Coagulation & Flocculation Lab Report PDF

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Coagulation & Flocculation Laboratory Report Joel Taylor (1506692) School of Engineering, University of Technology, Jamaica Wastewater Treatment CHE 4018 Dr. L. Bramwell December 7, 2020

2 Coagulation & Flocculation Laboratory Report

Abstract The aim of this experiment was to determine the optimum dosage for 2 coagulants (ferric chloride and aluminium sulphate) and to determine which coagulant performs better. The jar testing method was employed for seven different samples that were treated with each coagulant at various concentrations, followed by the use of standard testing methods (HACH 8156, HACH 8237 and HACH 8025) to analyze the pH, turbidity and color of each sample. The results showed that an increase in the concentration of both coagulants will result in a decrease in turbidity, color, time of floc formation and pH for each sample. Furthermore, the highest turbidity removal efficiency provided by ferric chloride was 97.8% at a dose of 9 mL compared to 95% that was achieved by aluminum sulphate at a dose of 3 mL. The results suggest that the optimum dosage for ferric chloride and aluminium sulphate were 9 mL and 3 mL respectively, with ferric chloride providing the greatest turbidity removal efficiency.

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Introduction Wastewater contains both dissolved and suspended solids. Coagulation and flocculation are used to separate the suspended solids from the water. Suspended particles vary in source, charge, particle size, shape, and density. Correct application of coagulation and flocculation depends upon these factors. Suspended solids in water have a negative charge and since they have the same type of surface charge, they repel each other when they come close together. Therefore, suspended solids will remain in suspension and will not clump together and settle out of the water without the use of coagulation and flocculation. Coagulation and flocculation occurs in successive steps, allowing particle collision and growth of floc. This is then followed by sedimentation. If coagulation is incomplete, the flocculation step will be unsuccessful, and if flocculation is incomplete, sedimentation will be unsuccessful. Coagulant chemicals with charges opposite those of the suspended solids are added to the water to neutralize the negative charges on non-settleable solids. Once the charge is neutralized, the small suspended particles are capable of sticking together. These slightly larger particles are called microflocs, and are not visible to the naked eye. Water surrounding the newly formed microflocs should be clear. A high-energy, rapid-mix to properly disperse 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. Contact time in the rapidmix chamber is typically one to three minutes. Flocculation, a gentle mixing stage, increases the particle size from submicroscopic microfloc to visible suspended particles. Microfloc particles collide, causing them to bond to produce larger, visible flocs called pinflocs. Floc size continues to build with additional collisions and interaction with added inorganic polymers (coagulant) or organic polymers.

4 Macroflocs are formed and high molecular weight polymers, called coagulant aids, may be added to help bridge, bind, and strengthen the floc, add weight, and increase settling rate. The most commonly used coagulant aids are synthetic polyelectrolytes (Brandt and Ratnayaka, 2017). Once the floc has reached its optimum size and strength, the water is ready for sedimentation. Design contact times for flocculation range from fifteen to twenty minutes to an hour or more, and flocculation requires careful attention to the mixing velocity and amount of mix energy. To prevent floc from tearing apart or shearing, the mixing velocity and energy are usually tapered off as the size of floc increases. Once flocs are torn apart, it is difficult to get them to reform to their optimum size and strength. Turbidity is a measurement of the amount of light that is scattered by material in the water when a light is shined through the water sample. It is a measure of water clarity and it is caused by suspended solids which makes it an indirect measure of suspended solids. The higher the intensity of scattered light, the higher the turbidity. Material that causes water to be turbid include clay, silt, very tiny inorganic and organic matter, algae, dissolved colored organic compounds, and plankton and other microscopic organisms. Turbidity makes water cloudy or opaque. True color is caused by dissolved compounds in water. It can be natural or anthropocentric. Dissolved and suspended solids (together) cause apparent color. For example, brown colored water could be the result of dissolved byproducts of plant biodegradation (true color) or suspended clay particles (apparent color) or both (also apparent color). Color is measured in Platinum-Cobalt units (Pt-Co) and can be measured using light with a wavelength of 455 nm.

5 Method Two coagulants, namely iron (III) chloride / ferric chloride (FeCl3) and aluminium sulfate (Al2(SO4)3), were tested at various concentrations using the jar testing method. Seven different samples were treated with each coagulant and the following five parameters were tested: colour (HACH 8025), pH (HACH 8156), turbidity (HACH 8237), time of floc formation and depth of sludge.

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Results Table 1 Values Obtained for the Analyses Conducted with Ferric Chloride Name of Coagulant Beaker No.

Ferric Chloride Volume of Time of Floc Coagulant Formation (s) (mL)

Color (Pt-Co)

pH

Turbidity (NTU)

Depth of the Sludge (mm)

1

0

0

128

8.4

366

0

2

1

75

31

6.11

15.54

13

3

3

65

46

6.13

13.07

15

4

5

50

52

5.98

13.31

16

5

7

45

8

5.74

12.21

18

6

9

30

12

5.59

8.04

22

7

12

20

20

5.4

9.53

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7 Table 2 Values Obtained for the Analyses Conducted with Aluminium Sulphate Aluminium Sulphate

Name of Coagulant Beaker No.

Volume of Time of Floc Coagulant Formation (s) (mL)

Color (Pt-Co)

pH

Turbidity (NTU)

Depth of the Sludge (mm)

1

0

0

124

8.38

364

0

2

1

165

122

6.42

23.8

5

3

3

138

128

7.27

17.3

7

4

5

110

138

6.07

22

9

5

7

60

116

5.78

18.6

7

6

9

58

130

5.86

20.8

6

7

12

50

115

5.78

21

6.5

8 Figure 1 Graph of Ferric Chloride Dose vs Turbidity Remaining

9 Figure 2 Graph of Aluminium Sulphate Dose vs Turbidity Remaining

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Discussion Figures 1 and 2 presented the turbidity removal of ferric chloride and aluminium sulphate under different coagulant concentrations. The various doses for both coagulants were 1, 3, 5, 7, 9 and 12 mL. It was also observed from the results obtained in Table 1 and 2 that the pH, turbidity and color of the samples decreased with an increase in the concentration of the coagulants. As shown in both Tables 1 and 2, the addition of both coagulants significantly reduced the turbidity of the samples by more than 90 % compared to the control sample (beaker 1) that had no coagulant added to it. Tchobangolous, Burton and Stensel (2004) reported that the flocculation phenomenon was likely to be attributed to simple charge neutralization. As the coagulant dose further increased, more of the positively charged coagulant molecules could neutralize the negatively charged suspended solids, which allowed more flocs to form and settle to the bottom reducing the color, pH and turbidity of the water. On the other hand, if the coagulant dose is too high, the positive charge will become more dominant, which leads to electrostatic repulsion between the suspended particles. In contrast, both the depth of the sludge and the time of floc formation increased with an increase in coagulant concentration. Fast floc formation will allow the solids to settle faster reducing the detention time in the primary sedimentation tank. In order to maximize efficiency and reduce the operating costs of the treatment plant, it is crucial to determine the optimum dosage of coagulant. The optimum dosage of coagulant is the minimum dose of coagulant that will result in maximum turbidity removal. Based on the results obtained in Table 1, the optimum dosage of ferric chloride was observed to be 9 mL, as it drastically reduced the turbidity to a minimum value of 8.04 NTU. Additionally, the results obtained in Table 2 showed that 3 mL was the optimum dosage of aluminium sulphate, reducing the turbidity to a minimum value of 17.3 NTU.

11 Based on the results obtained in Tables 1 and 2, ferric chloride was more effective at reducing the turbidity than aluminum sulphate. Ferric chloride produced the greatest turbidity removal efficiency of 97.8% taking just 30 seconds for floc formation. In comparison, aluminum sulphate’s highest turbidity removal efficiency was 95% and floc formation took 138 seconds.

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Conclusion The goal of this experiment was to determine the optimum doses for 2 coagulants and to determine the more effective of the two coagulants. It was hypothesized that raising the concentration of each coagulant would provide a greater turbidity removal due to an increase in the number of positively charged coagulant molecules that can be neutralized by the negatively charged suspended solid particles. The findings indicated drastic changes in the turbidity removal efficiency as the concentration of each coagulant was increased. The results showed that the ferric chloride provided the greatest turbidity removal efficiency of 97.8% at an optimum dosage of 9 mL, whereas aluminium sulphates’s turbidity removal efficiency was 95% with an optimum dosage of 3 mL. The results of the experiment supports the hypothesis that increasing the coagulant dosage will also increase the turbidity removal efficiency.

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References Brandt, M., & Ratnayaka, D. (2017). Coagulant Aid. https://www.sciencedirect.com/topics/engineering/coagulant-aid Bulger, K. (2019). Industrial Wastewater Jar Testing in 9 Steps. https://www.dober.com/greenfloc/resources/jar-testing Ramavandi, B. (2014). Treatment of Water Turbidity and Bacteria by using a Coagulant Extracted from Plantago Ovata. https://www.sciencedirect.com/science/article/pii/S2212371714000171#:~:text=The%20t urbidity%20removal%20efficiency%20(TRE,NTU)%20of%20water%2C%20respectivey Tchobanoglous, G., Burton, F., Stencil, H. (2004). Wastewater Engineering: Treatment and Reuse. https://ptabdata.blob.core.windows.net/files/2017/IPR201701468/v22_FWS1016%20-%20Metcalf.pdf...