FE Civil Environmental Engineering
Practice Test 2027 Edition | Updated
2026–27 Questions, Correct Answers &
Rationales
1. A municipal wastewater treatment plant receives an average flow of 3.0
MGD with an influent BOD₅ concentration of 220 mg/L. What is the
approximate daily BOD₅ load?
A. 3,300 lb/day
B. 4,500 lb/day
C. 5,505 lb/day
D. 6,750 lb/day
Answer: C. 5,505 lb/day
Rationale: The BOD load is calculated as L=8.34QCL=8.34QC, where QQ is in MGD
and CC is in mg/L. Thus, L=8.34(3.0)(220)≈5,505L=8.34(3.0)(220)\approx5,505
lb/day.
, 2. A water treatment facility uses rapid mixing followed by flocculation. The
primary purpose of rapid mixing is to:
A. Increase dissolved oxygen
B. Uniformly disperse the coagulant
C. Remove settled solids
D. Reduce alkalinity
Answer: B. Uniformly disperse the coagulant
Rationale: Rapid mixing provides sufficient turbulence to distribute the chemical
coagulant throughout the water before flocculation begins.
3. A sedimentation basin treats 2.5 MGD and has a surface area of 10,000 ft².
What is the approximate surface overflow rate?
A. 125 gpd/ft²
B. 250 gpd/ft²
C. 350 gpd/ft²
D. 500 gpd/ft²
Answer: B. 250 gpd/ft²
Rationale: Convert flow to gallons per day: 2.52.5 MGD = 2,500,000 gpd.
Therefore, Q/A=2,500,000/10,000=250Q/A=2,500,000/10,000=250 gpd/ft².
4. Which parameter is most directly associated with the oxygen demand
exerted by biodegradable organic matter in wastewater?
A. Total dissolved solids
B. BOD₅
,C. Alkalinity
D. Turbidity
Answer: B. BOD₅
Rationale: Biochemical oxygen demand measures the oxygen consumed by
microorganisms during biological degradation of biodegradable organic matter.
5. A wastewater treatment plant has an influent BOD of 250 mg/L and an
effluent BOD of 25 mg/L. What is the approximate BOD removal efficiency?
A. 80%
B. 85%
C. 90%
D. 95%
Answer: C. 90%
Rationale: Removal efficiency is (250−25)/250×100=90%(250-
25)/250\times100=90\%.
6. Which treatment process is primarily responsible for removing dissolved
biodegradable organic matter from municipal wastewater?
A. Screening
B. Grit removal
C. Biological treatment
D. Primary sedimentation
Answer: C. Biological treatment
Rationale: Biological reactors use microorganisms to metabolize dissolved and
colloidal biodegradable organics.
, 7. A secondary wastewater treatment system operates with an unusually low
dissolved oxygen concentration. Which condition is most likely to develop?
A. Enhanced nitrification
B. Improved aerobic oxidation
C. Reduced biological treatment performance
D. Increased chlorine residual
Answer: C. Reduced biological treatment performance
Rationale: Aerobic microorganisms require adequate dissolved oxygen. Low DO
can inhibit oxidation of organic matter and nitrification.
8. Which wastewater parameter is particularly important when evaluating
whether sufficient alkalinity exists for nitrification?
A. Chloride
B. Alkalinity
C. Turbidity
D. Total suspended solids
Answer: B. Alkalinity
Rationale: Nitrification consumes alkalinity because ammonia is biologically
oxidized to nitrate. Insufficient alkalinity can cause pH depression and inhibit
nitrifiers.
9. During nitrification, ammonia nitrogen is ultimately converted primarily
into:
A. Methane
B. Sulfate
C. Nitrate
D. Phosphate
Practice Test 2027 Edition | Updated
2026–27 Questions, Correct Answers &
Rationales
1. A municipal wastewater treatment plant receives an average flow of 3.0
MGD with an influent BOD₅ concentration of 220 mg/L. What is the
approximate daily BOD₅ load?
A. 3,300 lb/day
B. 4,500 lb/day
C. 5,505 lb/day
D. 6,750 lb/day
Answer: C. 5,505 lb/day
Rationale: The BOD load is calculated as L=8.34QCL=8.34QC, where QQ is in MGD
and CC is in mg/L. Thus, L=8.34(3.0)(220)≈5,505L=8.34(3.0)(220)\approx5,505
lb/day.
, 2. A water treatment facility uses rapid mixing followed by flocculation. The
primary purpose of rapid mixing is to:
A. Increase dissolved oxygen
B. Uniformly disperse the coagulant
C. Remove settled solids
D. Reduce alkalinity
Answer: B. Uniformly disperse the coagulant
Rationale: Rapid mixing provides sufficient turbulence to distribute the chemical
coagulant throughout the water before flocculation begins.
3. A sedimentation basin treats 2.5 MGD and has a surface area of 10,000 ft².
What is the approximate surface overflow rate?
A. 125 gpd/ft²
B. 250 gpd/ft²
C. 350 gpd/ft²
D. 500 gpd/ft²
Answer: B. 250 gpd/ft²
Rationale: Convert flow to gallons per day: 2.52.5 MGD = 2,500,000 gpd.
Therefore, Q/A=2,500,000/10,000=250Q/A=2,500,000/10,000=250 gpd/ft².
4. Which parameter is most directly associated with the oxygen demand
exerted by biodegradable organic matter in wastewater?
A. Total dissolved solids
B. BOD₅
,C. Alkalinity
D. Turbidity
Answer: B. BOD₅
Rationale: Biochemical oxygen demand measures the oxygen consumed by
microorganisms during biological degradation of biodegradable organic matter.
5. A wastewater treatment plant has an influent BOD of 250 mg/L and an
effluent BOD of 25 mg/L. What is the approximate BOD removal efficiency?
A. 80%
B. 85%
C. 90%
D. 95%
Answer: C. 90%
Rationale: Removal efficiency is (250−25)/250×100=90%(250-
25)/250\times100=90\%.
6. Which treatment process is primarily responsible for removing dissolved
biodegradable organic matter from municipal wastewater?
A. Screening
B. Grit removal
C. Biological treatment
D. Primary sedimentation
Answer: C. Biological treatment
Rationale: Biological reactors use microorganisms to metabolize dissolved and
colloidal biodegradable organics.
, 7. A secondary wastewater treatment system operates with an unusually low
dissolved oxygen concentration. Which condition is most likely to develop?
A. Enhanced nitrification
B. Improved aerobic oxidation
C. Reduced biological treatment performance
D. Increased chlorine residual
Answer: C. Reduced biological treatment performance
Rationale: Aerobic microorganisms require adequate dissolved oxygen. Low DO
can inhibit oxidation of organic matter and nitrification.
8. Which wastewater parameter is particularly important when evaluating
whether sufficient alkalinity exists for nitrification?
A. Chloride
B. Alkalinity
C. Turbidity
D. Total suspended solids
Answer: B. Alkalinity
Rationale: Nitrification consumes alkalinity because ammonia is biologically
oxidized to nitrate. Insufficient alkalinity can cause pH depression and inhibit
nitrifiers.
9. During nitrification, ammonia nitrogen is ultimately converted primarily
into:
A. Methane
B. Sulfate
C. Nitrate
D. Phosphate
