environmental engineering past paper 2006

environmental engineering past paper 2006 - THE UNIVERSITY...

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Unformatted text preview: THE UNIVERSITY OF HONG KONG BACHELOR OF ENGINEERING: LEVEL; I )EXAMINATION DEPARTMENT OF CIVIL ENGINEERING Environmental Engineering December 22 , 2006 CIVL 1005 TIME: 2:30 — 14:30 pm (2 hours) Answer any 25 out of the following 30 questions. All questions carry equal marks; one mark will be deducted for each wrong answer. Use of Electronic Calculators: Candidates may use any calculator which fillfils 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. 1. 2. What is the closest value of k (reaction rate constant) for a wastewater sample which has a BODZ of 130 mg/l and a BOD5 of200 mg/l: (a) 0.2, (b) 0.3, (c) 0.4, or (d) 0.5. A room with volume 500 m3 has 50 smokers in it, each smoking two cigarettes per hour. An individual cigarette emits about 1.4 mg of formaldehyde (HCHO). Formaldehyde converts to carbon dioxide with a reaction rate coefficient of K = 0.40/hr. Fresh air enters the room at the rate of 1000 m3/hr, and stale air leaves at the same rate. Assuming complete mixing, what is the steady state concentration of formaldehyde in the air at 25°C: (a) 0.080 ppm, (b) 0.085 ppm, (c) 0.090 ppm, or (d) 0.095 ppm. (Atomic weight: C 12; O 16; H 1) Living organisms in nature store food in cells in the form of polysaccharides, of which starch is the most abundant in plants and glycogen in animals. Polysaccharides have the chemical formula of (C5H1005)n, where n is the number of repeated units. Based on this chemical formula, what is the closest estimate of theoretical oxygen demand for each gram of starch: (a) 1.0 g, (b) 1.5 g, (c) 2.0 g, or (d) 2.5 g. There are four sources of noise with respective levels of 68, 75, 79 and 84 db. What is the combined level of these four noises: (a) 86 db, (b) 153 db, (0) 306 db, (d) 1223 db? 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 pig/m3 sulphur dioxide: (a) 8.1, (b) 81, (c) 810, or (d) 8100. (Atomic weight: S 32, O 16). Which one of the following descriptions of aluminum is false: (a) an element rich in soil, (b) tri- valent aluminum ion is toxic, (c) it is an element crucial to many enzymatic activities, (d) many minerals rich in aluminum have buffering capacity at low pH. Calcium (Ca2+), magnesium (Mg2+) and aluminum (A1“) are among the most common cations page 1 of 3 10. 11. 12. 13. 14. 15. 16. 17. 18 19. 20. 21. 22. 23. found in groundwater. Which of the following waters has the highest degree of hardness as expressed by CaC03 equivalent? Water (a) containing 100 mg/l of Ca2+, or (b) containing 50 mg/l of Ca2+ and 50 mg/l of Mg”, or (0) containing 35 mg/l of Ca“, 35 mg/l of Mg2+ and 35 mg/l of Al“, or ((1) containing 50 mg/l of Mg2+ and 50 mg/l of Al“. (Atomic weights are: Ca 40; Mg 24.3; and Al 27.) Ammonia (NH3) dissolves in water forming NH4+ and OH'. The equilibrium constant for this reaction is 1.82 x 105. In order to remove NH4+ from water by stripping, the pH of the water has to be adjusted. At which of the following pH levels that over 99.8% of NI-I4+ becomes Nng (a) 10.5, (b) 11, (c) 11.5, or (d) 12. A sample of groundwater has 100 rug/L of Ca2+ and 10 mg/L of Mg”. (Atomic weights: Ca 40.1; Mg 24.3; C 12; O 16). What are the hardness expressed in meq/L and mg/L as CaC03: (a) 5.8 meq/L and 291 mg/L; (b) 2.9 meq/L and 291 mg/L; (c) 5.8 meq/L and 146 mg/L; or (d) 2.9 meq/L and 146 mg/L. Which of the following elements is not a major nutrient required for the growth of living organisms: (a) phosphorus, (b) nitrogen, (c) sulphur, or (d) chloride. 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 —0.5L (L = BOD). If re- degradation reaction rate (mg 02/L-d) can be described by dL dt 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 (c) 12,000, or ((1) 13,000 m. Nitrogen is municipal wastewater is mainly present in the form of organic-nitrogen or ammonia. Which of the following statement regarding ammonia is false? (a) it can be stripped from wastewater by lowing the pH, (b) it has a pungent odor, (c) it is highly toxic to aquatic life, or (c) its solubility in water follows the Henry’s Law. Which one of the following descriptions for a secondary sewage treatment plant is false: (a) suspended solids in the sewage accounted for over 1/3 of total BOD, (b) solids removed from the primary settling tank are mostly biomass, (c) sludge handling and disposal are as expensive as BOD reduction, or (d) chlorination of treated effluent is not required in Hong Kong. Disinfection is the final treatment process in many water treatment plants. Although chlorination is the most commonly used, there are many other disinfection processes being used. Identify the process in the following which is not a disinfection process: (a) activated carbon, (b) reverse osmosis, (c) ozonation, or ((1) UV irradiation. Activated carbon is effective for the removal of (a) bacteria, (b) Ca2+ and Mg2+, (c) Al3+ and Fe3+, (d) organic pesticides. Which one of the following statement regarding coagulation is false: (3) it always followed by the flocculation process, (b) it always requires addition of chemicals, (c) it requires only a very mild mixing, and (d) it is used for both water and wastewater treatment in Hong Kong. . Nearly all the wastewater collected at both sides of the Victoria Harbour is presently treated at the Stonecutters Wastewater Treatment Works using a CEPT process. What is the chemical used currently in this process: (a) ferric chloride, (b) aluminium sulfate, (c) calcium carbonate, or (d) calcium bicarbonate. Which one of the following description is a false description of dissolved oxygen (D0) which is one of the most critical parameter on water quality: its solubility in water decreases with (a) the increase of pH, (b) increase of altitude, (c) increase of temperature, or ((1) increase of salinity. A reverse osmosis plant treats daily 5000 tons of feedwater containing 1500 mg/L of salt, and yields 3000 tons of product water with 75 mg/L of salt. What is the salt concentration in the rejected brine: (a) 3600 mg/L, (b) 2600 mg/L, (0) 1600 mg/L or (d) 600 mg/L? Radon is a radioactive gas that is part of a natural decay chain beginning with A and ending with B, where A and B are: (a) uranium and lead, (b) uranium and iron, (0) plutonium and lead, (d) plutonium and iron. Asbestos can lead to a number of life-threatening diseases, including asbestosis, lung cancer and mesothelioma. Asbestos is thus a very serious indoor air pollutant. Asbestos is released due to (a) cigarette smoking, (b) its use as construction material, (c) incomplete combustion of stoves or heaters, or (d) natural decay of radon. Which one of the following is an incorrect description of BTX: (a) pollutants found in soil of the old Kai Tak airport , (b) petrol additives to boost octane rating, (c) water pollutants due to high water solubility, or (d) can increase formation of photochemical smog. page 2 of 3 24. 25. 26. 27. 28. 29. Chlorofluorocarbons (CFCs) are known to cause the depletion of stratospheric ozone. They had been widely used in numerous industrial applications due to certain physicochemical properties until the recent decade. Which of the following descriptions of CFCs is false: (a) nontoxic, (b) water soluble, (c) nonflammable, or (d) nonreactive. Which one of the following statement regarding the stratosphere is correct: (a) temperature increases with altitude due to the increased UV absorption of Oz and 03, (b) temperature increases with altitude due to increased UV absorption of CFCs, (c) temperature decreases with altitude due to the decreased UV absorption of 02 and 03, ((1) temperature decreases with altitude due to decreased UV absorption of CF Cs. A concentration level for N02 is at 300 ug/m3. 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 16, respectively. Express the concentration level of NO; in ppm: (a) 0.15 ppm, (b) 0.16 ppm, (0) 0.18 ppm, or (d) 0.24 ppm. CFCs are a group of (a) viruses, (b) pathogens, (c) green house gases, or (d) coagulants used in wastewater treatment plants. A convective kerosene heater is tested in a well—mixed 27m3 chamber having an air exchange rate of 0.39 air exchanges per hour. After one hour of operation, the NO concentration reached 4.7 ppm. Treating NO as a conservative pollutant, what is the NO source strength of the heater (in mg/hr): (a) 210 mg-NO/hr, (b) 200 mg-NO/hr, (c) 190 mg-NO/hr or (d) 180 mg-NO/hr. Cyclone is a very cost effective device for air pollution control. Its efiiciency is relatively independent of: (a) particle size, (b) temperature, (c) particle density, or (d) air velocity. 30. NOx is a crucial air pollutant resulting mainly from the combustion of fossil fuel. Which of the following statements about NOx is false? The formation of NOx may be affected by (a) the N content in fossil fuel, (b) the combustion temperature, (c) the air-fuel ratio, or (d) the size of the combustion chamber. - END OF PAPER - page 3 of 3 ...
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This note was uploaded on 10/02/2010 for the course CIVIL ENGI 09332005 taught by Professor Kaiminshi during the Spring '10 term at Hong Kong Baptist University, China.

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environmental engineering past paper 2006 - THE UNIVERSITY...

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