ENV 4001: ENVIRONMENTAL SYSTEMS ENGINEERING. University of South Florida Civil & Environmental Eng.

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1 ENV 4001: ENVIRONMENTAL SYSTEMS ENGINEERING Fall 2017 Quiz #2 Wednesday, October 25 University of South Florida Civil & Environmental Eng. Prof. J.A. Cunningham Instructions: 1. You may read these instructions, but do not turn the page or begin working until instructed to do so. 2. This quiz contains two questions. Answer both. 3. Some questions might have multiple parts. In those cases, the point value of each part is indicated. The total number of points possible is Unit conversion factors and other potentially useful information are provided on the back of this page, and on the page after that. 5. Answer each question in the space provided. If you need more space, you can attach additional pages as needed, but make sure to put your name on them. 6. Show your work and state any important assumptions you make. I cannot award partial credit if I can t follow what you did. 7. Report a reasonable number of significant digits in your answers. 8. Include units in your answers. An answer without proper units is not correct! 9. You are allowed to use your text book, your course notes, or other printed materials. You may not receive help from another person. 10. A hand-held calculator is recommended. Other electronic devices are not permitted. 11. Please make sure your mobile telephone is off and put away. 12. Time limit: 60 minutes. Stop working when asked. If you continue working after time has been called, you will be penalized at a rate of 1 point per minute. 13. Don t cheat. Cheating will result in appropriate disciplinary action according to university policy. More importantly, cheating indicates a lack of personal integrity. 14. Please print your name legibly in the space provided below, and turn in this quiz at the end of the period. 15. Hints: Read each question carefully and answer the question that is asked. Watch your units. If you take good care of your units, they will take good care of you. Work carefully and don t rush. Name: p 1/9

2 Potentially useful constants: Ideal gas constant, R: Pa m 3 mol 1 K 1 = atm m 3 mol 1 K 1 Gravitational acceleration, g: 9.81 m/s 2 Molecular weight of water, H 2 O: g/mole Density of water at 20 C: g/ml = 998 kg/m 3 Viscosity of water at 20 C: Pa sec Density of air at 25 C: 1.18 kg/m 3 Viscosity of air at 25 C: Pa sec Potentially useful conversion factors: Pressure: 1 atm = 760 mm Hg = 760 torr = Pa 1 Pa = 1 N/m 2 = 1 kg/(m sec 2 ) Mass: 1 kg = 1000 g = 10 6 mg = 10 9 µg 1 kg = lb mass 1 t (metric tonne) = 1000 kg = 2207 lb mass 1 ton (English ton) = 2000 lb mass Length: 1 km = 1000 m = 10 5 cm = 10 6 mm = 10 9 µm 1 ft = 12 in = cm = m Temperature: 25 C = K Volume: 1 m 3 = 1000 L = 10 6 ml = 10 6 cm 3 1 gal = L Work/Energy: 1 BTU = kj Power: 1 MW = 10 6 W = 10 6 J/s = 10 6 N m/s Area : 1 ha = 10 4 m 2 Atomic Masses: H = g/mole C = g/mole N = g/mole O = g/mole P = g/mole S = g/mole Cl = g/mole Br = g/mole Na = g/mole Mg = g/mole Ca = g/mole Fe = g/mole Equilibrium Concentrations of Oxygen (O2) in Fresh Water (air/water equilibrium): Temperature Equil. Conc. of O 2 Temperature Equil. Conc. of O 2 ( C) (mg/l) ( C) (mg/l) p 2/9

3 from Principles of Environmental Engineering and Science, 2nd edition, by Davis and Masten p 3/8

4 1. (30 pts) The city of Bettsville just finished construction on a new drinking-water treatment plant that will treat L/d of ground water from a local aquifer. Unfortunately, almost as soon as construction was finished, it was discovered that the source water for the new plant has been contaminated by methylene chloride (CH 2 Cl 2 ), which causes cancer. The concentration of CH 2 Cl 2 in the source water is approximately 500 µg/l (equivalent to 0.5 mg/l). To address this problem, the city will add a new reactor to the treatment plant to remove CH 2 Cl 2 from the treated drinking water. The reactor will be a completely mixed flow reactor (CMFR), and the city estimates that CH 2 Cl 2 removal in the reactor will follow first-order kinetics with a rate coefficient of 0.2 min 1. Estimate/calculate the reactor volume required to reduce the methylene chloride concentration to a level that presents an acceptable cancer risk to Bettsville residents who drink the water. For this problem, you can ignore risk from inhalation or dermal absorption. Clearly state all your relevant assumptions here: Begin your calculations here, and show all your work: more space to work on problem 1 p 4/8

5 1. continued more space to work on problem 1 p 5/8

6 2. (30 pts) People who live near the Devers River have been complaining ever since a new factory started discharging its waste into the river. They say that there are now far fewer fish in the river downstream of the factory. Some wildlife biologists said that the fish need at least 5.0 mg/l of dissolved oxygen to thrive, and maybe the factory waste is depleting the oxygen in the river. A factory spokesperson said We are not the cause of the problem. We went out and measured the dissolved oxygen concentration in the river just a little bit downstream of our factory discharge. The concentration was 7.36 mg/l. That is well above 5 mg/l. So the factory is not harming the fish. a. (5 pts) Does the reasoning of the factory spokesperson make sense? Why or why not? Some residents of the town were not convinced. They took water samples from 10 km and from 20 km downstream of the factory discharge. They measured the BOD 5 of the water samples. The BOD 5 was 13.3 mg/l in the 10-km sample, and it was 11.6 mg/l in the 20-km sample. In the region of interest (i.e., downstream of the factory discharge), the Devers River has a temperature of 17 C, a depth of 2.0 m, a width of 25 m, and a volumetric flow rate of 12.5 m 3 /s. b. (10 pts) Estimate/calculate the apparent first-order rate coefficient for biodegradation in the river. Also estimate the BOD 5 and the BOD ult immediately downstream of the factory discharge. problem 2 continues p 6/8

7 2. continued b. more space to work on part b c. (15 pts) How far downstream of the factory will the concentration of dissolved oxygen be at its lowest? Do you expect the concentration of dissolved oxygen to drop below the threshold value of 5 mg/l cited by the wildlife biologists? Show your calculations. You can assume that the first-order rate coefficient for deoxygenation in the river is equal to the first-order rate coefficient for degradation of the organic compounds that exert BOD. more space to work on problem 2 p 7/8

8 2. continued more space to work on problem 2 END OF QUIZ p 8/8