Name ____SOLUTIONS________________________ CE3501 FUNDAMENTALS OF ENVIRONMENTAL ENGINEERING ENVIRONMENTAL BIOLOGY 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 ecosystems, the rate of photosynthesis nearly equals the rate of respiration. TRUE ___X_______ FALSE _____________ 2. Combustion of fossil fuels disrupts the global nitrogen cycle primarily by oxidizing organic nitrogen to N2. TRUE ____________ FALSE _____X________ 3. Eutrophication can occur naturally in lakes. TRUE _____X_____ FALSE _____________ 4. The communities around deep sea thermal vents are supported by energy first captured and converted to organic matter by chemoautotrophs or lithotrophs. TRUE ______X____ FALSE _____________ 5. The nutrient most often limiting in freshwater lakes is oxygen. TRUE ____________ FALSE ____X_________ 6. Eutrophic or nutrient-rich conditions promote the existence of complex food webs. TRUE ____________ FALSE _____X________ Indicate (circle or cross out) the one that does NOT match: (3 pts each) 7a. Lithotroph b. Chemosynthetic c. Chemoautotroph d. Nitrification e. Sulfate reduction 8a. Electron acceptor b. Oxygen c. Sulfate d. Methane e. Iron oxide 1 9a. Electron donor b. Organic matter c. Nitrate d. Ammonia e. Sulfide 10a. Herbivore b. Primary consumer c. Vegetarian d. Heterotroph e. Omnivore Short answer: (fill in the blanks): 11-13. What are the three most important functions of sewage treatment plants? (3 pts each) REMOVAL OF PATHOGENS REMOVAL OF BOD REMOVAL OF NUTRIENTS 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. Protozoa _c,f,e,(g,d,a) a. Secondary consumer 2. Algae __b,(c) b. Primary producer 3. Virus _c______ c. Pathogen 4. Microcrustacean _a,d,e,f,g d. Herbivore 5. Macrophyte _b________ e. Zooplankton 6. Fish __a,d,f,g f. Heterotrophic 7. Fungi __f,(c,a)_ g. Carnivore 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 lake might comprise the fish __?__ ____COMMUNITY (POPULATION also accepted) (4 pts) 2 17. Balance the following redox 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 plant 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 bacteria 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 ----------------------------------------------------------------------------------------------------------- 3 20. A population of microorganisms has a maximum specific growth rate coefficient equal to 0.45 d-1, a half saturation constant of 0.7 mg/m3 for phosphorus, 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 population size 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 4.