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wastewater grade 3 > Activated Sludge 11.1 > Flashcards

Activated Sludge 11.1 Flashcards

1
Q

During increased flow from storms, what problems can arise? (Combined Sewer System)

A
  • Reduced wastewater time in treatment units (hydraulic overloading)
  • Increased amounts of grit and silt which lower the volatile content of solids
  • increased organic load during initial washout of accumulated sewer deposits
  • Rapid changes in wastewater temp and solids content
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2
Q

What could happen if a long deactivated lift station is brought back online or a blockage cleared?

A
  • Large volumes of septic wastewater could cause a shock load on the treatment process
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3
Q

What are required water quality indicators

A
  • Chemical Oxygen Demand (COD)
  • Suspended Solids
  • Nitrogen
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4
Q

What factors could have changed if the desired effluent quality is not achieved?

A
  • Higher COD or BOD load applied to the aerator (influent load)
  • More difficult to treat wastes
  • Unsuitable MLSS concentration in the aerator
  • Lower or Higher rate of WAS
  • Unsuitable RAS rate
  • Higher solids concentrationts in digester supernatant returned to plant flow or return too rapid
  • drop of oxygen levels
  • increase or decrease in wastewater temp
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5
Q

What two major variables affect the way an activated sludge plant is operated?

A
  • Dischargers to the collection system
  • in-plant operational variables
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6
Q

Besides storm flows, what other variables in the collection system can affect the operation of an activated sludge plant?

A
  • wastes discharged
  • maintenance activities
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7
Q

Besides the operator, who should be present during the start up of a new activated sludge plant? Why?

A
  • design engineers
  • vendors
  • OTHER nearby operators
  • specialists
  • equipment manufacturers
  • contractors
  • To make sure that any equipment breakdowns are not caused by improper startup
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8
Q

Where can record data for suspended solids and volatile content be collected from?

A
  • Primary effluent
  • aerator mixed liquor
  • return sludge
  • final clarifier or secondary sedimentation tank effluent
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9
Q

Where can record data for BOD, COD, or TOC2 (total organic carbon) be collected?

A
  • Plant influent
  • Primary effluent
  • Final clarifier or secondary sedimentation tank effluent
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10
Q

How long can results be given on a COD test?

A

4 hours

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11
Q

What disadvantages does a BOD test have in terms of operational control?

A
  • Procedural errors can cause a large variation in results
  • 5 days of waiting are required before results are available
  • Only a portion of the load on the activated sludge process is measured by the test
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12
Q

Where can record data for Dissolved Oxygen (DO) be collected?

A
  • Aerator
  • Final Clarifier or secondary sedimentation tank (inside the effluent weir)
  • Final effluent
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13
Q

Where can record data for Settleable Solids be collected?

A
  • Influent
  • Mixed liquor settleability test
  • Digester supernatant
  • Final effluent
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14
Q

Where can record data for temperature be collected?

A
  • Influent
  • Aerator
  • Final effluent
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15
Q

Where can record data for pH be collected?

A
  • Influent
  • primary effluent
  • aerator (measure immediately off aerator)
  • Final effluent
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16
Q

Where can record data for clarity (secchi disk) or turbidity (turbidimeter) be collected?

A

Final clarifier

17
Q

Where can record data for Chlorine demand be collected?

A

Final clarifier effluent

18
Q

Where can record data for Coliform Group Bacteria be collected?

A

Plant effluent

19
Q

What record data for meter readings and calculations should be collected?

A
  • daily flow
  • pounds of solids under aeration
  • pounds of COD or BOD to aerators
  • pounds of solids in effluent
  • RAS rate
  • WAS rate
  • air to aerators (diffused air system); hours operated at various speeds (mechanical aeration)
  • Sludge age
  • pounds of solids in sludge to digester
  • pounds of solids in digester supernatant
  • power cost
20
Q

What daily observations must be made for daily records?

A
  • odors
  • Influent (color and level of inflow)
  • Primary Clarifier (Scum and color)
  • Aeration tank (Turbulence, color, and amount of surface foam/scum)
  • Secondary Clarifier (Effluent clear or turbid, type of solids on surface and influent)
  • RAS: Color and Odor
  • Equipment & Motors
  • Condition of receiving waters both upstream and downstream of discharge point
21
Q

Why should aerator pH be measured in the aerator instead of the lab?

A

pH can change rapidly outside the aerator

22
Q

What are two methods to supply oxygen from the air to bacteria?

A
  • Mechanical Aeration
  • Diffused Aeration
23
Q

What is the formula to determine Sludge Age?

A

(Suspended Solids under aeration, lbs)/(Suspended solids added, lbs/day)

24
Q

Define High-Rate activated Sludge

A
  • Highest loading of F/M ratio
  • age ranges 0.5-2.0 days
  • lower quality effluent
  • more easily upset; requires tighter control
25
Q

Define Conventional Activated Sludge

A
  • Most common type
  • Sludge Age; 3-7 days
  • 50% lower f/m loading than high rate
  • high quality effluent
  • able to absorb some shock loads
26
Q

Define extended aeration

A
  • most common is smaller package plants (complete oxidation systems)
  • most stable due to light F/M loading
  • Sludge age; greater than 10 days
  • Higher effluent suspended solids than conventional loadings
27
Q

What is the purpose of aeration?

A
  • providing DO
  • Mixing of the mixed liquor and wasterwater in aeration tank
28
Q

What types of aeration are there?

A
  • diffused aeration
  • mechanical aeration
  • pure oxygen systems
29
Q

How is mechanical aeration achieved?

A

Motor-driven roating impeller or a brush rotor splash the mixed liquor into the atmosphere, mixing in oxygen.

30
Q

How does Diffused Aeration work?

A

Numerous diffusers connected to air headers at the bottom of the tank, pump tiny air bubbles through the mixed liquor to oxygenate the mixed liquor

31
Q

Why are diffusors at the bottom of the tank?

A
  • Maximize contact time
  • encourage mixing
  • discourage deposits on bottom of tank
32
Q

What are the two types of aeration blowers?

A
  • Positive displacement
  • Centrifugal
33
Q

What is a Volute?

A

Spiral-shaped casing which surrounds a pump, blower, or turbine impeller and collects liquid or gas discharged by the impeller

34
Q

Characteristics of Positive displacement blowers

A
  • provides constant volume (cubic feet/min; cfm) per revolution of rotors/lobes
  • low rpms
  • less than 20,000 Cubic feet/min (CFM)
35
Q

Characteristics of Centrifual Blowers

A
  • variable air output controlled by guide vanes
  • high rpms
  • 20,000 - 150,000 CFM
36
Q

Define Aerobes

A

Bacteria that must have melecular DO to survive

37
Q

Effectiveness of the activated sludge treatment process in reducing the waste load depends on what?

A
  • The amount of activated sludge solids in the the system
  • Health of the organisms
38
Q

How much activated sludge can be wasted?

A

1-20% of the total incoming flow (try not to change more than 10-15% from one day to the next)

wastewater grade 3 (1 decks)

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