Question

1. A rectangular, well-mixed aeration lagoon is 75 m long, 5 m wide, and 2 m deep. It receives 400 m³/d of wastewater with a BOD₅of 367mg BOD₅/L for treatment. The biodegradation rate constants for the wastewater are the following: yield coefficient = 0.8 mg VSS/mg BOD₅, endogenous decay constant = 0.08 d^-1, maximum specific microbial growth rate = 1 d^-1, and half velocity constant = 76.0 mg BOD₅/L.                                                                                                              

1. What must the hydraulic detention time be in the aeration pond? (days)

2. What is the efficiency of the lagoon?   (%)                                                                                                      

3. The pond’s efficiency depends on oxygen being always available for the microbes to use in degrading the wastewater organic carbon. How much oxygen must be supplied daily to the pond? (in kg)

4. What mass of microbes will be produced in the pond each day? (in kg)

5. Suppose the operators decide to perform a recycle of the lagoon’s effluent to boost the efficiency. They decide to pump sludge from where it accumulates at the bottom of the pond to mix with the influent such that the incoming flow contains the same concentration of bacteria as the pond itself (X₀= X). What will the new treatment efficiency be? (%)

Answer 1

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