The stream shown below has a flow of 28,000 m³/d, and a cross-sectional area of 35 m². The stream is saturated with dissolved oxygen (C* = 10 mg/L) and its BOD concentration is 0.5 mg/L. At point (A) 7 km upstream from the stream's confluence with another much larger river. a food processing industry is continuously discharging 1,500 m³/day of wastewater with an average organic composition of CH₂O (which is 90% degradable). The wastewater has a dissolved oxygen concentration of 2 mg/L. A stream sample taken just before the confluence of stream and river has a BOD, 20°C of 3.0 mg/L (k = 0.24/day for BOD assimilation in the lab). a) Calculate the concentration of the wastewater (in units of mg CH₂O/L) before it is mixed in the river. Relevant constants are given below. b) Determine whether the D.O. level in the stream remains above 5 mg/L between point A and confluence of the stream with the larger river. You may assume the following: i) plug flow ii) instantaneous mixing of stream and wastewater iii) stream and wastewater temperatures are 15°C and the applicable 15°C rate constants are: K= 0.18/day for BOD assimilation in the river k3= 0.01/day for BOD sedimentation in the river = 0.23/day for reaeration k₂ iv) C for the stream = 10.0 mg/L c) If the wastewater D.O. is raised to the saturation value of 10 mg/L what degree of waste treatment (% removal), if any, would be needed to keep the D.O. above 5 mg/L in the stream? Q=28,000 m³/d C=C= 10 mg/l BODL= 0.5 mg/L Stream -7 km Area - 35 m river
The stream shown below has a flow of 28,000 m³/d, and a cross-sectional area of 35 m². The stream is saturated with dissolved oxygen (C* = 10 mg/L) and its BOD concentration is 0.5 mg/L. At point (A) 7 km upstream from the stream's confluence with another much larger river. a food processing industry is continuously discharging 1,500 m³/day of wastewater with an average organic composition of CH₂O (which is 90% degradable). The wastewater has a dissolved oxygen concentration of 2 mg/L. A stream sample taken just before the confluence of stream and river has a BOD, 20°C of 3.0 mg/L (k = 0.24/day for BOD assimilation in the lab). a) Calculate the concentration of the wastewater (in units of mg CH₂O/L) before it is mixed in the river. Relevant constants are given below. b) Determine whether the D.O. level in the stream remains above 5 mg/L between point A and confluence of the stream with the larger river. You may assume the following: i) plug flow ii) instantaneous mixing of stream and wastewater iii) stream and wastewater temperatures are 15°C and the applicable 15°C rate constants are: K= 0.18/day for BOD assimilation in the river k3= 0.01/day for BOD sedimentation in the river = 0.23/day for reaeration k₂ iv) C for the stream = 10.0 mg/L c) If the wastewater D.O. is raised to the saturation value of 10 mg/L what degree of waste treatment (% removal), if any, would be needed to keep the D.O. above 5 mg/L in the stream? Q=28,000 m³/d C=C= 10 mg/l BODL= 0.5 mg/L Stream -7 km Area - 35 m river
Chapter2: Loads On Structures
Section: Chapter Questions
Problem 1P
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Transcribed Image Text:4.
The stream shown below has a flow of 28,000 m/d, and a cross-sectional area of 35 m2. The
stream is saturated with dissolved oxygen (C* = 10 mg/L) and its BOD, concentration is 0.5
mg/L. At point (A)7 km upstream from the stream's confluence with another much larger river,
a food processing industry is continuously discharging 1,500 m/day of wastewater with an
average organic composition of CH,0 (which is 90% degradable). The wastewater has a
dissolved oxygen concentration of 2 mg/L. A stream sample taken just before the confluence of
stream and river has a BOD, 20°C of 3.0 mg/L ( k = 0.24/day for BOD assimilation in the lab).
a) Calculate the concentration of the wastewater (in units of mg CH,0/L) before it is mixed
in the river. Relevant constants are given below.
b) Determine whether the D.O. level in the stream remains above 5 mg/L between point A
and confluence of the stream with the larger river. You may assume the following:
i) plug flow
ii) instantaneous mixing of stream and wastewater
iii) stream and wastewater temperatures are 15°C and the applicable 15°C rate constants
ki = 0.18/day for BOD assimilation in the river
k3 = 0.01/day for BOD sedimentation in the river
k, = 0.23/day for reaeration
are:
iv) C* for the stream = 10.0 mg/L
c) If the wastewater D.O. is raised to the saturation value of 10 mg/L what degree of waste
treatment (% removal), if any, would be needed to keep the D.O. above 5 mg/L in the
stream?
river
Q = 28,000 m' /d
Stream
Area = 35 m
C=C* = 10 mg/L
BODL = 0.5 mg/L
-7 km
Sample
BODC = 3.0 mg/L
Wastewater Q 1,500 m/day
Input
Corganic = ?? mg/L of CH,0
D.O. = 2.0 mg/L
C' = 10 mg/L.
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