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Water Treatment > Coagulation & Flocculation > Flashcards

Coagulation & Flocculation Flashcards

1
Q

Dentention time in flocculation basins are usually designed to provide for ________.

a. 5 to 15 minutes.
b. 15 to 45 minutes.
c. 45 to 60 minutes.
d. 60 to 90 minutes.

A

b. 15 to 45 minutes

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2
Q

Alum works best in a pH range of _________.

a. less than 4.0
b. 4.0 to 5.5
c. 5.8 to 7.5
d. Greater than 9.0

A

c. 5.8 to 7.5 pH

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3
Q

Which statement is true concerning colloidal particles?

a. Colloidal particles are so small that gravity has little effect on them.
b. The zeta potential between colloidal particles is balanced by covalent bonding.
c. Electrical phenomenon of colloidal particles predominate and control their behavior.
d. The surface area of colloidal particles is very small compared to their mass.

A

a. Colloidal particles are so small that gravity has little effect on them.

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4
Q

Which natural electrical force keeps colloidal particles apart in water treatment?

a. van der Waals forces
b. Ionic forces
c. Zeta potential
d. Quantum forces

A

c. Zeta Potential

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5
Q

The Zeta potential measures the number of excess _______ found on the surface of all particulate matter.

a. electrons
b. ions
c. cations
d. protons

A

a. electrons

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6
Q

Low temperature water can be compensated for when using alum by _________.

a. increasing the pH.
b. decreasing the pH.
c. increasing the alum dosage.
d. decreasing the alum dosage.

A

c. increasing the alum dosage.

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7
Q

Which is the optimal pH range for the removal of particulate matter when using alum as a coagulant?

a. 4.5 to 5.7
b. 5.8 to 6.5
c. 6.5 to 7.2
d. 7.3 to 8.1

A

c. 6.5 to 7.2 pH

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8
Q

Which forces will pull particles together once they have been destabilized in the coagulation-flocculation process?

a. van der Waals forces
b. Zeta potential
c. Ionic forces
d. Quantum forces

A

a. Van der Waals forces

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9
Q

Which is a common mistake that operators make in regards to flocculation units?

a. Excessive flocculation time.
b. Lack of food-grade NSF-approved grease on the flocculator bearings.
c. Keeping the mixing energy the same in all flocculation units.
d. Too short a flocculation time.

A

a. Excessive flocculation time

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10
Q

Ferric Sulfate has which advantage over Aluminum Sulfate (alum)?

a. Less staining characteristics
b. Less cost
c. More dense floc
d. Not as corrosive

A

c. More dense floc

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11
Q

How much alkalinity as CaCO3 will dry-basis alum consume?

a. 0.5 mg/L
b. 0.8 mg/L
c. 1.2 mg/L
d. 1.5 mg/L

A

a. 0.5 mg/L

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12
Q

Natural zeolites used for softening that have become exhausted with use are regenerated by immersing them in a strong solution of which chemical?

a. NaCl
b. NaOH
c. HCl
d. H2SO4

A

a. NaCl

Sodium chloride

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13
Q

The zeta potential on a particular sample of water is -2. The degree of coagulation is best described as ________.

a. poor.
b. fair.
c. excellent.
d. maximum.

A

c. Excellent

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14
Q

Which is a disadvantage of using static mixers?

a. They do not provide good mixing
b. They are not economical
c. They increase head loss
d. They require too much maintenance

A

c. They increase head loss

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15
Q

Which is the usual effective pH range of iron salt coagulants?

a. 3.5 to 9.0
b. 6.5 to 8.8
c. 3.0 to 9.5
d. 4.2 to 9.0

A

a. 3.5 to 9.0 pH

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16
Q

To help avoid short circuiting, which is the minimum recommended number of flocculation basins in a series?

a. 2
b. 3
c. 4
d. 5

A

b. 3

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17
Q

Which type of polymers are sometimes formulated with regulated substances?

a. Polyethylene
b. Divinylbenzene
c. Polypropylene and polyethylene
d. Nonionic and anionic polymers

A

d. Nonionic and Anionic polymers

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18
Q

Which is the most probable solution if rotifers are visible in the finished water?

a. Superchlorinate the water plant.
b. Optimize coagulation, flocculation, and filtration.
c. Use aeration followed by lime softening before the settling process.
d. Use oxygen deprivation.

A

b. Optimize Coagulation, Flocculation, and Filtration.

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19
Q

The best addition for water that is highly colored due to organic matter would be?

a. the addition of lime.
b. lime addition with increase in the coagulant being used.
c. a small increase in a nonionic polymer.
d. the addition of an acid to lower pH before coagulation.

A

d. The addition of an acid to lower pH before coagulation.

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20
Q

If the activation process of silica is not carefully controlled, _______.

a. the silica could splash due to high heat of reactants.
b. it could inhibit floc formation.
c. it could corrode and destroy the metal and rubber in the flocculators.
d. It could deposit silica on the flocculators and the gears, bringing it eventually to a grinding halt.

A

b. It could inhibit floc formation.

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21
Q

How many steps are in the coagulation process?

a. 3
b. 4
c. 5
d. 6

A

a. Three (3)

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22
Q

Polymers used as flocculants are _________.

a. water-soluble inorganic electrolytes.
b. water-insoluble organic polyelectrolytes.
c. water-insoluble inorganic electrolytes.
d. water-soluble organic polyelectrolytes.

A

d. Water-soluble organic polyelectrolytes.

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23
Q

Which is the Zeta Potential?

a. Electrical charge on a suspended particle
b. Electrical resistance of a suspende particle
c. Electrical potential of a suspended particle
d. Electrical charge of a suspended particle as it relates electrochemically to the coagulate being used

A

a. Electrical charge on a suspended particle

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24
Q

All colloids are _________.

a. sols.
b. hydrophobic.
c. electrically charged.
d. emulsoids.

A

c. Electrically charged

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25
Q

Colloidial particle movement and aggregation caused by thermal energy is called _________.

a. orthokinetic flocculation.
b. parakinetic dynamism.
c. Brownian movement.
d. thermodynamic flocculation.

A

c. Brownian movement

26
Q

When used with alum, which chemical improves coagulation?

a. Ferric chloride
b. Ferric sulfate
c. Sodium aluminate
d. Aluminum sulfate

A

c. Sodium aluminate

27
Q

The coagulant alum reacts with natural alkalinity in the water forming _________.

a. aluminum hydroxide.
b. aluminum carbonate.
c. aluminum bicarbonate.
d. aluminum oxide.

A

a. aluminum hydroxide.

28
Q

When ferric coagulants react with natural alkalinity in the water they form _________.

a. ferric hydroxide.
b. ferric carbonate.
c. ferric bicarbonate.
d. ferric oxide.

A

a. ferric hydroxide.

29
Q

Detention time in mechanical mixers usually ranges from _________.

a. 5 to 15 seconds.
b. 15 to 45 seconds.
c. 1 to 2 minutes.
d. 2 to 4 minutes.

A

b. 15 to 45 seconds.

30
Q

The aluminum ions in Alum neutralize the negatively charged particles in the raw water in about ________.

a. 1 to 2 seconds.
b. 3 to 5 seconds.
c. 5 to 8 seconds.
d. 5 to 12 seconds.

A

a. 1 to 2 seconds.

31
Q

Suspended and colloidal solids found in natural water are usually ________.

a. positively charged.
b. negatively charged.
c. neutral.
d. polyionic.

A

b. negatively charged.

32
Q

After the oxidation treatment, H2S in the water turns a Milky-Blue color because of elemental sulfur (solid sulfur). Which is the best procedure to remove this sulfur?

a. Adsorption
b. Sedimentation
c. Coagulation and filtration
d. Lime-soda ash softening

A

c. Coagulation and Filtration

33
Q

Particles will stay in suspension as long as the ________.

a. ionic forces are stronger than the van der Waals forces.
b. zeta potential is stronger than the van der Waals forces.
c. van der Waals forces are stronger than the ionic forces.
d. van der Waals forces are stronger than the zeta potential.

A

b. Zeta potential is stronger than the Van der Waals forces.

34
Q

The most probable effective ratio of the coagulants aluminum sulfate to hydrated lime is __________.

a. 1:1 aluminum sulfate to hydrated lime.
b. 3:1 aluminum sulfate to hydrated lime.
c. 5:1 aluminum sulfate to hydrated lime.
d. 6:1 aluminum sulfate to hydrated lime.

A

b. 3:1 aluminum sulfate to hydrated lime.

35
Q

What should the “Tip Speed” of the flocculator be in water, assuming the water is not extremely cold?

a. 0.2 ft/sec
b. 0.5 ft/sec
c. 1.0 ft/sec
d. 2.0 ft/sec

A

c. 1.0 ft/sec

36
Q

Coagulants consisting of trivalent ions are how much more effective than bivalent ions?

a. 50 to 60 times
b. 100 to 120 times
c. 200 to 250 times
d. 1,000 times

A

a. 50 to 60 times

37
Q

When Tip velocities of the impellers reach speeds greater than _______, localized shearing of floc occurs.

a. 6.0 fps
b. 8.0 fps
c. 10.0 fps
d. 10.5 fps

A

b. 8.0 fps

38
Q

In the flash mixing process, which type of rapid mixing system has the most significant head loss?

a. Mechanical mixers
b. Static mixers
c. Pumps and conduits
d. Baffled chambers

A

b. Static mixers

39
Q

When these types of chemicals are used, flash mixing becomes less critical, but thorough mixing (flocculation) remains very important.

a. Ferric or ferrous chloride
b. Aluminum sulfates
c. Lime, soda ash, or caustic soda
d. Polymers

A

d. Polymers

40
Q

Weighing agents are used primarily to treat water that is ________.

a. low in color and mineral content and high in turbiity.
b. high in color and mineral content and low in turbidity.
c. low in turbidity and mineral content and high in color.
d. high in turbidity and mineral content and low in color.

A

c. low in turbidity and mineral content and high in color.

41
Q

The flash mixing process that has the best control features are _________.

a. mechanical mixers.
b. static mixers.
c. pumps an conduits.
d. baffled chambers.

A

a. mechanical mixers

42
Q

The zeta potential on a particular sample of water is +2. The degree of coagulation is best described as _______.

a. poor.
b. fair.
c. excellent.
d. maximum.

A

d. Maximum

43
Q

The most effective ratio of the coagulant ferric sulfate to the oxidant chlorine is __________.

a. 2:1 ferric sulfate to chlorine.
b. 4:1 ferric sulfate to chlorine.
c. 5:1 ferric sulfate to chlorine.
d. 8:1 ferric sulfate to chlorine.

A

d. 8:1 ferric sulfate to chlorine.

44
Q

Mixing of a coagulant is least influenced by flow when using ________.

a. a static mixer.
b. a baffled chamber.
c. a pump (adding coagulant on suction side).
d. pipe grids that have been perforated.

A

c. a pump (adding coagulant on suction side).

45
Q

When alum or ferric coagulants are used to treat water, the reactions are governed by all the following. Which one is critical to floc formation?

a. Initial application at point of highest mixing intensity
b. Temperature and ratio of turbidity to coagulant
c. Alkalinity
d. Amount of turbidity

A

a. Initial application at point of highest mixing intensity

46
Q

The major advantage for using activated silica is that it will ________.

A

strengthen the floc.

47
Q

How can the problem of poorly formed floc be solved?

A

Use a coagulant aid.

48
Q

A conventional water treatment plant has six flocculators with a detention time of 1 hr and 15 min. What should the operator do for the best results?

A

Turn off the last three flocculators.

49
Q

The reduction of color would most likely occur

after ________.

A

Coagulation, Flocculation, and Sedimentation.

50
Q

After microscreening, there should be a significant reduction in _________.

A

algae

51
Q

A cloudy appearance in the last flocculation chamber is usully caused by ________.

A

Inadequate coagulant dosage.

52
Q

Alum requires ________ to be present naturally or added for proper coagulation, and about ________ is required for each milligram of alum added per liter.

A
  • alkalinity
  • 0.5 mg/L
53
Q

In general, the size of floc that has been found to be optimal for settling efficiency is ________.

A

Pinhead-size floc

54
Q

In a pulsator clarifier, what is the purpose of the pulses, and how often are pulses generated?

A

To maintain a uniform sludge layer and

Pulsing at 40 to 50

55
Q

Coagulation and flocculation are _______ processess.

A

chemical and mechanical

56
Q

The success of the conventional treatment design is primarily due to the _________ process.

A

coagulation, sedimentation, and filtration

57
Q

Weak floc is usually due to ________.

A

inadequate mixing in the rapid-mix or flocculation basins.

58
Q

What is an operating factor that would affect floc formation?

A

Inadequate flocculation time.

59
Q

An effective way to remove ________ is through ________.

A
  • cryptosporidium oocysts
  • coagulation and filtration
60
Q

What type of instrument will help operators improve the coagulation process the most?

A

Streaming current monitors.

61
Q

In the flocculation basins, as the floc grows in size they become _______, so the mixing must be ________ so that the floc ________.

A
  • fragile
  • slowed
  • does not shear

Water Treatment (16 decks)

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