Clairification & Sedimentation

Question 1

Which device collects the settled water as it leaves the sedimentation basin?

a. Effluent weir
b. Effluent flow box
c. Effluent baffle
d. Effluent launder

Answer 1

d. Effluent Launder

Question 2

In solid-contact basins with fairly constant water quality parameters, how often should the solids concentration be determined?

a. At least once per week
b. At least every other day
c. At least once per month
d. At least twice per day

Answer 2

d. At least twice per day.

Question 3

The definition of decant is ________.

a. to draw off a liquid layer from a vessel of any size without disturbing any layer(s) above or below.
b. to draw off the sediment at the bottom of a vessel of any size without disturbing the overlying liquid layer(s).
c. to remove the precipitate at the bottom of any size vessel.
d. to draw off the liquid from a vessel of any size without stirring up bottom sediment.

Answer 3

d. To draw off the liquid from a vessel of any size without stirring up bottom sediment.

Question 4

How often should sedimentation basins with mechanical sludge removal equipment be drained and inspected?

a. Twice a year
b. Once a year
c. Every other year
d. Every three years

Answer 4

b. Once a year

Question 5

Which is the most important reason to reduce turbidity?

a. To reduce taste and odor problems
b. To remove pathogens
c. To reduce corrosion
d. To determine the efficiency of coagulation and filtration

Answer 5

b. To remove pathogens

Question 6

If enteric disease-causing protozoans have been found in the effluent of a water plant, which is the most probable solution?

a. Where possible, use powdered activated carbon (PAC) throughout water plant; backwashing filters will remove the PAC.
b. Use PAC only in the sedimentation basin; backwashing the filters will remove the PAC.
c. Use multibarrier approach - coagulation, flocculation, sedimentation, and filtration.
d. Superchlorinate the water plant.

Answer 6

c. Use multibarrier approach, Coagulation, Flocculation, Sedimentation, and Filtration.

Question 7

Which is the major cause of short circuiting in a sedimentation basin?

a. Open basins that are subject to algal growths and thick slime growths on the side of the basin.
b. Basins without a wind break
c. Poor inlet baffling
d. Density currents

Answer 7

c. Poor inlet baffling

Question 8

Conventional sedimentation has a ________ removal of Cryptosporidium oocysts.

a. less than 0.5-log
b. 0.5-log
c. 1.0-log
d. 2.0-log

Answer 8

a. Less than 0.5-log

Question 9

In solids-contact basins, the weir loading normally should not exceed ________ of weir length.

a. 1 gpm/ft
b. 2 gpm/ft
c. 5 gpm/ft
d. 10 gpm/ft

Answer 9

d. 10 gpm/ft

Question 10

Dissolved-air flotation is particularly good for removing ________.

a. sulfides.
b. inorganics.
c. manganese and iron.
d. algae.

Answer 10

d. algae

Question 11

Which determines whether or not colloidal-sized particles in suspension repel each other, stay in suspension, or agglomerate and eventually settle?

a. Number of collisions
b. Flow and temperature of the water
c. Types of chemical bonding
d. Magnitude of the charges

Answer 11

d. Magnitude of the charges.

Question 12

If the sludge in a sedimentation basin becomes too thick, which could happen?

a. Gases from decomposition will rise through the settled sludge accelerating normal floc settling.
b. Abundant trihalomethanes and haloacetic acids will form.
c. Solids can become resuspended or taste and odors can develop.
d. The sludge will compact at the bottom of the basin making it very difficult to remove.

Answer 12

c. Solids can become resuspended or taste and odors can develop.

Question 13

In basins using Tube and Plate Settlers, which parameter must be much better than Conventional treatment basins?

a. Metals must be oxidized before reaching the tubes and plates.
b. Floc rate must be 2 to 3 times slower than conventional basins.
c. Floc rate must be 3 to 4 times faster than conventional basins.
d. Floc must have good settling characteristics.

Answer 13

d. Floc must have good settling characteristics.

Question 14

Which type of sedimentation basins have the flow of water admitted at an angle?

a. Rectangular settling basins
b. Square settling basins
c. Center-feed settling basins
d. Spiral-flow basins

Answer 14

d. Spiral-flow basins

Question 15

At which minimum angle must self-cleaning tube settlers be placed?

a. 50^o
b. 60^o
c. 65^o
d. 70^o

Answer 15

a. 50^o

Question 16

If nematodes are interfering with the disinfectant, which is the most probable solution?

a. Optimize the settling process
b. Use chloramines
c. Decrease detention time of finished water in clearwell and tanks
d. Use oxyen deprivation

Answer 16

a. Optimize the settling process.

Question 17

At which angle should the parallel inclined plates be installed when using the shallow-depth sedimentation method?

a. 35^o
b. 45^o
c. 50^o
d. 60^o

Answer 17

b. 45⁰

Question 18

Why do solids-contact basins have much shorter detention times then conventional treatment basins?

a. Because chemical reactions take place throughout the basin
b. Because the settling zone water moves upward, while at the same time the mixing zone moves upward.
c. Because the gentle upward flow of the water throughout the basin is conducive for producing larger settleable floc.
d. Because of the recycled materials from the sludge blanket, the chemical reactions occur more quickly and completely in the mixing area.

Answer 18

d. Because of the recycled materials from the sludge blanket, the chemical reactions occur more quickly and completely in the mixing area.

Question 19

The pulsating energy in a Pulsator Clarifier helps to_______.

a. maintain a uniform sludge blanket layer.
b. mix the coagulants with the raw water.
c. mix the coagulant aids with the primary coagulant and the water to help in flocculation.
d. raise the sludge blanket over the weir for wasting.

Answer 19

a. Maintain a uniform sludge blanket layer.

Question 20

Pulsator clarifiers are used to treat water that is________.

a. low in temperature, usually < 10^oC.
b. high in color and low in turbidity.
c. low in color and high in turbidity.
d. high in organic acids.

Answer 20

b. High in color and low in turbidity.

Question 21

Sedimentation depends on ________.

a. size of flocculated particles.
b. gravity.
c. the depth of the basin.
d. the type of coagulant used.

Answer 21

b. gravity

Question 22

Most clarifiers are designed to have a theoretical detention time of about ________ when the plant is at its maximum flow.

a. 1 hour
b. 2 hours
c. 3 hours
d. 4 hours

Answer 22

d. 4 hours

Question 23

Which percentage of source water turbidity do sedimentation basins typically remove?

a. 80% or more
b. 90% or more
c. 95% or more
d. 96% or more

Answer 23

b. 90% or more

Question 24

How many zones are defined in all sedimentation basins?

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

Answer 24

b. 4 zones

Question 25

Which sedimentation zone is particularly affected by the other zones?

a. Influent zone
b. Settling zone
c. Effluent zone
d. Sludge zone

Answer 25

b. Settling zone

Question 26

The material that accumulates on the surface of a dissolved-air flotation unit is called ________.

a. scum.
b. sludge.
c. float.
d. floc cake.

Answer 26

c. Float

Question 27

At what rate are overflow rates from outlet weirs of conventional basins commonly designed not to exceed?

a. 10,000 gpd/ft
b. 20,000 gpd/ft
c. 25,000 gpd/ft
d. 30,000 gpd/ft

Answer 27

b. 20,000 gpd/ft

Question 28

Name the two major areas in solids-contact clarifiers?

a. Reaction and settling zones
b. Reaction and mixing zones
c. Mixing and settling zones
d. Sludge and reaction zones

Answer 28

c. Mixing and Settling zones

Question 29

Lamella plates are usually inclined ________.

a. 20.0 to 30.0 degrees.
b. 33.7 degrees.
c. 55.0 degrees.
d. 67.7 degrees.

Answer 29

c. 55 degrees

Question 30

Which high rate process has the objective of producing Pin-sized floc?

a. Tube settlers
b. Superpulsators
c. Actiflo process
d. Dissolved air flotation

Answer 30

d. Dissolved air flotation

Question 31

Slime growth in uncovered sedimentation basins can be eliminated by coating the walls with _________.

a. copper sulfate and lime.
b. copper sulfate.
c. lime and potassium permanganate.
d. copper sulfate and potassium permanganate.

Answer 31

a. Copper Sulfate and lime.

Question 32

Which is the most probable result of high winds on a sedimentation basin?

a. Sheared floc
b. Short-circuiting
c. Density currents
d. Floc will be partially resuspended and it will be more difficult to settle the floc

Answer 32

b. Short-Circuiting

Question 33

How often is the vent valve opened to release the vacuum that produces pulsating energy in a pulsator clarifier?

a. Every 5 to 10 seconds
b. Every 40 to 50 seconds
c. Every 2 to 3 minutes
d. Every 4 to 6 minutes

Answer 33

b. Every 40 to 50 seconds.

Question 34

Typically, the time between backwashing of trident contact adsorption clarifiers averages _________.

a. 4 to 8 hours.
b. 16 to 24 hours.
c. 1 to 2 days.
d. 3 to 5 days.

Answer 34

a. 4 to 8 hours

Question 35

Which will result if the influent water to a sedimentation basin contains more suspended solids than the water in the basin?

a. Too much sludge will settle at the inlet of the basin
b. Poor floc formation
c. Septic conditions will begin to occur
d. Density current

Answer 35

d. Density current

Question 36

Horizontal tube settlers ________.

a. are actually inclined about 5 degrees.
b. work independently with the downstream filter(s).
c. require jet sprayers to clean the collected sludge out of the tubes.
d. have high maintenance requirements due to frequent cleaning.

Answer 36

a. are actually inclined about 5 degrees.

Question 37

Which high rate process uses microsand?

a. Tube settlers
b. Superpulsators
c. Actiflo process
d. Dissolved air flotation

Answer 37

c. Actiflo process

Question 38

Which high rate process applies a vacuum?

a. Tube settlers
b. Superpulsators
c. Actiflo process
d. dissolved air flotation

Answer 38

b. Superpulsators

Question 39

Dissolved air flotation has a _______ removal of cryptosporidium oocysts.

a. 0.5-log
b. 1.0-log
c. 1.5-log
d. 2.0-log

Answer 39

d. 2.0-log

Question 40

In dissolved-air flotation units, mechanical rubber scrappers travel over the tank surface and push the float over a ramp called a ________.

a. trap.
b. beach.
c. launder.
d. loading plate.

Answer 40

b. Beach.

Question 41

Which is the most effective method of reducing nematode concentrations in surface water treatment plants?

a. Coagulation
b. Free chlorine
c. Rapid sand filters
d. Settling

Answer 41

d. Settling

Question 42

Which is the angle of inclination from the horizontal for the plates in a superpulsator clairifier?

a. 30^o
b. 33^o
c. 45^o
d. 60^o

Answer 42

d. 60 degrees

Question 43

Which high rate process has the highest surface overflow rate?

a. Tube settlers
b. Superpulsators
c. Actiflo process
d. Dissolved air flotation

Answer 43

c. Actiflo process

Question 44

How high can surface overflow rates for Actiflo process reach?

a. 8 gpm/ft²
b. 12 gpm/ft²
c. 16 gpm/ft²
d. 20 gpm/ft²

Answer 44

c. 16 gpm/ft²

Question 45

Which is the best process for the removal of radium (226 and 228)?

a. Anion exchange
b. Coagulation, sedimentation, and filtration
c. Aeration and stripping
d. Chemical oxidation

Answer 45

b. Coagulation, Sedimentation, and Filtration

Question 46

What type of pretreatment must be cleaned manually when the amount of debris is relatively small?

Answer 46

Sand trap

Question 47

After screening and presedimentation, there should be a significant reduction in ______.

Answer 47

Sediment and other debris.

Question 48

Presedimentation basins can be converted with a retrofit of _______ and this can help _______.

Answer 48

• Lamella plates
• control the growth of algae.

Question 49

Mechanical mixers should never be used in conjunction with __________.

Answer 49

Saturators