Test: Oxygen Deficit Curve - Civil Engineering (CE) MCQ

The green curve represents the reoxygenation curve, which depicts the supply of oxygen from the atmosphere to counterbalance the oxygen deficit.

The yellow curve represents the deoxygenation curve, which depicts the depletion of dissolved oxygen in the absence of aeration.

The oxygen sag curve is represented by the red curve. It is also called as an oxygen deficit curve.

The maximum deficiency of dissolved oxygen is represented by the dotted blue line. It is finding with respect to the equilibrium concentration of oxygen.

When the BOD of wastewater increases, the amount of dissolved oxygen decreases, so the rate of oxygen deficit increases.

The rate of oxygen deficit is the sum of the rate of reaeration and the rate of deoxygenation and it is maximum when the rate of reaeration equals the rate of deoxygenation.

Oxygen sag curve of river manifest dissolved oxygen deficit.
The difference between saturated dissolved oxygen content and the actual dissolved oxygen content in the stream at any point during self-purification process is called Oxygen sag 

Oxygen sag curve or oxygen deficit curve is obtained by algebraic addition of deoxygenation and reoxygenation curve.

The reoxygenation constant at temperature ‘T’, K_RT = K_R20 (1.016)^T-20, where K_R20 is the reoxygenation constant at 20ºC.