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/L
0
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?