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Colorado Wastewater Treatment Operator Class A Exam
ACTUAL EXAM COMPLETE QUESTIONS AND CORRECT
ANSWERS LATEST UPDATE THIS YEAR
SUMMARIZED EXAM COVERAGE (QUICK STUDY VERSION)
The Colorado Wastewater Treatment Operator Class A Exam focuses on advanced wastewater plant
operation, regulatory compliance, and process optimization. The exam heavily emphasizes activated
sludge control, nitrification/denitrification, nutrient removal, clarifier performance, sludge handling, and
disinfection. Operators must understand laboratory testing procedures and use results to adjust
RAS/WAS rates, MLSS levels, aeration, and chemical feed systems. Strong calculation skills are required
for flow conversions, loading rates, SRT/F/M ratios, chemical dosages, and oxygen requirements. The
exam also evaluates mechanical maintenance knowledge, safety practices such as confined space entry
and LOTO, and troubleshooting strategies for bulking sludge, washout, foaming, and toxic industrial
discharges.
1.
A plant operator notices effluent ammonia levels rising steadily even though influent ammonia has not
changed. What is the most likely operational cause?
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A. Excessive sludge wasting increasing SRT
B. Loss of nitrifying bacteria due to low sludge age
C. Increased clarifier detention time improving nitrification
D. Reduced organic loading improving nitrification performance
Answer: B
Rationale: Nitrifiers require long SRT; low sludge age reduces their population.
2.
During winter operations, an activated sludge system experiences reduced nitrification even though
dissolved oxygen is maintained. What is the most likely reason?
A. Lower temperatures slow nitrifying bacteria growth rates significantly
B. High temperature increases ammonia stripping from aeration basin
C. Increased alkalinity always reduces nitrification efficiency
D. Reduced influent flow causes nitrification to completely stop
Answer: A
Rationale: Cold temperatures slow nitrification bacteria activity, requiring longer SRT.
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3.
A wastewater operator observes thick, brown foam on the aeration basin surface that persists for days.
What is the most likely cause?
A. Excess dissolved oxygen causing immediate sludge settling
B. Filamentous organisms such as Nocardia associated with high grease loads
C. Low influent BOD preventing biological growth
D. Excessive chlorine residual entering aeration basin improving stability
Answer: B
Rationale: Persistent brown foam is commonly linked to Nocardia and grease.
4.
A secondary clarifier begins experiencing solids carryover into effluent during peak wet weather flow.
What is the most likely reason?
A. Excessive clarifier overflow rate causing washout
B. Reduced influent flow increasing detention time
C. High chlorine dosage improving settling
D. Decreased RAS pumping causing improved sludge blanket control
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Answer: A
Rationale: High flow increases overflow rate, reducing settling time and causing solids loss.
5.
A plant has a low sludge volume index (SVI) but still experiences cloudy effluent from the secondary
clarifier. What is the most likely explanation?
A. Dispersed growth or pin floc formation reducing settling clarity
B. High SVI always indicates poor settling and cloudy effluent
C. Excessive filamentous bulking improving clarifier performance
D. Too much scum removal causing nitrification failure
Answer: A
Rationale: Low SVI does not guarantee clear effluent if pin floc or dispersed growth exists.
6.
A wastewater operator is adjusting RAS flow to improve clarifier performance. Which outcome is most
likely if RAS flow is too low?
Colorado Wastewater Treatment Operator Class A Exam
ACTUAL EXAM COMPLETE QUESTIONS AND CORRECT
ANSWERS LATEST UPDATE THIS YEAR
SUMMARIZED EXAM COVERAGE (QUICK STUDY VERSION)
The Colorado Wastewater Treatment Operator Class A Exam focuses on advanced wastewater plant
operation, regulatory compliance, and process optimization. The exam heavily emphasizes activated
sludge control, nitrification/denitrification, nutrient removal, clarifier performance, sludge handling, and
disinfection. Operators must understand laboratory testing procedures and use results to adjust
RAS/WAS rates, MLSS levels, aeration, and chemical feed systems. Strong calculation skills are required
for flow conversions, loading rates, SRT/F/M ratios, chemical dosages, and oxygen requirements. The
exam also evaluates mechanical maintenance knowledge, safety practices such as confined space entry
and LOTO, and troubleshooting strategies for bulking sludge, washout, foaming, and toxic industrial
discharges.
1.
A plant operator notices effluent ammonia levels rising steadily even though influent ammonia has not
changed. What is the most likely operational cause?
, Page 2 of 121
A. Excessive sludge wasting increasing SRT
B. Loss of nitrifying bacteria due to low sludge age
C. Increased clarifier detention time improving nitrification
D. Reduced organic loading improving nitrification performance
Answer: B
Rationale: Nitrifiers require long SRT; low sludge age reduces their population.
2.
During winter operations, an activated sludge system experiences reduced nitrification even though
dissolved oxygen is maintained. What is the most likely reason?
A. Lower temperatures slow nitrifying bacteria growth rates significantly
B. High temperature increases ammonia stripping from aeration basin
C. Increased alkalinity always reduces nitrification efficiency
D. Reduced influent flow causes nitrification to completely stop
Answer: A
Rationale: Cold temperatures slow nitrification bacteria activity, requiring longer SRT.
, Page 3 of 121
3.
A wastewater operator observes thick, brown foam on the aeration basin surface that persists for days.
What is the most likely cause?
A. Excess dissolved oxygen causing immediate sludge settling
B. Filamentous organisms such as Nocardia associated with high grease loads
C. Low influent BOD preventing biological growth
D. Excessive chlorine residual entering aeration basin improving stability
Answer: B
Rationale: Persistent brown foam is commonly linked to Nocardia and grease.
4.
A secondary clarifier begins experiencing solids carryover into effluent during peak wet weather flow.
What is the most likely reason?
A. Excessive clarifier overflow rate causing washout
B. Reduced influent flow increasing detention time
C. High chlorine dosage improving settling
D. Decreased RAS pumping causing improved sludge blanket control
, Page 4 of 121
Answer: A
Rationale: High flow increases overflow rate, reducing settling time and causing solids loss.
5.
A plant has a low sludge volume index (SVI) but still experiences cloudy effluent from the secondary
clarifier. What is the most likely explanation?
A. Dispersed growth or pin floc formation reducing settling clarity
B. High SVI always indicates poor settling and cloudy effluent
C. Excessive filamentous bulking improving clarifier performance
D. Too much scum removal causing nitrification failure
Answer: A
Rationale: Low SVI does not guarantee clear effluent if pin floc or dispersed growth exists.
6.
A wastewater operator is adjusting RAS flow to improve clarifier performance. Which outcome is most
likely if RAS flow is too low?
