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Wastewater Treatment Basic Operations > Fixed Film Secondary Treatment > Flashcards

Fixed Film Secondary Treatment Flashcards

1
Q

What is a rotating biological contactor?

A

Fixed film biological treatment where biological slime growth is rotated through the waste stream and air to remove BOD and dissolved solids

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2
Q

Components of an RBC

A 
Biological slime growth on the media
Rotating shaft
Tanks - sits about 40% submerged
Baffles
Covers
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3
Q

Why are RBCs almost always preceded by primary treatment?

A

If settlable solids arent removed the filter can plug, the basin can fill which decreases detent time, and the basin can go septic

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4
Q

What is sloughing?

A

When extra biological growth detaches from the media as it becomes heavier. It is then carried to the secondary clarifier

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5
Q

How does RBC sludge compare to waste activated sludge?

A

Generally much thicker/denser because it is typically older

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6
Q

What is the purpose of the voids in the media?

A

Allow growth of bacteria
Evenly distribute wastewater
Allow airflow for the aerobic process

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7
Q

How is biological growth accomplished on RBC media?

A

Via adsorption absorption

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8
Q

What is the typical surface area of standard density RBC media?

A

90,000-110,000 square feet

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9
Q

What is the surface area of high density RBC media?

A

120,000 to 160,000 square feet

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10
Q

What is the typical hydraulic detention time of an RBC?

A

1-4 hours

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11
Q

Can RBCs have stages?

A

Yes, typically separated by baffles. BOD levels reduce from stage to stage and late stages can be used for nitrification

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12
Q

RBC shaft rotation speed

A

About 1.5 RPM while 40% immersed

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13
Q

What is the typical length if an RBC shaft?

A

25 feet

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14
Q

How are RBC shafts driven?

A

Mechanical drives or air drives

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15
Q

Advantages of mechanical drive RBC

A

Lower energy consumption
Uniform rotation speed
Speed adjustments are easier

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16
Q

Disadvantages of mechanical drive RBC

A

Supplemental aeration may be required

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17
Q

Air drive RBC advantages

A 
Adds dissolved oxygen
Less maintenance
Aids in nitrification
Strips off extra zoogleal mass
Less torque on the drive
Minimizes solids accumulation in the tank
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18
Q

Disadvantages of air drive RBC

A

Speed control is not exact
Prone to growth imbalance
Can strip off too much zoogleal mass
Higher power requirements

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19
Q

What is the purpose of an RBC cover?

A
  • Protects from weather
  • Prevent hard rain from washing slime
  • Prevents algae growth
  • Protects media from becoming brittle from sunlight exposure
  • Contains odors
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20
Q

Factors affecting RBC treatment

A 
F:M ratio
Dissolved oxygen
Temp
Nutrients
Toxicity
Flow
Rotational speed
Disc submergence
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21
Q

pH requirements for nitrifying

A

pH needs to be higher than typical domestic wastewater, around 8.4

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22
Q

Typical domestic wastewater pH

A

6.5-8.5

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23
Q

How much alkalinity is required for nitrifying?

A

7.14 times the concentration of the influent NH3

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24
Q

Dissolved oxygen for an RBC designed for primary effluent

A

0.5-1.0 mg/L in the first stage

1-3 mg/L at the end of the first stage

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25
Q

Dissolved oxygen in an RBC designed for nitrification

A

1-3 mg/L in the first stage

4-6 mg/L by the final stage

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26
Q

Temperature impact on RBC

A

More sensitive to temp than suspended growth

<55 degrees F will result in decreased BOD removal

Nitrification will be affected first

27
Q

RBC Hydraulic loading for BOD removal

A

1.5-6 GPD/square foot

28
Q

RBC hydraulic loading rate for nitrogen removal

A

1.5 - 1.8 GPD/square foot

29
Q

Organic loading rate for RBC

A

Soluble BOD: 2.5-4lbs BOD/Day/1,000 sq feet

Total BOD 6-8lbs BOD/Day/1,000 sq feet

30
Q

How are RBCs affected by toxicity?

A

Generally less vulnerable than suspended growth

Toxic impact is directly related to dose and duration of exposure

31
Q

Examples of submerged fixed film

A

Moving bed biological reactors
Fixed film biological reactors
Integrated fixed film activated sludge

32
Q

Advantages of submerged fixed film

A

More efficient, more biomass, longer detent times, similar footprint

33
Q

What is an MBBR?

A

A tank partially filled with free floating plastic media that the biomass attaches to.

34
Q

Advantages of an MBBR

A 
Smaller footprint
No return
Biomass is self regulated
Less sensitive to toxics
Nitrification is possible
Increase capacity with more media
35
Q

Disadvantages of MBBR

A

Higher energy costs
Cant remove phosphorus biologically
Proprietary media
Need additional screening

36
Q

What is Integrated Fixed Film Activated Sludge?

A

Media is submerged in mixed liquor and a return is set up on the clarifier

37
Q

Advantages of IFAS?

A

Higher level of treatment in smaller footprint
Biological phosphorous removal
Nitrification

38
Q

What should biological growth look like during normal operations?

A

Brown to grey
No algae
Shaggy and fairly uniform in coverage

39
Q

What would black slime growth imply?

A

Solid or BOD overload with probable low dissolved oxygen

40
Q

What would white appearance of slime imply?

A

Sulfer loving bacteria are present (filaments)

Industrial discharges containing sulfer
Sludge deposits accumulating in tank

41
Q

What colors are present on media when Nitrifying In an RBC?

A

1st stage is usually light brown, later stages can be gold/rusty/reddish

42
Q

What are characteristics of an RBC designed for BOD removal?

A

Standard density media

Thicker biofilm

43
Q

What are characteristics of an RBC designed for nitrification?

A

High density media

Thinner biofilm

44
Q

What is plug flow in an RBc?

A

When the waste is introduced to a portion of the RBC rather than the entire surface area at once, and the waste is polished in later stages

45
Q

What is completely mixed flow in an RBC?

A

The flow is introduced to the entire reactor volume simultaneously

46
Q

What are the two primary types of trickling filters?

A

Fixed nozzle

Rotary distributor

47
Q

Pros of a fixed nozzle trickling filter

A

Even flow distribution

48
Q

Cons of a fixed nozzle trickling filter

A

Maintenance is difficult

49
Q

Benefits of random media in a trickling filter?

A

Increases detention time. Ideal in low organic matter applications with few particles

50
Q

Benefits of vertical flow media in trickling filter

A

Less prone to clogging, efficient in removing excess biomass.

Useful in high BOD loading applications

51
Q

Cross flow media benefits in a trickling filter

A

Improved pollution removal

Effective with low to medium BOD loading

52
Q

Purpose of recirculation in a trickling filter

A 
Increases removal efficiency
Increase ventilation
Promotes uniform sloughing
Decreased snails and flies (psychoda)
Reduces strength of wastewater applied
53
Q

Purpose of the underdrain system if a trickling filter

A

Collect effluent
Supports the media
Permits airflow

54
Q

How does oxygen affect trickling filter treatment?

A

Recirculation increases dissolved oxgen

Maintain a 1.5-2.0mg/L DO in effluent

55
Q

How does temperature affect trickling filter operation?

A

Lower temperatures lower removal efficiencies

Recirculation lowers temp

56
Q

What is the appropriate pH range for a trickling filter?

A

5.5-8.5 (stay higher if you want to nitrify)

57
Q

What are the classifications of trickling filters based on organic-loading rate?

A

Low-rate <25 lbs/day/1000ft
Intermediate-rate 25-40lbs/day/1000ft
High-rate 40-100 lbs/day/1000ft
Roughing filter 100-300 lbs/day/1000ft

58
Q

What is the purpose of a low-rate trickling filter?

A

Achieve high BOD removal and may perform nitrification

59
Q

What is the purpose of intermediate rate trickling filters?

A

Removal of BOD without complete nitrification

60
Q

What is the purpose if high-rate trickling filters?

A

Need to treat high incoming BOD; they likely need to be combined with another process

61
Q

What is the purpose of a roughing trickling filter?

A

To reduce the required size of the second stage treatment process; often in industrial pretreatment

62
Q

Organic loading rate for a nitrifying trickling filter

A

3-10lbs BOD/day/1000ft with rock

6-18lbs BOD/Day/1000ft with synthetic

63
Q

What conditions are required to nitrify in a trickling filter?

A

Greater surface area
More DO
Adequate alkalinity
Warmer temps

64
Q

What are causes of psychoda and snails in a trickling filter?

A

Poor distribution and insufficient hydraulic loading

Wastewater Treatment Basic Operations (16 decks)

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