1.0 INTRODUCTION

1.1 BACKGROUND OF STUDY

Coagulation and flocculation are essential processes in various disciplines.

In potable water treatment, clarification of water using coagulating agents has

been practiced from ancient times. As early as 2000 BC the Egyptians used

almonds smeared around vessels to clarify river water. The use of alum as a

coagulant by the Romans was mentioned in around 77 AD. By 1757, alum was

being used for coagulation in municipal water treatment in England.

In modern water treatment, coagulation and flocculation are still essential

components of the overall suite of treatment processes – understandably, because

since 1989 the regulatory limit in the US for treated water turbidity has

progressively reduced from 1.0 NTU in 1989 to 0.3 NTU today. Many water

utilities are committed to consistently producing treated water turbidities of less

than 0.1 NTU to guard against pathogen contamination.

Coagulation is also important in several wastewater treatment operations.

A common example is chemical phosphorus removal and another, in

overloaded wastewater treatment plants, is the practice of chemically enhancing

primary treatment to reduce suspended solids and organic loads from primary

clarifiers.

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1.2 OBJECTIVE OF STUDY

To study the treatment of waste water using coagulation and flocculation method.

1.3 SCOPE OF STUDY

1. To determine the effectiveness of coagulation and flocculation methods

towards reduction of turbidity.

2. To investigate the optimal amount of coagulant.

1.4 SIGNIFICANCE OF STUDY

Stated below are the significance of the study:

i. To understand the process of coagulation and flocculation in waste water

treatment.

ii. To understand how to determine the optimal amount of coagulant needed

based on the different types of waste water.

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2.0 LITERATURE REVIEW

All waters, especially surface water, contain both dissolved and suspended

particles. Coagulation and flocculation processes are used to separate the suspended

solids portion from the water. The suspended particles vary considerably in source,

composition charge, particle size, shape, and density. Correct application of coagulation

and flocculation processes and selection of the coagulants depend upon understanding the

interaction between these factors. The small particles are stabilized by the action of

physical forces on the particles themselves. One of the forces playing a dominant role in

stabilization results from the surface charge present on the particles. Most solids

suspended in water possess a negative charge and, since they have the same type of

surface charge, repel each other when they come close together. Therefore, they will

remain in suspension rather than clump together and settle out of the water.

In coagulation, the first step destabilizes the particle’s charges. Coagulants with

charges opposite those of the suspended solids are added to the water to neutralize the

negative charges on dispersed non-settable solids such as clay and color- producing

organic substances. Once the charge is neutralized, the small suspended particles are

capable of sticking together. The slightly larger particles formed through this process and

called microflocs, are not visible to the naked eye. The water surrounding the newly

formed microflocs should be clear. If it is not, all the particles’ charges have not been

neutralized, and coagulation has not been carried to completion. More coagulant may

need to be added. High- energy, rapid- mix to properly disperse the coagulant and

promote particle collisions is needed to achieve good coagulation. Over- mixing does not

affect coagulation, but insufficient mixing will leave this step incomplete. Coagulants

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should be added where sufficient mixing will occur. Proper contact time in the rapid- mix

chamber is typically 1 to 3 minutes.

Following the first step of coagulation, a second process called flocculation.

Flocculation, a gentle mixing stage, increases the particle size from submicroscopic

microflocs to visible suspended particles. The microflocs are brought into contact with

each other through the process of slow mixing. Collisions of the microfloc particles cause

them to bond to produce larger, visible flocs called pinflocs. The floc size continues to

build through additional collisions and interaction with inorganic polymers formed by the

coagulant or with organic polymer added. Macroflocs are formed. High molecular weight

polymers, called coagulant aids, may be added during this step to help bridge, bind and

strengthen the floc, add weight, and increase settling rate. Once the floc has reached it

optimum size and strength, the water is ready for the sedimentation process. Design

contact times for flocculation range from 15 to 20 minutes to an hour or more.

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3.0 METHODOLOGY

1. The plastic jar that contains the wastewater sample was shaken.

2. Turbidity in NTU and pH of the sample were measured.

3. 1L of sample was filled in six different beakers and all the beakers were labeled with

number 1 to 6.

4. Beaker 1 was used as the control beaker.

5. The coagulant ( Al(SO4)3 or FeCI3) was weighted according to these dosage:

Beaker Number Amount of Coagulant (g)

1 0.0

2 0.2

3 0.4

4 0.6

5 0.8

6 1.0

6. The paddles were lowered in each beaker and the paddles were set at 250rpm. When

the speed was stable, the coagulant was poured in side each beaker simultaneously.

The mixing was left for 1 to 3 minutes (the starting time was recorded).

7. The paddles speed was changed to 30rpm for 30 minutes for flocculation process.

8. After 30 minutes, the paddles were removed and the mixtures were left to settle for

another 30 minutes.

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9. A sample from each beaker was taken by using a syringe. The turbidity and pH for

each sample was measured.

4.0 RESULTS

Initial turbidity of the water sample (NTU): 240

Initial pH value of the water sample: 5.45

Fixed variable:

Volume of water = 1 L (fixed for the six beakers)

Time to pour coagulant = Simultaneously in each beaker

Paddle speed = 30 rpm

Duration flocculation process = 30 minutes with the paddles + 30

minutes to settle

Table 1: Amount of Coagulant added and The Quality of Water End of the Experiment

Beaker NumberAmount of

Coagulant, Al2(SO4)3

(g)

End Quality Water

Turbidity (NTU) pH

1 0.0 26.80 5.55

2 0.2 8.49 3.82

3 0.4 11.69 3.76

4 0.6 11.3 3.66

5 0.8 8.35 3.58

6 1.0 9.60 3.46

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Table 1 shows the amount of coagulant which is Al2(SO4)3 added for each beaker during

the experiment. At the end of the experiment, the turbidity and the pH value is measured. From

the data obtained, a graph of turbidity against coagulant amount is plotted as shown in figure 1.

0 0.2 0.4 0.6 0.8 10

5

10

15

20

25

30

Coagulant (g)

Turb

idit

y (N

TU)

Figure 1: Effect of alum dosage on pH and turbidity

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5.0 DISCUSSIONS

1.1 Determination of Optimal Amount of Coagulant (Aluminium Sulfate) in

Wastewater Sample.

A total of 6 jar test experiments were conducted by varying parameters such as pH

and amount of coagulant (aluminium sulfate). The main objectives of the experiments

were to determine the optimum amount of coagulant to be added to the wastewater

sample and pH for turbidity removal. Changes in pH and turbidity were noted. Jar tests

have been used to evaluate the effectiveness of various coagulants and flocculants under a

variety of operating conditions for water treatment. This procedure allows individual

polymers to be compared on such criteria as floc formation, settling

characteristics, and clarity. Generally, the best performing products provide fast floc

formation, rapid settling rate, and clear supernatant. This test should be performed on-

site, since large amounts of water may be required for testing.

By varying the coagulant and fixing the initial pH of the sample, the optimum

amount of coagulant required for turbidity removal was determined. Coagulants varying

from 0- 1.0 g were chosen. The effects of the turbidity and final pH were compared in

figure 1.

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0 0.2 0.4 0.6 0.8 10.00

5.00

10.00

15.00

20.00

25.00

30.00

NTUPH

Amount of coagulant (g)

Mea

sure

d pH

and

Tur

bidi

ty (N

TU)

Figure 2: Effect of alum dosage on pH and turbidity

Based on this experiment, the first jar is serving as a control and no coagulant was

added. (Figure 1). Besides, it shows the highest turbidity. This is because, in the absence

of coagulants, the particles cannot become destabilized and clump together. Then,

turbidity showed a gradual decrease with increase in amount of coagulant. Optimal

coagulant dosages are critical to proper floc formation and filter performance.

Maintaining the proper control of these chemicals can mean the difference between an

optimized surface plant and a poorly run surface plant. Inadequate mixing of chemicals or

their addition at inappropriate points in the treatment plant can also limit performance.

Hence, an optimal amount of coagulant in this experiment is at 0.8 g since it achieves the

lowest turbidity.

Other than that, the graph above shows that the pH value of wastewater sample

was decreased when the amount of coagulant is increased. From that, we can know that if

the water is poorly buffered, any addition of coagulants results in a drop in pH. In our

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study, addition of 1.2 g of coagulant resulted in a drop of approximately 0.1 pH unit.  The

pH of the water plays an important role when aluminium sulfate is used for coagulation

because the solubility of the aluminium species in water is pH dependent. If the pH of the

water is between 4 and 5, alum is generally present in the form of positive ions (i.e.,

Al(OH)2+, Al8(OH)4+, and Al3+).

1.2 Determination of effectiveness of coagulant and flocculation methods toward

reduction method.

As we know in introduction, all waters, especially surface waters, contain both

dissolved and suspended particles. Coagulation and flocculation processes are used to

separate the suspended solids portion from the water. They occur in successive steps

intended to overcome the forces stabilizing the suspended particles, allowing particle

collision and growth of flocs. If step one is incomplete, the following step will be

unsuccessful.

In the flash mixer, coagulant chemicals are added to the water and the water is

mixed quickly and violently. The purpose of this step is to evenly distribute the chemicals

through the water. Flash mixing typically lasts a minute or less. If the water is mixed for

less than thirty seconds, then the chemicals will not be properly mixed into the water.

However, if the water is mixed for more than sixty seconds, then the mixer blades will

shear the newly forming floc back into small particles.

After flash mixing, coagulation occurs. During coagulation, the coagulant

chemicals neutralize the electrical charges of the fine particles in the water, allowing the

particles to come closer together and form large clumps.

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The final step is flocculation. During flocculation, a process of gentle mixing

brings the fine particles formed by coagulation into contact with each other. Flocculation

typically lasts for about thirty to forty-five minutes. The flocculation basin often has a

number of compartments with decreasing mixing speed by slow down the paddles speed

as the water advances through the basin. This compartmentalized chamber allows

increasingly large floc to form without being broken apart by the mixing blades.

The end product of a well-regulated coagulation/flocculation process is water in

which the majority of the turbidity has been collected into floc, clumps of bacteria and

particulate impurities that have come together and formed a cluster. The floc will then

settle out in the sedimentation basin, with remaining floc being removed in the filter.

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6.0 CONCLUSION

As conclusion, this experiment is successfully been done and it is because the

objective of this experiment which to conduct experiments on chemical coagulation and

flocculation and to determine the optimum amount of coagulant which will produce the

highest removal of wastewater sample has achieved.

Jar testing is an experimental method where optimal conditions are determined

empirically rather than theoretically. Jar test are meant to mimic the conditions and

processes that take place in the clarification portion of water and wastewater treatment

plants. The values that are obtained through the experiment are correlated and adjusted in

order to account for the actual treatment system. After the experiment, graph turbidity and

pH versus amount of coagulant are plot, from the graph we get the optimal amount of

coagulant is 0.8 g at pH 3.58.

The proper type and concentration of coagulant are essential to the coagulation

process. The coagulant choice will depend on the conditions at the plant. The

concentration of coagulant also depends on the water conditions, and a jar test can be

used to determine the correct concentration to use at any given time. So, by determine the

optimum dose and increase coagulant dose as required, we can increase the effectiveness

of coagulation and flocculation method. Besides that, effectiveness may increase by

adjusting flocculators’ speed or changing flow rate of the paddles.

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REFERENCES

1. IWA Water Wiki, Coagulation and flocculation in water and waste water treatment,

retrieved on 29th September 2013, from

http://www.iwawaterwiki.org/xwiki/bin/view/Articles/CoagulationandFlocculationinWat

erandWastewaterTreatment

2. MECC, Coagulation and Flocculation, retrieved on 30th September 2013, from

http://water.me.vccs.edu/courses/env110/lesson4.htm

3. Ecologix Environmental Systems, Water & Wastewater Treatment Systems, retrieved on

30th September 2013, from http://www.ecologixsystems.com/product-specialty-

chemicals-coag-floc.php

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