Primary Treatment Practice Questions for Washington Level II

1. Question 1

   Primary sludge in a hopper turns black, gas bubbles appear, and odors increase. What is the likely cause?

   1. Anaerobic breakdown of stored sludge.
   2. Hydraulic washout of settled solids.
   3. Excess surface skimming of floating scum.
   4. Dilution of sludge by high influent flow.
   Show the answer

   Answer: A. Anaerobic breakdown of stored sludge.

   Primary sludge can turn septic when it remains in the hopper too long. Anaerobic breakdown can darken the sludge and produce gas and odors.

2. Question 2

   What is the primary purpose of a scum baffle located ahead of a clarifier effluent weir?

   1. Direct settled sludge toward the center hopper.
   2. Increase the velocity beneath the inlet structure.
   3. Keep floating material from leaving with the effluent.
   4. Measure the depth of the sludge blanket.
   Show the answer

   Answer: C. Keep floating material from leaving with the effluent.

   The scum baffle blocks floating grease, foam, and debris from passing over the effluent weir.

3. Question 3

   Heavy scum repeatedly collects on a primary clarifier. What influent condition commonly contributes to it?

   1. A high load of dense mineral solids
   2. A high load of dissolved, nonfloatable material
   3. A low load of floatable organic material
   4. A high load of fats, oils, and grease
   Show the answer

   Answer: D. A high load of fats, oils, and grease

   Fats, oils, and grease are less dense than water and tend to float, so elevated influent FOG commonly increases primary scum.

Operator Master has 3 Level II primary treatment 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
• Solids Handling7 questions
• Secondary Clarification5 questions
• Grit Removal2 questions