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CEE 153 F07 PS4

CEE 153 F07 PS4 - UNIVERSITY OF CALIFORNIA LOS ANGELES...

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UNIVERSITY OF CALIFORNIA, LOS ANGELES Civil and Environmental Engineering Department CEE 153 Introduction to Environmental Engineering Science Fall Term 2007 T-Th 2-4 PM 4000A Math Science Prof. K. D. Stolzenbach 5732J Boelter Hall, 206-7624 [email protected] Problem Set # 4 (due Thursday November 1) _____________________________________________________________________________ 1. The ultimate BOD of a river just below a sewage outfall is 50.0 mg/L and the DO is at the saturation value of 10.0 mg/L. The deoxygenation rate coefficient k d is 0.3/day and the reaeration rate coefficient k r is 0.90/day. The river is flowing at the speed of 48.0 miles/day. The only source of BOD on this river is this single outfall. a) Find the critical distance downstream at which the DO in the river is a minimum. [87.9 miles] b) Find the minimum DO value. [0.38 mg/L] c) If a wastewater treatment plant is to be built, what fraction of the BOD would have to be removed from the sewage to assure a minimum of 5.0 mg/L of DO everywhere downstream? [48%] 2. Wastewater saturated with dissolved oxygen (DO sat = 12 mg/L) is discharged into a river that has zero BOD and is saturated with oxygen (also DO sat = 12 mg/L) upstream from the point of discharge. The minimum DO in the river downstream from the discharge is DO min = 2 mg/L. Calculate the five-day biological oxygen demand (BOD 5 ) of the wastewater being discharged, assuming that k d = 0.2/day, k r = 0.42/day, Q a = 1 m 3 /sec, and Q e = 0.1 m 3 /sec. [286 mg/L]
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3. A well-mixed reservoir has a constant volume V = 10 7 m 3 and a horizontal cross-sectional area A = 10 6 m 2 . The steady flows of water into and out of the reservoir are the river inflow Q in , the outflow Q out , the rainfall P, and the evaporation E.
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