Texas Wastewater Operator Class D Exam Practice Questions
And Correct Answers (Verified Answers) Plus Rationales 2026
Q&A | Instant Download Pdf
1. What is the primary purpose of a wastewater treatment plant?
A. Increase water hardness
B. Reduce pollutants to protect public health
C. Remove all microorganisms
D. Increase water temperature
Answer: B
Rationale: The main goal of a wastewater treatment plant is to
remove contaminants from wastewater to protect public health and
the environment.
,2. Which of the following is considered a domestic wastewater
pollutant?
A. Oil
B. Heavy metals
C. Human waste
D. Pesticides
Answer: C
Rationale: Domestic wastewater primarily contains human waste,
soaps, and food residues.
3. Which process in wastewater treatment removes large solids?
A. Filtration
B. Screening
C. Chlorination
D. Sedimentation
Answer: B
Rationale: Screening uses physical barriers to remove large objects like
rags, sticks, and plastics from wastewater.
4. What is the primary function of primary sedimentation?
A. Remove dissolved chemicals
B. Settle suspended solids
C. Kill bacteria
D. Reduce odors
Answer: B
, Rationale: Primary sedimentation allows heavier solids to settle out of
the wastewater.
5. What is BOD?
A. Biochemical Oxygen Demand
B. Biochemical Oxygen Demand
C. Basic Oxidation Density
D. Biological Organic Distribution
Answer: B
Rationale: BOD measures the amount of oxygen microorganisms
require to decompose organic matter in wastewater.
6. A high BOD indicates:
A. Low organic content
B. High organic content
C. Low solids
D. High chlorine
Answer: B
Rationale: High BOD means there is a large amount of organic
material for bacteria to consume.
7. What type of bacteria is primarily responsible for decomposing
organic matter in wastewater?
A. Cyanobacteria
B. Heterotrophic bacteria
C. Autotrophic bacteria
, D. Algae
Answer: B
Rationale: Heterotrophic bacteria consume organic matter and
convert it into simpler compounds.
8. Which treatment process is aerobic?
A. Anaerobic digester
B. Activated sludge process
C. Septic tank
D. Trickling filter under anaerobic conditions
Answer: B
Rationale: Activated sludge relies on oxygen and aerobic bacteria to
break down organic matter.
9. Which unit operation is primarily used to remove nitrogen in
wastewater?
A. Primary sedimentation
B. Biological nitrification/denitrification
C. Chlorination
D. Screening
Answer: B
Rationale: Nitrification and denitrification are biological processes that
convert ammonia into nitrogen gas.
10. What is the main function of a trickling filter?
A. Chlorinate wastewater
And Correct Answers (Verified Answers) Plus Rationales 2026
Q&A | Instant Download Pdf
1. What is the primary purpose of a wastewater treatment plant?
A. Increase water hardness
B. Reduce pollutants to protect public health
C. Remove all microorganisms
D. Increase water temperature
Answer: B
Rationale: The main goal of a wastewater treatment plant is to
remove contaminants from wastewater to protect public health and
the environment.
,2. Which of the following is considered a domestic wastewater
pollutant?
A. Oil
B. Heavy metals
C. Human waste
D. Pesticides
Answer: C
Rationale: Domestic wastewater primarily contains human waste,
soaps, and food residues.
3. Which process in wastewater treatment removes large solids?
A. Filtration
B. Screening
C. Chlorination
D. Sedimentation
Answer: B
Rationale: Screening uses physical barriers to remove large objects like
rags, sticks, and plastics from wastewater.
4. What is the primary function of primary sedimentation?
A. Remove dissolved chemicals
B. Settle suspended solids
C. Kill bacteria
D. Reduce odors
Answer: B
, Rationale: Primary sedimentation allows heavier solids to settle out of
the wastewater.
5. What is BOD?
A. Biochemical Oxygen Demand
B. Biochemical Oxygen Demand
C. Basic Oxidation Density
D. Biological Organic Distribution
Answer: B
Rationale: BOD measures the amount of oxygen microorganisms
require to decompose organic matter in wastewater.
6. A high BOD indicates:
A. Low organic content
B. High organic content
C. Low solids
D. High chlorine
Answer: B
Rationale: High BOD means there is a large amount of organic
material for bacteria to consume.
7. What type of bacteria is primarily responsible for decomposing
organic matter in wastewater?
A. Cyanobacteria
B. Heterotrophic bacteria
C. Autotrophic bacteria
, D. Algae
Answer: B
Rationale: Heterotrophic bacteria consume organic matter and
convert it into simpler compounds.
8. Which treatment process is aerobic?
A. Anaerobic digester
B. Activated sludge process
C. Septic tank
D. Trickling filter under anaerobic conditions
Answer: B
Rationale: Activated sludge relies on oxygen and aerobic bacteria to
break down organic matter.
9. Which unit operation is primarily used to remove nitrogen in
wastewater?
A. Primary sedimentation
B. Biological nitrification/denitrification
C. Chlorination
D. Screening
Answer: B
Rationale: Nitrification and denitrification are biological processes that
convert ammonia into nitrogen gas.
10. What is the main function of a trickling filter?
A. Chlorinate wastewater
