Poorly treated municipal wastewater is discharged to a stream. The river flow rate upstream of the discharge point is add 8.7 m35. The discharge occurs at a flow of Qd = 0.9 es and has a BOD concentration of 50.0 mg 1.72. 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 day)