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FACULTY OF ENGINEERING

DEPARTMENT OF CHEMICAL AND

METALLURGICAL ENGINEERING

CHEMICAL ENGINEERING LABORATORY

EXPERIMENT: _SEDIMENTATION

Name: MOFOKENG

L.S_____________________________________________________________

Student Number: _211131357___________________________________________________

Group: _5____________________________________________________________

Date Experiment Performed:8/032012__________________________________________

Date Experiment Submitted: _27/03/2012_________________________________________

Submitted to: _MR

Mosesane______________________________________________________

%


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TSHWANEUNIVERSITY OF TECHNOLOGY

DEPARTMENT OF CHEMICAL AND METTALURGICAL ENGINEERING

REPORT GRADING FORM

Name of Student: _MOFOKENG L.S

Student Number: 211131357

Title of Report: SEDIMENTATION

Term: _______________________________ DATE: __________________

Subject Max Mark Actual Mark

1. Title Page 1

2. Abstract 6

3. Introduction 2

4. Theoretical Background 3

5. Procedure 2

6. Results 6

7. Discussion of Results 10

8. Conclusion and Recommendations 4

9. Literature Cited 110. Nomenclature 1

11. Organization and Neatness 2

Appendix

A1 Raw Data 2

A2 Data analysis and SampleCalculations

10

TOTAL 50

Signed: ____________________________________

Comments:


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TABLE OF CONTENTS

ABSTRACTION..2 INTRODUCTION3 THEORY.4 EXPERIMENTAL..5-20 DISCUSSION..21 CONCLUSION AND RECOMMENDATION21 LITERATURE CITED.22


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ABSTRACT

The experiment is about supplementing particles that have poor settling

characteristics by increasing their size and mass through a process of coagulation

and flocculation. In this experiment coagulants used are aluminium and ferric

sulphate which are multivalent ions and are positively charged. For part A

different dosages of these salts are used (10g, 20g, 30g, 40g respectively) to

determine the optimum dosage, and it is found to be 20g. This shows that the

quantity of the coagulant does not have that much effect on coagulation itself.

Flocculation is the binding together of particles that are suspended in

wastewater. Flocculation aids coagulation which results in the formation of flocs.

In this experiment the 4 beakers are placed on a flocculator which then stirs the

solutions at different rotations per minute (rpm) to determine the pH and

turbidity at different time intervals for 20 minutes. Flocculation process acts as a

catalyst because it speeds up coagulation to fit the 20 minutes time slot.

The other factors that influenced the coagulation process is the addition of a base

and acid at part B. A very strong base (sodium hydroxide) and a strong acid

(sulphuric acid) are used to adjust the pH to determine the effect of alkalinity on

the coagulation process. This experiment shows that the higher the pH the clearer

the water which is shown by a small turbidity value. Thus the coagulation occurs

at a faster rate for basic solutions.


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INTRODUCTION

Coagulation and Flocculation removes particles that cannot be removed by

sedimentation and filtration alone. Coagulation is the addition of chemical

coagulants to supplement light particles while flocculation is the binding of very

fine particles in water by gentle mixing after the addition of a coagulant that aid

floc formation. These two processes go hand in hand. Most particles in

wastewater are negatively charged therefore the coagulants added are those of

the opposite charge (positively charged).

Chemicals that are commonly used as coagulants are aluminiumsulphate and iron

sulphate mainly because they possess positive ions (cations) that neutralize the

negatively charged particles to enable the particles to aggregate. The choice of

the coagulant depends on the following:

Suspended particles Wastewater conditions(temperature, pH e.t.c)

Treatment process Cost of coagulants necessary to yield the desired results

For particles to bind the flocculator must distribute a uniform energy throughout

the container in which this processes are taking place. Microflocs are brought

together by gentle mixing to form flocs that are heavier in mass and visible to the

naked eye. Once the flocs have reached the required size and mass a

sedimentation process immediately takes place.


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THEORY

A coagulation process is carried out on different jars with different dosagesof colaminate(10g, 20g, 30g and 40g each)

The rpm of the flocculator is set to decrease after certain time intervals indecreasing order for gentle mixing(250rpm, 60rpm, 25rpm)

Out of the 4 jars the jar with the optimum dosage is chosen and theexperiment is performed again, but with the same chosen dosage.

The pH of the sample is then adjusted by addition of sodium hydroxide orsulfuric acid depending on the initial value of pH to get required values of

pH(6, 7, 8, 9 respectively) on each jar.

Then the samples are calibrated to get the values of turbidity, after takingthe results graphs are constructed, they are as follows:

Turbidity v.s dosageInverse of turbidity v.s dosagepH v.s time log inverse of turbidity v.s time(Phv.s turbidity

After sketching all the graphs it is then when the rate of floc formation andthe influence on which the alkalinity or acidity has on floc formation.


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EXPERIMENTAL

1.APPARATUS Jar test apparatus and beaker Magnetic stirrer plus magnetic stirring bars Spectrophotometer or colour comparator Turbidity pH meter Assorted measurement syringes Stop watch Ringstands and rings

2.PROCEDUREPART A

Collect 20 to 40 litres of natural water or alternatively makeup synthetic water.

Pour 1litre of the water in each of the 4 beakers. Pour 0.228g of colominate on each of the 4 beakers. Set-up the flocculator for 250rpm before the addition of

coagulant.

Add aluminiumsulphateas a coagulant (10g, 20g, 30g and 40grespectively) on each beaker.

Measure the pH and turbidity of each beaker after 1min for250rpm, 9min for 60rpm, 4min for25rpm, 2min for 10rpm and

20min for 0rpm.

After the settling time of 20minutes, you add the indicatorphenolphthalein in all 4 beakers.

Mix 20g of NaOH in half a litre of water. Pour the mixture in each beaker until a change of colour is

observed.

Take the turbidity and dosage in all beakers.


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Measure the depth of the sludge that has settled.PART B

Choose the beaker with the optimum dosage.

Use the same chosen optimum dosage for all 4 beakers. Adjust the pH on each beaker to 6,7,8,9 respectively by

adding NaOH or H2SO4 depending on the initial pH.

Repeat the same procedure in part A. Measure the height of the sludge that has settled. Then measure the pH and turbidity.

3 .RESULT

TABLE :1

Temperature = 18.6

(constant)

Beaker 1 Beaker 2 Beaker 3 Beaker 4

pH 250

Rpm

8.61 8.54 8.47 8.47

Turbidity 335 257 271 271

1 min

pH 60

Rpm

8.33 5.32 8.30 8.28

Turbidity 355 428 502 453

9 min

pH 25

Rpm

8.21 7.96 8.01 7.96

Turbidity 873 888 68.1 135

4 min

pH 10

Rpm

8.07 8.62 8.27 8.20

Turbidity 663 97.3 103 220

2 min

pH 0

Rpm

7.20 7.22 7.22 7.75

Turbidity 565 39.5 22.5 26.2

20 min

Height (mm) 16 16 17 15

Colour


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TABLE :2

Temperature =21(constant) Beaker 1 Beaker 2 Beaker 3 Beaker 4

pH 250

Rpm

6.61 7.69 8.12 8.99

Turbidity 536 374 325 283

1 minpH 60

Rpm

6.60 7.73 8.16 8.97

Turbidity 625 479 854 417

9 min

pH 25

Rpm

6.70 7.73 5.16 8.98

Turbidity 603 105 244 196

4 min

pH 10

Rpm

7.73 7.75 8.18 8.98

Turbidity 240 88.6 32 85.2

2 min

pH 0Rpm

6.75 7.75 8.18 8.96Turbidity 52.4 39.5 14.6 33.3

20 min

Height (mm) 17 16 17 16

Colour Light Pink Medium Pink Pink Dark pink

0

0.001

0.002

0.003

0.004

0.005

0 10 20 30 40 50inve

rseofturbidity

dosage

Graph of inverse turbidity v.s

Dosage(1min)

Series1


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0

0.0005

0.001

0.0015

0.002

0.0025

0.003

0 10 20 30 40 50

inverse

turbidity

dosage

inverse of turbidity v.s dosage(9 min)

0

0.002

0.004

0.006

0.008

0.01

0.012

0.014

0.016

0 10 20 30 40 50

inv

erse

turbidity

dosage

inverse turbidity v.s dosage (4 min)


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0

0.02

0.04

0.06

0.08

0.1

0.12

0 10 20 30 40 50

inverse

turbidity

dosage

inverse of turbidity v.s dosage 2 min

0

0.01

0.02

0.03

0.04

0.05

0 10 20 30 40 50

inverse

tur

idity

dosage

inverse of turbidity v.s dosage (20

min)


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0

50

100

150

200

250

300

350

400

0 10 20 30 40 50

turbidity

dosage

turbidity v.s dosage (1 min)

0

100

200

300

400

500

600

0 10 20 30 40 50

tu

rbidity

dosage

turbidity v.s dosage 9 min


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0

100

200

300

400

500

600700

800

900

1000

0 10 20 30 40 50

turbidity

dosage


0

100

200

300

400

500

600

700

0 10 20 30 40 50

t

u

r

b

i

d

i

t

y

dosage



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-100

0

100

200

300

400

500

600

0 10 20 30 40 50

turbidity

dosage


0

0.0005

0.001

0.0015

0.002

0.0025

0.003

0.0035

0 5 10 15 20 25

Inve

rse

ofturbidity

Time(min)

inverse turbidity Vs time B1


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-0.005

0

0.005

0.01

0.015

0.02

0.025

0.03

0 5 10 15 20 25

Inverse

ofturbidity

Time(min)


0

0.005

0.010.015

0.02

0.025

0.03

0.035

0.04

0.045

0.05

0 5 10 15 20 25

Inve

rse

ofturbidity

Time(min)

inv turb Vs time B3


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0

0.005

0.01

0.015

0.020.025

0.03

0.035

0.04

0.045

0 5 10 15 20 25

Inverse

oftu

rbidity

Time(min)


7

7.2

7.47.6

7.8

8

8.2

8.4

8.6

8.8

0 5 10 15 20 25

pH

Time

pH Vs time B1

pH


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0

1

2

3

4

5

6

7

8

9

10

0 5 10 15 20 25

pH

Time

pH Vs time B2

7.2

7.4

7.6

7.8

8

8.2

8.4

8.6

0 5 10 15 20 25

pH

Time

pH Vs time B3


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7.7

7.8

7.9

8

8.1

8.2

8.3

8.4

8.5

8.6

0 5 10 15 20 25

pH

Time

pH Vs timeB4

0

100

200

300

400

500

600

700

800

900

1000

0 5 10 15 20 25

Tuurbidity

Time

turbidity Vs time B1


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0

100

200

300

400

500

600

700

800

900

1000

0 5 10 15 20 25

Turbidity

Time


0

100

200

300

400

500

600

0 5 10 15 20 25

Turbidity

Time



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0

100

200

300

400

500

600

0 5 10 15 20 25

Turbidity

Time

turbidity Vs time b4

-3

-2.95

-2.9

-2.85

-2.8

-2.75-2.7

-2.65

-2.6

-2.55

-2.5

0 5 10 15 20 25

Loginverse

turbidity

Time

log inverse turbidity Vs time

(Beaker1)


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-3.5

-3

-2.5

-2

-1.5

-1

-0.5

0

0 5 10 15 20 25

Log

inverse

turbidity

Time

log inverse turbidity Vs time (beaker

2)

-3

-2.5

-2

-1.5

-1

-0.5

0

0 5 10 15 20 25

LogInverse

turbidity

Time

log inverse turbidity Vs time (beaker3)


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-3

-2.5

-2

-1.5

-1

-0.5

0

0 5 10 15 20 25

Loginverse

turbidity

Time

log inverse turbidity Vs time

(Beaker4)

0

10

20

30

40

50

60

0 2 4 6 8 10

Turb

idity

pH

turbidity v.s pH


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DISCUSSION

From the results it is observed that pH is inversely proportional to turbidity, this

means that basic solutions get clearer at a faster rate than acidic solutions. Beaker

1 showed to be less clearer than all the other beakers and it had a pH value of 6

which is acidic, the solution at beaker 4 was the most clear solution of them all

with the highest pH value of 9. The second beaker and third beaker did not differ

that much from each other as they were both close to neutrality and thus the

readings were roughly close.

The error which occurred was that of part A which resulted from the sample not

being calibrated properly, this resulted to a very complex structured table 1.1

which made it very hard to choose the optimum dosage. Thus turbidity in Part A

was misread. Beaker 2 was more reasonable and it complemented the theory

which explains the proportionality of pH and turbidity.

Part B came out as expected, pHwas adjusted with increasing order and the value

of turbidity is decreasing as pH increases. This shows that the more basic a

solution is the faster the settling time.

CONCLUSION AND RECOMMENDATIONS

pH is inversely proportional to turbidity, the particles settle faster for basic

solutions and slowly for acidic solutions. This experiment can be improved by

increasing the number of beakers and because it has to be done at certain timeintervals and fast more personnel is required. And also the sample calibrated has

got to be cleaned every time to ensure accurate results.


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LITERATURE CITED

1. Class Notes2. Hammer, Mark J., Water and Wastewater Technology, 2nd Ed., John Wiley

& Sons, New York, 1986

3. www.cityofsite.com

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