1DO and Streeter PhelpsLecture#47Introduction to Oxygen Sag CurveStreeter Phelp’s EquationICP#39Reading V: Ch. 7 (pg. 145-153); Streeter Phelps Equation Handout (Resource Folder)What you should know1. What is an oxygen deficit (D)?2. What impact does biodegradation have on dissolved oxygen concentration (DO) and D?3. What impact does re-aeration have on dissolved oxygen concentration (DO) and D?4. What is the oxygen sag curve and how to we estimate the critical deficit (Dc) and critical distance (xc) downstream from a discharge?Oxygen Deficit and Streeter-Phelpsquestion: What happens to oxygen in a river when wastewater with high organic content is discharged into a river?answer: It produces an oxygen deficitStreeter-Phelps equation allows a prediction of impact of waste on river oxygen as a function of distance from dischargeOxygen Deficit and Streeter-PhelpsD = DOsat- DOtBiodegradation of organics removes oxygen and increases deficitReaeration generates oxygen and reduced deficitνStreeter-Phelps and Oxygen Sag CurveWastewater discharge point: assume to be instantaneously and well-mixed across riverOxygen Deficit and Streeter-PhelpsD = DOsat– DOt(DO ≡dissolved oxygen)Do mass flow balance on D (deficit)rate of mass in – rate of mass out + rate of generation – rate of decay = rate of mass accumulationrate of “generation” of deficit = biodegradation (deoxygenation generates deficit)rate of “decay” of deficit = reaeration(reoxygenation reduces deficit)
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