A wastewater treatment plant discharges 2.0 m^3/s of effluent having an ultimate BOD of 40.0 mg/L into a stream flowing at 15.0 m^3/s. Just upstream from the discharge point, the stream has an ultimate BOD of 3.5 mg/L. The deoxygenation constant kd is estimated at 0.22/day. a. Assuming complete and instantaneous mixing, find the ultimate BOD of the mixture of wastewater and river just downstream from the outfall.
b. Assuming a constant cross sectional area for the stream equal to 55 m^2 , what ultimate BOD would you expect to find at a point 10,000 m downstream?