2. A wastewater treatment plant discharges 1m3/s of effluent with an ultimate BOD of 40mg/L into a stream flowing at 10m3/s. Just upstream of the discharge point, the stream has an ultimate BOD of 3mg/L. The deoxygenation constant (kd) is estimated to be 0.221/d. (a) Assuming complete and instantaneous mixing, find the ultimate BOD of the mixture of the waste and the river just downstream of the outfall. (b) Assuming a constant cross-sectional area for the stream equal to 55m2, what ultimate BOD would you expect to find at a point 10,000m downstream? (c) The wastewater has a DO concentration of 4mg/L when it is discharged. The river, just upstream of the outfall, has a DO concentration of 8mg/L. The temperatures of the sewage and river are 15C; at this temperature the saturated DO concentration is 10.08mg/L. What is the initial oxygen deficit of the mixture, just downstream of the discharge point