Solids Handling Practice Questions for Level 4 · Expert

1. Question 1

   A gravity thickener has stable blanket depth and underflow concentration, but drive torque rises and one rake arm lags once per revolution. A second thickener can carry the load for six hours. Which plan best protects equipment and confirms readiness to return?

   1. Increase polymer dose and keep the unit online
   2. Lower the overflow weir and compare torque through one revolution
   3. Transfer load, correct the rake fault, and test before return
   4. Increase underflow pumping until the lag disappears
   Show the answer

   Answer: C. Transfer load, correct the rake fault, and test before return

   The repeatable mechanical lag warrants isolation. Available redundancy permits inspection and correction of the rake, track, or drive fault, followed by a controlled test before solids loading resumes.

2. Question 2

   DAF feed rises 30%, thickened-solids concentration falls, and the air-to-solids ratio drops. Saturator pressure is normal, the recycle pump is already at its approved maximum, and an idle parallel DAF unit is available. What is the best response?

   1. Increase skimmer speed and leave all flow on one unit
   2. Split feed and verify both float blankets
   3. Lower polymer dose until the float layer thins
   4. Reduce saturator pressure to make larger bubbles
   Show the answer

   Answer: B. Split feed and verify both float blankets

   The loaded unit has no approved recycle capacity left. Dividing solids loading restores air available per unit of solids without forcing equipment beyond its limit.

3. Question 3

   Digester gas production exceeds current use, and the gas holder level is rising. The boiler is meeting heat demand, while the cogeneration engine is below rated load and the plant is buying power. What should be adjusted first?

   1. Reduce digester mixing until gas production falls
   2. Raise boiler firing above the current heat demand
   3. Hold gas for relief
   4. Raise engine load within its approved range
   Show the answer

   Answer: D. Raise engine load within its approved range

   Available gas can displace purchased power by increasing engine load while the boiler is already meeting the heat requirement.

4. Question 4

   A centrifuge trips on high vibration only after feed begins. The bowl is clean and smooth when empty. Feed solids vary widely, and the feed tank mixer cycles off before each trip. After the machine is safely stopped, what should be corrected before restart?

   1. Increase the vibration trip setting
   2. Stabilize mixing and feed solids
   3. Increase bowl speed during feeding
   4. Reduce the polymer solution strength
   Show the answer

   Answer: B. Stabilize mixing and feed solids

5. Question 5

   A centrate tank can hold one full day of production. Returning centrate in four hours causes a daily ammonia peak. Overnight total ammonia load is lowest, and aeration has enough unused capacity then. Which return strategy best uses the storage?

   1. Return all centrate during peak influent flow
   2. Return centrate at the dewatering rate
   3. Pace centrate through the low-load period
   4. Hold centrate until the tank is completely full
   Show the answer

   Answer: C. Pace centrate through the low-load period

Operator Master has 11 Level 4 · Expert solids handling questions, free.

• Plant Operations35 questions
• Biological Treatment9 questions
• Disinfection7 questions
• Laboratory7 questions
• Math and Calculations5 questions
• Pumps and Hydraulics5 questions
• Safety4 questions
• Secondary Clarification3 questions
• Grit Removal2 questions
• Headworks and Screening2 questions
• Primary Treatment2 questions
• Regulations and Compliance2 questions