ABC WASTEWATER LEVEL 3 -
ACTIVATED SLUDGE EXAM
QUESTIONS AND ANSWERS 2026
Performance problems in the activated sludge process can be caused by
____________.
A. Poor solids dewatering
B. Inadequate chlorination of effluent
C. Consistent influent characteristics
D. Insufficient operator training - ANSWERSD. Insufficient operator training
Solids that float to the surface of the clarifier are referred to as ____________.
A. Mixed liquor
B. Film
C. Residual solids
D. Scum - ANSWERSD. Scum
Solids that settle to the bottom of clarifiers and are removed from the process are
referred to as ___________.
A. RAS
B. WAS
C. TSS
D. Total residual chlorine - ANSWERSB. WAS
Large amounts of filamentous bacteria can improve floc structure and speed the settling
of the mixed liquor.
A. True
B. False - ANSWERSB. False
Protozoans are much more abundant than bacteria in activated sludge.
A. True
B. False - ANSWERSB. False
Under normal conditions, fungi (yeast and molds) are present in activated sludge
processes.
A. True
B. False - ANSWERSB. False
Algae are microscopic plants that can become a nuisance in clarifier launders.
A. True
B. False - ANSWERSA. True
, Which of the following does not result from a pH imbalance in an activated sludge
process?
A. Power consumption
B. Inability to maintain a healthy biomass
C. Damage to process equipment
D. Increased cost because of chemical addition - ANSWERSA. Power consumption
Because of industrial flows and the nitrification process, pH imbalances may become a
concern for activated sludge processes if sufficient __________ is not present.
A. TSS
B. Alkalinity
C. Ammonia
D. BOD - ANSWERSB. Alkalinity
Which of the following is NOT a phase of a typical sequencing batch reactor treatment
cycle?
A. Filter
B. Fill
C. Decant
D. Settle - ANSWERSA. Filter
Because multiple steps occur in a single reactor, the sequencing batch reactor process
provides little control over effluent quality.
A. True
B. False - ANSWERSB. False
Which of the following terms is used to describe biological reactors arranged in a
parallel configuration?
A. Parallel processors
B. Parallel-lined systems
C. Multiple process trains
D. Reactor chains - ANSWERSC. Multiple process trains
Using portable DO meters can be more economical than using permanently installed,
continuous-read units.
A. True
B. False - ANSWERSA. True
What equipment can be used with surface aerators to aid mixing in deep reactors?
A. Draft tubes
B. Rotor extensions
C. Turbo injectors
D. Extended impellers - ANSWERSA. Draft tubes
What type of problem can the splashing of surface aerators cause in or around a
reactor?
ACTIVATED SLUDGE EXAM
QUESTIONS AND ANSWERS 2026
Performance problems in the activated sludge process can be caused by
____________.
A. Poor solids dewatering
B. Inadequate chlorination of effluent
C. Consistent influent characteristics
D. Insufficient operator training - ANSWERSD. Insufficient operator training
Solids that float to the surface of the clarifier are referred to as ____________.
A. Mixed liquor
B. Film
C. Residual solids
D. Scum - ANSWERSD. Scum
Solids that settle to the bottom of clarifiers and are removed from the process are
referred to as ___________.
A. RAS
B. WAS
C. TSS
D. Total residual chlorine - ANSWERSB. WAS
Large amounts of filamentous bacteria can improve floc structure and speed the settling
of the mixed liquor.
A. True
B. False - ANSWERSB. False
Protozoans are much more abundant than bacteria in activated sludge.
A. True
B. False - ANSWERSB. False
Under normal conditions, fungi (yeast and molds) are present in activated sludge
processes.
A. True
B. False - ANSWERSB. False
Algae are microscopic plants that can become a nuisance in clarifier launders.
A. True
B. False - ANSWERSA. True
, Which of the following does not result from a pH imbalance in an activated sludge
process?
A. Power consumption
B. Inability to maintain a healthy biomass
C. Damage to process equipment
D. Increased cost because of chemical addition - ANSWERSA. Power consumption
Because of industrial flows and the nitrification process, pH imbalances may become a
concern for activated sludge processes if sufficient __________ is not present.
A. TSS
B. Alkalinity
C. Ammonia
D. BOD - ANSWERSB. Alkalinity
Which of the following is NOT a phase of a typical sequencing batch reactor treatment
cycle?
A. Filter
B. Fill
C. Decant
D. Settle - ANSWERSA. Filter
Because multiple steps occur in a single reactor, the sequencing batch reactor process
provides little control over effluent quality.
A. True
B. False - ANSWERSB. False
Which of the following terms is used to describe biological reactors arranged in a
parallel configuration?
A. Parallel processors
B. Parallel-lined systems
C. Multiple process trains
D. Reactor chains - ANSWERSC. Multiple process trains
Using portable DO meters can be more economical than using permanently installed,
continuous-read units.
A. True
B. False - ANSWERSA. True
What equipment can be used with surface aerators to aid mixing in deep reactors?
A. Draft tubes
B. Rotor extensions
C. Turbo injectors
D. Extended impellers - ANSWERSA. Draft tubes
What type of problem can the splashing of surface aerators cause in or around a
reactor?
