Poorly treated municipal wastewater is discharged to a stream. the river flow rate upstream of the discharge point is qu/s = 8.7 m3/s. the discharge occurs at a flow of qd= 0.9 m3/s and has a bod concentration of 50.0 mg/l. assuming that the upstream bod concentration is negligible. (a)what is the bod concentration just downstream of the discharge point? (b) if the stream has a cross-sectional area of 10 m2, what would the bod concentration be 50 km downstream? (bod is removed with a first-order decay rate constant equal to 0.20/da

Answer

given,

Q u  = 8.7 m³/s

Q d= 0.9 m³/s

BOD concentration = 50 mg/L

a) BOD concentration at the down stream

               = 4.69 mg/L

b) discharge = 9.6 m³/s

cross sectional area = 10 m²

velocity steam =

                        = 0.96 m/s

time taken to move 50 km down stream =

                                                                  = 52083.3 s

                                                                  =

                                                                   = 0.6 days

now,

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