Environmental Engineering Practice Exam –
100 Question Test Bank 2026 questions
&answers with rationales in italic INSTANT
DOWNLOAD PDF 1Which of the following is the most
common disinfectant used in municipal water treatment?
A) Ozone
B) Chlorine
C) UV light
D) Bromine
Answer: B) Chlorine
Chlorine is widely used in municipal water treatment due to its
effectiveness, low cost, and ability to maintain a residual in
distribution systems.
2. The Biochemical Oxygen Demand (BOD) test primarily measures:
A) Total organic carbon
B) Oxygen demand from chemical oxidants
C) Microbial oxidation of organic matter
D) Dissolved oxygen in water
Answer: C) Microbial oxidation of organic matter
BOD measures the amount of oxygen consumed by microorganisms
during the decomposition of organic matter over a standard period,
usually 5 days at 20°C.
3. Which of the following is considered a primary treatment process
in wastewater treatment?
A) Activated sludge process
, B) Trickling filter
C) Sedimentation
D) Chlorination
Answer: C) Sedimentation
Primary treatment removes settleable solids from wastewater
through sedimentation before biological treatment processes.
4. Nitrification in wastewater treatment refers to:
A) Conversion of ammonia to nitrate
B) Conversion of nitrate to ammonia
C) Denitrification of nitrate to nitrogen gas
D) Biological phosphorous removal
Answer: A) Conversion of ammonia to nitrate
Nitrification is a two-step aerobic process: first ammonia is oxidized to
nitrite, then nitrite is oxidized to nitrate by specialized bacteria.
5. The primary purpose of aeration in a wastewater treatment plant
is:
A) To settle suspended solids
B) To promote aerobic microbial degradation
C) To remove heavy metals
D) To disinfect the effluent
Answer: B) To promote aerobic microbial degradation
Aeration supplies oxygen to microorganisms, enabling them to oxidize
organic pollutants effectively.
6. The safe drinking water standard for total coliform bacteria is:
A) 10 CFU/100 mL
B) 1 CFU/100 mL
, C) 0 CFU/100 mL
D) 100 CFU/100 mL
Answer: C) 0 CFU/100 mL
Total coliform bacteria should be absent in 100 mL of drinking water
to ensure microbial safety, according to EPA standards.
7. The sludge produced in a primary clarifier is called:
A) Primary sludge
B) Secondary sludge
C) Mixed liquor
D) Digested sludge
Answer: A) Primary sludge
Primary sludge consists of settleable solids removed during the
primary sedimentation step before biological treatment.
8. The function of a trickling filter in wastewater treatment is:
A) Chemical precipitation
B) Anaerobic digestion
C) Biological treatment using biofilm
D) Disinfection
Answer: C) Biological treatment using biofilm
Trickling filters use a biofilm of microorganisms on media to degrade
organic matter in wastewater as it flows over the surface.
9. Activated sludge is:
A) Chemically treated sludge
B) A mixture of microorganisms and wastewater
C) Anaerobically digested sludge
D) Sludge used for fertilizer
, Answer: B) A mixture of microorganisms and wastewater
Activated sludge contains aerobic microorganisms that consume
organic matter in the wastewater during the aeration process.
10. Which of the following is an advantage of using UV light for
disinfection?
A) Provides residual disinfectant
B) No formation of disinfection by-products
C) Cheap and easy to maintain
D) Kills all viruses and bacteria immediately
Answer: B) No formation of disinfection by-products
UV disinfection inactivates microorganisms without adding chemicals,
thus avoiding the formation of harmful by-products like
trihalomethanes.
11. The main purpose of sedimentation in water treatment is:
A) Remove dissolved salts
B) Remove suspended solids
C) Kill microorganisms
D) Adjust pH
Answer: B) Remove suspended solids
Sedimentation allows suspended particles to settle by gravity,
reducing turbidity before further treatment.
12. In coagulation, the most commonly used coagulant is:
A) Sodium hypochlorite
B) Aluminum sulfate
100 Question Test Bank 2026 questions
&answers with rationales in italic INSTANT
DOWNLOAD PDF 1Which of the following is the most
common disinfectant used in municipal water treatment?
A) Ozone
B) Chlorine
C) UV light
D) Bromine
Answer: B) Chlorine
Chlorine is widely used in municipal water treatment due to its
effectiveness, low cost, and ability to maintain a residual in
distribution systems.
2. The Biochemical Oxygen Demand (BOD) test primarily measures:
A) Total organic carbon
B) Oxygen demand from chemical oxidants
C) Microbial oxidation of organic matter
D) Dissolved oxygen in water
Answer: C) Microbial oxidation of organic matter
BOD measures the amount of oxygen consumed by microorganisms
during the decomposition of organic matter over a standard period,
usually 5 days at 20°C.
3. Which of the following is considered a primary treatment process
in wastewater treatment?
A) Activated sludge process
, B) Trickling filter
C) Sedimentation
D) Chlorination
Answer: C) Sedimentation
Primary treatment removes settleable solids from wastewater
through sedimentation before biological treatment processes.
4. Nitrification in wastewater treatment refers to:
A) Conversion of ammonia to nitrate
B) Conversion of nitrate to ammonia
C) Denitrification of nitrate to nitrogen gas
D) Biological phosphorous removal
Answer: A) Conversion of ammonia to nitrate
Nitrification is a two-step aerobic process: first ammonia is oxidized to
nitrite, then nitrite is oxidized to nitrate by specialized bacteria.
5. The primary purpose of aeration in a wastewater treatment plant
is:
A) To settle suspended solids
B) To promote aerobic microbial degradation
C) To remove heavy metals
D) To disinfect the effluent
Answer: B) To promote aerobic microbial degradation
Aeration supplies oxygen to microorganisms, enabling them to oxidize
organic pollutants effectively.
6. The safe drinking water standard for total coliform bacteria is:
A) 10 CFU/100 mL
B) 1 CFU/100 mL
, C) 0 CFU/100 mL
D) 100 CFU/100 mL
Answer: C) 0 CFU/100 mL
Total coliform bacteria should be absent in 100 mL of drinking water
to ensure microbial safety, according to EPA standards.
7. The sludge produced in a primary clarifier is called:
A) Primary sludge
B) Secondary sludge
C) Mixed liquor
D) Digested sludge
Answer: A) Primary sludge
Primary sludge consists of settleable solids removed during the
primary sedimentation step before biological treatment.
8. The function of a trickling filter in wastewater treatment is:
A) Chemical precipitation
B) Anaerobic digestion
C) Biological treatment using biofilm
D) Disinfection
Answer: C) Biological treatment using biofilm
Trickling filters use a biofilm of microorganisms on media to degrade
organic matter in wastewater as it flows over the surface.
9. Activated sludge is:
A) Chemically treated sludge
B) A mixture of microorganisms and wastewater
C) Anaerobically digested sludge
D) Sludge used for fertilizer
, Answer: B) A mixture of microorganisms and wastewater
Activated sludge contains aerobic microorganisms that consume
organic matter in the wastewater during the aeration process.
10. Which of the following is an advantage of using UV light for
disinfection?
A) Provides residual disinfectant
B) No formation of disinfection by-products
C) Cheap and easy to maintain
D) Kills all viruses and bacteria immediately
Answer: B) No formation of disinfection by-products
UV disinfection inactivates microorganisms without adding chemicals,
thus avoiding the formation of harmful by-products like
trihalomethanes.
11. The main purpose of sedimentation in water treatment is:
A) Remove dissolved salts
B) Remove suspended solids
C) Kill microorganisms
D) Adjust pH
Answer: B) Remove suspended solids
Sedimentation allows suspended particles to settle by gravity,
reducing turbidity before further treatment.
12. In coagulation, the most commonly used coagulant is:
A) Sodium hypochlorite
B) Aluminum sulfate
