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Name ____SOLUTIONS______

CE3501 FUNDAMENTALS OF ENVIRONMENTAL ENGINEERING ENVIRONMENTAL 1-hr in-class Exam

A list of equations is given on the last page of the exam. True-False – put a check in the appropriate space: (2 pts each)

1. In most , the rate of nearly equals the rate of respiration. TRUE ___X______FALSE ______

2. Combustion of fuels disrupts the global cycle primarily by oxidizing organic nitrogen to N2. TRUE ______FALSE _____X______

3. Eutrophication can occur naturally in . TRUE _____X_____ FALSE ______

4. The communities around deep sea thermal vents are supported by first captured and converted to organic matter by chemoautotrophs or . TRUE ______X____ FALSE ______

5. The most often limiting in freshwater lakes is . TRUE ______FALSE ____X______

6. Eutrophic or nutrient-rich conditions promote the existence of complex webs. TRUE ______FALSE _____X______

Indicate (circle or cross out) the one that does NOT match: (3 pts each)

7a. b. Chemosynthetic c. Chemoautotroph d. Nitrification e. reduction

8a. acceptor b. Oxygen c. Sulfate d. e. Iron oxide

1 9a. b. Organic matter c. d. e.

10a. b. Primary c. Vegetarian d. e.

Short answer: (fill in the blanks):

11-13. What are the three most important functions of sewage treatment ? (3 pts each)

REMOVAL OF PATHOGENS

REMOVAL OF BOD

REMOVAL OF

14. Match the following lists of words by putting on the line next to each numbered term, all of the letters from the second column that could possibly correspond to that numbered term. (14 pts) 1. _c,f,e,(g,d,a) a. Secondary consumer 2. __b,(c) b. Primary producer 3. Virus _c______c. Pathogen 4. Microcrustacean _a,d,e,f,g d. Herbivore 5. Macrophyte _b______e. 6. __a,d,f,g f. Heterotrophic 7. Fungi __f,(c,a)_ g.

15. Nitrogen is removed from wastewater through the anaerobic conversion of nitrate to nitrogen gas. What is the name of this process? (4 pts)

_____DENITRIFICATION

16. All of the bass, pike, perch, and walleye in a might comprise the fish __?__

____COMMUNITY (POPULATION also accepted) (4 pts)

2 17. Balance the following reactions (4 pts each) 2- H2S + O2 Î S2O3 + H2O

- 2- + OH + 2H2S + 2O2 Î S2O3 + 2H2O + H

C6H6 + O2 Î CO2 + H2O

C6H6 + 7.5O2 Î 6CO2 + 3H2O

18. A tank truck full of industrial waste is discovered abandoned on a highway. The waste is still warm and thus hasn’t been gone from the very long. A laboratory technician determines that the waste has a 5-day CBOD of 50 mg•L-1. There are three factories in the vicinity generating wastes with ultimate CBODs of 50 mg•L-1 (winery), 80 mg•L-1 (vinegar manufacturer), and 200 mg•L-1 (pharmaceutical plant). Identify the source of the waste and support your selection with calculations. The CBOD rate constant is 0.2 d-1. (15 pts)

SOLUTION -1 You are given that Y5 = 50 mg/L, kL = 0.2 d . Calculate Lo to determine to which waste it is most similar. Lo = Y5/(1-exp(-0.2*5) = 79 mg/L This ultimate BOD is very similar to that of the vinegar manufacturer and would implicate that company as the source of the waste.

------19. Combined sewer overflow runoff associated with a severe summer storm resulted in the discharge of millions of gallons of untreated wastewater to an urban lake and led to the closing of bathing beaches. The public health standard for associated with contact recreation (swimming) is 200 cells·mL-1. Following the storm, bacterial concentrations in the lake were 10,000 cells·mL-1. Assuming first-order kinetics, with a decay constant of 0.5 d-1, determine how many days it will be before the beaches are re- opened. [10 points]

SOLUTION: X = Xo exp(-kd*t) This would be the equation for the decay of the population t = (-1/kd)ln(X/Xo) = (-1/0.5)*ln(200/10,000) = 7.8 d

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3 20. A population of has a maximum specific growth rate coefficient equal to 0.45 d-1, a half saturation constant of 0.7 mg/m3 for , and a respiration rate coefficient of 0.15 d-1. The phosphorus concentration is 0.3 mg/m3. a. Write the differential equation describing a mass balance for this population in a batch reactor (i.e. no inflow or outflow). (7 pts)

SOLUTION: dX⎛⎞⎛⎞ S =−μ kX ⎜⎟max ⎜⎟d dt⎝⎠⎝⎠ S+ Ks

b. Calculate the after 10 days if the initial population is 100 cells•mL-1. Assume that the phosphorus concentration is maintained constant. (10 pts)

SOLUTION: ⎛⎞⎛⎞S μ −kt ⎜⎟max ⎜⎟d ⎝⎠⎝⎠KSS + XXe= 0 ⎛⎞⎛⎞mg 0.3 cells ⎜⎟⎜⎟3 X =⋅100 exp⎜⎟ 0.45ddd−−11m − 0.15 10 ⎜⎟mg mg mL ⎜⎟⎜⎟ ⎜⎟0.333+ 0.7 ⎝⎠⎝⎠mm cells X = 86 mL

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