NPDES Chemical Oxygen Demand
(COD/BOD) Testing Exam Practice
Questions And Correct Answers
(Verified Answers) Plus Rationales 2026
Q&A | Instant Download Pdf
1. What does BOD primarily measure in water samples?
A. Heavy metals
B. Oxygen required by microorganisms to decompose organic matter
C. Total dissolved solids
D. pH level
Answer: B
Rationale: BOD measures the amount of oxygen consumed by
microbes while breaking down biodegradable organic matter.
2. Standard BOD test incubation period is:
A. 1 day
B. 3 days
C. 5 days
, D. 7 days
Answer: C
Rationale: The standard BOD test uses a 5-day incubation at 20°C
(BOD₅).
3. COD primarily measures:
A. Biologically available oxygen demand only
B. Total oxygen required to chemically oxidize organic matter
C. Nitrogen compounds only
D. Dissolved oxygen in water
Answer: B
Rationale: COD measures oxygen equivalent needed to chemically
oxidize both biodegradable and non-biodegradable substances.
4. Which reagent is commonly used in COD testing?
A. Sodium chloride
B. Potassium dichromate
C. Calcium carbonate
D. Sodium hydroxide
Answer: B
Rationale: Potassium dichromate is a strong oxidizing agent used in
COD digestion.
5. What temperature is used for BOD incubation?
A. 4°C
B. 15°C
, C. 20°C
D. 37°C
Answer: C
Rationale: BOD samples are incubated at 20°C to simulate natural
environmental conditions.
6. Which parameter is most affected by nitrification in BOD testing?
A. COD
B. BOD
C. TSS
D. pH
Answer: B
Rationale: Nitrification can increase oxygen demand, inflating BOD
results.
7. COD testing is generally faster than BOD because:
A. It uses bacteria
B. It requires no incubation period
C. It measures only dissolved oxygen
D. It uses field sensors only
Answer: B
Rationale: COD is a chemical test that can be completed in a few
hours without microbial incubation.
8. What is the purpose of a BOD blank?
A. Measure solids
, B. Correct for dilution water oxygen demand
C. Measure COD
D. Adjust pH
Answer: B
Rationale: The blank corrects for oxygen demand from dilution water
and reagents.
9. What does DO stand for in BOD testing?
A. Dissolved Oxygen
B. Direct Oxidation
C. Dilution Output
D. Dynamic Oxygen
Answer: A
Rationale: DO refers to dissolved oxygen in the water sample.
10. COD results are typically expressed in:
A. mg/L oxygen equivalent
B. mg/L solids
C. pH units
D. NTU
Answer: A
Rationale: COD is expressed as oxygen equivalent in milligrams per
liter.
11. Which factor can interfere with BOD results?
A. Heavy metals
(COD/BOD) Testing Exam Practice
Questions And Correct Answers
(Verified Answers) Plus Rationales 2026
Q&A | Instant Download Pdf
1. What does BOD primarily measure in water samples?
A. Heavy metals
B. Oxygen required by microorganisms to decompose organic matter
C. Total dissolved solids
D. pH level
Answer: B
Rationale: BOD measures the amount of oxygen consumed by
microbes while breaking down biodegradable organic matter.
2. Standard BOD test incubation period is:
A. 1 day
B. 3 days
C. 5 days
, D. 7 days
Answer: C
Rationale: The standard BOD test uses a 5-day incubation at 20°C
(BOD₅).
3. COD primarily measures:
A. Biologically available oxygen demand only
B. Total oxygen required to chemically oxidize organic matter
C. Nitrogen compounds only
D. Dissolved oxygen in water
Answer: B
Rationale: COD measures oxygen equivalent needed to chemically
oxidize both biodegradable and non-biodegradable substances.
4. Which reagent is commonly used in COD testing?
A. Sodium chloride
B. Potassium dichromate
C. Calcium carbonate
D. Sodium hydroxide
Answer: B
Rationale: Potassium dichromate is a strong oxidizing agent used in
COD digestion.
5. What temperature is used for BOD incubation?
A. 4°C
B. 15°C
, C. 20°C
D. 37°C
Answer: C
Rationale: BOD samples are incubated at 20°C to simulate natural
environmental conditions.
6. Which parameter is most affected by nitrification in BOD testing?
A. COD
B. BOD
C. TSS
D. pH
Answer: B
Rationale: Nitrification can increase oxygen demand, inflating BOD
results.
7. COD testing is generally faster than BOD because:
A. It uses bacteria
B. It requires no incubation period
C. It measures only dissolved oxygen
D. It uses field sensors only
Answer: B
Rationale: COD is a chemical test that can be completed in a few
hours without microbial incubation.
8. What is the purpose of a BOD blank?
A. Measure solids
, B. Correct for dilution water oxygen demand
C. Measure COD
D. Adjust pH
Answer: B
Rationale: The blank corrects for oxygen demand from dilution water
and reagents.
9. What does DO stand for in BOD testing?
A. Dissolved Oxygen
B. Direct Oxidation
C. Dilution Output
D. Dynamic Oxygen
Answer: A
Rationale: DO refers to dissolved oxygen in the water sample.
10. COD results are typically expressed in:
A. mg/L oxygen equivalent
B. mg/L solids
C. pH units
D. NTU
Answer: A
Rationale: COD is expressed as oxygen equivalent in milligrams per
liter.
11. Which factor can interfere with BOD results?
A. Heavy metals
