Civil Engineering MCQJE Level Civil Engineering
Minimum dissolved oxygen (DO) required in water for survival of fish is:
Environmental EngineeringEnvironmental EngineeringMEDIUM
Choose the correct answer
A
1 mg/L
B
4 mg/L
C
8 mg/L
D
15 mg/L
Correct Answer
B. 4 mg/L
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Fish require DO ≥ 4 mg/L (often cited as 5 mg/L for cold-water fish). DO saturation in water at 20°C ≈ 9.1 mg/L. DO depletes due to organic pollution (BOD exertion). DO sag curve (Streeter-Phelps) models oxygen depletion and recovery in rivers. Critical point: minimum DO in sag curve.
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