Page 1 of 57
Wastewater Treatment Operator Certification Test 3&4
2026-2027 COMPLETE 180 QUESTIONS AND VERIFIED
SOLUTIONS LATEST UPDATE THIS YEAR
Wastewater Treatment Operator Certification Test 3
QUESTION: What change would most likely be made to an activated sludge process during the
winter?
A) Decrease solids under aeration
B) Increase pH
C) Increase solids under aeration
D) Add chlorine to the influent of the aeration tank - ANSWER-C) Increase solids under aeration
(v.2 pg 71)
QUESTION: If the influent solids loading rate to an activated sludge system increases, what
should be done?
,Page 2 of 57
A) Increase sludge waste rate
B) Decrease MLSS
C) Decrease temperature of aeration tank
D) Reduce wasting rate of the sludge - ANSWER-D) Reduce wasting rate of the sludge (v.2 pg
53)
QUESTION: What could happen if a valve is closed to quickly?
A) Water hammer
B) Cavitation
C) Tuberculation
D) Gasification - ANSWER-A) Water hammer
QUESTION: Which part of a facultative pond would you most likely find abundant algae growth?
A) Middle layer
,Page 3 of 57
B) Lower layer
C) Upper layer
D) Algae grows evenly in every layer - ANSWER-C) Upper layer (v.1 pg 299)
QUESTION: What is the main purpose of primary treatment?
A) Convert dissolved or suspended solids into a form more readily separated from wastewater.
B) To remove substances that readily settle or float
C) To remove debris and trash, such as wood, roots and rags.
D) To remove heavy inorganic material such as sand, eggshells, gravel, and cinders - ANSWER-B)
To remove substances that readily settle or float (v.1 pg 43)
QUESTION: What may be the problem if solids in the secondary clarifier are settling very
slowly?
A) Denitrification
, Page 4 of 57
B) Nitrification
C) Sludge bulking
D) Excessive sludge pumping - ANSWER-C) Sludge bulking (v.2 pg 71)
QUESTION: What will happen if the influent BOD increases in an activated sludge system?
A) Less oxygen will be required in the aeration tank
B) Hydrogen sulfide production will increase during normal operation
C) Temperature in the secondary clarifier will decrease
D) More oxygen will be required in the aeration tank - ANSWER-D) More oxygen will be
required in the aeration tank (v.2 pg 19)
QUESTION: Which of the following is the most likely cause of oxygen depletion in the receiving
waters, downstream of a wastewater treatment plant?
A) Dissolved solids
Wastewater Treatment Operator Certification Test 3&4
2026-2027 COMPLETE 180 QUESTIONS AND VERIFIED
SOLUTIONS LATEST UPDATE THIS YEAR
Wastewater Treatment Operator Certification Test 3
QUESTION: What change would most likely be made to an activated sludge process during the
winter?
A) Decrease solids under aeration
B) Increase pH
C) Increase solids under aeration
D) Add chlorine to the influent of the aeration tank - ANSWER-C) Increase solids under aeration
(v.2 pg 71)
QUESTION: If the influent solids loading rate to an activated sludge system increases, what
should be done?
,Page 2 of 57
A) Increase sludge waste rate
B) Decrease MLSS
C) Decrease temperature of aeration tank
D) Reduce wasting rate of the sludge - ANSWER-D) Reduce wasting rate of the sludge (v.2 pg
53)
QUESTION: What could happen if a valve is closed to quickly?
A) Water hammer
B) Cavitation
C) Tuberculation
D) Gasification - ANSWER-A) Water hammer
QUESTION: Which part of a facultative pond would you most likely find abundant algae growth?
A) Middle layer
,Page 3 of 57
B) Lower layer
C) Upper layer
D) Algae grows evenly in every layer - ANSWER-C) Upper layer (v.1 pg 299)
QUESTION: What is the main purpose of primary treatment?
A) Convert dissolved or suspended solids into a form more readily separated from wastewater.
B) To remove substances that readily settle or float
C) To remove debris and trash, such as wood, roots and rags.
D) To remove heavy inorganic material such as sand, eggshells, gravel, and cinders - ANSWER-B)
To remove substances that readily settle or float (v.1 pg 43)
QUESTION: What may be the problem if solids in the secondary clarifier are settling very
slowly?
A) Denitrification
, Page 4 of 57
B) Nitrification
C) Sludge bulking
D) Excessive sludge pumping - ANSWER-C) Sludge bulking (v.2 pg 71)
QUESTION: What will happen if the influent BOD increases in an activated sludge system?
A) Less oxygen will be required in the aeration tank
B) Hydrogen sulfide production will increase during normal operation
C) Temperature in the secondary clarifier will decrease
D) More oxygen will be required in the aeration tank - ANSWER-D) More oxygen will be
required in the aeration tank (v.2 pg 19)
QUESTION: Which of the following is the most likely cause of oxygen depletion in the receiving
waters, downstream of a wastewater treatment plant?
A) Dissolved solids
