1. Coagulation and Flocculation
CE 544
Coagulation and Flocculation

2. Background Importance of the Processes Why experiment
Destabilization of particles (coagulation)
Formation of bigger particles (flocculation)
Remove Suspended Solids and color
Why experiment
Needed to design treatment plants

3. Coagulants Aluminum and Iron salts are used
Form settleable floc composed of hydrous metal oxides and impurities
Coagulate particles

4. Jar Test Used to control of plant operations
Routinely used by operators
Indicate optimum coagulant dose
Indicates optimum pH
Indicates rate of agglomeration as a function of energy input (paddle speed)

5. Jar Test Indicates settleability of formed flocs
Indicates clarity and pH of supernatant
Used to study kinetic reaction
Indicates removal of trace constituents

6. Objectives Conduct jar tests on synthetic surface water to:
estimate optimum coagulant dose and optimum pH
observe rate of floc formation
observe rate of flocculation

7. Optimum Dose
Constitute 50 liters of synthetic surface water and determine: pH
Turbidity
Color (after filtration)
Alkalinity
Water temperature
Ambient temperature

8. Use coffee and clay to augment turbidity (40 NTU) and color (80 color units)
Calculate alkalinity required to react with max dose of coagulant
If alkalinity is not enough, use Na2CO3 to reach at least 0.5 meq/l (25 mg/l as CaCO3) and measure pH
Prepare coagulants: Aluminum and ferric sulfates
Use the jar test apparatus (6 jars)

9. Add coagulant to 5 jars and perform rapid mix at 100 rpm for 1 minute (keep the sixth jar as a control)
Flocculate at three different speeds and for three different times
In each case, record elapsed time before a visible floc is formed
Remove paddles and settle till most of the flocs are removed from suspension
Collect samples every two minutes till settling is complete

10. Analyze samples for turbidity and plot turbidity vs. time
Measure pH and depth of sludge
Estimate volume of sludge
Select optimum dose based on clarity of supernatant and settleability of flocs
Repeat test with different range of coagulant dose, if results are not satisfactory or need to narrow down the range of optimum dose

11. Optimum pH
Repeat the test using optimum coagulant dose but adjusting pH to 6, 7, 8, 9 with NaOH or H2SO4 before adding the coagulant
Measure final pH and turbidity of each collected sample
Measure depth of sludge
Plot turbidity vs initial pH and final pH
Select optimum pH

12. Microscopic Examination
Examine samples of water before and after treatment
Describe the nature of materials observed
Estimate the size of particle

13. Coagulation + Activated Carbon
If color was not removed efficiently, use activated carbon at different doses
Develop a procedure such that color can be removed effectively

14. Effect of Mixing Time (Tapered)
Prepare identical optimum coagulant dose for all the six jars
Use rapid mix for all (as before)
Reduce mixing to 30 rpm (slow mixing)
Use different times for slow mixing (5, 10, 15, 20, 30, 45 minutes) for the six jars
Stop mixing and carefully lift the paddles

15. Allow 30 minutes for settling
Measure turbidity and pH of the supernatant

16. Removal of Microorganisms
With prepared culture, examine the efficiency of removal at optimum dose and pH

17. Analysis and Problems
See manual