1. A new wastewater-treatment plant proposes a discharge of 5 m3/s of treated waste to a river. State regulations prohibit discharges that would raise the ultimate CBOD of the river above 10 mg/L The river has a flow of 5 m3/s and an ultimate CBOD of 2 mg/L Calculate the maximum 5-day CBOD that can be discharged without violating state regulations. Assume a CBOD decay coefficient of 0.1 day-1 for both the river and the proposed treatment plant.
2.A river flowing with a velocity of 20 km/d has an ultimate CBOD of 20 mg/L. If the organic matter has a decay coefficient of 0.2 day-1, what is the ultimate CBOD 40 km downstream?