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

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1 ENV 4001: ENVIRONMENTAL SYSTEMS ENGINEERING Fall 2018 Quiz #2 Wednesday, October 24 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 four questions. Answer question 1. Then, answer any two of the final three questions. 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 2O: 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 3/11

4 This page is left blank intentionally. p 4/11

5 1. (10 pts) a. (2 pts) What is the title of Sustainable Development Goal (SDG) #6 on the United Nations list of SDGs? b. (2 pts) Summarize the goal in one sentence. (Hint: you can use the U.N. wording.) c. (6 pts) What are two targets that this goal would like to achieve by the year 2030? p 5/11

6 2. (25 pts) A very old wastewater treatment plant, which is not functioning properly, discharges its wastewater into the Moreland River. The local regulatory agency is concerned because an endangered species of fish, the Myke Carp, lives in the river. If the oxygen level in the river drops below 6.0 mg/l, the Myke Carp cannot survive. During the summer, the temperature of the Moreland River is 22 C. Upstream of the treatment plant discharge, the flow rate of the Moreland River is 7.5 m 3 /s, the concentration of dissolved oxygen is 8.0 mg/l, and the concentration of contamination in the river (expressed as BOD5) is 3.3 mg/l. The treatment plant discharge rate is 0.48 m 3 /s, the concentration of contamination in the discharge (expressed as BOD5) is 80 mg/l, and there is no dissolved oxygen. Downstream of the discharge, the river is 40 m wide and 2 m deep on average. The rate coefficient for degradation of the contamination is 0.22 d 1. (You can assume this is also the rate coefficient for deoxygenation in the river.) The rate coefficient for reaeration of the river is 0.44 d 1. Your job is to estimate what section of the river has a dissolved oxygen concentration below 6.0 mg/l. This is the section where the Myke Carp might have problems. Report your answer as a range of distances downstream of the treatment plant discharge, using units of km. (Example: the dissolved oxygen concentration drops below 6.0 mg/l between 0.4 km and 0.9 km downstream of the discharge. except those won t be the actual answers.) Hint: you will run into some seemingly messy algebra. There is a trick you can use to simplify the algebra. Notice that one of the rate coefficients is twice as big as the other one. This will enable you to deal with some exponential terms that will appear in your mathematical equation, because exp( 2 α x) = [exp( α x)] 2. p 6/11

7 more space to work on problem 2 p 7/11

8 3. (25 pts) Jacqueline (known as Jackie to her friends) has a vacation house on Lake Bradley, where she spends almost every weekend. Jackie found out that the water in Lake Bradley is contaminated with the chemical tetrachloroethylene (also called perchloroethylene, or PCE), which is a carcinogen. The concentration of PCE in the lake water is 50 µg/l, or mg/l. Jackie is not worried about exposure to tetrachloroethylene because she drinks only bottled water. (Don t get me started on that.) However, Jackie is not thinking about the fact that she eats fish caught from the lake (about 250 g of fish each weekend), and she breathes the air. The bioconcentration factor for PCE in the fish is 500 L/kg. On average, the partial pressure of PCE in the air near the lake is Pa (because some of the PCE moves from the lake to the nearby air), and the air temperature is 25 C. The molar mass of PCE is g/mol. Jackie is a 50-year-old woman with a body mass of 65 kg. She has owned her house for 10 years so far. Assuming that she owns her house for a total of 30 years, and she continues to spend her weekends there, estimate/calculate her lifetime risk of contracting cancer from the PCE in Lake Bradley. Should she sell her house, or is it OK to keep visiting every weekend? Be sure to show your work and to state all your assumptions very clearly! p 8/11

9 more space to work on problem 3 p 9/11

10 4. (25 pts) The drinking-water treatment plant in Barnesville uses the Brasier River as the source of their drinking water. Because they use surface water as their source, they use coagulation/flocculation as part of their treatment process. They have a single flocculation basin with an average hydraulic residence time of 12 min; we can treat the flocculation basin as a completely mixed flow reactor. The concentration of particles entering the flocculation basin is particles/m 3. a. (3 pts) Should the concentration of particles exiting the flocculation basin be equal to the influent concentration, greater than the influent concentration, or less than the influent concentration? Why? explain briefly (a sentence or two). b. (7 pts) One way to model the rate of flocculation (units of particles/(vol time)) is with the following expression: R = 4 π α G Ω N where α is a collision efficiency (equal to 1.0 in the Barnesville plant), G is the mixing speed (equal to 60 s 1 in the Barnesville plant), Ω is the volume fraction of the flocs in the basin (equal to in the Barnesville plant), and N is the number concentration of the flocs in the basin (number of particles per volume). Based on this model, estimate/calculate the number concentration of flocs exiting the flocculation basin. You can assume that the plant operates at steady state. Hint: what kind of reaction kinetics are described by the rate expression above? p 10/11

11 4. continued c. (10 pts) Another way to model the rate of flocculation is with the following expression: RR = 2 3 αα GG dd3 NN 2 where d is the average diameter of the flocs in the basin (equal to 31 µm in the Barnesville plant). Using this expression, write a material balance for the number of flocs in the flocculation basin. Substitute appropriate mathematical expressions for each of the terms in the material balance. Define terms as needed. Hint: where you would usually use mass concentration (mass/volume), now use number concentration (number/volume). d. (5 pts) Solve the equation from part (c) to estimate the number concentration of flocs exiting the basin. Compare your estimate to your answer from part (b). What do you conclude about the two possible methods for modeling flocculation? (Hint: this is only a 5-point problem, so don t spend a lot of time on it if you are short on time, skip this question, then come back to it later, if you decide you have time.) END OF QUIZ p 11/11