Coagulation and Flocculation Flashcards

1
Q

What is coagulation?

A

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

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2
Q

How big are colloidal particles?

A

1-200nm

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3
Q

Removal of colloids by coagulation depends on?

A
  • their nature and concentration
  • the use of both coagulants and coagulant aids (polymers)
  • pH
  • temperature
  • ionic strength
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4
Q

What are the four mechanisms of coagulation/flocculation?

A

1) Double Layer Compression
2) Charge Neutralization
3) Enmeshment in Precipitate (Sweep Coagulation)
4) Particle Bridging

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5
Q

What is the standard coagulant used in water treatment?

A

Aluminum Sulfate (alum)

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6
Q

Explain the difference between using lime and soda ash

A

Lime: causes permanent hardness, less expensive

Soda ash: does not cause hardness, more expensive

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7
Q

What does alum consume in water?

A

Alkalinity

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8
Q

What do lime and soda ash help with in water treatment?

A

They increase alkalinity and control pH

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9
Q

Ferric sulfate and ferric chloride are what?

A

Coagulants

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10
Q

What are the advantages and disadvantages to using ferric salts?

A

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

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11
Q

Polymers are commonly used as coagulant aids, true or false?

A

True

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12
Q

Polymers have reduced sludge production compared to metal salt, true or false?

A

True

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13
Q

Rapid mixing is for coagulation while gentle mixing is for flocculation, true or false?

A

True

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14
Q

The higher the G value the more violent the mixing, true or false?

A

True

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15
Q

What are the mixer types for rapid mixing?

A
  • In-line Mechanical Mixing (In-line Blending)
  • In-line Static Mixing
  • Mechanical Mixing in Stirred Tanks
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16
Q

What are the mixer types for gentle mixing?

A
  • Paddle Flocculators
  • Baffled Chambers
  • Arial Flow Impellers
17
Q

What are the typical G values for coagulation (rapid mixing)?

A

3000 to 5000/s for adsorption/destabilization

600 to 1000/s for sweep coagulation

18
Q

What are the typical coagulation mixing times?

A

0.5 seconds for adsorption/destabilization

1 to 10 seconds for sweep coagulation

19
Q

What are the typical G values for flocculation (gentle mixing)?

A

10 to 75/s for mechanical mixer

30 to 60/s for paddle mixer

20
Q

What are the typical flocculation mixing times?

A

20 min for 20 deg C
+7% for 15 deg C
+15% for 10 deg C
+25% for 5 deg C

21
Q

In simple terms explain coagulation and flocculation?

A

Coagulation is the clumping together or clumping of particles, while flocculation is the settling of those coagulated particles