Thanks in advance 18. Two streams flow together with the following data: Stream

Question

Thanks in advance 18. Two streams flow together with the following data: Stream name DO McLear Creek | 6.6mg/l Lions Creek | 8.7mg/l Combined DO deficit BODult Temp | 15°C | 15°C 15 Flow vol.Velocity 29.5 mg/ 7.3 cfs Xxx 6.2 mg/ 4.1 cfs Xx 1.6 ft. sec a. Calculate the new data for the combined stream, including combined DO, BOD, flow volume, and the DO deficit for each. (6 pts) [Hint: Not all of these are calculated via mass balance.] b. If the combined stream above has a deoxygenation rate of 0.42/d, and a reaeration rate of 0.56/d at the above temperature, calculate the time critical for the stream and the maximum oxygen deficit

Explanation / Answer

a) combine Do = Qr*DOr+ Qw*DOw / Q1+Q2

= (7.3*6.6)+(4.1+8.7) / 7.3+4.1

=48.18+35.67 / 11.4

=7.3 mg/l

combine BOD = QrBODr+ QwBODw /Q1+Q2

= (7.3*29.5) + (4.1*6.2) / 11.4

=215.35+25.42 / 11.4

=21.12mg/l

combine flow volume = Qc= Qr+Qw

=7.3+4.1

=11.4

DO deficit= dD/dt = Kd(lt)- Kr (D)

Kd= deoxegeneted rate

Lt= BOD rate at time t

Kr= reaeration rate

= (0.42*21.12)- (0.56*7.3)

=8.87-4.08

DO deficit=4.79

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