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environmental engineering past paper 2005-5 - THE...

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Unformatted text preview: THE UNIVERSITY OF HONG KONG BACHELOR OF ENGINEERING: LEVEL Ill EXAMINATION E / . .~" ./ DEPARTMENT OF CIVIL ENGINEERING / 7/ 3 . .. / /' ENVIRONMENTAL ENGINEERING (CIVL 1005) - [“07 MAY 28, 2005 TIME: 9:30 — 11:30 AM (2 hours) INS TR UC T ION ABOUT N UMBER OF QUESTIONS TO BE ANSWERED: Answer ALL questions INF ORAM T ION ABOUT THE MARK VALUE OF QUESTIONS Only one correct answer for each question. Giving more than one answer to a question is considered a wrong answer. Each question carries 4 marks. One mark will be deducted for each wrong answer. Use of Electronic Calculators: Candidates may use any calculator, Which fulfils the following criteria: (a) (b) (C) (d) it should be self-contained, silent, battery—operated and pocket-sized; it should have numeral-display facilities only and should be used only for the purpose of calculation; it should not have any printing device, alphanumeric keyboard, or graphic display; and it should not contain any recorded data or program. It is the candidate's responsibility to ensure that the calculator operates satisfactorily and the candidate must record the name and type of the calculator on the front page of the examination scripts. Lists of permitted/prohibited calculators will not be made available to candidates for reference, and the onus will be on the candidate to ensure that the calculator used will not be in violation of the criteria listed above. - A 1000-MW coal-fired power plant in Hong Kong has an efficiency of 33.3% with 15% of the waste heat being released to the atmosphere as stack heat and the other 85% taken away in the cooling water. If the cooling water is allowed a rise in temperature by 8.0°C, what flow rate would be required, in m3/s: (a) 40.8, (b) 50.8, (c) 60.8, or (d) 80.8. The same 1000—MW coal-fired power plant, without air pollution control, would generate 216 t/d of sulphur emissions. Assuming 85% efficiency of the sulphur emission control system, how many cubic kilometres of clean air volume will be required daily for dilution in order to meet the air quality objective of 80 ug/m3 sulphur dioxide: (a) 8.1, (b) 81, (c) 810, or (d) 8100. (Atomic weight: S 32, O 16). In most marine waters, nitrogen is the limiting nutrient for the growth of algae, with 0.3 mg/L considered as the critical concentration. At what concentration would phosphorus become the limiting nutrient: (a) 10 mg/L, (b) 1 mg/L, (c) 0.1 mg/L, or (d) 0.01 mg/L. Eutrophication is a nutrient enrichment process of natural waters. Which one of the following statements is false: Eutrophication may result in (a) increased growth of algae, 1 L‘ 10. 11. 12. 13. 14. 15. 16. (b) increased water turbidity, (c) increased fish production, and (d) decreased dissolved oxygen during night time on the water surface. Dissolved oxygen, one of the most important water quality parameters, is greatly affected by both eutrophication and stratification. Which one of the following statements is false: Stratification in a water body is caused by (a) vertical temperature difierences, (b) acidification, (c) vertical salinity differences, or (d) inhibition of vertical mixing. The purpose of Water treatment systems is to bring raw water up to' drinking water quality. Which one of the following statements is false: A typical water treatment plant in Hong Kong may include the following treatment processes: (a) flocculation, (b) sedimentation, (c) filtration, and (d) desalination. An important source of Hong Kong drinking water, is the East River (Dongjiang) in Guangdong. The recently discovered presence of Cryptosporidium in East River raw water has caused Hong Kong Water Supplies Department to modify its disinfection process. Which is the newly introduced disinfection process: (a) chlorination, (b) ozonation, (c) ultraviolet radiation, or (d) reverse osmosis. Drinking water quality is defined by physical, chemical and microbiological standards. Which one of the following statements is false: The public of Hong Kong commonly requests the following parameters of drinking water quality: (a) hardness, (b) chloride, (c) iron, and (d) nitrogen. An industrial wastewater (BODS = 1,000 mg/L, total nitrogen = 10 mg/L, flow rate = 1 Us) is discharged into a public sewer and mixed with domestic sewage (BOD5 = 200 mg/L, total nitrogen = 40 mg/L, flow rate = 1,000 m3/d). What is the ratio of BOD5 to total nitrogen ofthe mixture: (a) 4:1, (b) 5:1, (c) 6:1, or (d) 7:1. Which one of the following statements is false: A conventional secondary wastewater treatment plant in Hong Kong may include the following treatment processes: (a) primary treatment, (b) biological treatment, (c) filtration, and (d) disinfection. Activated sludge is a (a) physical treatment process, (b) biological treatment process, (0) chemical treatment process, or (d) sludge treatment process. The approximate effluent quality of a conventional secondary wastewater treatment plant has been determined in the laboratory and reported as follows: (a) BOD5 = 30 mg/L, (b) dissolved solids = 30 mg/L, (c) total nitrogen = 25 mg/L, and (d) total phosphorus = 5 mg/L. Where has the laboratory technician made a mistake? Which one of the following descriptions of a Hong Kong municipal solid waste landfill is false: (a) landfill gas consists mostly of methane and carbon dioxide, (b) the generated landfill gas may be used to produce electricity, (c) landfill leachate may emit methane to the atmosphere and contribute to global warming, and (d) landfilling municipal solid waste requires more space than a municipal solid waste incineration plant. Traffic noise at a location due to a nearby highway has a present value of 65.5 dB(A). In two years time, the traffic volume in the highway will increase by 35%. What will be the traffic noise level at the location? (a) 88.4 dB, (b) 76.1 dB, (c) 66.8 dB, or (d) 68.1 dB. Which of the following statements are true?: (a) A 2 dB drop in sound pressure level will be experienced for a doubling of the distance from the sound source, (b) A 3 dB drop in sound pressure level will be experienced for a doubling of the distance from the sound source, (c) A 2 dB increase in sound pressure level is caused by a doubling of the sound power, or (d) A 3 dB increase in sound pressure level is caused by a doubling of the sound pressure. A concentration level for N02 is at 300 ug/mS. Given that one mole of an ideal gas occupies 24.5 litres at 25°C and 1 atm, and the molecular weights of N and O are 14 and 2 L\ 17. 18. 19. 20. 21. 22. 23. 24. 25. 16, respectively. Express the concentration level of NO2 in ppm: (a) 0.16 ppm, (b) 0.15 ppm, (0) 0.18 ppm, or (d) 0.24 ppm. Which one of the following meteorological conditions will most likely promote vertical mixing and leads to clear skies: (a) a cold front approaching, (b) a cold front arrived for a while, (0) a warm front approaching, (d) a warm front arrived for a while. Car engines are designed to have combustion at higher temperatures. This will lead to more environmentally acceptable emissions. However, which air pollutant in the following will be emitted in higher concentration: (a) hydrocarbons, (b) CO2, (c) NOX, or (d) ozone. _ Which of the following statements is most likely to be false: (a) building ventilation and air conditioning are two different indoor environment engineering systems, (b) indoor air quality can be more significant than outdoor air quality in terms of impact on our health, (c) ventilation is just about supplying fresh outdoor air into a building, or (d) indoor air quality in offices affects to the productivity of workers. Commercial kitchen exhausts are important air pollutant emitters in Hong Kong. Which one of the following is the commonest device used to control these exhausts?: (a) kitchen hood with powerful exhaust fan and oil drip, (b) cyclone collector; (c) absorption tower; or (d) scrubber. " A pure glucose solution contains 200 mg/L of glucose (C6H1206, atomic weight: C 12, H 1, O 16). The theoretical oxygen demand of the solution in mg O2/L is (a) 174, (b) 190, (c) 202, or (d) 214. ‘_ .~\ fr; Ammonia (NH3, atomic weight: N 14) dissolves in Water forming NH4+ and OH'. The equilibrium constant for this reaction is 1.82 x (10—5: T7he sewage of Hong Kong contains 28 mg/L of total NH3-N (sum of NH3-N and/NHf-N) at pH=7.26 and T=25°C. According to Henry’s law (KH = 26.6 mole/L-atm for NH3), the concentration of NH3 in the sewer atmosphere (1 atrn, 25°C) in ppm by volume is around (a) 0.55, (b) 0.62, (c) 0.75, or (d) 0.83. The initial growth of fish in a new pond had a doubling time of 100 days. When the fish population reached a density of 30/m2, its doubling time of growth extended to 250 days. The carrying capacity (/m2) of the pond for growing fish is (a) 40, (b) 50, (c) 60, or (d) 80. A wastewater is discharged into a river and mixed immediately with the river water. The river is rather flat and straight with an average flow velocity of 0.1 m/sec. Just downstream from the discharge point, the river has an ultimate BOD of 12 mg/L and a D0 of 6 mg/L. The BOD degradation reaction rate (mg O2/L-d) can be described by det = -O.5L (L = BOD). If re—aeration and other processes are neglected, from the discharge point the D0 of the river would decrease to zero after about (a) 10,000, (b 11,000 (0) 12,000, or (d) 13,000 m. ' In marine waters, organic nitrogen (Org-N) from sewage disposal would normally go through the transformation of (a) Org-N —> Ammonia-N —-—> Nitrite —> Nitrate, (b) Org-N ——> Ammonia-N —> Nitrite ——> N2, (0) Org-N -—-> Nitrite —> Ammonia-N —> Nitrate, or (d) Org-N —) Ammonia-N —> N2 -—> Nitrate. - END OF PAPER - ' 7Z/7 Lg/f/mwfi/ ...
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