Question

You have wastewater plant discharging into a clean river. The BOD of the Wastewater flow is 300 mg/L, the wastewater flow is 15 m3/sec, the river flow upstream of the mixing point is 120 m3/sec and BOD upstream of river is 0. The DO of the river at the mixed point is 8 mg/L and the saturation DO in the river would be 10 mg/L, the deoxygenation rate coefficient is 0.30/day and the reaeration constant is 0.90/day. The river is flowing 50 km/day and has no other BOD sources. (A) Find the critical distance downstream where BOD is a minimum, (B) Find the minimum DO at this point. (C) Draw a curve roughly to show the DO curve shape from the location of the mixing point downstream: your Y axis should be DO, your X axis should be distance, show the DO saturation line, the Do, the critical point distance, and DOmin.

Answer 1