Problem:
An industrial WWTP discharges 0.5 m3/s of industrial wastewater containing an ultimate BOD concentration of 220 mg/L at a temperature of 26°C and a DO concentration of 2.0 mg/L into a large river. The velocity of the river is 0.85 m/s. Upstream of the point of discharge, the river has a temperature of 12°C, an ultimate BOD of 15 mg/L, and flow rate of 2.5 m3/s. The deoxygenation and reaeration-rate coefficients are 0.2 d-1 and 0.4 d-1 at 20°C.
Required:
Question 1: Calculate the dissolved-oxygen concentration (mg/L) at the point of discharge.
Question 2: Calculate the dissolved-oxygen deficit (Do) in mg/L at the point of discharge.
Question 3: Calculate the ultimate biochemical oxygen demand (Lo) in mg/L at the point of discharge.
Question 4: Calculate the dissolved-oxygen deficit (mg/L) 50 km downstream, assuming that the temperature in the river remains the same as it is at the point of discharge.
Question 5: Plot the DO versus time upto just beyond the critical point.
Show the pedigree and your calculation.