2026-2027 CALIFORNIA WASTEWATER TREATMENT
OPERATOR GRADE V EXAM QUESTIONS AND CORRECT
DETAILED ANSWERS A NEW UPDATED VERSION LATEST
2026-2027 FULLY REVISED EXAM VERSION (CORRECT
VERIFIED ANSWERS) ALREADY GRADED A+
In an activated sludge system, the primary purpose of returning activated
sludge (RAS) is to:
A) Increase oxygen transfer in the aeration tank
B) Maintain a high concentration of microorganisms in the aeration tank
C) Remove nutrients from the final effluent
D) Increase the chlorine demand for disinfection
Answer: B
RAS returns settled microorganisms from the secondary clarifier to the
aeration tank to maintain a high biomass concentration for organic matter
degradation .
A sudden increase in sludge blanket depth in the secondary clarifier is most
likely caused by:
A) Excessive aeration in the aeration tank
,B) High return activated sludge (RAS) rate
C) Sludge bulking
D) Low mixed liquor suspended solids (MLSS) concentration
Answer: C
Sludge bulking occurs when filamentous bacteria proliferate and interfere with
sludge settling, causing the sludge blanket to rise .
Which parameter indicates the settleability of activated sludge?
A) Mean Cell Residence Time (MCRT)
B) Sludge Volume Index (SVI)
C) Food to Microorganism Ratio (F/M)
D) Dissolved Oxygen (DO) concentration
Answer: B
SVI is calculated from the 30-minute settled sludge volume and MLSS
concentration, providing a measure of how well the sludge will settle in the
secondary clarifier .
What is the typical SVI value indicating good settling sludge?
A) 50-100 mL/g
B) 150-200 mL/g
C) 200-250 mL/g
D) >300 mL/g
Answer: A
An SVI between 50 and 100 mL/g indicates excellent settling characteristics;
values above 150 mL/g suggest bulking .
,A high Food to Microorganism (F/M) ratio typically results in:
A) Pinpoint floc and high effluent TSS
B) Excellent sludge compaction
C) Low oxygen demand
D) High sludge volume index
Answer: A
High F/M ratios lead to rapid bacterial growth and weaker floc formation,
resulting in pinpoint floc and high effluent suspended solids .
Which of the following best describes the term “Mean Cell Residence Time”
(MCRT)?
A) The time wastewater remains in the aeration tank
B) The average time microorganisms remain in the activated sludge system
C) The time sludge remains in the secondary clarifier
D) The time required for BOD reduction
Answer: B
MCRT is the average time that microorganisms are retained in the activated
sludge system, controlling the biological population and process stability .
A sudden drop in dissolved oxygen in the aeration tank is observed. What is
the most likely cause?
A) Decreased influent BOD loading
B) A sudden increase in influent BOD concentration
C) Waste activated sludge (WAS) rate is too high
, D) Return activated sludge (RAS) rate is too high
Answer: B
Increased BOD load increases oxygen demand, potentially exceeding aeration
capacity and causing DO to drop .
Which operational change would reduce the F/M ratio in an activated sludge
system?
A) Increase the MLVSS concentration
B) Increase the influent flow rate
C) Decrease the aeration tank volume
D) Decrease the return activated sludge (RAS) rate
Answer: A
F/M = (BOD load) ÷ (MLVSS). Increasing MLVSS (more microorganisms)
reduces F/M while keeping load constant .
A high Sludge Volume Index (SVI) value indicates:
A) Poor sludge settleability
B) Excellent sludge compaction
C) High MLSS concentration
D) Low WAS wasting rate
Answer: A
High SVI (>150 mL/g) indicates sludge bulking and poor settling, leading to
high effluent TSS .
The primary purpose of an equalization basin is to:
OPERATOR GRADE V EXAM QUESTIONS AND CORRECT
DETAILED ANSWERS A NEW UPDATED VERSION LATEST
2026-2027 FULLY REVISED EXAM VERSION (CORRECT
VERIFIED ANSWERS) ALREADY GRADED A+
In an activated sludge system, the primary purpose of returning activated
sludge (RAS) is to:
A) Increase oxygen transfer in the aeration tank
B) Maintain a high concentration of microorganisms in the aeration tank
C) Remove nutrients from the final effluent
D) Increase the chlorine demand for disinfection
Answer: B
RAS returns settled microorganisms from the secondary clarifier to the
aeration tank to maintain a high biomass concentration for organic matter
degradation .
A sudden increase in sludge blanket depth in the secondary clarifier is most
likely caused by:
A) Excessive aeration in the aeration tank
,B) High return activated sludge (RAS) rate
C) Sludge bulking
D) Low mixed liquor suspended solids (MLSS) concentration
Answer: C
Sludge bulking occurs when filamentous bacteria proliferate and interfere with
sludge settling, causing the sludge blanket to rise .
Which parameter indicates the settleability of activated sludge?
A) Mean Cell Residence Time (MCRT)
B) Sludge Volume Index (SVI)
C) Food to Microorganism Ratio (F/M)
D) Dissolved Oxygen (DO) concentration
Answer: B
SVI is calculated from the 30-minute settled sludge volume and MLSS
concentration, providing a measure of how well the sludge will settle in the
secondary clarifier .
What is the typical SVI value indicating good settling sludge?
A) 50-100 mL/g
B) 150-200 mL/g
C) 200-250 mL/g
D) >300 mL/g
Answer: A
An SVI between 50 and 100 mL/g indicates excellent settling characteristics;
values above 150 mL/g suggest bulking .
,A high Food to Microorganism (F/M) ratio typically results in:
A) Pinpoint floc and high effluent TSS
B) Excellent sludge compaction
C) Low oxygen demand
D) High sludge volume index
Answer: A
High F/M ratios lead to rapid bacterial growth and weaker floc formation,
resulting in pinpoint floc and high effluent suspended solids .
Which of the following best describes the term “Mean Cell Residence Time”
(MCRT)?
A) The time wastewater remains in the aeration tank
B) The average time microorganisms remain in the activated sludge system
C) The time sludge remains in the secondary clarifier
D) The time required for BOD reduction
Answer: B
MCRT is the average time that microorganisms are retained in the activated
sludge system, controlling the biological population and process stability .
A sudden drop in dissolved oxygen in the aeration tank is observed. What is
the most likely cause?
A) Decreased influent BOD loading
B) A sudden increase in influent BOD concentration
C) Waste activated sludge (WAS) rate is too high
, D) Return activated sludge (RAS) rate is too high
Answer: B
Increased BOD load increases oxygen demand, potentially exceeding aeration
capacity and causing DO to drop .
Which operational change would reduce the F/M ratio in an activated sludge
system?
A) Increase the MLVSS concentration
B) Increase the influent flow rate
C) Decrease the aeration tank volume
D) Decrease the return activated sludge (RAS) rate
Answer: A
F/M = (BOD load) ÷ (MLVSS). Increasing MLVSS (more microorganisms)
reduces F/M while keeping load constant .
A high Sludge Volume Index (SVI) value indicates:
A) Poor sludge settleability
B) Excellent sludge compaction
C) High MLSS concentration
D) Low WAS wasting rate
Answer: A
High SVI (>150 mL/g) indicates sludge bulking and poor settling, leading to
high effluent TSS .
The primary purpose of an equalization basin is to:
