A city discharges 100 cumecs of sewage into a river, which is fully saturated with oxygen and flowing at the rate of 1500 cumec during its lean days with a velocity of 0.1 m/sec. The 5 days BOD of sewage at the given temperature is 280 mg/1. Assume coefficient of purification of the stream (f) as 4.0 and coefficient of deoxygenation (ko base 10) is 0.1 day1. The critical dissolved oxygen deficit is the river is: [Assume D0 of sewage is nil.] [Take river water dissolved oxygen as 9.2 mg/1]

A city wishes to discharge wastewater primary effluent to a river which supports a trout. The state requires the city to show that the trout population is protected.  Trout require a minimum of 4 mg/l of dissolved oxygen to survive.  Determine the minimum downstream dissolved oxygen concentration from the following information about the wastewater discharge and river.  Does the minimum dissolved oxygen concentration meet the requirements? Wastewater discharge=0.45m3/s, river flow rate= 8.5 m3/s, river cross-sectional area=19m2, dissolved Oxygen concentration in the wastewater= 0.2mg/l, dissolved oxygen content of the river upstream = 8.1mg/l, saturation dissolved oxygen concentration at 20 C= 9.0 mg/l, BOD concentration in wastewater = 85 mg/l, BOD concentration upstream in the river= 0.2 mg/l, BOD decay constant = 0.2 d-1, and the reaeration constant for the river= 0.4 d-1.