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

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1 ENV 4001: ENVIRONMENTAL SYSTEMS ENGINEERING Spring 2015 Quiz #2 Wednesday, March 18 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 three questions. Answer any two. 3. If you attempt more than two, make sure that you indicate clearly which two you want me to grade. If it isn t clear, then I will choose which two I feel like grading. 4. 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. 6. 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. 7. Show your work and state any important assumptions you make. I cannot award partial credit if I can t follow what you did. 8. Report a reasonable number of significant digits in your answers. 9. Include units in your answers. An answer without proper units is not correct! 10. You are allowed to use your text book, your course notes, or other printed materials. You may not receive help from another person. 11. A hand-held calculator is recommended. Other electronic devices are not permitted. 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 2O: g/mole Density of water at 25 C: g/ml = 997 kg/m 3 Viscosity of water at 25 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 3/9

4 1. (30 pts) A factory discharges its industrial waste into the Schilling River. We are worried about the effects that the discharge might have on the health of the river. Here is what we know: In the section of the river about which we are concerned, the Schilling River flows with a velocity of 0.22 m/s. Other than the factory, there are no other major sources of contamination into the river for about 100 km in either direction. The temperature in the river is 18 C. Just downstream of where the factory discharge mixes into the river, the concentration of dissolved oxygen is 8.04 mg/l. The reaeration rate coefficient for the river is estimated to be 0.60 d 1. The deoxygenation rate coefficient for the river can be assumed equal to the BOD decay rate coefficient in the river. Some environmental engineers took a water sample from the river at a distance 38 km downstream of the discharge point. They found that, at that location, the BOD ult in the river is 10.9 mg/l and the BOD 5 in the river is 8.47 mg/l. (a) (5 pts) Estimate/calculate the BOD decay rate coefficient in the river. Report your answer in units of d 1. (b) (6 pts) Estimate/calculate the BODult in the river just downstream of the factory s discharge point. Report your answer in units of mg/l. Hint: how is the BOD ult at a distance 38 km downstream related to the BOD ult at the discharge point? p 4/9

5 Problem 1, continued (c) (8 pts) How far downstream of the factory do you expect the concentration of dissolved oxygen to be the lowest? Report your answer in units of km. (d) (8 pts) Estimate/calculate the concentration of dissolved oxygen in the river at the distance you reported in part (c). Report your answer in units of mg/l. (e) (3 pts) Do you think the factory discharge is creating a problem in this river, or is it OK? Explain briefly. A few sentences should suffice. Use your calculations to support your answer. p 5/9

6 2. (30 pts) An engineer at a drinking water treatment plant is worried about contamination of the drinking water by a recently-discovered bacterium, Vomitus horribilus. The engineer decides to run some tests to determine if V. horribilus can be effectively inactivated by chlorine disinfectant. She runs her tests in a batch reactor. Her experimental data show that disinfection of V. horribilus follows first-order kinetics. Also, by maintaining the chlorine concentration in the reactor at 4.00 mg/l, she can inactivate 99.0% of V. horribilus in a time of 12.0 min. (a) (6 pts) If she keeps the chlorine concentration at 4.00 mg/l, how long will it take to achieve 99.9% inactivation of V. horribilus in the batch reactor? (b) (6 pts) If she wants to keep the reaction time to no greater than 16.0 min, what concentration of chlorine would be required to achieve 99.99% inactivation of V. horribilus? p 6/9

7 Problem 2, continued After running the batch tests, the engineer is ready to think about how to disinfect the water at the drinking water plant. The plant treats 53 m 3 /min (about 20 million gallons per day). The plant uses chlorine as its disinfectant. The chlorine concentration in the disinfection reactors can be assumed to be 4.00 mg/l. (c) (6 pts) Which type of reactor would you recommend for disinfection plug flow reactor or completely mixed flow reactor? Why? Explain in a sentence or two. (d) (6 pts) For the type of reactor that you recommended in part (c), how much residence time is required if you want to be sure that 99.9% of V. horribilus is inactivated? What volume of reactor would be required (in units of m 3 )? (e) (6 pts) Compare the contact time you required in part (a) to the residence time you required in part (d). Is the residence time from part (d) greater than the contact time from part (a), less than the contact time from part (a), or equal to the contact time from part (a)? Explain briefly. p 7/9

8 3. (30 pts) Camp Lejeune is a military base for the United States Marine Corps (USMC) located in North Carolina. Some of the drinking water at the base was contaminated for a period of about 11 years, from 1975 through (This is a true story, I am sad to say.) The base has eight water treatment plants, and two of them were found to be using contaminated ground water as their water source. Recently, a study was published that examines whether the water contamination has led to an increased rate of cancer among Marines who lived on the base. Bove FJ, Ruckart PZ, Maslia M, Larson TC, Evaluation of mortality among Marines and Navy personnel exposed to contaminated drinking water at USMC base Camp Lejeune: A retrospective cohort study. Environmental Health, 13:10. Below is some information from the study. About 155,000 Marines were stationed at Camp Lejeune at some point during the time period under consideration. By an interesting coincidence, about 155,000 Marines were also stationed at Camp Pendleton (in California) during the same period. The drinking water at Camp Pendleton was not contaminated. The Tarawa Terrace distribution system at Camp Lejeune had a median concentration of about 85 µg/l of tetrachloroethylene during Let s assume that 20,000 out of the 155,000 Marines at the base used this water as their principal source of drinking water. The Hadnot Point distribution system at Camp Lejeune had a median concentration of about 22 µg/l of vinyl chloride during the time period. Let s assume that 20,000 out of the 155,000 Marines at the base used this water as their principal source of drinking water. On average, Marines who were stationed at Camp Lejeune lived on the base for a period of 18 months. (a) (20 pts) Let s suppose that 25,000 of the 155,000 Marines stationed at Camp Pendleton in California will contract cancer during their life. This is just an estimate, but it seems reasonable. Based on that, estimate how many Marines from the Camp Lejeune cohort are expected to contract cancer during their lives. p 8/9

9 3. continued (a) more space to work on part (a) (b) (5 pts) Compare the cancer rate at Camp Pendleton to the cancer rate you estimated at Camp Lejeune. From your estimate, does the water contamination at Camp Lejeune appear to pose a significant health risk? Explain briefly (a few sentences). (c) (5 pts) The study found that, so far, the cancer rate among the Camp Lejeune Marines is about 10% higher than the cancer rate among the Camp Pendleton Marines. This suggests that the water contamination at Camp Lejeune has had a significant effect on the health of the Marines stationed there. Does this agree with your estimates and analysis above? If not, what might be a reasonable explanation for why not? END OF QUIZ p 9/9