Question

5. The City of Maskeliya disposes of 2.15m3/s of treated sewage that still has a BODu of 32.0 mg/L and 2.2 mg/L of DO into a river. Upstream from the outfall, the river has a flow rate of 6.50m3/s and a velocity of 0.45 m/s. At this point, BODu and the DO in the river are 3.25 and 7.3 mg/L respectively. The saturation value od DO (at the temperature of the river) is 8.9 mg/L, The deoxygenation coefficient, kd , is 0.61 day-1, and the reaeration coefficient, kr , is 0.74 day-1 . Assume complete mixing and that the velocity in the river is the same upstream and downstream of the outfall (30 points) 1. What is the oxygen deficit and the BODu just downstream from the outfall (just after mixing, before any reaction can occur?) 2. What is the DO 12 km downstream? 3. Calculate the critical time and distance 4. What is the minimum DO

Answer 1