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CIVIL AND ENVIRONMENTAL ENGINEERING CIVL 6602 Biological Treatment of Aqueous Wastes 1 Module 5 Problem Set Problem 1 An aerobic pond treats a wastewater flow of 0.5 MGD from a community located at 25 oN latitude. What size pond is required if the wastewater has an ultimate BOD of 150 mg/l and 90% removal is required? The critical design month is January when cloud cover exists 40% of the time and the temperature averages 60 oF. Assume a mean algal cell composition of 52% carbon, 9% hydrogen, 32% oxygen, and 7% nitrogen. The elevation is 100 ft above mean sea level and BOD 5 = 0.70 BOD L. Use a value of 0.04 for the energy utilization efficiency. Problem 2 A facultative pond is designed for a community of 5000 people. Summer wastewater flow is 2000 m 3/d and BOD 5 is 180 mg/l. Winter flow and BOD 5 values are 6000 m 3/d and 90 g/m 3 respectively. Average pond temperatures are 20 oC in the summer and 10 oC in the winter. Assuming that a CFSTR model is appropriate and that oxygen transfer will not be a problem, determine the pond volume required to reduce the influent BOD 5 to 20 mg/l. Problem 3 A stabilization pond system is to be designed for a design population of 4800 persons, and the system is to have secondary treatment. Primary treatment consisting of a primary clarifier and an anaerobic digester is to be provided. Pertinent data are: average flow = 100 gal/cap-day (380 l/cap-d), influent BOD 5 = 200 mg/l, the primary clarifier removes 33% of the BOD 5. BOD 5 = 0.68 BOD u, four ponds in parallel are to be used length to width ratio = 2:1 and winter operating temperature of the pond = 45 °F. Given f= f’ = 1 Design equation:     ff QS A T i      38 2 085.1 10 148.2 where A = pond area, acres for a depth of 5 ft + 1 ft sludge storage C = 2.148 10 -2 Q = flowrate, MGD Determine, using USCS units: 1. The total area of the ponds 2. The applied BOD 5 loading 3. The dimensions of the ponds Problem 4 Design an aerated lagoon to treat 10000 m 3/d of wastewater under the following conditions: 1. Influent soluble BOD and suspended solids = 150 mg/l CIVIL AND ENVIRONMENTAL ENGINEERING CIVL 6602 Biological Treatment of Aqueous Wastes 2 2. Overall first-order BOD removal rate constant = 2.0 d -1 at 20 oC 3. Summer temperature = 27 oC 4. Winter temperature = 7 oC 5. Wastewater temperature = 15 oC 6. Temperature coefficient = 1.07 7.  = 0.85 and  = 1.0 8. Elevation = 1250 m 9. Oxygen concentration to be maintained = 2.0 mg/l 10. Lagoon depth = 2.0 m 11. Hydraulic residence time = 10 d 12. Temperature proportionality constant f = 12 10 6 Determine the surface area, summer and winter temperatures in the lagoon, and the effluent BOD iin summer and winter. If the growth yield is approximately 0.5 (BOD basis), determine the biological solids concentration in the lagoon, the oxygen requirements, and the power for summer and winter conditions. Use surface aerators rated at 1.5 kg O 2/kWh,

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