |

30 |

29 |

29 |

1

r

26 |

27 |

27 |

27 I

28 |

28 |

29 I

29 l

30 I

| 30

1 30



- 78 -

TABLE B3-2

Performance of the Inclined Tune Settler for fcaw Water

Turbidity of 3b UTU to 45 «T0

Flow :15.0 1/ain Average Effluent Turoidity: 7.7 NTU

Flow Velocity : b.O m/n Average Efficiency : 80.3b %

Overflow Hate :20.07

a

3

/»*

d Alum Concentration : 32 ag/1

r

( O p e r a t i n g

| T i a e

1 (M

1 0

| 1

I

2

| J

4

| 5

I

b

I 7

y

y

L .

I 1

| Raw W a t e r

| T u m i d i t y

| (HTU)

i

I

| 36

1

1 37 |

i

l

1 4 0 j

1

1 3 6 |

j

I 45

i

1

j 4 0 |

j 3 9 |

i

1

1 35

1

| 40

|

^

i

i

| 40

i

..... . _.. ,


W a t e r

(HTU)

2 b

2 9

2 9

2 1

2 b

2 7

2 b

2 9

2 9

2 7

2 d

1

1

E f f l u e n t |

T u r b i a i t y

(SITU)

1 9 . 0

9 . 0

7 . 5

7 . 3

7 . 0 , ,

7 . 1

7 . 0

b . O

9 . 0

d . O

«

„

. ,

E f f i c i e n c y

5 0 . 0 0

7 5 . b b

6 1 . 2 5

7 9 . 7 2

8 4 . 4 4

d 2 . 2 5

8 1 . 5 4

6 0 . 0 0

8 0 . 0 0

7 b . y 2

6 0 . 0 0

»

T e a p e r a t u r

° C

2 7

2 7

2 8

2 d

2 9

2 9

2 9

3 0

3 0

3 1

3 1

•

I



- 79 -

TABLE B3-3

P e r f o n a n c e of tue Inclined Tube Settler tor Raw Water

Turbxdity of 36 JJTO to 45 NTO

Plow :20.U

1/iain

Average Efflue nt Tur Did ity: 9.8 NTU

Plow Veloc ity : b.O u/h Ave rag e Eff ici enc y : 74.41 %

Overflow Rate :2b.7b a^/a^ d Aiua Con cen tra tio n : 32 ay/ 1

Operating

Time

<h)

0

Saw Mater

Turbidity

(NTU)

41

37

36

H-

39

39

39

39

3d

36

Flocculated

Water

(NTU)

2b

29

2a

27

2b

2b

26

27

2b

Effluent lEfficiency

TurDidity |

(NTO) | *

12.5

10.0

9.5

9.5

9.0

10.a

10.0

10.o

1o.5

b9.5l

72.97

75.00

75.bu

7b.92

74.36

74.3b

73.bb

72.37

Temperature

°C

32

32

32

33

33

33

33

32

3 2

O



o

- 80 -

TABLE B4-1

Performance of tne Inclined Tuoe Settler at Different

Overflow Bate and at Different Alum Concentration

Temperature: 27-33 °C

r — • ~t • — — » — - • - - - i - • • • - - • . , - - . . — . • - ,

(Saw » a t e r | A l u m D o s e | O v e r t l o w R a t e | E f f i c i e n c y | E f f l u e n t T u r i j i d i t y l

| (NTO) | ( a g / 1 ) J ( a s / r g i d) | (%) | (STU) |

i l l I I i

i l l i I l

I | | 8 . 0 3 | 8 7 . 1 9 | 4 . 8 5 |

| 2 5 - 3 7 | 2 2 | 1 0 . 7 0 | 6 1 . 4 5 | 6 . 4 0 |

| | | l b . 0 b | 7 6 . 6 9 | 8 . 2 0 |

i l l I I i

I I 1 1 1

t

| | | 2 . 6 d | 8 9 . 6 3 | 2 . 8 0 |

| | I b . 7 0 | 8 6 . 7 2 j 4 . 5 0 |

| 2 5 - 3 7 | 2 8 | 1 3 . 3 6 | 7 9 . 2 4 | 6 . 5 0 |

| | | 2 0 . 0 7 | 7 6 . 7 5 | 7 . 3 0 I

| | | 2 b . 7 b i b b . 3 3 | 6 . 9 0 |

i l l 1 1 i

1 l I 1 t

| | | 10 .7(J | 6 5 . 7 6 | 5 . 8 0 |

| 3 b - 4 5 | 3 2 | 2 0 . 0 7 | 8 0 . 3 b | 7 . 7 0 |

| | | 2 b . 7 b | 7 4 . 4 1 1 9 . 8 0 |

u



- 81 -

TABLE B5-1

LEAST SQOAHES METHODS Of ANALYSIS i

Regression of Vsc Vs Tumidity Removal for Tumidity of 25-37 NTO

i - r i

I I y» '

I 189.63

| 186.72

1 |79.24

| 168.33

:

i i

I I

|Sum|

•

y=ln y'

4.4957

4.4627

4.3725

4.2244

17.5553

i - 1

20.2113

I 19.9157

19.1188

17.0456

77.0913

i

X

2.60

I 6.70

13.38

26

.76

49.52

i

i

x* |

i

(

7.1624

|

44.6900 |

179.024m

71e.0976|

i

1

947.19441

i

xy |

•

1

12.0485 |

29.9001 |

58.5041 I

113.0049|

213.4976|

•

Xa7

Yav

B1

Bo

12.3800

4.3888

-0.01140

4.52993

Equation:

In E = 4.52993 -

0.01140 x Vsc

r = 0.99147

r2 = 96.30

TABLE B5-2

LEAST SQUARES METiiODS OE ANALYSIS

Regression of Vsc

Vs

& Tumidity Reaofai for Turbidity of 36-45 NTU

1 •• I

i i y

i 1

| |85.7b

| |80.36

I |74.41

• i

1

1

| Sum |

i -

\

|

y=in y•

| 4.4518

| 4.3665

|

4.3096

I 13.1479

- •

-

• l

19.6164

19.2415

18.5726

57.63^5

....

X

10.70

20 .07

26.76

57.53

i

x* 1

114.49

402.8049

716.0976

1233.392

i

i

xy |

47.63411 |

86.03740

|

113.3246

|

250.99613|

Eq

Xav

lav

B1

Bo

=

=

=

=

uation:

• r

r*

=1

=

19.1767

4.38263

-0.006732

4.55006

in E = 4

(.9862

97.65

.55006

- 0.00873

x Vsc



- 82 -

TABLE 86-1

Performance ot tae Inclined TuDe Settler at Different

Flow Velocity and at Different Alba Concentration

Teaperature: 27-33 °C

O

|B aw rfater|Alum D o s e | P i o w V e l o c i t y | E f f i c i e n c y | isf f l u e n t T u r o i d i t y |

| (NTU) | : ( a g / 1 ) | (m 3/i»2

fl

) j {% ) | (NTO) J

| 1; | 2 .4 0 | 8 7 . 1 9 | 4 . 8 5 |

| 2 5 - 3 7

\\

2 2 | 3 . 2 0 | 8 1 . 4 5 | b . 4 0 |

| I; 1 ' •-bO | 7 b . 6 9 l b_ 20 |

I I I I 1 i

| 1: | 0 .8 0 | 8 9 . b 3 | 2 .8 0 |

| | | 2 .U0 | d b . 7 2 | 4 . 5 0 |

| 2 5 - 3 7 | 2 8 | 4 . 0 0 | 7 9 . 2 4 | b . 5 0 |

j li | fa.00 | 7 b . 7 5 | 7 . 3 0 |

| | | B.UO | o & .3 3 | b . 9 0 |

i j i l i i

| | 1 3 . 2 0 | 8 5 . 7 8 | 5 .8 0 |

\ 3b -4 5 |, 32 | o .OO | 8 0 . 3 6 | 7 .7 0 |

| 1 1 8 . 0 0 | 7 4 . 4 1 | 9 . 8 0 |



- 83 -

APPENDIX C

COLUMN SETTLING ANALYSIS

U



- 84 -

Column Settling Analysis

of Column : Square

Depta : 10 cm

ion Factor : 2.8

Raw Water Turoidity :

30 STU

Alum Concentration : 28 mg/i

• 1

i

i 1

Effective aexgnt

(ci)

10.0

9.7

9.4

9.1

8.8

8.5

8.2

7^9

7.b

7,3

L , , : 1

Effluent Turoid

(NTU)

4.6

3.8

3.4

2.5

2.4

2.3

2.1

1.95

1.9

1.8

xty

• 1

|* Turuxdity

| Removal

| 84.o7

1 87.33

1 88.o7

| 91.b7

I 92.00

I 92.33

| 93.00

1 93.50

I 93.o7

| 94.00

• i

Overflow |

Rate (a/d)|

24.00 |

13.90 |

9.02 |

4.37 |

2.62 |

2.04 |

0.98 |

0.63 |

0.4b |

0.35 |

• i



- 85 -


: Circular

: 10 cm

: 2.8

Baw Water Turoidity : 30 NTO

Alua Concentration : 28 ag/i

i - - '••• T - - — x 1 r

| E f f e c t i v e h e i g h t | K f f i u e n t T u m i d i t y

\%

T u r o i d i t y | 0 \r e r f i o w |

) | (en ) | (MTU) | R e a o v a l | t t a t e (a /d ) |

i 1 1 1

| 1 0 . 0 | 5 . 0 | 8 3 . 3 3 I 2 4 . 0 0 |

I I 1 1 1

. 1 7 | 9 . 7 | 4 . 0 | 6 6 . o 7 | 1 3 . 9 0 |

I 1 i l l

. 2 5 | 9 . a | 3 . 6 I 8 8 . 0 0 | 9 . 0 2 |

1 1 1 1

. 5 0 | 9 . 1 | 3 . 0 | 9 0 . 0 0 | 4 . 3 7 |

1 1 i l l

. 7 5 | 8 . 8 | 2 . 8 | 9 0 . t>7 [ 2 . 8 2 |

I i 1 1 1

0 0 | 8 . 5 | 2 . 6 | 9 1 . 3 3 | 2 . 0 4 |

i l i l l

1 I I I

0 0 | 8 . 2 | 2 . 3 | 9 2 . 3 3 | 0 . 9 8 |

I

1 1 1 1

. 0 0 | 7 . 9 | 2 . 1 | 9 3 . 0 0 | 0 . 6 3 |

I l 1 1 1

1 1 I I I

0 0

i

7 . 6 | 1 . 7 | 9 4 . 3 3 | 0 . 4 b |

I 1 I I I

. 0 0 | 7 . 3 | 1 . 5 | 9 5 . 0 0 | 0 . 3 5 |

l

. . . . . . . . . . . X . . .

1 « _ 1

o



- 86 -

O

Colusa Settling Analysis

of Coluan j

: Circular

: 30 ca

: 1.5

Raw Hater Tumi di ty : 43 NTO

Aiua Coaceatratioa : 28 «g/i

— —

T

• • — - i - - , , ,

J E f f e c t i v e h e i g h t j E f f i u e n t T u m i d i t y j % T u m i d i t y j O v e r f lo w |

( h) | ( c a ) | (NTO) | B e a o v a l j t i a t e ( a / d ) |

0 . 2 5 | 3 0 . 0 | 1 1 . 0 | 7 4 . 4 9 | 2 8 . 8 0 |

0 . 5 0 | 2 y . 7 | 7 . 5 | 8 2 . 5 o | 1 4 . 2 b |

0 . 7 5 | 2 9 . 4 J b . O I 8 6 . 0 5 | 9 . 4 1 J

1 . 0 0 | 2 9 . 1 | 5 . 0 | 8 9 . 7 7 | 6 . 9 8 |

2 . 0 0 | 2 8 . b | 3 . 9 [ 9 1 . b b | 3 . 4 b |

3 . 0 0 | 2 8 . 5 I 3 . 3 | 9 2 . 7 9 | 2 . 2 8 |

4 . 0 0 | 2 8 . 2 | 2 . 9 5 I 9 3 . 1 4 \ 1 .6 9 |

1 l i t

5 . 0 0 | 2 7 . 9 | 2 . 6 I 9 3 . 9 5 | 1 . 3 4 |



- 87 -


Circular

52.5 c»

1.2

Baw Hater Turbidity : 33 MTU

Alum Concentration : 28 ag/i

O

- i

b.oo

r —

-• i

Effective heignt

\

(ca) |

52.5

i 1

52.2

51.4 '

5 1 I J 1

51.J

51.0

, 50.7

50.14

50.1

I 49.0

[ 49.5

i — - ••' - i

Efflu ent Turbidity j

(NTU) |

6.5 i

6.9

5.9

5.0

4.0

3.1

2.9

2.7

2.0

1-7

1 l.b

* Turbidity

tienoval

74.^4 i

79.10

B2.12

84.85

87.86

90.b1

91.21

91.82

93.94

94.85

1 95.15

i

Overflow [

Bat e (m/d) |

25.20 |

16.70 |

12.46 |

6.19 |

4.10 1

3.06 |

2.43 j

2.02 |

1.72 I

1-49 |

i 1.32 |



- 88 -


: Cxrcuiar

: 72.0 cm

: 0.5

Raw Water Turbidity : 46 HTU

Aiaa Concentration : 28 ing/1

- • ' - 1

i

E f f e c t i v e a e i g n t

( C J )

7 1 . 7

7 1 ^ 4

7 1 . 1

7 0 i d

7 0 i S

7 0 . 2

b y . 9

i 6 9 - b

E f f l u e n t T u m i d

(NTU)

l fa .O

1 3 . 0

1 0 . 0

y . 5

b .O

7 . 5

7 . 0

b .O

i t y

%

T u r c i d i t y

B e a o v a l

6 5 . 7 9

' 7 1 . 7 4

6 6 .

o 7

6 8 . 3 3

7 3 . J 3

7 5 . U 0

7 6 . 6 7

b O . 0 0

a

O v e r f l o w |

S a t e ( a / d ) |

2 4 . 5 8 |

1 7 . 1 4 J

8 . 5 3 J

6 . 2 9 |

1

1

4 . 2 3 |

3 . 3 7 |

2 . 8 0 |

2 . 7 8 |



- 89 -

Coluan Settling Analysis

of Coluan : Circular Bav Hater Turbiuxty : 30 NTU

Depth : 100 cm Aluia Concentration : 28 ag/1

Factor : 0.17b

i m e

(h)

1 . 0 0

2 . 0 0

3 . 0 0

4 . 0 0

5 . 0 0

fa.00

7 . 0 0

8 . 0 0

8 . 4 8

E f f e c t i v e h e i y n t

( c a )

9 9 . 7

9 9 . 4

9 9 . 1

9 8 . 8

9 8 . 5

9 8 . 2

9 7 . 9

9 7 . o

1 9 7 . 3

E f f l u e n t T u r o i d i t y

(NTU) i

1 2 . 0

1 0 . 0

9 . 3

b . 4

7 . 9

7 . b

7.1*

7 . 2

1 7 . 0

* T u m i d i t y |

R e a o v a i

6 0 . 0 0

b o . o 7

b 9 . 0 0

7 2 . 0 0

7 3 . b b

7 4 . b b

7 5 . 3 3

i

: 7 b . 0 0

0 7 b . b 7

O v e r f l o w

i t a t e ( A / a )

2 3 . 9 3

1 1 . 9 3

7 . 9 3

5 . 9 J

4 . 7 3

J . 9 3

3 . 3 b

2 . 9 3

2 . 7 5

I

I : 1 »

i

I



I

APPENDIX D

PLENUM DESIGN

Q



- 91 -

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RE D 1 : T o S now t h e D x a e n s x o n s o r t h e P i e n u a i

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XI 12 A3 X4 15



- 92 -

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Using LEAST SÔAiiiiS tUKTUQD t o f i n d t h e C o r r e l a t i o n

P a c t o r F o r V a r i o u s C olu mn S e t t l i n g D e p t h s

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2

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2

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1 1 (y ^c m ) i l l l |

I I 1 1 1 1 1

I I 1 1 1 I I

| | 2 . 6 | 1 0 . 0 | 7 . 8 4 | 1 0 0 . 0 | 2 8 . 0 |

I I

i i i

I I

I I 1 1 1 I I

| | 1 . 5 | J0 .O 1 2 .2 5 | 9 0 0 .0 I 4 5 .0 I

I I 1 1 1 1 1

| | 1 . 2 | 5 2 . 5 | 1 . 4 4 | 2 7 5 6 . 2 5 | 6 J . 0 |

t i i i i i t

l l 1 1 1 I I

| | 0 . 5 | 7 2 . 0 | 0 . 2 5 | 5 1 6 4 . 0 0 | 3 b . 0 |

l l i i I i i

I I I I l

l

1

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I I

i i

I I

i

1 1 1 1 1 I - r

| S u m | 6 . 1 7 5 | 2 D 4 . 5 | 1 1 . 6 1 1 | 1 6 9 4 0 . 2 S | 1 6 y . 5 |

T h e r e f o r e ,

S . F . = 2 .

7 0 1 4 - 0 .

0 2 7 7 2 h c

O



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TABLE K1-4

U s i a y L EA ST sgO AU iiS HiiTHOb t o f i a a t h e C o r r e l a t i o n

F a c t o r J*or V a r i o u s C olu m n S e t t l i n g D e p t h s

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S . F .

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4 5 . 0 |

6 3 . 0 |

3 6 . 0 |

1 7 . 5 |

1 b y . 5 |

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