Basic Wastewater Operator Practice Exam 2026 | 200 Real
Questions & Verified Answers
Question 1
What is the typical influent BOD to a wastewater plant?
A) 20 to 30 mg/L
B) 100 to 125 mg/L
C) 200 to 250 mg/L
D) 500 to 600 mg/L
Answer: C) 200 to 250 mg/L.
Rationale: Typical influent BOD to a wastewater treatment plant is approximately 200
to 250 mg/L.
Question 2
What does the term FOG in wastewater mean?
A) Fats, oils, and grease
B) Flow overflow guard
C) Free oxygen generation
D) Federal operator guidelines
Answer: A) Fats, oils, and grease.
Rationale: FOG stands for fats, oils, and grease, which can cause blockages and
operational problems in collection systems and treatment plants.
Question 3
Wastewater originating from households is described as:
A) Industrial wastewater
B) Domestic wastewater
C) Stormwater
D) Infiltration
,Answer: B) Domestic wastewater.
Rationale: Domestic wastewater originates from households and includes water from
toilets, sinks, showers, and appliances.
Question 4
If raw wastewater develops a blackish color with an unpleasant sour odor and pH
drops from 7.2 to 6.1, this indicates:
A) High infiltration
B) High oxygen content
C) Anaerobic decomposition (septic wastewater)
D) Possible discharge of acid waste
Answer: C) Anaerobic decomposition (septic wastewater).
Rationale: Blackish color, sour odor, and decreased pH indicate anaerobic
decomposition, meaning the wastewater has become septic.
Question 5
What are typical safety issues in a wastewater treatment plant?
A) Chlorine safety, confined space entry, explosion hazards, fall hazards, electrical
hazards
B) Only chlorine safety
C) Only confined space entry
D) Only electrical hazards
Answer: A) Chlorine safety, confined space entry, explosion hazards, fall
hazards, electrical hazards.
Rationale: Typical safety issues include chlorine safety, confined space entry, explosion
hazards from digester methane gas, fall hazards, and electrical hazards.
Question 6
What is the most common cause of death from an on-the-job accident for collection
system operators?
,A) Electrical shock
B) Falls
C) Asphyxiation
D) Burns
Answer: C) Asphyxiation.
Rationale: Most common cause of death for collection system operators is through
asphyxiation, typically in confined spaces.
Question 7
What communicable diseases could be transmitted via untreated wastewater?
A) Typhoid, cholera, dysentery, polio, hepatitis
B) Only typhoid
C) Only hepatitis
D) Only cholera
Answer: A) Typhoid, cholera, dysentery, polio, hepatitis.
Rationale: Communicable diseases that could be transmitted via untreated wastewater
include typhoid, cholera, dysentery, polio, and hepatitis.
Question 8
What is eutrophication?
A) Lack of nutrients in a receiving stream
B) Excessive nutrient availability that results in overgrowth of aquatic plants and
algae
C) Excessive growth of fish
D) Pleasing taste and odor in drinking water
Answer: B) Excessive nutrient availability that results in overgrowth of aquatic
plants and algae.
Rationale: Eutrophication is excessive nutrient availability that results in overgrowth of
aquatic plants and algae.
, Question 9
What is stabilization?
A) The process of converting a waste to a form that resists change
B) The process of adding chemicals
C) The process of removing solids
D) The process of increasing flow
Answer: A) The process of converting a waste to a form that resists change.
Rationale: Stabilization is the process of converting a waste to a form that resists
change.
Question 10
What happens to dissolved oxygen in water as temperature increases?
A) It increases
B) It decreases
C) It stays the same
D) It fluctuates randomly
Answer: B) It decreases.
Rationale: An increase in wastewater temperature results in a decreased ability to
retain dissolved oxygen.
SECTION 2: PRIMARY TREATMENT & SEDIMENTATION
Question 11
What is the principal function of a primary clarifier?
A) Biological treatment
B) Disinfection
C) Remove settleable solids and floating materials
D) Remove dissolved solids
Questions & Verified Answers
Question 1
What is the typical influent BOD to a wastewater plant?
A) 20 to 30 mg/L
B) 100 to 125 mg/L
C) 200 to 250 mg/L
D) 500 to 600 mg/L
Answer: C) 200 to 250 mg/L.
Rationale: Typical influent BOD to a wastewater treatment plant is approximately 200
to 250 mg/L.
Question 2
What does the term FOG in wastewater mean?
A) Fats, oils, and grease
B) Flow overflow guard
C) Free oxygen generation
D) Federal operator guidelines
Answer: A) Fats, oils, and grease.
Rationale: FOG stands for fats, oils, and grease, which can cause blockages and
operational problems in collection systems and treatment plants.
Question 3
Wastewater originating from households is described as:
A) Industrial wastewater
B) Domestic wastewater
C) Stormwater
D) Infiltration
,Answer: B) Domestic wastewater.
Rationale: Domestic wastewater originates from households and includes water from
toilets, sinks, showers, and appliances.
Question 4
If raw wastewater develops a blackish color with an unpleasant sour odor and pH
drops from 7.2 to 6.1, this indicates:
A) High infiltration
B) High oxygen content
C) Anaerobic decomposition (septic wastewater)
D) Possible discharge of acid waste
Answer: C) Anaerobic decomposition (septic wastewater).
Rationale: Blackish color, sour odor, and decreased pH indicate anaerobic
decomposition, meaning the wastewater has become septic.
Question 5
What are typical safety issues in a wastewater treatment plant?
A) Chlorine safety, confined space entry, explosion hazards, fall hazards, electrical
hazards
B) Only chlorine safety
C) Only confined space entry
D) Only electrical hazards
Answer: A) Chlorine safety, confined space entry, explosion hazards, fall
hazards, electrical hazards.
Rationale: Typical safety issues include chlorine safety, confined space entry, explosion
hazards from digester methane gas, fall hazards, and electrical hazards.
Question 6
What is the most common cause of death from an on-the-job accident for collection
system operators?
,A) Electrical shock
B) Falls
C) Asphyxiation
D) Burns
Answer: C) Asphyxiation.
Rationale: Most common cause of death for collection system operators is through
asphyxiation, typically in confined spaces.
Question 7
What communicable diseases could be transmitted via untreated wastewater?
A) Typhoid, cholera, dysentery, polio, hepatitis
B) Only typhoid
C) Only hepatitis
D) Only cholera
Answer: A) Typhoid, cholera, dysentery, polio, hepatitis.
Rationale: Communicable diseases that could be transmitted via untreated wastewater
include typhoid, cholera, dysentery, polio, and hepatitis.
Question 8
What is eutrophication?
A) Lack of nutrients in a receiving stream
B) Excessive nutrient availability that results in overgrowth of aquatic plants and
algae
C) Excessive growth of fish
D) Pleasing taste and odor in drinking water
Answer: B) Excessive nutrient availability that results in overgrowth of aquatic
plants and algae.
Rationale: Eutrophication is excessive nutrient availability that results in overgrowth of
aquatic plants and algae.
, Question 9
What is stabilization?
A) The process of converting a waste to a form that resists change
B) The process of adding chemicals
C) The process of removing solids
D) The process of increasing flow
Answer: A) The process of converting a waste to a form that resists change.
Rationale: Stabilization is the process of converting a waste to a form that resists
change.
Question 10
What happens to dissolved oxygen in water as temperature increases?
A) It increases
B) It decreases
C) It stays the same
D) It fluctuates randomly
Answer: B) It decreases.
Rationale: An increase in wastewater temperature results in a decreased ability to
retain dissolved oxygen.
SECTION 2: PRIMARY TREATMENT & SEDIMENTATION
Question 11
What is the principal function of a primary clarifier?
A) Biological treatment
B) Disinfection
C) Remove settleable solids and floating materials
D) Remove dissolved solids
