A manufacturer proposes to City L to discharge wastewater into a freshwater stream. The stream has a minimum flow of 5 m3 /s and negligible BOD. The highest water temperature in a year is 20o C. At this temperature, laboratory studies indicate that the oxygen depletion (due to BOD) rate constant is 0.25 day-1 and re-aeration rate constant is 0.40 day-1 . The stream has an initial oxygen at saturation. DO in the wastewater is 1.0 mg/L. The initial proposal suggests that the manufacturer plans to discharge 1000 L/s of wastewater with 30 mg/L BOD, determine the followings: a. the level of DO and D immediately after mixing.
b. the critical point DO and tc using Streeter-Phelps Oxygen Sag equation.