Primary Treatment Practice Questions for Level 1 · Entry

1. Question 1

   What is the main purpose of a **primary clarifier**?

   1. Keep incoming solids suspended by continuous mixing
   2. Allow settleable solids to sink for removal
   3. Add oxygen for microorganisms to treat wastewater
   4. Separate biological solids after aeration
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   Answer: B. Allow settleable solids to sink for removal

   A primary clarifier slows wastewater so readily settleable solids sink and can be removed as primary sludge.

2. Question 2

   What is the main purpose of primary clarification?

   1. To remove settleable and floatable solids
   2. To convert ammonia into nitrate
   3. To destroy organisms with ultraviolet light
   4. To dry sludge before disposal
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   Answer: A. To remove settleable and floatable solids

   Primary clarification separates solids that settle to the bottom and material that floats to the surface.

3. Question 3

   A primary clarifier skimmer moves the surface mat into its collection box. The box level stays high, and the scum sump receives no flow. What should the operator check first?

   1. Adjust the skimmer blade
   2. Clear the effluent weir
   3. Increase sludge withdrawal
   4. Inspect the scum drain
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   Answer: D. Inspect the scum drain

   The skimmer delivers the mat to the collection box, but no flow reaches the sump, so a restricted scum drain is the direct first check. Adjusting the blade does not fit successful delivery to the box; the effluent weir and sludge withdrawal do not carry scum from the box.

4. Question 4

   A primary clarifier sludge blanket is rising. The sludge totalizer shows 9,000 gal/day removed, compared with the usual 18,000 gal/day. What should the operator do first?

   1. Raise collector speed
   2. Increase scum-removal cycles
   3. Add coagulant at inlet
   4. Restore sludge withdrawal
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   Answer: D. Restore sludge withdrawal

   The removed volume fell from the usual 18,000 gal/day to 9,000 gal/day, a decrease of 9,000 gal/day. That evidence supports insufficient sludge withdrawal, so restoring normal withdrawal is the first response. Raising collector speed, increasing scum-removal cycles, or adding coagulant does not correct the reduced underflow volume.

5. Question 5

   One section of a primary clarifier has turbid effluent and a surface current from the inlet. The blanket is low, and other weir sections are clear. What is the likely condition?

   1. Uneven basin flow
   2. Broken collector flight
   3. Clogged effluent-weir section
   4. Sludge bulking
   Show the answer

   Answer: A. Uneven basin flow

   The localized surface current from the inlet and turbidity at one outlet section indicate uneven basin flow. A broken collector flight primarily disrupts solids collection, a clogged effluent-weir section changes withdrawal at the clogged section, and sludge bulking is not consistent with the low blanket and localized inlet-to-outlet current.

Operator Master has 6 Level 1 · Entry primary treatment questions, free.

• Plant Operations54 questions
• Math and Calculations50 questions
• Laboratory13 questions
• Safety13 questions
• Biological Treatment12 questions
• Disinfection10 questions
• Pumps and Hydraulics8 questions
• Regulations and Compliance8 questions
• Solids Handling8 questions
• Secondary Clarification5 questions
• Grit Removal4 questions
• Headworks and Screening4 questions