Q3. The initial ultimate BOD after mixing of the Bergelmir River is 12.0 mg/L. The DO in the Bergelmir River after the wastewater and river have mixed is at saturation. The river temperature is 10°C. At 100 C, the deoxygenation rate constant (k) is 0.30 day and the reaeration rate constant (k) is 0.40 day1. Determine the critical point (t) and the critical DO Q4. Assuming that the mixed oxygen deficit (D,) is zero and the ultimate BOD (L) of the Manc Capac river above the wastewater outfall from Urcaguary is zero, calculate the amount of ultimate BOD (in kg.day') that can be discharged if the DO must be kept at 4.00 mg/L at a point 8.05 km downstream. The stream deoxygenation rate (kd) is 1.80 day at 12°C, and the reaeration rate (k.) is 2.20 day" at 120C. The river flow is 5.95 m/s with a speed of 0.3 m/s. The Urcaguary wastewater flow is 0.013 m3/s. (Assume at T= 120C, DOS 10.83 mg/L)