Two communities, A and B, are found on two opposite sides of flowing river with a 9.10 m3 /s rate of volumetric flow, an uniform average speed of 0.25 m/s, an average depth of 4.0 m, an average temperature of 13°C, a chloride concentration of 8.0 mg/L, a 5.0 mg/L concentration of ultimate BOD, and an 8.0 mg/L concentration of dissolved oxygen. Both communities continuously discharge wastewater at the same point in the river where instantaneous mixing is assumed. The discharge of community A, which has an ultimate BOD of 48.2 mg/L and a dissolved oxygen concentration of 2.50 mg/L, is 2.10 m3 /s. On the other hand, community B discharges 1.80 m3 /s of wastewater, which has an ultimate BOD of 62.9 mg/L and a dissolved oxygen concentration of 1.50 mg/L. Just downstream of the downfall of both point sources, the deoxygenation rate constant is observed to be 0.22 day-1 . (a) What are the ultimate BOD and the initial oxygen deficit of the river and wastewater mixture just downstream of the downfall? (b) Locate the point downstream within which the minimum amount of dissolved oxygen is reached and the time it will take to reach this point along the river length downstream. (c) What is the minimum value of the dissolved oxygen at this point? (d) What is the BOD and the dissolved oxygen concentration of a water sample at 36 km downstream of the point of wastewater discharge?
Two communities, A and B, are found on two opposite sides of flowing river with a 9.10 m3 /s rate of volumetric flow, an uniform average speed of 0.25 m/s, an average depth of 4.0 m, an average temperature of 13°C, a chloride concentration of 8.0 mg/L, a 5.0 mg/L concentration of ultimate BOD, and an 8.0 mg/L concentration of dissolved oxygen. Both communities continuously discharge wastewater at the same point in the river where instantaneous mixing is assumed. The discharge of community A, which has an ultimate BOD of 48.2 mg/L and a dissolved oxygen concentration of 2.50 mg/L, is 2.10 m3 /s. On the other hand, community B discharges 1.80 m3 /s of wastewater, which has an ultimate BOD of 62.9 mg/L and a dissolved oxygen concentration of 1.50 mg/L. Just downstream of the downfall of both point sources, the deoxygenation rate constant is observed to be 0.22 day-1 .
(a) What are the ultimate BOD and the initial oxygen deficit of the river and wastewater mixture just downstream of the downfall?
(b) Locate the point downstream within which the minimum amount of dissolved oxygen is reached and the time it will take to reach this point along the river length downstream.
(c) What is the minimum value of the dissolved oxygen at this point?
(d) What is the BOD and the dissolved oxygen concentration of a water sample at 36 km downstream of the point of wastewater discharge?
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