CEEn 351

Midterm Examination

Dr. M. Brett Borup

Part I: Open Book (75% of total score)

Name______

Each problem has equal value.

1) A test was conducted to determine the effectiveness of an ozone contactor. Water in the mixed batch contactor was dosed with ozone. Samples were then taken from the tank at various times and analyzed for ozone concentration. The following results were obtained:

Time, minutes / Dye Concentration, mg/L
0 / 10.0
1 / 9.5
5 / 9.15
10 / 8.0
20 / 5.5
30 / 2.7

Determine: (A) the order of the reaction (10 points)

(B) The reaction rate constant (don=t forget the units. 10 points).

2) Black currant jam is being produced at a food processing plant. The jam is made by combining black currants and sugar at a weight ratio of 45:55. The mixture is heated to evaporate the water until the final jam contains 1/3 water. If the black currants originally contain 80% water, how many kilograms of berries are needed to make one kilogram of jam? (15 points)

3) A wastewater containing 210 mg/L of particulate BOD is treated in a series of three completely mixed reactors each having a volume of 250 m3. The wastewater has a flow rate of 1000 m3/day. The effluent concentration is found to be 20 mg/L. If the flow rate changes to 1500 m3/day, what is the new effluent concentration? (Hint: The influent concentration and volume of each reactor does not change. 20 points) I forgot to specify what order reaction was occurring!

4) A stream has a dissolved oxygen level of 9 mg/L, an ultimate oxygen demand of 12 mf/L, and an average flow of 0.2 m3/s. An industrial waste at zero dissolved oxygen with an ultimate oxygen demand of 20,000 mg/L and a flow of 0.006 m3/s is discharged into the stream.

(A) What is the ultimate oxygen demand in the stream immediately below the point of discharge? (10 points)

(B) What is the dissolved oxygen concentration in the stream immediately below the point of discharge? (10 points)