Secondary Clarification Practice Questions for Washington Level I

1. Question 1

   What is the purpose of an **effluent weir** in a clarifier?

   1. Allow clarified water to leave near the surface
   2. Remove settled sludge from the tank floor
   3. Skim floating material from the water surface
   4. Measure the depth of the sludge blanket
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   Answer: A. Allow clarified water to leave near the surface

   Clarified water flows over the effluent weir near the water surface and enters a channel or launder that carries it from the clarifier.

2. Question 2

   What is the main purpose of **secondary treatment**?

   1. Separate settleable solids by gravity
   2. Filter particles remaining after biological treatment
   3. Biologically remove biodegradable waste
   4. Hold incoming flow to reduce flow peaks
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   Answer: C. Biologically remove biodegradable waste

   Secondary treatment uses biological processes to remove biodegradable material remaining after earlier physical treatment steps.

3. Question 3

   Where does settled sludge collect in a clarifier?

   1. Above the effluent weirs
   2. At the bottom of the tank
   3. Inside the influent pipe
   4. On top of the scum layer
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   Answer: B. At the bottom of the tank

   Settleable solids move to the bottom of the clarifier and form the sludge blanket.

4. Question 4

   Why does activated sludge flow to a secondary clarifier after aeration?

   1. To return grit to the headworks
   2. To add more oxygen to the wastewater
   3. To disinfect the water with chlorine
   4. To separate biomass from treated water
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   Answer: D. To separate biomass from treated water

   The secondary clarifier separates biological solids from treated water after aeration; some settled biomass may be returned and the remainder wasted.

5. Question 5

   What does a surface skimmer remove from a clarifier?

   1. Settled sludge from the tank bottom
   2. Floating grease, oil, and scum
   3. Dissolved oxygen from the water
   4. Sand carried through the grit chamber
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   Answer: B. Floating grease, oil, and scum

   A surface skimmer collects floating material such as grease, oil, and scum so it can be removed from the clarifier.

Operator Master has 5 Level I secondary clarification questions, free, with an explanation after every answer.

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• Headworks and Screening4 questions
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• Laboratory2 questions
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