In the Streeter-Phelps DO sag curve equation, the critical deficit Dc (maximum oxygen deficit) occurs when:
Choose the correct answer
The deoxygenation rate equals zero
The reaeration rate equals the deoxygenation rate (dD/dt = 0)
The BOD is completely exhausted
At the point of effluent discharge
Correct Answer
B. The reaeration rate equals the deoxygenation rate (dD/dt = 0)
AI Detailed Explanation & IS Code Reference
Unlock the reasoning, formula path and code-linked notes inside your student dashboard.
Streeter-Phelps: dD/dt = Kd x L - Kr x D (Kd = deoxygenation, Kr = reaeration, D = deficit). Critical point: Kd x L = Kr x Dc, giving Dc = Kd x L0 / Kr. Critical time: tc = (1/(Kr-Kd)) ln[(Kr/Kd)(1 - Dc(Kr-Kd)/(Kd x L0))].
ScoreCardAI links this solution with subject, topic and difficulty signals so your scorecard can identify weak areas after a full mock test.
Practice more Civil Engineering questions
This MCQ belongs to AE Level Premium Test Series. Full tests include timed attempts, rank comparison and subject-wise analysis.