Solids Handling Practice Questions for Washington Level II

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

   During a dewatering trial, feed solids, flow, mixing, and polymer make-down remain stable. Capture improves as dose rises, then weakens and produces cloudier centrate after another dose increase. Which interpretation best fits the dose-response pattern?

   1. The final dose remained below the minimum effective conditioning range.
   2. The final dose exceeded the useful conditioning range.
   3. The polymer reached its best dose only after capture began declining.
   4. Polymer dose had no relationship to the repeated change in capture.
   Show the answer

   Answer: B. The final dose exceeded the useful conditioning range.

   With the other variables controlled, deterioration after the optimum supports polymer overdose.

4. Question 4

   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.

5. Question 5

   What does mixed-liquor volatile suspended solids most closely represent in an activated-sludge basin?

   1. The fixed inorganic portion remaining after ignition.
   2. The volatile organic fraction of the mixed-liquor suspended solids.
   3. The combined dissolved and suspended mineral fraction.
   4. The total suspended solids without separation into volatile and fixed fractions.
   Show the answer

   Answer: B. The volatile organic fraction of the mixed-liquor suspended solids.

   MLVSS estimates the volatile organic portion, which includes biomass and other volatile organic solids.

Operator Master has 7 Level II solids handling questions, free, with an explanation after every answer.

• Plant Operations35 questions
• Math and Calculations21 questions
• Pumps and Hydraulics18 questions
• Biological Treatment11 questions
• Laboratory9 questions
• Disinfection7 questions
• Secondary Clarification5 questions
• Primary Treatment3 questions
• Grit Removal2 questions