Solids Handling Practice Questions for Level 3 · Advanced

1. Question 1

   Which trend most strongly indicates that an anaerobic digester is becoming unstable?

   1. Volatile acids fall while alkalinity remains stable.
   2. Gas production rises while pH remains stable.
   3. Volatile acids remain stable while temperature holds.
   4. Volatile acids rise while alkalinity is being consumed.
   Show the answer

   Answer: D. Volatile acids rise while alkalinity is being consumed.

   Rising volatile acids with declining buffering capacity indicates that acid production is outpacing conversion and the digester is losing stability.

2. Question 2

   Underflow withdrawal from a gravity thickener decreases while feed solids loading and settling characteristics remain stable. Which response is most likely?

   1. Solids inventory and blanket depth increase, raising carryover risk.
   2. Solids inventory decreases while overflow solids increase.
   3. Blanket depth decreases while underflow concentration increases.
   4. Solids inventory remains constant while detention time decreases.
   Show the answer

   Answer: A. Solids inventory and blanket depth increase, raising carryover risk.

   Reduced underflow removal allows solids to accumulate and can increase carryover.

3. Question 3

   How does a dissolved-air flotation unit lift suspended solids to the surface?

   1. Large air pockets push the entire tank contents upward.
   2. Heated recycle water makes the solids less dense.
   3. Fine bubbles attach to solids and increase their buoyancy.
   4. Mechanical paddles sweep settled solids toward the surface.
   Show the answer

   Answer: C. Fine bubbles attach to solids and increase their buoyancy.

   Pressure release creates fine bubbles that attach to particles and float them to the surface for removal.

4. Question 4

   What does a properly determined anaerobic-digester volatile-solids reduction, calculated with an appropriate solids mass balance, principally indicate?

   1. Liquid-volume reduction caused by sludge thickening alone.
   2. Pathogen reduction demonstrated independently of the required pathogen criteria.
   3. Destruction and stabilization of biodegradable organic solids.
   4. Solids-capture performance of downstream dewatering equipment.
   Show the answer

   Answer: C. Destruction and stabilization of biodegradable organic solids.

   Volatile-solids reduction is a measure of organic destruction and stabilization, not every compliance criterion.

5. Question 5

   A belt press makes wetter cake after maintenance. Feed solids and polymer drawdown are steady. Wash-water pressure is normal, but the belt wanders toward one edge and the measured tension changes each pass. Which part should be checked first?

   1. Polymer injection mixer
   2. Feed-sludge transfer pump
   3. Belt tracking and tension
   4. Filtrate return control valve
   Show the answer

   Answer: C. Belt tracking and tension

   The performance change follows maintenance, and the belt now wanders while its tension varies. With feed, polymer, and wash-water conditions steady, the evidence points to the belt tracking and tension setup.

Operator Master has 10 Level 3 · Advanced solids handling questions, free.

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