Coagulation and Flocculation Flashcards
What is coagulation?
The process of adding chemicals to surface waters to collect small particulate matters (colloidal matter) into clusters that can be removed through sedimentation and filtration
How big are colloidal particles?
1-200nm
Removal of colloids by coagulation depends on?
- their nature and concentration
- the use of both coagulants and coagulant aids (polymers)
- pH
- temperature
- ionic strength
What are the four mechanisms of coagulation/flocculation?
1) Double Layer Compression
2) Charge Neutralization
3) Enmeshment in Precipitate (Sweep Coagulation)
4) Particle Bridging
What is the standard coagulant used in water treatment?
Aluminum Sulfate (alum)
Explain the difference between using lime and soda ash
Lime: causes permanent hardness, less expensive
Soda ash: does not cause hardness, more expensive
What does alum consume in water?
Alkalinity
What do lime and soda ash help with in water treatment?
They increase alkalinity and control pH
Ferric sulfate and ferric chloride are what?
Coagulants
What are the advantages and disadvantages to using ferric salts?
Advantages:
- Coagulation is possible over a wide range of pH
- The floc settles better than alum floc
- Better removal of NOM and odour/taste compounds
Disadvantage:
- cost more than alum salts
Polymers are commonly used as coagulant aids, true or false?
True
Polymers have reduced sludge production compared to metal salt, true or false?
True
Rapid mixing is for coagulation while gentle mixing is for flocculation, true or false?
True
The higher the G value the more violent the mixing, true or false?
True
What are the mixer types for rapid mixing?
- In-line Mechanical Mixing (In-line Blending)
- In-line Static Mixing
- Mechanical Mixing in Stirred Tanks
What are the mixer types for gentle mixing?
- Paddle Flocculators
- Baffled Chambers
- Arial Flow Impellers
What are the typical G values for coagulation (rapid mixing)?
3000 to 5000/s for adsorption/destabilization
600 to 1000/s for sweep coagulation
What are the typical coagulation mixing times?
0.5 seconds for adsorption/destabilization
1 to 10 seconds for sweep coagulation
What are the typical G values for flocculation (gentle mixing)?
10 to 75/s for mechanical mixer
30 to 60/s for paddle mixer
What are the typical flocculation mixing times?
20 min for 20 deg C
+7% for 15 deg C
+15% for 10 deg C
+25% for 5 deg C
In simple terms explain coagulation and flocculation?
Coagulation is the clumping together or clumping of particles, while flocculation is the settling of those coagulated particles
