Lecture 45

# Lecture 45 - DO and Streeter Phelps Lecture#45 Finish...

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DO and Streeter Phelps ± Lecture#45 ± Finish ICP#38 ± Review BOD (CMFR-PFR Problems) ± Introduction to Oxygen Sag Curve ± Streeter Phelp’s Equation ± ICP#39 ± Reading V: Ch. 7 (pg. 145-153); Streeter Phelps Equation Handout (Resource Folder) What you should know ± 1. How is BOD removed from wastewater? ± 2. What type of reactors are commonly used in BOD treatment processes? ± 3. What reactor concepts and methods can we use to assess the extent of removal of BOD from rivers and lakes? Aeration in Wastewater Treatment ± ICP #38 ± A completely mixed aerated lagoon with a liquid volume of 4956 m 3 was built to treat an average of 0.20 mgd (million gallons per day) (7.58x10 2 m 3 /day) of wastewater with a BOD 5 (20 ° C) of 550 mg/L in an area where the air temperature is 10 ° C. To provide adequate oxygen for waste degradation, two 15-hp surface aerators, with an oxygen transfer rate of 2.5 lb/hp.hr, are recommended. Based on laboratory studies, the wastewater has a k d of 0.68 day -l at 20 ° C. For a minimum BOD reduction of 75%, is the lagoon adequately sized? Do aerators provide adequate oxygen? ICP#38 (cont.) Q IN C IN Lagoon V L = 4956 m 3 k= 0.68day -1 Q OUT C OUT Q IN = Q OUT = Q = 7.58x10 2 m 3 /day C IN = BOD 5 = 550 mg/L Want C OUT = 0.25C IN ± Biodegradation results in a first order decay of dissolved oxygen, L t , that is related directly to the ultimate BOD, L 0 , which is, in turn related to BOD 5 ± For a CMFR, 1 st order decay, at steady-state, ± m in - m out + m rxn = 0 ± m rxn = -kC out V ± QC IN –QC OUT –kC OUT V=0 ± For a minimum BOD reduction of 75%, is the lagoon adequately sized? ICP#38 (cont.) dm/dt = m in - m out +m rxn 0 Biochemical Oxygen Demand (BOD) ± Biochemical Oxygen Demand (BOD) ± rate at which organics are consumed is assumed to be first order ± dL t /dt = -kL t (where L t ( mg/L) is the oxygen equivalent of the organics at time, t, and k ( d -1 ) is the first order reaction constant) ± integrating gives first order decay result: ± L t = L 0 exp(-kt) (L 0 , total oxygen equivalent of organics at t = 0 and L t the amount remaining at time t)

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BOD: lakes/rivers CMFR/PFR ± CMFR; steady state; 1 st order kinetics ± Q IN L 0,IN –Q OUT L 0,OUT –k d L 0,OUT V =0 ± Use k d at temperature of lake ± Use ultimate BOD (L
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## This note was uploaded on 04/17/2008 for the course CEE 260 taught by Professor Kimf.hayes during the Fall '06 term at University of Michigan.

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Lecture 45 - DO and Streeter Phelps Lecture#45 Finish...

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