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Wastewater > Preliminary Treatment of Wastewater > Flashcards

Preliminary Treatment of Wastewater Flashcards

1
Q

T/F All WRRF headworks include screening, grit removal, and flow measurement?

A

False, Headworks may contain all or none of these depending on the size and complexity of the WRRF.

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2
Q

T/F Screening and grit removal must be completed before flow measurement?

A

False, flow measurement can come before either screening or grit removal

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3
Q

This device may be used to direct flow to or around a screen or grit basin:
a: Cogwheel
b: Slide gate
c: Weir block
d: Fraser valve

A

B

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4
Q

A bar screen may not prevent this type of material from entering the WRRF:
a: sticks
b: large sticks
c: rags
d: pallets

A

C

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5
Q

Grit basins typically remove sand, gravel, eggshells, and coffee grounds by:
a: Placing wire mesh in the flow path as a strainer
b: scooping the surface of the water
c: introducing microorganisms to consume them
d: Decreasing water velocity and allowing them to settle

A

D

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6
Q

T/F: Removal of grit, rags, and other debris is often necessary to protect downstream equipment from harm.

A

True

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7
Q

T/F: If too much organic material is removed at the WRRF headworks, the downstream biological process can be affected

A

True

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8
Q

T/F: Head loss is the difference in water level between the upstream and downstream sides of a screen?

A

True

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9
Q

One consequence of allowing excess organic material to be removed along with rags and other inert debris is:
a: Oxygen generation
b: Reduced capture of rags
c: Generation of odors
d: Reduced disposal costs

A

C

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10
Q

This type of screen has the widest openings and only stops the largest debris:
a: trash rack
b: manual bar screen
c: mechanical bar screen
d: step screen

A

A

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11
Q

A WRRF currently has a bar screen with 50-mm (2 in) openings. Operators of the WRRF are considering replacing the screen with one that has 25 mm (1 in) openings. How much should they expect the volume of screenings removed to change?
a: Volume will remain about the same
b: Screening volume will double
c: Screening volume will increase by a factor of 4
d: Screening volume will decrease by 50%

A

C. The amount of screened material doubles for every 13 mm (0.5 in) reduction of clear opening size.

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12
Q

What is the most likely effect of receiving large quantities of grease on a perforated plate type screen?
a: Blinding of the screen
b: Decreased cleaning frequency
c: Passage of hair and rags into the WRRF
d: Improved cog lubrication

A

A

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13
Q

Place the following screen types in order from the smallest opening size to the largerst:
a: fine screen
b: trash rack
c: bar screen
d: micro screen

A

D-Micro screen
A-Fine screen
C-Bar screen
B-Trash rack

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14
Q

T/F: Trash and bar racks are installed at a 30 to 45 degree angle from the vertical.

A

True

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15
Q

T/F: Mechanical cleaning of bar screens increases labor costs because of increased maintenance.

A

False. Mechanical cleaning reduces labor costs.

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16
Q

T/F: Fine screens capture fewer organic solids than coarse screens.

A

False. Fine screens capture more of everything than coarse screens, including organic matter.

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17
Q

T/F: Rollback occurs when screened material falls back down the face of the screen, possibly being returned to the wastewater flow.

A

True

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18
Q

A pond WRRF is most likely to have this type of screen in its headworks:
a: Manual bar screen
b: Perforated plate screen
c: Stair screen
d: Micro screen

A

A

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19
Q

Match the screen type to its identifying characteristic:
1: Trash rack a: Single operating cycle
2: Manual bar screen b: Interlocking links, no lower sprocket
3: Single rake screen c: Efficiently removes hair and stringy material
4: Catenary screen d: Integrate wash press
5: Continuous self-cleaning screen e: Remove only largest debris
6: Perforated plate screen f: Rectangular openings limited in height/width
7: Stair screen g: May be located in a bypass channel
8: Inclined cylindrical screen h: Two sets of lamella lift solids up stairs

A

1=E
2=G
3=A
4=B
5=F
6=C
7=H
8=D

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20
Q

On a single rake screen, a limit switch:
a: Sets the upper and lower limits of travel for the rake
b: Adjust input line voltage
c: Modifies the minimum particle size captured
d: Turns off the drive motor if the rake is jammed

A

D

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21
Q

One disadvantage of using comminutors or grinders is:
a: Reduced potential for clogged pipes and damaged equipment
b: Increased screenings disposal costs
c: Shredded materials reduces treatment downstream
d: More frequent overflows of the influent channel

A

C

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22
Q

T/F: A WRRF with a combined sewer system is expecting a large storm. The manual bar screens are normally cleaned every hour. The operator should plan to decrease the cleaning frequency time during the and immediately after the storm.

A

False: Combined sewers bring both sewage and stormwater to the WRRF. After a storm, expect accumulated debris to be flushed from the collection system and into the WRRF. Cleaning frequency should increase.

23
Q

T/F: A shear pin is designed to break under a certain amount of force or pressure to prevent additional damage to equipment.

A

True

24
Q

Screens should be cleaned before the head loss across the screen reaches __________ or according to the screen manufacturer’s recommendations.
a: 2.5 cm (1 in)
b: 7.6 cm (3 in)
c: 12.7 cm (5 in)
d: 17.8 cm (7 in)

A

B

25
Q

This type of control mechanism is best suited for storm events or other conditions that produce highly variable amounts of screenable material:
a: Clock timer
b: Level sensor
c: Particle counter
d: HOA switch

A

B

26
Q

T/F: The volume of grit removed for every cubic meter (mgd) of flow received is very consistent from one facility to the next?

A

False: The volume of grit removed is highly dependent on the activities in the service area, condition of the collection system, type of collection system, and other factors

27
Q

T/F: As flow velocity through the basin increases, larger, denser, particles will pass through to the next process

A

True

28
Q

All of the following characteristics will influence the settling velocity of a particle EXCEPT:
a: Density
b: Size
c: Color
d: Shape

A

C

29
Q

Gravity pulls particles straight down, but this pushes them forward toward the outlet of the grit basin:
a: Velocity
b: Density
c: Viscosity
d: Conductivity

A

A

30
Q

Which of the following particles should settle the fastest through a column of water?
a: Corn kernel
b: Coffee grounds
c: Sand
d: Gravel

A

D

31
Q

A grit basin has a flow velocity of 0.5 m/s at 9 AM. As flows increase throughout the day, grit basin performance will be affected in this way:
a: The percentage of organic material captured will increase
b: Grit removal efficiency will decrease
c: Velocity through the basin will decrease
d: Air consumption will increase

A

B

32
Q

T/F: Velocity is calculated by multiplying the flowrate by the cross-sectional area

A

False: Velocity is calculated by dividing the flowrate by the cross-sectional area. Alternatively, velocity can also be calculated by dividing the distance traveled by time

33
Q

T/F: Grit classifiers return organic material to the wastewater flow and remove excess water from the grit

A

True

34
Q

A WRRF currently has one grit basin in service. The flow velocity through the basin is 0.8 m/s. How many grit basins should be in service to maintain a flow velocity between 0.24 and 0.3 m/s?
a: 1
b: 2
c: 3
d: 4

A

C. To solve this problem, divide the current velocity by the desired velocity. The current velocity is 0.8 m/s. The maximum desired velocity is 0.3 m/s. 0.8 % 0.3 =2.7 basins in service. The minimum desired velocity is 0.24 m/s. 0.8 % 0.24 =3.3 basins in service.

35
Q

Flow-proportional weirs are used in velocity control horizontal flow grit basins for this purpose:
a: produce a constant discharge rate
b: reduce buildup of grit behind the weir
c: measure flowrate
d: maintain a constant velocity

A

D

36
Q

In an aerated grit basin, this process control parameter influences which particles will sink and which will continue on to the next process:
a: Velocity of the roll pattern
b: Depth of the basin
c: Vortex dimensions
d: Flow-proportional weir setting

A

A

37
Q

This type of grit basin may use paddles to maintain the flow circulation pattern:
a: detritus tank
b: aerated grit basin
c: vortex grit basin
d: velocity control

A

C

38
Q

An operator must bypass their aerated grit basin for several days while annual maintenance is performed on the diffusers. Which of the following statements is true:
a: Airflow should be set to 50% of maximum after basin dewatering
b: Grit may pass through and cause damage to downstream equipment
c: The organic loading to downstream processes with increase
d: Screenings will accumulate in the grit channel

A

B

39
Q

Grit is typically removed from a vortex-type grit basin in this way:
a: Manual removal with shovels
b: Chain-and-flight system
c: Screw auger
d: Grit pumps

A

D

40
Q

T/F: Increased equipment run time will increase O&M costs

A

True

41
Q

T/F: When grit pumps are used to remove grit from a hopper, a timed cycle of 10 minutes of operation once every 30 minutes should always be used?

A

False: The pump run time should be coordinated with both the time needed to fill the hopper and the pumping time needed to empty the hopper

42
Q

T/F: When placing a rectangular grit basin with a chain-and-flight system into service, the basin should be filled completely before starting the mechanism

A

False: The mechanism should be started as soon as the flights are covered with water. Waiting until the basin is full will result in excessive amounts of grit accumulating around the flights. When finally started, the mechanism may not be able to move at all.

43
Q

A sample of grit is grayish in color and smells like rotten eggs. The operator should consider:
a: Slowing down the vortex paddle
b: Increasing flow velocity through the grit basin
c: Decreasing the rinse water to the grit classifier
d: Placing another grit basin into service

A

B

44
Q

The lower port of a grit cyclone is partially blocked by a piece of trash. The blockage will likely cause:
a: Excessive vibration of the cyclone
b: Increasing flow velocity through the grit basin
c: Decreasing the rinse water to the grit classifier
d: Linear delamination

A

A

45
Q

The headworks building at a new WRRF shows evidence metal and concrete corrosion. The problem seems to be even worse in covered channels. The most likely cause is:
a: Industrial discharges
b: Grease buildup
c: Inadequate ventilation
d: Over-aeration

A

C

46
Q

An operator is used to seeing an even mixing pattern on the surface of the aerated grit basin. Today, the surface is fairly smooth and does not show signs of good mixing. The operator should:
a: Increase the airflow rate to the basin
b: Check the diffusers for rags
c: Replace broken headers and diffusers
d: Adjust the outlet weir

A

B

47
Q

T/F: The water level in flow equalization basins should fluctuate over a 24-hour period.

A

True

48
Q

T/F: Because septic waste is already partially treated, it tends to be lower strength than typical domestic wastewater

A

False: Septage tends to be higher strength than domestic wastewater

49
Q

T/F: Septage can contain rocks and other debris, which can damage downstream equipment if it is not screened out

A

True

50
Q

T/F: Grease trap waste can be accepted and treated by most WRRFs under the 503 regulations as long as it comes from restaurants and not categorical industrial users

A

False: Grease trap waste is considered industrial and commercial waste, not domestic. It is regulated under 40 CFR

51
Q

A septage hauling a receipt manifest should include all of the following information EXCEPT:
a: Source, type, and amount of septage
b: Signed certification by the generator
c: Hauler’s commercial driver’s license number
d: Septage receipt date

A

C

52
Q

Septage wastes received by WRRFs should be monitored and tracked to:
a: Proportion cost of service to customers
b: Ensure treatment capacity is not exceeded
c: Calculate percentage of industrial septage received
d: Meet paint filter test requirements

A

B

53
Q

This test measures the amount of free water in screenings and grit:
a: total suspended solids
b: Mesh size
c: Biochemical oxygen demand
d: Paint filter

A

D

Wastewater (20 decks)

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