The town of River City is situated along a scenic stretch of the Sweetnpure River. The city is seeking a waiver from state regulators to permit it to discharge its partially treated wastewater into the Sweetnpure River. The regulators will give permission for the discharge if the city can show that the native rainbow trout population in the river is sufficiently protected. The trout require a minimum of 7 mg/L of dissolved oxygen for survival. Given the following information about the wastewater discharge and the river, determine the minimum downstream dissolved oxygen concentration to determine whether or not the city should be required to upgrade its treatment system.
Maximum steady-state waste discharge = 0.5 m3/s
Minimum steady-state river flow = 9 m3/s
Average cross-sectional area of the river = 20 m2
DO content in the wastewater = 0.2 mg/L
DO content in the upstream river = 8.9 mg/L
DO saturation concentration at 15°C = 10.1 mg/L
BOD concentration in the wastewater = 80 mg/L
BOD concentration in the upstream river = 0.1 mg/L
BOD decay rate constant = 0.2 d-1
Reaeration rate constant in the river = 0.4 d-1
The town of River City is situated along a scenic stretch of the Sweetnpure River. The city is seeking a waiver from state regulators to permit it to discharge its partially treated wastewater into the Sweetnpure River. The regulators will give permission for the discharge if the city can show that the native rainbow trout population in the river is sufficiently protected. The trout require a minimum of 7 mg/L of dissolved oxygen for survival. Given the following information about the wastewater discharge and the river, determine the minimum downstream dissolved oxygen concentration to determine whether or not the city should be required to upgrade its treatment system.
Maximum steady-state waste discharge = 0.5 m3/s
Minimum steady-state river flow = 9 m3/s
Average cross-sectional area of the river = 20 m2
DO content in the wastewater = 0.2 mg/L
DO content in the upstream river = 8.9 mg/L
DO saturation concentration at 15°C = 10.1 mg/L
BOD concentration in the wastewater = 80 mg/L
BOD concentration in the upstream river = 0.1 mg/L
BOD decay rate constant = 0.2 d-1
Reaeration rate constant in the river = 0.4 d-1
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