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LEcture 47 - DO and Streeter Phelps Lecture#47 Introduction...

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1 DO and Streeter Phelps Lecture#47 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. 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 (D c ) and critical distance (x c ) downstream from a discharge? Oxygen Deficit and Streeter-Phelps question: What happens to oxygen in a river when wastewater with high organic content is discharged into a river? answer: It produces an oxygen deficit Streeter-Phelps equation allows a prediction of impact of waste on river oxygen as a function of distance from discharge Oxygen Deficit and Streeter-Phelps D = DO sat - DO t Biodegradation of organics removes oxygen and increases deficit Reaeration generates oxygen and reduced deficit ν Streeter-Phelps and Oxygen Sag Curve Wastewater discharge point: assume to be instantaneously and well-mixed across river Oxygen Deficit and Streeter-Phelps D = DO sat – DO t (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 accumulation rate of “generation” of deficit = biodegradation (deoxygenation generates deficit) rate of “decay” of deficit = reaeration (reoxygenation reduces deficit)
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