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LIBRARY INTERNATIONAL REFERENCE'.'CENTRE
FORCOMMUNITY WATER SUPPLY. AND SANITATION (IRQ
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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^— , ^ _ r ^ 1983 CENTRE FOR CDI.-inUX'iTV WATSR SL;?:'J: .V AND SAr^lATiOM {KG; P.O. Enx 93190, 2L.C3 AJ '.v.3 •! >c>~ Va!. (O'/O) 3!43':': sxt ••/r./.".<J?.
i :t
ACKNOWLEDGEMENTS
The author wishes to express his profound gratitude to Professor N.C. Thanh for h .s guidance, invaluable suggestions and friendly discussions throughout the course of this research.
Sincere thanks are extended to Dr. B.N. Lohani and Dr. S. Vigneswaran for serving as the committee members. Credits should also go to the Directors and the Deputy Directors of the Bang Khen Water Treatment Plant for providing such an excellent facility and friendly cooperation. Many thanks to the staff in the Plant for their understanding and cooperation during the course of experimentation.
Much appreciation is addressed to the staff of the Environmental Engineering Division for providing all assistance to make the experiment possible. Thanks also to my friends in the Division for their aids.
The author is extremely grateful to AIT and The King's (Royal Thai Government) Scholarship for providing the financial assistance during his stay in AIT.
Last but not least, this research is delicated to his parents for their endless encouragement and patience throughout the study.
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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 flocculated water at various turbidity ranges and flow rates. Experimental results reviewed that addition of polyelectrolytes does not impart significant effect upon the settling efficiency. If 80% of removal efficiency is acceptable as the design criteria, then the overflow rates of 12.75 m3/m d and 18.50 m3/m2d 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 m3/m2d 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 m3/m2d 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. Empirical 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.
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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 (hQ = 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
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LIST OF SYMBOLS (CONT'D)
U Velocity in x direction
V^ Displacement velocity
VQ Overflow rate
Vs Settling velocity
V Velocity of particle in x direction
Vpy Velocity of particle in y direction
Vsc Critical overflow rate
x x coordinate
X Distance across the plenum length s y y coordinate
Greek Symbols
8 Angle of inclination to horizontal
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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
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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
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28 28
33 33 33 42 46 47
52
52 52 52 53 54 56
57
59
60
64
68
83
90
97
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I INTRODUCTION
1.1 General !
The thirst of civilized man is unsatisfiable. The more sophisticated he becomes the thirstier he seems to be. In the so-called developing countries 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 living 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 hazardous 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 Coverage f o r Dr in ic ing-Water Supply i n Deve lop ing C o u n t r i e s , 1970-1980*
i 1 1 1 1
JYear | 197U | 1975 | 1980 | I 1 1 1 1 1 1 1 j |Population|Percentage|Population j Percentage|Population(Percentage| | |Served (in|ol Total |Served (in|of Total |Served (in|of Total \ | |aillion) |Population|iailnon) |Population!million) |Population|
I 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 | 49b | 29 | 763 | 38 | 995 | 43 | i L — 1 1 » 1 1 _ i
»WH0 (1981) lUni teu N a t i o n s Document A/35/150) F i g u r e s do 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 .
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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 adoption 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 settlements.
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 coagulation 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 upgrading 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
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tube settler make it essential to develop design criteria for the clarification of tropical turbid waters.
In the developing countries where resources are scarce, therefore seeking toward appropriate technology which could lead to a cost-effective system, for water treatment is of prime importance. In Asian Institute of Technology, 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.
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(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 m3/m2-d);
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TABLE 1-2 Past Researches oa Inclined Tube Settler Undertaken at The Asian institute of Tecnnoiogy, BangKO/c, Tnailand.
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|Author j
IAMIN 1(197a) |
ILIEHG- | |CHARE-IHNS1T 1(1975)
(VASANA-|DILOKL-| |ERT |(197b)
|CHEN I (1979)
|PANNE-|ERSEL-|VAtt I (1962)
_. ., , Description or Research |
Aia: To evaluate tne performance | of horizontal tuDe settler;
Source: A.I.T. jclong's water; Tumidity: JO - yS wTU. |
Aim: Application of oanouo and | corrugated asbestos AS tune settlers; |
Source: A.I.T. k l o n u ^ water; Tumidity: 10u - 140 NTU.
Aim: Practical application or baa»boo tube settler in | water treatment plant;
Source: Cnao Enya iiiver; Tumidity: 60 - 72 WTO. j
Aiiu: Developed aesign criteria for inclined tune settler and plenua;
Source: Synthetic water; Tumidity: 20 - 1OU NTU.
Aim: To! study tne performance of inclined tuoe settler, relative lenytn of lb ana b = t>0 degrees;
Source: Syntnetic water; [Tumidity: 50 - IbU NTU.
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Conclusions of researcn I
Effective in the turbidity | removal and continuous I sludge removal is achieved. | Tube settler gave comparaolel efficiency wnen compared to | upflow contact basin but it I has shorter detention time. |
80 % efficiency acnieved I with length of 120 ca and | Vsc or 8 m3/iB* d. Angle | of inclination of 60 deg. | was tae best. Corrugated I asoestos tune settler gave | better performance tnan | baoiboo settler but it cost | more. [
i r
Re&ovai etficiency of 93.8% I was acnieved with tube | length 12ocui, dia. 6.3 cm, | Vsc of 2.5 a V n i d at | 9=45 deg.. Cost of bamboo | 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 economical value tor | square tuDe. ttatheaatical | formulations were developed | tor tne etficiency or the | tune system and tne plenua | design was investigated. |
r Recounnended overtlow rate | and flow velocity of 4 | m-Via* d and 4 n J/u i h | respectively. Column | settling can provide scale- |
[ up for tne p n o t scale tube | settler system. A safety | tactor of 2 was applicable. |
| Plenum design was also | investigated. |
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influent raw turbidity (25 NTU to 45 NTU); flow velocities (2 m3/ra2-h to 8 m3/m2-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 specific 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.
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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 suspended 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 /m2-h, and overflow rate of 27 m3/m2-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 longitudinal, horizontal or vertical baffles in the basin.
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HAZEN and CULP (1967) reported that longitudinal flow through the tubes with diameter of few inches offered theoretically optimum hydraulic conditions 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 m3/m2-h compared with 2.45 m3/m2-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 equation for overflow rate developed by YAO in 1973. From CHEN model, he recommended that the relative length of 14.9 and the flow rate should keep below 10.7 m3/m2-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:
VSC/VQ = Sc/(Sin6 + LCosO) (2.1)
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where L is the relative length,
Vsc is the overflow rate,((^A ' '
V0 is the average flow velocity,
Sc 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 Sc 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 Sc for each case to be 4/3, 1, 11/8, and 1, respectively. Therefore, in chosing the tube shape, the following criteria 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 fulfilling 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 the1 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 velocities 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.
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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 settling performance and its consequence depends very much upon the characteristics 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 m3/m2-d can be used. WILLIS (1978) specified the maximum overflow rate value has varied from 3.6 m3/m2-d to 16 m3/m2-d based upon the tube end area. AMIN (1974) recommended that the overflow rate should not exceed 13 ra3/m2-d while PANNEERSELVAM (1982) concluded that the overflow rate of 4 m3/m2-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 experimental 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 capacity 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 m3/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.
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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 submerged water jets, module agitation or air scrubber. It was recommended that the loading should not exceed 3 m /m2-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 distribution of suspension under the tube and rapid growth of algae during Summer time.
, Tubes have also been used for secondary clarification in trickling filter plant, for example in the Philomath, Oregon Sewage Treatment 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.
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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 concentration 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 m3/m2-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 supplement solids separation so that the filter may continue to operate efficiently even during severe upset of secondary plant. Data published show that such system continuous to operate efficiently even with secondary 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 clarification 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 designed rate of the parallel conventional units, while producing an average effluent of 0.5 unit. The installation of tubes in the conventional units permits a more than doubling of the clarifier capacity.
- 12 -
•ftssayt*.
Fig. 2.1 - Installation of Steeplyo 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 m3/d to 170,325 m3/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 m3/min to 7.57 m3/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 /m2-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 possible 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 overflow 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 Author | N a t u r e of Water | haw Viater T u r o i d i t y | Depth | S a f e t y Fac te I I 1 (NTU) | (cm) |
| YAO | N a t u r a l Baw | 100 - 280 | 7b | 2 . 0 | (197y) | H a t e r | (May-Sept) | |
| | I 14 - 70 | 78 | 2 . 0 I 1 1 (Sept-Nov) I |
| | U n c o a g u l a t e d | I | | | S y n t h e t x c | 100 - 280 | 78 | 2 . 0 | | Haw Mater | | |
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(1982) | Ka 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 discharge, 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 suspended 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. = vPy = -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-ySin 8 + Vs x Cos 8 = C (3.4)
where
<-'' C' is the integral constant
Dividing equation (3.4) with Vo, the average flow velocity, and d, the depth of the flow measured normal to the direction of flow.
'vb ' dy • If ' Y * sia 8 + H ' x ' Cos 9 = cl (3'5)
o
- 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 conditions,
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 » ( / £ • dy) 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 velocity, 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 (m3/m2-d), then C - 14.4.
- 18 -
e . ANGLE OF INCLINATION OF HIGH-RATE SETTLER
,,i 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, coalescence 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 applicability 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
MT- UB*. ARY
For practical operation, CHEN recommended that ho should be maintained equal to Co«Qo in which Co = 3.1 s/m2 and Q is in terms of m3 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 requirements 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 m3/d and by the year of 2000, the production will escalate to 4,800,000 m3/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-effectiveness 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 cm2. Figure .-42 l/i gives the detailed dimensions of the unit.
• • •: l - i "
- 23 -
TABLE 4 . 1 Haw wa te r Q u 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 t o J a n u a r y 1983 )
,,_ ... _. .__ . ., 1 . . . , | . Parameter , | Range of value (ppnt) I i * i i ITurbidity (NTD) | 1 7 - 6 0 |
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 | 8 4 - 9 0 |
|Chloride las Chlorine | 1 2 - 1 4 |
|Free Ain&onia - N | 0.074 - 0.207 |
|Ni t ra te - N | tfIL |
l a i t r i t e 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 WO
_> < 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 facilitate ease of replacing the plenum bundle of different settling depths. The plenum bundle is provided with a clear PVC window to facilitate measurement 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 5m. A total detention time is about 100 minutes with approximately 13 minutes detention time provided under the recirculation cone. The loading rate is about 95 m /m2-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 measurements 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 apparatus:. 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 coagulation and flocculation take place. The flocculated water was then introduced 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 terminated 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 experiment 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 suspension. 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«
-46
Sludge Oroin Pipe
PLAN
ft* [—15—f-15—
Outlet 2oie 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 cm2
—I S J-
<
— 55 EFTLUENT LAUNDER
(SECTION B-B)
NOT TO SCALE ALL DIMENSIONS ARE IN cm
FIG.4.2- DETAILS OF INCLINED TUBE SETTLER.
Al-T. LlBRARY
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 discussion 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, respectively. Table Al-1 also illustrates that if the flocculation and sedimentation 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 concentration 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 efficiency than those of lower turbidity.
- 29 -
3 1 -<£. lO CM
ity
T l
urbi
0>
E F o> c
ttl
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 (OIN) Aijpsqjnilonpisay
CM CM
- 30 -
100
9 0 -
^ 8 0 ->» u c
.2? *o £ 7 0 UJ
6 0 -
50
-
-
"•• 1 1 1
^**^o > v
25 - 37 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 20 25
Overflow Rate , (m3/m2- d)
Fig; 5 . 2 - Effect of Overflow Rate on Efficiency
30 35
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 criteria is to safeguard the filter system from overloading. From the graph, at optimum alum dose of 28 mg/Jl, overflow rate of 8.75 m3/m2-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 m3/m2-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 |PANtlr.iiE- | P r e s e n t | fiate ( T u r o m x t y | | lLGKL£r.T | |S£LVatt ( S t u d y | ( a J / m ^ a) i (tj'rii") | ( l y 7 j ) | ( l yVb) | ( 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 |b5 .0u*> | - | 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 % |ba .50 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 ftdw rfater 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 m3/m2-d for raw water turbidity of 25-37 NTU and 18.5 m3/m2-d for raw water turbidity of 36-47 NTU can be used within the limits of experimental conditions.
If effluent quality of 5 NTU is insisted, then the overflow rate of 8.75 m3/m2i-d and 8.5 m3/m2-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 /m2-d is recommended for raw water turbidity range of 25-37 NTU.
Table; 5.2 shows the practical operational overflow rates for most experimental conditions.
TABLE 5.2 The Perrormance of the Inclined Tube b'ettier at Various overflow Kates, Alua Dose, ana Raw Water Turbidity
T 1
Effluent | yuaiity J (MTU) J
|Haw Water I T u m i d i t y | (NTO)
£J.UIU D o s e
(31U/1)
u v e r i l o w fiate
(la^/m* a)
E f f i c i e n c y
A
| 25 -37 I
J | 3b -45
2^
2b
b .00
d .OU b . 7 5
ti3 .00
b4 .30 bJ .b0
5 . 0
4.8 5.0
I
I 125-37 I
a .i>0 bb . 5 0 5 . 0
no 12 .75 oO .00 7 . 9
J36-45 32 la .50 dO .0u d . d
Since the removal efficiency i s a function of overflow r a t e (for a l l other parameters are f ixed) , a regression analysis was used to produce formulations which f i t best for the experimental data obtained for removal efficiency and overflow r a t e .
For raw water tu rb id i 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 efficiency 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 settling. 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 m3/m2-h, 2 m3/m2-h, 4 m3/m2-h, 6 m3/m2-h, and 8 m3/m2-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 reviews 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 /m2-h and 5.43 m3/m2-h are recommended for raw water turbidity of 25-37 NTU and 36-45 NTU, respectively under the optimum alum dose. If to comply with the effluent requirement of 5 NTU, the flow velocity of 2.67 m3/m2-h and 2.55 m3/m2-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 empirical 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 Velocity,(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
44
u | 4 . 3 "3 i t
4.2
4.1-
0,
o In E = 4.55008 - 0.00873 V, sc
A In E = 4.52993-0.01140 V, sc
D 5 10 15 20 25 Flow Velocity,(m/h)
Fig. 5.5 — In ( Efficiency) vs Overflow Rote
30 35
- 35 -
TAESLE 5-J
iJr<ri"<=iit. ; t u u y rtj.tii t-iiji.i£,2.i<JciL7.'ii.J
1 •
| V e l o c i t y
|P<itfN£LSii
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 Turo ia 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
~1 itl
1 1 / ' j .< .
4 b ;<!'
1 I ~
._ ,.. i *^
U
1 I
u
I 1
. 6
7z
b J
—
-
r • -
I fa.O
| -
| —
1 1 7 o .
1 | bO.
— i
. d
. 4
r •
d . U
b b
7y
l | o b
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 m3/m2-h, 6 m3/m2-h and 8 m3/m2-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 = 3.2m/h
V = 8 m/h V = 6 m / h
8 24 12 16 20 Operation Time,(hour)
Fig. 5.6 - Efficiency vs Operation Time for Plenum Design
28
12
A Velocity 8.0 m/h
D Velocity 6.0 m/h
o Velocity 3.2 m/h
2 -
8 12 16 20 24 Distance across the Plenum Length (cm)
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 Deptn A t t t r o r iours of Co t t t i nuous u p e r a t i o n a t Var ious V e l o c i t i e s
1 • — i
Siuuge Deptn Alter b Hours of Operation (est)
|P low | Flow V e l o c i t y I ( 1 / m i a ) | (%J/ia^ a) I
X I X2 X3 X4 X5
| 8 . 0 0 I
3 . 2 2.b5 2.bU 3.0U 3 .55 5 .65
| 1 5 . 0 6 . U 4.30 a . 6 5 7 . 9 0 9 . 2 0
| 2 0 . 0 8 . 0 4.o5 5 .10 5 . y o 8 . 9 0 10.45
depth as a func t ion of time and the flow v e l o c i t y . F i g . 5.9 i l l u s t r a t e s the regressed va lues of In (Sludge Depth) ve rsus In ( V e l o c i t y ) .
For 8 hours of ope ra t ion and for t u r b i d i t y range of 36-40 NTU,
h s , x = 0 (cm) = 1.28499 x V0 i 5 8 9 1 7
0.68808 h s , x = 32 (cm) = 2.57147 x V
where h s , x = 0 i s the s e t t l e d s ludge depth a t x = 0 cm,
h s , x = 32 i s the s e t t l e d s ludge depth a t x = 32 cm.
For t hour of o p e r a t i o n , Table E l -2 (Appendix E) confirms 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) = 2.57147 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 0-57992
(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 Plenum Deptn A c r o s s t n e Pieuuiu Widtn t o r V a r i o u s Flow V e l o c i t y
Raw Water ' 1 ' y ro i a i t y t l t uu iu b u n a i e ll££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 Velcci / * * • 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
XM
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 accordance 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 . 293.6 V 0 5 7 " 2
^ X( = 0 cm
o X5 = 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
Comparison or trie T o t a i t ienum Deptn u o u i n e a oy PArJ;jKc;iii;iiLVi»i*. ana t n e t -Lesent S tuay
P a r a m e t e r ~t 1 ~»
| ^t-AKNESftSLLVaa C P r f e s e a t S tudy
Capac i ty (:nVa) 1000 1000
Flow V e l o c i t y ( u - V ^ a)
a ( Wititn i n ca ) 320 320
Lp ( plenum l e n c t i i iu CM ) l o o 100
t ( f requency or aesiua<jfc ) 2 d a y s 2 d a y s H
T o t a l plenum 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 ^ 133 .d7*
»Hx=0 (ca) = 0-b77 x v 0 - 0 7 ^ (t:/10) (32/Lp) (a /33) + ho 2Hx=Lp (cm) = 0 .979 x V*. o j r * ( t / 1 0 ) (3^/Lp) ( a /33
• 0 i = O ( 1 - X / L p ) ° ' J
*Hx=0 (cm) = 1.26499 x V ° - 6 i 4 1 ? ( t / o j (32/Lp) ( a / J j ) + 1 4 . 9 2 . I S x V° -» ; i S , / *
•tfx=Lp {coil - 2 .57147 x v o . o a a o a ( t / t i ) (32/Lp) ( a / j 3 ) + 4 .2931o x l f ° - s ^ ^
5 S y n t n « t i c «aw w a t e r #as Useu •"Natural ndv water «4as Usea
which contributed to the above differences. F i r s t l y , PANNEERSELVAM conducted the experiment based on 10 hours of operat ion, and during that 10 hours period, three different flow ve loc i t i e s were used and toward the t rans i t ional point for each ve loc i ty , the s e t t l ed sludge depths at entrance and at x = 3/4 I along the plenum length were measured. But the f inal equations arrived at by him for the s e t t l ed sludge deaths, i . e .
hx = 0 : (cm) - 0.8770 x V '&?2 ( t /10)(32/Lp)(a/33) (5.13)
hx - Lp1 (cm) - 0.9792 x y 1 * 0 7 2 ( t /10)(32/Lp)(a/33) (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)
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 processed and transformed into the respective overflow rate and percent of turbidity removal. For all the experimental runs, optimum alum concentration of 28 mg/I was used.
Fig. 5.11 shows the plot of percent turbidity removal versus the overflow 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 indicates 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 comparison of the results obtained from the column settling and the tube settler. 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
TAELL 3 . 7
TAOLL 5 . 6
- 44 -
E t r e c t or i t r t t i i n o L»tv.-T.ii Upon Upon t i u Cof . rexu n o : ; F a c t o r
i 1 — 1
| ; i c t t i i n o Drfpta | C o r r e l a t i o n i ' a c t c c I (CJIJ |
10 .U
jO.O
5 2 . 0
7 2 . u
l u u . u
2 , b
!C*b
1 . i i
0 . 5
u . 175
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 cy Coiu.un S « t t l i r . y t o t , i c Ttiue 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 .er |:Xarf ( i c t c l I'UX 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.aj | |
| YAO | :i.. t a r u i :•;.». w j luO - i b u | / o | 2 . 0 | | (1^7^) | •.•iutdC | l a ^ y - o t u t ) | | |
| | | m - 70 | 7c | 2.0 | I I 1 i ^ e p t - r . o v ) I | |
| I Jnc:)ni_;ui^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 PA^MlLL-t-| i ; n t ; i c t i c I l e u | l u o | 1.0 J | S^LVJ^i | i i o c c u i c a j a I 1<.0 | lOo | 1.4 | | ( V . ' u ; ) | t a t . e e 1 ou | 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 Jb 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 100 | 0 . 1 7 5 |
3.0 - 45 -
U.
o a
o
0
I i o Experimental Value
SF = 2.7014 - 0.0277 h„
I
A Regressed Value
D 20 40 60 80 100
Settling Column Depth,(hc= cm)
Fig. 5.12 - Safety Factor vs Settling Column Depth
120 140
X 90 >» o c a> o UJ
85-
80
1 1
; V \ O
i i
l I
!*-C^^-^o
i i
I 1
Column
o 10 cm Square
o 10 cm Circular
o
I .. i
-
-
0 4 8 12 16 20 24 28 Overflow Rate, (m 3 /m^ d)
Fig. 5.13 — Efficiency vs Overflow Rate for Square & Circular Column
- 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 flocculated 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 overflow 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 occasionally 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 impossible 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 directly 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 m3/m2-d or flow velocity of 2.43 m3/m2-h can be used.
TABLE 5 .9 Design TdDie I n d i c a t e s t n e aecodiiflendeu Va lues t o r Overf low Hate and flow V e l o c i t y and 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 are the design table which can be used to calculate the to t a l number of tubes required for flow veloci ty at 2.43 m3/m2-h and 3.87 m3/m2-h respect ively . Table 5.12 aAvl Table 5.13 indicate the to ta l plenum depths needed for various frequencies of desludging and plenum lengths.
EXAMPLE; A tube s e t t l e r system i s to be designed to serve a population of 10,000 people with per capita consumption of water amount to 100 X./c»d. The influent tu rb id i ty i s around 25 NTU to 40 NTU and i t i s preferable that the c l a r i f i ed water should not be more than 5 NTU.
- 48 - O
TABLE 5.10' Design Table for Tne To ta l Nuaioer of Tunes Required
Flow Velocity Probaole Efflueat Haw Hater Turbidity Temperature Operation period
= 2.4 3 m-»/ia2 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 , 6D0 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 o1,/J0 92,b00 12J,460 154,J30
100,000 34,300 oo,5y0 102,b90 137, 160 171,470
O
- 49 -
TABLE 5 .11 Des ign Tao le roc The T o t a l Numoer of Tunes Hequ i red
Flow 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 Tempera tu re O p e r a t i o n p e n o a
3 .87 a - y ^ a o . 1 - b . 7 NTU 2 5 - 4 5 MTU 27 - 33 °C 24 Hours
Alum Oose Angle Tuoe iengtn Tune Size
2 2 - j 2 a g / l o0° 0 . 9 in 0 . 5 c a 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 00 ;
I 5o,uoo:
| 6 0 , 0 u 0 |
| 7 0 , 0 0 0
| b 0 , O U O
I yo,uuO
1100,ouo
" -P e r
5 0
*., 160
4 , 3 1 0
b , 4 b 0
b , o 2 0
1 0 , 7 7 0
1zI,!:>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 20
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 , 140
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 , 140
9 o , 9 0 0
1 0 7 , 6 7 0
i
• 1
i I
- 50 -
TABLE 5 .12 Design T a b l e f o r t n e T o t a l Plenum Depths
Plow 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 Water 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 Tube Wiath (a) = 4 in
Alum Dose = 2 2 - 3 2 m g / l Angle = 60° 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^auui Length ( Lp (m) ) | i i 1 i i i i 1 IFreguency of | 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 (day) I 1 1 1 1 1 1
| 1 | Mlx = 0 I 0 .70 | 0 . 4 3 | 0 .34 | 0 . 3 0 l 0 . 2 b | | , | *HX=Lp | l . l b | 0 . b 2 | 0 .44 | 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 | 1.23 | 0 . 70 J 0 . 5 2 | 0 . 4 4 | 0 . 3 5 j | | Hx=Lp | 2 .28 | 1.1b | O.bl l 0 . 6 2 | 0 . 4 4 |
| 3 ' | Ux=0 | 1.75 | 0 .9o | 0 . 7 0 | 0 . 5 7 | 0 . 4 3 | | I | Hx = Lp | J . J b | 1.73 | 1.11 | 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.bb | 0 . 7 0 | 0 . 5 2 | | | Hx = Lp | 4 . 4 * | 2 . 2 b | 1.55 | l . l b J 0 .B1 J i ' i i i i i < i
*rix = 0 \:a) - t o t a l plenum aepcn a t e n t r a n c e 2 h x = L ; (m) t o t a i pienuni a e p t n a t a i n s t a n c e x = Lp
- 51 -
TA.ELE 5 .13 Des ign T a b l e t o e t n e 1'ocdi Plenum Ucp tns
Flow 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 Water T u r o i u i t y Tempera tu re Tube H i a t a (a)
3 . 6 / i V i 2 h 6 . 1 - b . 7 KU 25 - 45 STU 27 - J j °C 4 ai
Alum Dose aiiylfe 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 Plenuni Lenqtn ( Lp (m) ) I i i 1 i i i i
| F r e q u e n c / ot| Symbol 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 (aay) | | | l | |
I 1 | 1rix=0 | O.dy | 0 . 5 3 | 0 . 4 ^ | 0 . 3 6 | 0 . 3 0 ' J | 2Hx=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 .14 | 1.62 | 1.11 | 0 . 7 6 | 0 . 5 1
| 3 1 Hx=0 | 2 .31 | 1.25 l 0 .09 | 0 . 7 1 | 0 . 5 3 | | Hx=Lp 1 4 . 6 5 | 2 . 3 7 | 1.62 | 1.24 | 0 . 8 5
| 4 | Hx=0 | 3 .02 1 1.60 | 1.13 | 0 . 8 9 | 0 . 6 5 | | Hx = Lp | b . 1 7 | 3 . 1 J j i2.12 | 1.o2 | 1.10 i ; 1 1 1 1 — ' 1 _ L
»Hx = 0 (!) *tix = Lp (a.)
t o t a l plenum d e p t h a t e n t r a n c e t o t a l plenum d e p t n a t a a i s ^ n c e x = Lp
SOLUTION: From Table 5 .9 , flow veloci ty of 2.43 m3/m2-h wi l l provide an effluent qual i ty of 5 NTU. For th i s flow ve loc i ty , Table 5.10 gives the t o t a l number of tubes required, i . e . 6,860 (tube d i mensions: 5 cm x 5 cm x 90 cm).
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%.
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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, economical 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) (m3/h)
62.5 m3/h
I
o
- 53 -
TASL£ 6.;1 ChecK List (1yd2 - lybJ bangKok's Market Price)
1 _ , - . . - . . . . , .__. . . — — . _. _ —,
I Itttoi j Cos t (Tnai ban t ) j
| C o n c r e t e [ 1,025 b a n t / a 3 [ | For'is WOEK | 25 Baht/.s< ! [ J Plywood (u mm) | yo b a h t / a ^ | | S t e e l | y baht/Kvj |
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 m3
= 4 m + 1 m (free board)
= 125/4
= 31.25 m2
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 m3/h
W = 1.56 m2
W = 1.6 m2
- 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 m2, 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 m3
Unit cost of concrete + labour =» 1,025 Baht/m3
Total cost of concrete + labour = 50,840 Baht ,
Steel reinforcement = 50 kg/m3 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) Contigency 10% =« 8,396 Baht
• 2,480 kg
= 9 Baht/kg I
= 22,320 Baht
= (20 x 5) x ^ + (1 .6 x 5) x 4
- 432 m2
= 25 Baht / j i 2
" 10,800 Baht
= 50,840 + 22,320 + 10,800 (Baht)
= 83,960 Baht
= P (c r f ) (HARBOLD, 1980)
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 m3/n.
= 3.87 m/h
= 62.5/3.87 (m2)
- 16.15 m2
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 frequency 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 m2
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 m3 , 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 m2 (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%, therefore 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 conventional 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 significant 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, maximum overflow rate of 8.75 m3/m2-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 performing at the 'economic' alum" dose and at 8 m /m2-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 m3/m2-d and 18.5 m3/m2-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 efficiency (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 m3/m2-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 accumulated 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 (m3/m2-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 +hx = 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 = 1.28499V0,63917 (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 m3/m2-h, respectively. To comply with the effluent requirement of 5 NTU working under optimum alum dose, then velocity of 2.67 m3/m2-h should be used for raw water turbidity of 25-37 NTU.
(9) From the experimental observation, it is recommended that submerged 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 baffles, it appears possible to achieve activated sludge solids separation and return without a secondary clarifier structure, therefore the economic 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 deteriorate the effluent quality while cleaning on daily basis does not substantially deteriorate the effluent quality. To justify the above recommendation, 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 -
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.i
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i
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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 Treatment 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.
^WILLIS, 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, Switzerland.
"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 Technology, 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 Alum 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 ( J a r Number
• I 1
h + I 2
H I 3 I 5
+ I
+ -i lAlua Concent ra t ion (ag/1) J 14.0 |18-0 | 2 2 . 0 J26.0 |2d.O | 3 0 . 0 | I 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 Turb id i ty : 56 NT0 Optiiaua Alum Concen t ra t ion : 34 » g / l
| J a r Nuaoer I 1 1 2 h + +
I 1 _,
I 5
+ I <> I
+ H |Alua Concen t ra t 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 Number
I 2 I
H + 4 I
h I
+ | P o l y e l e c t r o l y t e (ag /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-00031
+ + + + + + + •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 | 20.0 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 5.7 5.5 4.9 4.7 5.1
|Jar number
H — |Alum Concentration (mg/1)
I »
22.0 | 22.0 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 To 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 on C o a g u l a t i o n and . P l o c c u l a t i o n P r o c e s s
Raw Mater T u r b i d i t y : 31 NTO
I . - . | J a r Hunber • i |A1UIB 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 • 1 |PAC 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
(uig/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 l
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 Tumidity: 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 Turoidi ty \
(NTU)
29 i
2 9
2 9
2 9
2 9
3 3
3 5
2 7
2b
2B
I 2b
1 27
. . . . _ , F loccu la ted
Hater | (N TO)
1 9
1b
1 7
I d
IB
1 7
l b
1 6
1b
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
i i f fxc iency
70 .69
74 .14
7b. 90
B1-04
62.14
B7.27
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
I
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 Tumidity: 4.5 NTU Flow Velocity :2.0 u/ii Average Eifxcxency : 86.72 % Overflow Rate : 6.70 IB3/"* 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 ; Water T u r b i d x t y
(NTO)
32
32
29
37
33
36
36
32
37
f l o c c u l a t e s Water (tfTU)
1 7
1b
20
2 1
20
2 1
2 1
l l b
17
• • • — 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 I 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 . 28
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 Tea > 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 a3/ia^ d Alua Concentration : 28 og/1
1 " 1 " •;•- - t i , . . . . . . „ _ . , ,
|Operating | aaw Water JPlocculatea [Eifluent |Efficiency JTeaperature| | Time | Turbidity | Water | Tumidity | | | 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 | .27 | 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 Tumidity: 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
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
•
Raw R a t e r T u r b i d i t y
(NTU)
33
33
29
29
3 2
1 37
', 30
: J 2
i
F l o c c u l a t e d Water (MTO)
2 7
30
19
1 9 . 5
20
2 2
2 1
28
i
fiffiuent 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 . 5o
8 1 . 0 6
7 4 . 6 7
7 7 . 5 0
T e m p e r a t u r t
27
27
2b
28
2 b
29
29
29
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 | | Txae J ' furoxdxty | Water 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 | 27 | 13 I 7 . 2 | 7 3 . 3 3 J 3 0 | 1 1 1 1 I i I | 2 1 2b | 21 | . 7 . 1 | 7 2 . 7 0 | 30 | i i i I I t 1 I 3 l 28 | 19 < a . 9 | b d . 2 1 J 30 | i l l I I i i | 4 | 27 | 2 5 | b . 7 | b 7 . 7 8 | 30 j I I I I I i 1 | 5 | , 30 | 2b | y .O | 7 0 . 0 0 | 30 | i l l i i i l 1 - • — 1 I I i l 1 1 6 1 28 t 20 | o . 9 | b 8 . 2 l | 29 f
t 7 J 28 | 20 t 9 . 0 | | 6 8 . 8 b | 29 | I I I | i 1 i | 8 | j 27 | 2 5 | b . b | O b 7 . 4 l | 28 | • 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 of t n e Tur>e S e t t l e r a t Econoaxca l Alua d o s e
Flow : fa.O 1 / i i D Average E f f l u e n t TurDx 'd i ty : 4 . 8 5 NTU Flow V e l o c i t y : 2-4 a / a Average E f f i c i e n c y : 8 7 . 1 9 i Overflow B a t e : 8 . 0 3 inVffl2 d Alua 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 | Txae
( 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
3d
3 o
3b
3 7
1 37
| t Jb
l— " 1 F l o c c u l a t e d
Mater (H TO)
1 5
l b
l b
1 9
14
1 4
1 7
2 2
i 2 3
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
6o . 5 b
6 6 . J 3
6 7 . 2 2
8 6 . 4 9
8 7 . 3 0
6 7 . 2 2
i — - •
T e m p e r a t u r e
°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 of t&e Tube S e t t l e r a t Econoiaxcal Alum d o s e
Plow : 8 .0 1 / a i n Average E f f l u e n t TurbiaLxty: 6 .40 NTO Flow V e l o c i t y : 3 .2 a / a Average E f f i c i e n c y : 8 1 . 4 5 % Overf low S a t e : 1 0 . 7 0 I D 3 / * * & Alua C o n c e n t r a t i o n : 22 tag/1
f J 1 1 I . . . . . . r . . . . _ ,
( O p e r a t i n g | Raw Water | 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 | Water 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 | 25 | 6 . b | 8 1 . 6 7 | 31 \
| 3 | 3 7 . 5 | 24 I 0 . 8 | 8 1 . 6 7 | 31 |
| 4 | 33 | 29 | 7 . 5 | 7 7 . 2 7 | 31 |
| 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 | 32 |
1 . 8 1 35 | 27 ( 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 a3/a2 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 | Water ( 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 | 3b | 25 I 9 . 2 I 74 .44 I 30 |
( 4 I 35 ( 18 | b . 9 | 7 4 . 5 7 I 30 |
( 5 | 34 | 23 | 8 . 7 | 7 4 . 4 1 | 30 |
| 6 I 35 [ 2 0 | 6 . 3 I 7 b . 2 1 | 30 |
| 7 | 3b | 29 | b . 2 | 77 .22 ( 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
(NT0) |
37 |
13 |
: 4 1 !
bO |
4 1 |
, 38 |
; 37 |
: 39 |
| 42 ,
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)
, 26 |
28 |
2 9 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
T e m p e r a t u r e 1
°C |
33 |
33 |
33 |
3 2 |
3 2 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 a3/»* 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
I 4
| 5
I b
I 7
I y
I 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 40 j 1 1 36 | j
I 45 i 1 j 40 |
j 39 | i 1 1 35 1 I | 40 | ! ^ i i | 40 i
..... . _.. , F l o c c u l a t e d
W a t e r (HTU)
2b
2 9
2 9
2 1
2b
2 7
2 b
2 9
2 9
2 7
2d 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
27
27
28
2d
29
29
29
30
30
3 1
3 1 •
I
- 79 -
TABLE B3-3 Perfonance of tue Inclined Tube Settler tor Raw Water Turbxdity of 36 JJTO to 45 NTO
Plow :20.U 1/iain Average Effluent TurDidity: 9.8 NTU Plow Velocity : b.O u/h Average Efficiency : 74.41 % Overflow Rate :2b.7b a^/a^ d Aiua Concentration : 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
32
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 Rate | 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) | ( ag /1 ) J (as / rg i d) | (%) | (STU) | i l l I I i i l l i I l I | | 8 . 03 | 8 7 . 1 9 | 4 . 8 5 | | 25-37 | 22 | 10 .70 | 6 1 . 4 5 | 6 . 40 | | | | l b . 0 b | 7 6 . 6 9 | 8 .20 | i l l I I i I I 1 1 1 t | | | 2 .6d | 8 9 . 6 3 | 2 . 8 0 | | | I b . 7 0 | 8 6 . 7 2 j 4 . 5 0 | | 25-37 | 28 | 13 .36 | 7 9 . 2 4 | 6 .50 | | | | 2 0 . 0 7 | 7 6 . 7 5 | 7 .30 I | | | 2b .7b i b b . 3 3 | 6 . 90 | i l l 1 1 i 1 1 l I 1 t | | | 10.7(J | 6 5 . 7 6 | 5 .80 | | 3b-45 | 32 | 2 0 . 0 7 | 8 0 . 3 b | 7 . 7 0 | | | | 2b .7b | 7 4 . 4 1 1 9 .80 |
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
i - • - • 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
|Baw rfater|Alum Dose |Piow 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) |: ( ag /1) | (m3/i»2 fl) j {%) | (NTO) J
| 1; | 2 .40 | 8 7 .19 | 4 . 8 5 | | 25-37 \\ 22 | 3 .20 | 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 .80 | 8 9 . b 3 | 2 . 8 0 | | |! | 2.U0 | d b . 7 2 | 4 . 5 0 | | 25-37 |! 28 | 4 .00 | 7 9 . 2 4 | b . 5 0 | j li | fa.00 | 7 b . 7 5 | 7 . 3 0 | | | | B.UO | o&.33 | b . 9 0 | i j i l i i | | 1 3 .20 | 8 5 . 7 8 | 5 . 80 | \ 3b-45 |, 32 | o.OO | 8 0 . 3 6 | 7 .70 | | 1 1 8 .00 | 7 4 . 4 1 | 9 .80 |
- 83 -
APPENDIX C
COLUMN SETTLING ANALYSIS
U
TABLE C1-1
- 84 -
Column Settling Analysis
Type of Column : Square Settling Depta : 10 cm Correlation Factor : 2.8
Raw Water Turoidity : 30 STU Alum Concentration : 28 mg/i
1 • 1
ITiae 1 (h)
I 0.10
I 0.17
| 0.25
| 0.50
| 0.75
| 1.00
I 2.00
I 3.00
| 4.00
| 5.00 t 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
TABLE C1-2
- 85 -
Column Settling Analysis
Type of Coluan Settling Depth Correlation Factor
: Circular : 10 cm : 2.8
Baw Water Turoidity : 30 NTO Alua Concentration : 28 ag/i
r — i - - '••• T - - — x 1 r |Time | 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\rerfiow | I (n) | (en) | (MTU) | Reaoval | ttate (a/d) | i i i 1 1 1 | O.lt) | 1 0 . 0 | 5 .0 | 8 3 . 3 3 I 2 4 . 0 0 | I I I 1 1 1 | 0 .17 | 9 . 7 | 4 .0 | 6 6 . o 7 | 13 .90 | I I 1 i l l | 0 . 25 | 9 .a | 3 .6 I 88 .00 | 9 .02 | I I 1 1 1 1 | 0 .50 | 9 . 1 | 3 . 0 | 90 .00 | 4 . 37 | 1 1 1 i l l | 0 .75 | 8 . 8 | 2 .8 | 9 0 . t>7 [ 2 . 8 2 | I I i 1 1 1 | 1 . 0 0 | 8 . 5 | 2 . 6 | 9 1 . 3 3 | 2 . 0 4 | i i l i l l I I 1 I I I | 2 .00 | 8 . 2 | 2 . 3 | 9 2 . 3 3 | 0 .98 | I I 1 1 1 1 | j . 0 0 | 7 . 9 | 2 .1 | 93 .00 | 0 . 63 | • I l 1 1 1 I 1 1 I I I | 4 . 0 0 i 7 . 6 | 1 .7 | 9 4 . 3 3 | 0 . 4 b | I I 1 I I I | 5 .00 | 7 . 3 | 1.5 | 9 5 . 0 0 | 0 . 35 | • l . . . . . . . . . . . X . . . 1 « _ 1
o
TABLE C1-3
- 86 -
O
Colusa Settling Analysis
Type of Coluan j Settling Depth Correlation Factor
: Circular : 30 ca : 1.5
Raw Hater Tumidity : 43 NTO Aiua Coaceatratioa : 28 «g/i
r — — T • • — - i - -, , ,
JTiae 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 jOverf low | I (h) | (ca) | (NTO) | B e a o v a l j t i a t e ( a / d ) |
| 0 . 25 | 3 0 . 0 | 1 1 . 0 | 7 4 . 49 | 2 8 . 8 0 |
| 0 .50 | 2 y . 7 | 7 . 5 | 8 2 . 5 o | 14 .2b |
| 0 . 75 | 2 9 . 4 J b.O I 8 6 . 0 5 | 9 .41 J
| 1.00 | 2 9 . 1 | 5 .0 | 8 9 . 7 7 | 6 . 98 |
J 2 . 00 | 2 8 . b | 3 .9 [ 91 .bb | 3 .4b |
| 3 .00 | 2 8 . 5 I 3 . 3 | 9 2 . 7 9 | 2 . 2 8 |
| 4 .00 | 2 8 . 2 | 2 . 9 5 I 93 .14 \ 1.69 | i i 1 l i t | 5 .00 | 2 7 . 9 | 2 . 6 I 9 3 . 9 5 | 1.34 |
TABLE C1-4
- 87 -
Column Settling Analysis
Type of Column Settling Depta Correlation Factor
Circular 52.5 c» 1.2
Baw Hater Turbidity : 33 MTU Alum Concentration : 28 ag/i
O r - i (Time | 1 (n) 1
| 0.50'
| 0.75
| 1.00
| 2.00
I 3.00
| 4.00
| 5.00
| 6.00
| 7.00
I b.oo
I 9.00
r — -• i
Effective heignt \ (ca) |
52.5
i 1 52.2
51.4 '
51.IJ 1
51.J
51.0
, 50.7
50.14
50.1
I 49.0
[ 49.5
i — - ••' - i
Effluent 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 [ Bate (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 -
TABLE C1-5 Column Settling Analysis
Type of Column Settling Deptn Correlation Factor
: Cxrcuiar : 72.0 cm : 0.5
Raw Water Turbidity : 46 HTU Aiaa Concentration : 28 ing/1
1 - • ' - 1
ITxae 1 (h)
| 0 . 7 0
| 1 . 0 0
I 2 - 0 0
I 2 . 7 0
| 4 . 0 0
| 5 . 0 0
| 6 . 0 0 1 | 7 . 3 3
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)
lfa.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 . o7
6 8 . 3 3
7 3 . J 3
7 5 . U 0
7 6 . 6 7
bO.00
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 -
TABLE C1-6 Coluan Settling Analysis
Type of Coluan : Circular Bav Hater Turbiuxty : 30 NTU Settling Depth : 100 cm Aluia Concentration : 28 ag/1 Correlation Factor : 0.17b
ime (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
bo . 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 ta 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 -
CD
FIGURE D1: To Snow t h e Dxaensxons or t h e Pienuai
Influent Ban Water
-> I 7\ Tuoe Settler
biundie
+-8ca-+-bCia-+-bca-+-faca--«-
XI 12 A3 X4 15
* All dimensions not to scale
- 92 -
Fig. b-i~Tube Bundle ondthe Plenum.
Flow Velocity ,v
Amount of Sludge,
-•
••
•'•
hP
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h 0 l aKQp
K S P ° 0
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Sp op V"
'P°P
hplpQp
SP°P le. h a ' Q
Subscript a denotes actual condition j p refers to present condition.
h0 = ( 'P /
lo ) ( q0 /
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- 93 -
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- 95 -
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APPENDIX E
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TABLE K1-4 Using LEAST S^OAiiiiS tUKTUQD t o f ind the C o r r e l a t i o n Pactor For Various Column S e t t l i n g Depths
| j S e t t l i n g | S.ir". 1 y 2 I X2 | xy | | | Depth 1 (X) | | t | 1 1 (y^cm) i l l l | I I 1 1 1 1 1 I I 1 1 1 I I | | 2 .6 | 10 .0 | 7 . 8 4 | 100.0 | 28 .0 | I I i i i I I I I 1 1 1 I I | | 1.5 | J0.O 1 2 . 2 5 | 900 .0 I 45 .0 I I I 1 1 1 1 1 | | 1.2 | 5 2 . 5 | 1.44 | 2756.25 | 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 | 5164.00 | 3b .0 | l l i i I i i I I I I l l 1 | | 0 .175 | 100.0 | u . J l | 10000.0 | 17 .5 I I I i i I I i 1 1 1 1 1 I - r |Sum| 6 .175 | 2 D 4 . 5 | 11 .611 | 16940 .2S| 16y.5 |
There fore , S .F . = 2 . 7 0 1 4 - 0 . 0 2 7 7 2 h c
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TABLE K1-4 Usiay LEAST sgOAUiiS 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 Column S e t t l i n g Depths
| | S e t t l i n g | JDepth 1 1 (y=rCIB)
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36 .0 |
17 .5 |
1by .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
