CEEn 351
Midterm Examination
Dr. M. Brett Borup
Part I: Open Book (75% of total score)
Name______
Each problem has equal value.
1) Activated carbon was added to a drum full of blue textile dye and the contents were mixed. Samples were taken from the drum with time and the dye concentration was measured in each sample. The following results were obtained:
Time, minutes / Dye Concentration, mg/L0 / 100
1 / 9.10
5 / 1.97
10 / 1.00
20 / 0.50
30 / 0.33
Determine the order of the reaction and the reaction rate constant (don=t forget the units).
2) An industry plans to discharge its liquid waste into a river that has a flow rate that varies between a high of 50 m3/s in the winter and 10 m3/s in the summer. The state regulatory agency is concerned that the concentration of phosphorous will be too high in the river downstream of the plant since the plants discharge contains 3000 micrograms of phosphorous per liter. The plant=s discharge flow rate will be 0.1 m3/s. Upstream of the plant the river already contains 20 micrograms per liter of phosphorous. If the state regulating agency has set a maximum limit of 100 microgram per liter of phosphorous in the river, will the industry be able to discharge the pollutant into the river without treatment to remove some of the phosphorous? Support your answer with the appropriate calculations. (Assume the phosphorous is non-reactive and that the river will be completely mixed)
3) How many pounds of coal must be burned to keep one 100-watt light bulb lit for one hour? Assume the efficiency of the power plant is 35%, the transmission losses are 10% of the delivered power, and the heating value of coal is 12,000 BTU/lb.
4) The removal of a volatile organic compound (VOC) from a wastewater can be described by a first order reaction with a reaction rate constant of 5 day-1. The wastewater has a flow rate of 150 m3/hr, and is treated in a series of two completely mixed flow reactors which each have an equal volume. If the influent VOC concentration is 10 mg/L, what should the volume of each reactor be to produce an effluent concentration of 0.1 mg/L?
5) A wastewater is discharged to a stream with a reoxygenation constant of 0.5 day-1 and a velocity of 1 m/sec. The oxygen saturation concentration in the stream is 11 mg/L. Immediately downstream of the discharge the oxygen concentration is 9 mg/L and the deoxygenation constant is 0.3 day-1. Upstream of the discharge the ultimate oxygen demand is 8 mg/L and the stream flows at 20 million gallons per day. The plant discharges a waste which has an ultimate oxygen demand of 30 mg/L and has a flow rate of 8 million gallons per day. What will the lowest dissolved oxygen concentration be downstream of the discharge and how far down the stream will it occur?