California Wastewater Treatment
Operator Grade V Exam ACTUAL
Exam ALL QUESTIONS AND
CORRECT,
SECTION 1: ACTIVATED SLUDGE PROCESS CONTROL (Questions 1-
20)
Question 1
Which of the following is the primary purpose of activated sludge in wastewater
treatment?
A) To filter out solids
B) To biologically remove organic matter
C) To disinfect the effluent
D) To increase pH
Correct Answer: B) To biologically remove organic matter
Rationale: Activated sludge uses a diverse population of microorganisms to
consume and break down organic pollutants, reducing Biochemical Oxygen
Demand (BOD) and improving water quality. Filtration (A) is a physical process,
disinfection (C) occurs after biological treatment, and pH adjustment (D) is a
chemical process .
Question 2
,Which parameter indicates the settleability of activated sludge?
A) Mean Cell Residence Time (MCRT)
B) Sludge Volume Index (SVI)
C) Biochemical Oxygen Demand (BOD)
D) Food to Microorganism (F/M) Ratio
Correct Answer: B) Sludge Volume Index (SVI)
Rationale: SVI measures how well sludge settles by comparing the volume
occupied by 1 gram of sludge after 30 minutes of settling to the MLSS
concentration. SVI = (Settled sludge volume (mL/L) × 1000) ÷ MLSS (mg/L). A
high SVI (>150 mL/g) typically indicates poor settling and possible bulking .
Question 3
What is the primary cause of sludge bulking in activated sludge systems?
A) Low dissolved oxygen
B) Nutrient deficiencies (N, P)
C) Low F/M ratio
D) All of the above
Correct Answer: D) All of the above
Rationale: Sludge bulking occurs when filamentous organisms proliferate and
interfere with sludge settling. Common causes include low dissolved oxygen,
nutrient deficiencies (nitrogen and phosphorus), and low F/M ratios. This condition
leads to poor solids-liquid separation and potential permit violations .
,Question 4
In wastewater treatment, BOD stands for:
A) Basic Oxidation Demand
B) Biological Oxygen Deficiency
C) Biochemical Oxygen Demand
D) Biological Oxidation Discharge
Correct Answer: C) Biochemical Oxygen Demand
Rationale: BOD measures the amount of oxygen microorganisms need to
decompose organic matter in water over a specific time, typically 5 days (BOD5).
It is a key indicator of the strength of organic pollution in wastewater .
Question 5
The term "MLSS" in wastewater treatment refers to:
A) Maximum Liquid Sludge Solids
B) Mixed Low Solids Suspension
C) Mixed Liquor Suspended Solids
D) Mean Linear Sludge Separation
Correct Answer: C) Mixed Liquor Suspended Solids
Rationale: MLSS measures the concentration of suspended solids, including
microorganisms, in the aeration tank. It is a critical process control parameter used
to calculate F/M ratio, SRT, and other operational indices .
, Question 6
What is the main reason for maintaining sludge age in an activated sludge process?
A) To control pH
B) To control the microbial population and treatment efficiency
C) To adjust temperature
D) To increase aeration
Correct Answer: B) To control the microbial population and treatment efficiency
Rationale: Sludge age (Mean Cell Residence Time or SRT) ensures a stable
microbial population capable of degrading organic matter and nitrifying ammonia.
Longer sludge ages favor nitrifying bacteria, while shorter ages favor carbonaceous
BOD removal .
Question 7
Which type of sludge is produced in primary sedimentation tanks?
A) Secondary sludge
B) Primary sludge
C) Digested sludge
D) Return activated sludge
Correct Answer: B) Primary sludge
Rationale: Primary sludge is the settled solids removed from raw wastewater
during the primary sedimentation process. It is typically gray and slimy, containing
3-6% solids. Secondary sludge (A) comes from biological treatment processes .
Operator Grade V Exam ACTUAL
Exam ALL QUESTIONS AND
CORRECT,
SECTION 1: ACTIVATED SLUDGE PROCESS CONTROL (Questions 1-
20)
Question 1
Which of the following is the primary purpose of activated sludge in wastewater
treatment?
A) To filter out solids
B) To biologically remove organic matter
C) To disinfect the effluent
D) To increase pH
Correct Answer: B) To biologically remove organic matter
Rationale: Activated sludge uses a diverse population of microorganisms to
consume and break down organic pollutants, reducing Biochemical Oxygen
Demand (BOD) and improving water quality. Filtration (A) is a physical process,
disinfection (C) occurs after biological treatment, and pH adjustment (D) is a
chemical process .
Question 2
,Which parameter indicates the settleability of activated sludge?
A) Mean Cell Residence Time (MCRT)
B) Sludge Volume Index (SVI)
C) Biochemical Oxygen Demand (BOD)
D) Food to Microorganism (F/M) Ratio
Correct Answer: B) Sludge Volume Index (SVI)
Rationale: SVI measures how well sludge settles by comparing the volume
occupied by 1 gram of sludge after 30 minutes of settling to the MLSS
concentration. SVI = (Settled sludge volume (mL/L) × 1000) ÷ MLSS (mg/L). A
high SVI (>150 mL/g) typically indicates poor settling and possible bulking .
Question 3
What is the primary cause of sludge bulking in activated sludge systems?
A) Low dissolved oxygen
B) Nutrient deficiencies (N, P)
C) Low F/M ratio
D) All of the above
Correct Answer: D) All of the above
Rationale: Sludge bulking occurs when filamentous organisms proliferate and
interfere with sludge settling. Common causes include low dissolved oxygen,
nutrient deficiencies (nitrogen and phosphorus), and low F/M ratios. This condition
leads to poor solids-liquid separation and potential permit violations .
,Question 4
In wastewater treatment, BOD stands for:
A) Basic Oxidation Demand
B) Biological Oxygen Deficiency
C) Biochemical Oxygen Demand
D) Biological Oxidation Discharge
Correct Answer: C) Biochemical Oxygen Demand
Rationale: BOD measures the amount of oxygen microorganisms need to
decompose organic matter in water over a specific time, typically 5 days (BOD5).
It is a key indicator of the strength of organic pollution in wastewater .
Question 5
The term "MLSS" in wastewater treatment refers to:
A) Maximum Liquid Sludge Solids
B) Mixed Low Solids Suspension
C) Mixed Liquor Suspended Solids
D) Mean Linear Sludge Separation
Correct Answer: C) Mixed Liquor Suspended Solids
Rationale: MLSS measures the concentration of suspended solids, including
microorganisms, in the aeration tank. It is a critical process control parameter used
to calculate F/M ratio, SRT, and other operational indices .
, Question 6
What is the main reason for maintaining sludge age in an activated sludge process?
A) To control pH
B) To control the microbial population and treatment efficiency
C) To adjust temperature
D) To increase aeration
Correct Answer: B) To control the microbial population and treatment efficiency
Rationale: Sludge age (Mean Cell Residence Time or SRT) ensures a stable
microbial population capable of degrading organic matter and nitrifying ammonia.
Longer sludge ages favor nitrifying bacteria, while shorter ages favor carbonaceous
BOD removal .
Question 7
Which type of sludge is produced in primary sedimentation tanks?
A) Secondary sludge
B) Primary sludge
C) Digested sludge
D) Return activated sludge
Correct Answer: B) Primary sludge
Rationale: Primary sludge is the settled solids removed from raw wastewater
during the primary sedimentation process. It is typically gray and slimy, containing
3-6% solids. Secondary sludge (A) comes from biological treatment processes .
