Is it possible to reduce the BOD of the effluent to maintain the DO above 7.0 mg/L at all downstream locations along the river? If so, what is the target BOD of the effluent?

Structural Analysis
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Author:KASSIMALI, Aslam.
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Chapter2: Loads On Structures
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What is the ultimate BOD 24 km downstream from the outfall?

> Answer: 3.89 g/m3

What is the DO deficit 24 km downstream of the effluent discharge?

> Answer: 3.192 g/m3

Question: Is it possible to reduce the BOD of the effluent to maintain the DO above 7.0 mg/L at all downstream locations along the river? If so, what is the target BOD of the effluent?

1. A river has an upstream flow of 2.27 m3/s, an ultimate BOD of 5 mg/L, and a DO of 6 mg/L. An
effluent enters the river with a flow of 0.283 m/s, a 5-d BOD of 20 mg/L, and a DO of zero. A
long-term CBOD test on the effluent has indicated a BOD decay constant of 0.25 d-1, and
there is negligible BOD removal by sedimentation. DO saturation in the river is 8.26 mg/L
at a temperature of 25 °C. The CBOD decay rate in the river is 0.6 d- at 25 °C, the velocity
is 25 cm/s, and the depth is 1.78 m. (Chin, 3rd ed., Problem 4.36)
(a) What is the ultimate BOD 24 km downstream from the outfall?
(b) What is the DO deficit 24 km downstream of the effluent discharge?
(c) At the location 15 km downstream of the effluent discharge, how much oxygen (k8/a)
would have to be added to have the DO at 7.0 mg/L?
(d) Is it possible to reduce the BOD of the effluent to maintain the DO above 7.0 mg/L at all
downstream locations along the river? If so, what is the target BOD of the effluent?
Transcribed Image Text:1. A river has an upstream flow of 2.27 m3/s, an ultimate BOD of 5 mg/L, and a DO of 6 mg/L. An effluent enters the river with a flow of 0.283 m/s, a 5-d BOD of 20 mg/L, and a DO of zero. A long-term CBOD test on the effluent has indicated a BOD decay constant of 0.25 d-1, and there is negligible BOD removal by sedimentation. DO saturation in the river is 8.26 mg/L at a temperature of 25 °C. The CBOD decay rate in the river is 0.6 d- at 25 °C, the velocity is 25 cm/s, and the depth is 1.78 m. (Chin, 3rd ed., Problem 4.36) (a) What is the ultimate BOD 24 km downstream from the outfall? (b) What is the DO deficit 24 km downstream of the effluent discharge? (c) At the location 15 km downstream of the effluent discharge, how much oxygen (k8/a) would have to be added to have the DO at 7.0 mg/L? (d) Is it possible to reduce the BOD of the effluent to maintain the DO above 7.0 mg/L at all downstream locations along the river? If so, what is the target BOD of the effluent?
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