Basic Wastewater Operator Practice Exam (2025/2026) aligned with ABC / entry-level municipal wastewater operator
standards.
What is the predominant organism in a healthy activated sludge treatment plant?
A. Stalked ciliates
B. rotifers
C. nematodes
D. amoebas - (ANSWER)A. Stalked Ciliates
A composite sample must be?
A. sporadically collected in the treatment plant
B. taken at one time
C. analyzed immediately
D. representative and sub-samples time spaced over 15 minutes apart - (ANSWER)D. representative and
sub-samples time spaced over 15 minutes apart
What is the standard volume for a BOD sample bottle?
A. 150 mL
B. 200 mL
C. 300 mL
D. 500 mL - (ANSWER)c. 300 mL
If you have a lime slurry feed line, what is the best valve to use?
A. plug valve
B. butterfly valve
,Basic Wastewater Operator Practice Exam (2025/2026) aligned with ABC / entry-level municipal wastewater operator
standards.
C. RPZ dual check valve
D. gate valve - (ANSWER)A. plug valve
5. If you notice a predominance of rotifers in your activated sludge sample while looking at it under a
microscope, what does this indicate?
A. healthy sludge
B. young sludge
C. old sludge
D. middle age sludge - (ANSWER)C. old sludge
Calculate the BOD using the given information:
Initial DO: 8.3
Final DO: 5.9
Milliliters of sample used: 2
a. 360 mg/L
b. 210 mg/L
c. 856 mg/L
d. 36 mg/L - (ANSWER)a. 360 mg/L
If your activated sludge plant begins to nitrify, what conditions would you expect to decrease?
A. settling in clarifiers
B. chlorine demand
C. BOD effluent
,Basic Wastewater Operator Practice Exam (2025/2026) aligned with ABC / entry-level municipal wastewater operator
standards.
D. TSS in effluent - (ANSWER)a. settling in the clarifiers
How do you calibrate a chemical feed pump?
A. by measuring the pump output
B. using the SWAG method
C. jar test
D. with a microscope - (ANSWER)A. by measuring the pump output
What is the chemical formula for sulfuric acid?
a. HNO3
b. HCl
c. NaOH
d. H2SO4 - (ANSWER)d. H2SO4
What is the most common type of activated sludge package plants?
a. extended aeration
b. sequential batch reactor
c. oxidation ditch
d. bardenpho - (ANSWER)a. extended aeration
What is the most appropriate method of reducing the F:M ratio?
A. increase wasting
, Basic Wastewater Operator Practice Exam (2025/2026) aligned with ABC / entry-level municipal wastewater operator
standards.
b. decrease wasting
c. reduce BOD from influent flow
D. add polymer to RAS to increase settling - (ANSWER)b. decrease wasting
An operator notices a portion of the aeration tank with large bubbles rising up. What is the most likely
problem?
a. equal air distribution
b. unequal air distribution caused by a blown/clogged diffuser
c. normal operation
d. reason to believe the air filter in the blower is clogged - (ANSWER)b. unequal air distribution caused
by a blown diffuser
What is suction lift?
a. a team approach to lifting heavy objects
b. the pressure on the suction side of the pump
c. the measurement of liquid pressure at the pump
d. the measure of how bad your workers lift heavy objects - (ANSWER)b. the pressure on the suction
side of the pump
The primary effluent to a RBC system is 350 mg/L BOD. The primary unit removes 83% the secondary
unit removes 50% and the final unit removes 25%. What is the BOD leaving the final unit of the RBC
train?
A. 290 mg/L
b. 60 mg/L
standards.
What is the predominant organism in a healthy activated sludge treatment plant?
A. Stalked ciliates
B. rotifers
C. nematodes
D. amoebas - (ANSWER)A. Stalked Ciliates
A composite sample must be?
A. sporadically collected in the treatment plant
B. taken at one time
C. analyzed immediately
D. representative and sub-samples time spaced over 15 minutes apart - (ANSWER)D. representative and
sub-samples time spaced over 15 minutes apart
What is the standard volume for a BOD sample bottle?
A. 150 mL
B. 200 mL
C. 300 mL
D. 500 mL - (ANSWER)c. 300 mL
If you have a lime slurry feed line, what is the best valve to use?
A. plug valve
B. butterfly valve
,Basic Wastewater Operator Practice Exam (2025/2026) aligned with ABC / entry-level municipal wastewater operator
standards.
C. RPZ dual check valve
D. gate valve - (ANSWER)A. plug valve
5. If you notice a predominance of rotifers in your activated sludge sample while looking at it under a
microscope, what does this indicate?
A. healthy sludge
B. young sludge
C. old sludge
D. middle age sludge - (ANSWER)C. old sludge
Calculate the BOD using the given information:
Initial DO: 8.3
Final DO: 5.9
Milliliters of sample used: 2
a. 360 mg/L
b. 210 mg/L
c. 856 mg/L
d. 36 mg/L - (ANSWER)a. 360 mg/L
If your activated sludge plant begins to nitrify, what conditions would you expect to decrease?
A. settling in clarifiers
B. chlorine demand
C. BOD effluent
,Basic Wastewater Operator Practice Exam (2025/2026) aligned with ABC / entry-level municipal wastewater operator
standards.
D. TSS in effluent - (ANSWER)a. settling in the clarifiers
How do you calibrate a chemical feed pump?
A. by measuring the pump output
B. using the SWAG method
C. jar test
D. with a microscope - (ANSWER)A. by measuring the pump output
What is the chemical formula for sulfuric acid?
a. HNO3
b. HCl
c. NaOH
d. H2SO4 - (ANSWER)d. H2SO4
What is the most common type of activated sludge package plants?
a. extended aeration
b. sequential batch reactor
c. oxidation ditch
d. bardenpho - (ANSWER)a. extended aeration
What is the most appropriate method of reducing the F:M ratio?
A. increase wasting
, Basic Wastewater Operator Practice Exam (2025/2026) aligned with ABC / entry-level municipal wastewater operator
standards.
b. decrease wasting
c. reduce BOD from influent flow
D. add polymer to RAS to increase settling - (ANSWER)b. decrease wasting
An operator notices a portion of the aeration tank with large bubbles rising up. What is the most likely
problem?
a. equal air distribution
b. unequal air distribution caused by a blown/clogged diffuser
c. normal operation
d. reason to believe the air filter in the blower is clogged - (ANSWER)b. unequal air distribution caused
by a blown diffuser
What is suction lift?
a. a team approach to lifting heavy objects
b. the pressure on the suction side of the pump
c. the measurement of liquid pressure at the pump
d. the measure of how bad your workers lift heavy objects - (ANSWER)b. the pressure on the suction
side of the pump
The primary effluent to a RBC system is 350 mg/L BOD. The primary unit removes 83% the secondary
unit removes 50% and the final unit removes 25%. What is the BOD leaving the final unit of the RBC
train?
A. 290 mg/L
b. 60 mg/L
