Question

A wastewater treatment plant discharges 1.0 m3/s of effluent having an ultimate BOD of 40 mg/L into a stream flowing at 10.0 m3/s. Just upstream from the discharge point, the stream has an ultimate BOD of 3.0 mg/L. The deoxygenation constant kd is estimated at 0.22/day. Assuming complete and instantaneous mixing and assuming a constant cross-sectional area for the stream equal to 55 m2, what BOD would you expect to find at a point 10,000 m downstream?

Answer 1

To determine the BOD at a point 10,000 m downstream, calculate the dilution factor based on the flow rate of the stream. The BOD at the downstream point is equal to the dilution factor multiplied by the BOD of the effluent, minus the dilution factor multiplied by the BOD of the upstream stream. In this case, the BOD at the downstream point is 370 mg/L.

Step-by-step explanation:

To determine the BOD at a point 10,000 m downstream, we need to calculate the dilution factor based on the flow rate of the stream. The dilution factor is given by the ratio of the stream flow rate to the effluent discharge rate. In this case, the dilution factor is 10.0 m³/s divided by 1.0 m³/s, which is 10.

The BOD at the downstream point can be calculated using the dilution factor and the BOD of the effluent and the upstream stream. The BOD at the downstream point is equal to the dilution factor multiplied by the BOD of the effluent, minus the dilution factor multiplied by the BOD of the upstream stream. In this case, the BOD at the downstream point is (10 * 40 mg/L) - (10 * 3.0 mg/L), which is 370 mg/L.

Therefore, the BOD at a point 10,000 m downstream is expected to be 370 mg/L.