WASTEWATER OPERATOR CLASS C EXAM PRACTICE QUESTIONS
WITH FULLY SOLVED ANSWERS 2025.
1) When Chlorine is combined with water what type of pipe should be used?
_ _ _ _ _ _ _ _ _ _ _ _
A. Ductile iron _
B. Asbestos concrete _
C. PVC
D. Carbon Steel -- Correct Answer ✔✔ C. PVC
_ _ _ _ _ _ _
2) A good settling sludge would consist of what type of protozoa?
_ _ _ _ _ _ _ _ _ _
A. Rotifers and nematodes _ _
B. Amoebas and Flagellates _ _
C. Stalked ciliates and mastagoria
_ _ _
D. Free swimmers and stalk ciliates -- Correct Answer ✔✔ D. Free swimmers
_ _ _ _ _ _ _ _ _ _ _ _
and stalk ciliates
_ _
3) What is Phenolphylein used for in titration
_ _ _ _ _ _
A. Oxidizer
B. Indicator
C. Acid reducer to lower pH
_ _ _ _
D. Applicator -- Correct Answer ✔✔ B. Indicator _ _ _ _ _ _
4) Your plant has an influent of 220 BOD and 163 TSS, and an effluent of 10 BOD, and 6
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
TSS. What is the BOD removal efficiency in your plant?
_ _ _ _ _ _ _ _ _ _
A. 92%
B. 94%
C. 95%
D. 96% -- Correct Answer ✔✔ C. 95%
_ _ _ _ _ _
,5) You suspect your anaerobic digester is going sour. What is the best way to verify its
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
condition?
A. pH
B. Foam type _
C. VA/ALK ratio _
D. DO -- Correct Answer ✔✔ C. VA/ALK ratio
_ _ _ _ _ _ _
6) Before operating any piece of equipment what should be done?
_ _ _ _ _ _ _ _ _
A. Lock out Tag out (remember, safety first!)
_ _ _ _ _ _
B. Read O & M manual _ _ _ _
C. Read manufacturers manual
_ _
D. Notify supervisor -- Correct Answer ✔✔ C. Read manufacturers manual
_ _ _ _ _ _ _ _ _
7) Detritus is noticed in your grit channel. What is the problem?
_ _ _ _ _ _ _ _ _ _
A. Velocity too fast with short D/T _ _ _ _ _
B. Velocity too low with long D/T _ _ _ _ _
C. Short circuiting _
D. Density currents -- Correct Answer ✔✔ B. Velocity too low with long D/T
_ _ _ _ _ _ _ _ _ _ _ _
8) What is considered normal operation of an aerobic digester?
_ _ _ _ _ _ _ _
A. Fill react _
B. Skim off foam when needed
_ _ _ _
C. Settle and Decant as needed _ _ _ _
D. Feed only during low flow or constant when the sun is out -- Correct Answer
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _
✔✔ C. Settle and Decant as needed
_ _ _ _ _ _
9) A plant with a flow of 1 MGD should be monitored
_ _ _ _ _ _ _ _ _ _
A. Continuously
B. Intermittently
C. Daily
, D. Every four hours depending on surface load -- Correct Answer ✔✔ A.
_ _ _ _ _ _ _ _ _ _ _ _
Continuously
10) What do total solids consist of?
_ _ _ _ _
A. Dissolved and settleable _ _
B. Floatable and settleable _ _
C. Suspended and dissolved _ _
D. Settleable and non-settleable -- Correct Answer ✔✔ C. Suspended and
_ _ _ _ _ _ _ _ _ _
dissolved
11) What would cause excessive wear on bearing?
_ _ _ _ _ _
A. Misalignment
B. Reduced Oil due to low viscosity_ _ _ _ _
C. Blow seal _
D. Over tubercation -- Correct Answer ✔✔ A. Misalignment
_ _ _ _ _ _ _
12) Amperometric titration is used to measure_ _ _ _ _
A. Dissolved solids _
B. Chlorine residual _
C. Colloids
D. Emulsions -- Correct Answer ✔✔ B. Chlorine residual
_ _ _ _ _ _ _
13) What growth phase is an aerobic digester operated in.
_ _ _ _ _ _ _ _
A. Log
B. Lag
C. Endogenous respiration _
D. Declining phase -- Correct Answer ✔✔ C. Endogenous respiration
_ _ _ _ _ _ _ _
14) If excessive pressure builds up in a chlorine tank due to excessive heat. What will
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _
prevent explosions?
_
A. Valve seat adjustments
_ _
WITH FULLY SOLVED ANSWERS 2025.
1) When Chlorine is combined with water what type of pipe should be used?
_ _ _ _ _ _ _ _ _ _ _ _
A. Ductile iron _
B. Asbestos concrete _
C. PVC
D. Carbon Steel -- Correct Answer ✔✔ C. PVC
_ _ _ _ _ _ _
2) A good settling sludge would consist of what type of protozoa?
_ _ _ _ _ _ _ _ _ _
A. Rotifers and nematodes _ _
B. Amoebas and Flagellates _ _
C. Stalked ciliates and mastagoria
_ _ _
D. Free swimmers and stalk ciliates -- Correct Answer ✔✔ D. Free swimmers
_ _ _ _ _ _ _ _ _ _ _ _
and stalk ciliates
_ _
3) What is Phenolphylein used for in titration
_ _ _ _ _ _
A. Oxidizer
B. Indicator
C. Acid reducer to lower pH
_ _ _ _
D. Applicator -- Correct Answer ✔✔ B. Indicator _ _ _ _ _ _
4) Your plant has an influent of 220 BOD and 163 TSS, and an effluent of 10 BOD, and 6
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
TSS. What is the BOD removal efficiency in your plant?
_ _ _ _ _ _ _ _ _ _
A. 92%
B. 94%
C. 95%
D. 96% -- Correct Answer ✔✔ C. 95%
_ _ _ _ _ _
,5) You suspect your anaerobic digester is going sour. What is the best way to verify its
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
condition?
A. pH
B. Foam type _
C. VA/ALK ratio _
D. DO -- Correct Answer ✔✔ C. VA/ALK ratio
_ _ _ _ _ _ _
6) Before operating any piece of equipment what should be done?
_ _ _ _ _ _ _ _ _
A. Lock out Tag out (remember, safety first!)
_ _ _ _ _ _
B. Read O & M manual _ _ _ _
C. Read manufacturers manual
_ _
D. Notify supervisor -- Correct Answer ✔✔ C. Read manufacturers manual
_ _ _ _ _ _ _ _ _
7) Detritus is noticed in your grit channel. What is the problem?
_ _ _ _ _ _ _ _ _ _
A. Velocity too fast with short D/T _ _ _ _ _
B. Velocity too low with long D/T _ _ _ _ _
C. Short circuiting _
D. Density currents -- Correct Answer ✔✔ B. Velocity too low with long D/T
_ _ _ _ _ _ _ _ _ _ _ _
8) What is considered normal operation of an aerobic digester?
_ _ _ _ _ _ _ _
A. Fill react _
B. Skim off foam when needed
_ _ _ _
C. Settle and Decant as needed _ _ _ _
D. Feed only during low flow or constant when the sun is out -- Correct Answer
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _
✔✔ C. Settle and Decant as needed
_ _ _ _ _ _
9) A plant with a flow of 1 MGD should be monitored
_ _ _ _ _ _ _ _ _ _
A. Continuously
B. Intermittently
C. Daily
, D. Every four hours depending on surface load -- Correct Answer ✔✔ A.
_ _ _ _ _ _ _ _ _ _ _ _
Continuously
10) What do total solids consist of?
_ _ _ _ _
A. Dissolved and settleable _ _
B. Floatable and settleable _ _
C. Suspended and dissolved _ _
D. Settleable and non-settleable -- Correct Answer ✔✔ C. Suspended and
_ _ _ _ _ _ _ _ _ _
dissolved
11) What would cause excessive wear on bearing?
_ _ _ _ _ _
A. Misalignment
B. Reduced Oil due to low viscosity_ _ _ _ _
C. Blow seal _
D. Over tubercation -- Correct Answer ✔✔ A. Misalignment
_ _ _ _ _ _ _
12) Amperometric titration is used to measure_ _ _ _ _
A. Dissolved solids _
B. Chlorine residual _
C. Colloids
D. Emulsions -- Correct Answer ✔✔ B. Chlorine residual
_ _ _ _ _ _ _
13) What growth phase is an aerobic digester operated in.
_ _ _ _ _ _ _ _
A. Log
B. Lag
C. Endogenous respiration _
D. Declining phase -- Correct Answer ✔✔ C. Endogenous respiration
_ _ _ _ _ _ _ _
14) If excessive pressure builds up in a chlorine tank due to excessive heat. What will
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _
prevent explosions?
_
A. Valve seat adjustments
_ _
