Module 4 - Practice Exam 2 Solutions.pdf

WATR 048 - Fall 2021 Practice Exam 2 - Solution Shabbir Basrai True/False Questions - 1 point each 1. MCRT refers to the average number of days that a cell remains in an activated sludge system. *a. True b. False 2. Activated sludge is an anaerobic process a. True *b. False 3. Secondary tre...

WATR 048 - Fall 2021 Practice Exam 2 - Solution Shabbir Basrai True/False Questions - 1 point each 1. MCRT refers to the average number of days that a cell remains in an activated sludge system. *a. True b. False 2. Activated sludge is an anaerobic process a. True *b. False 3. Secondary treatment is mainly to remove the organic content of the wastewater *a. True b. False 4. SVI is a measure of the sludge volume that needs to be wasted a. True *b. False 5. Although untreated wastewater contains many billions of bacteria per gallon, most of these are not harmful to humans, and some are even helpful in wastewater treatment. *a. True b. False 6. BOD is a measure of the organic content of wastewater *a. True b. False 7. The units ppm and % are considered roughly equivalent for wastewater treatment calculations. a. True *b. False Page 1 of 18 Practice Exam 2 - Solution Shabbir Basrai 8. A one acre wastewater treatment pond operated at a depth of 3 feet holds approximately 1 million gallons *a. True b. False 9. Compared to activated sludge, trickling lters are sturdy work units not easily up set by shock loads. *a. True b. False 10. Ponding on the surface of trickling lters is almost always caused by plugging of the underdrains immediately below the point of ponding a. True @Incorrect. Ponding is typically caused by plugging of media by zoogleal mass *b. False @Correct. Ponding is typically caused by plugging of media by zoogleal mass and not by plugging of the underdrains 11. Recirculation helps prevent excessive sloughing a. True *b. False 12. Series operation of trickling lter is the preferred mode during very low temperature conditions during winter a. True *b. False 13. The advantage of trickling lter over the activated sludge lies in its BOD removal eciency a. True *b. False 14. Hydrogen sulde gas in a moist atmosphere can result in corrosion of concrete structures *a. True b. False Page 2 of 18 WATR 048 - Fall 2021 Practice Exam 2 - Solution Shabbir Basrai 15. Presence of hydrogen sulde cannot always be detected by its characteristic odor *a. True b. False 16. A well-operated primary clarier, will remove between 90 and 95 percent of the inuent settleable solids. *a. True b. False 17. It is common for primary clariers to remove 80-85% of the BOD and 90-95% of the TSS. a. True *b. False 18. The only function of ights in a rectangular sedimentation tank is to push the settled sludge towards the hopper a. True *b. False 19. Detention time is the time required to ll a tank at a given ow. *a. True b. False 20. Primary treatment is a process that allows substances that will settle or oat to be separated from the wastewater being treated. *a. True b. False 21. Raw sludge pumped from a primary clarier generally contains about 3% to 6% total solids. *a. True b. False 22. The solids in primary sludge contain both volatile and xed parts. *a. True b. False Page 3 of 18 WATR 048 - Fall 2021 Practice Exam 2 - Solution Shabbir Basrai 23. A grit chamber with a faster ow velocity than recommended may allow appreciable organic matter to collect in the grit. a. True *b. False 24. A Parshall Flume is a device used to divide the incoming ow for equal distribution to a plant having more than one primary clarier. a. True *b. False 25. A Venturi meter measures the amount of electricity used and should be read when there is a high electrical demand. a. True *b. False 26. At most treatment plants preliminary treatment is used to protect pumping equipment and to facilitate subsequent treatment processes. *a. True b. False 27. Fresh wastewater is characterized by a blackish color, foul and unpleasant odors with oating materials and suspended solids. a. True *b. False 28. Inecient grit removal would tend to cause a decrease in percent volatile solids in raw primary sludge *a. True b. False 29. Too low a velocity of wastewater owing through a grit chamber would cause excessive amounts of organics to collect with the settled grit. *a. True b. False Page 4 of 18 WATR 048 - Fall 2021 Practice Exam 2 - Solution Shabbir Basrai 30. Algae is primarily responsible for the eective working of an anaerobic pond a. True *b. False 31. In a facultative pond, a drop in the pH will normally be accompanied by a rise in the dissolved oxygen. a. True *b. False 32. Operational depth of a wastewater pond is not used for calculating its organic loading *a. True b. False 33. Usually facultative ponds are mixed with mechanical aerators at night and on cloudy days to disperse food and bacteria evenly. a. True *b. False 34. Domestic wastewater generally contains only about 0.1% of solids. *a. True b. False 35. A 24-hr ow proportioned sample may be collected for a fecal coliform test a. True *b. False 36. Typical domestic wastewater BOD content is about 2000mg/l a. True *b. False 37. The MPN test is used to measure pathogen concentrations in wastewater. a. True *b. False Page 5 of 18 WATR 048 - Fall 2021 Practice Exam 2 - Solution Shabbir Basrai 38. The laboratory measurement of volatile solids is a fair approximation of the organic content of the wastewater. *a. True b. False 39. The units ppm and % are considered equivalent for wastewater treatment calculations. a. True *b. False 40. All 100- and 150-pound chlorine cylinders should be restrained or safety-chained to sturdy supports even when empty. Except when actually being moved to or from storage. *a. True b. False 41. Chlorine demand is dened as the amount of chlorine remaining in the waste water at the end of a specic contact period. a. True *b. False 42. Chlorine is used to sterilize wastewater in order to insure protection of public health. a. True *b. False 43. The chlorine dose rate plus the chlorine residual equals the chlorine demand. a. True *b. False 44. Sludge digestion is a process by which principally the inorganic matter in sludge is gasied and/or converted to a more stable form by the biological process. a. True *b. False Page 6 of 18 WATR 048 - Fall 2021 Practice Exam 2 - Solution Shabbir Basrai 45. The gas produced as part of the anaerobic digestion is of little or no value a. True *b. False 46. Volatile solids removal eciency of a digester is most commonly monitored utilizing the BOD test a. True *b. False 47. A combined sewer implies that it carries domestic and industrial wastes only a. True *b. False 48. Digester gas containing 60% methane by volume will likely explode when exposed to a spark or ame. a. True *b. False 49. A Combined sewer system is the one that brings the combined domestic and industrial wastewater ow to the treatment plant a. True *b. False 50. Inltration is when groundwater enters the sewage collections systems *a. True b. False Page 7 of 18 WATR 048 - Fall 2021 Practice Exam 2 - Solution Shabbir Basrai Multiple Choice Questions - 2 points each 51. The amount of air required in the operation of an activated sludge aeration tank is independent of the: a. temperature b. ow c. detention time d. organic loading *e. none of the above 52. The successful operation of an activated sludge plant requires the maintenance of proper solids concentration in the system. One major limiting factor is: a. mixed liquor tank volume b. euent ow *c. air supply d. chlorine demand e. none of the above 53. The main dierence between primary and secondary clariers is the: a. overall dimensions b. type of outlet weirs *c. density of sludge d. detention period e. ow distribution 54. What test is used to determine the organic matter found in the mixed liquor? a. COD b. MLSS *c. MLVSS d. TOC 55. The four (4) basic components of every activated sludge treatment system are: a. Primary treatment, secondary treatment, clarication and disinfection b. Pre-treatment, aeration, clarication and disinfection *c. Aeration, clarication, return sludge and waste sludge d. Pre-treatment, primary treatment, secondary treatment and disinfection Page 8 of 18 WATR 048 - Fall 2021 Practice Exam 2 - Solution Shabbir Basrai 56. Which of the following statements is not true regarding a wastewater collection system: *a. A sewer is designed to allow the waste to ow at a rate of approximately 1 ft/sec. b. Grease can be serious problem in a collection system. c. Inow and inltration are frequently problems in older collection systems. d. High concentrations of hydrogen sulde in a sewer can lead to corrosion of concrete. e. Scouring can be a problem if wastewater is owing too fast. 57. Velocity of ow in sewers is usually expressed in terms of *a. Feet per second b. Gallon per minute c. MGD d. Milligrams per liter e. Square feet 58. One of the reasons that air should be excluded from anaerobic digesters is because: a. gas storage capacity is reduced *b. the entrance of air mixed with the gas produced in the digester could create an explosive mixture c. air interferes with the action of the aerobic bacteria present d. harmful or pathogenic bacteria may be brought in with the air e. none of the above 59. The fundamental purpose of disinfection is to: a. Destroy fecal coliform bacteria b. Destroy all bacteria *c. Destroy pathogenic organisms d. Protect downstream users from waterborne diseases 60. The dierence between the amount of chlorine added and the amount of chlorine remaining after the contact period is referred to as: *a. the chlorine demand b. free chlorine residual c. total chlorine residual d. combined chlorine residual e. free available chlorine Page 9 of 18 WATR 048 - Fall 2021 Practice Exam 2 - Solution Shabbir Basrai 61. The ultimate measure of the eectiveness of chlorination in disinfection is: a. the measurement of chlorine dosage b. meeting the chlorine demand of the wastewater c. the establishment of a chlorine demand *d. eective reduction of the coliform count e. none of the above 62. TKN is the meausre of: a. Ammonia/Ammonium+Inorganic Nitrogen *b. Ammonia/Ammonium+Organic Nitrogen c. Nitrate+Nitrite+Organic Nitrogen d. Organic Nitrogen+Inorganic Nitrogen 63. Sludge with a specic gravity of 1.1 will weigh: a. 1.1lbs/gal b. 8.34lbs/gal *c. 9.17lbs/gal d. 7.58lbs/gal 64. An aerobic treatment process is one that requires the presence of: a. Ozone b. organic oxygen c. no oxygen d. combined oxygen *e. dissolved oxygen 65. In a properly operating facultative pond, algae live on carbon dioxide and nutrients during the day, and at night produce carbon dioxide. This has what eect on the pH? *a. pH increases during the day, and decreases at night b. pH decreases during the day, and increases at night c. pH stays the same no matter what time of day d. Carbon dioxide has no eect on pH Page 10 of 18 WATR 048 - Fall 2021 Practice Exam 2 - Solution Shabbir Basrai 66. pH of the facultative pond will be the highest *a. during daytime when the consumption of CO2 is the highest b. during daytime when the consumption of CO2 is the lowest c. during nighttime when the production of CO2 is highest d. during nighttime when the production of CO2 is lowest 67. The main function of algae in a facultative wastewater treatment pond is to: a. produce carbon dioxide, which is then used by the facultative bacteria. b. use up nutrients such as nitrogen and phosphorus. *c. produce oxygen during daylight hours. d. serve as a food source for essential protozoa e. break down complex organics in the wastewater. 68. The following device is used to measure the ow of wastewater: a. Comminutor b. Comparator *c. Parshall ume d. Sluice gate 69. Usually, preliminary treatment includes removal of most of the: a. Pathogenic bacteria. b. Biodegradable organics. c. Settleable solids. d. Dissolved solids. *e. Grit. 70. The purpose of comminution is to: a. Combine wastewater from dierent sewers prior to entry into the treatment facility. *b. Shred large debris and organic material into small particles. c. Liquefy chunks of grease in order to break it down. d. Mix the raw wastewater to distribute the organics. Page 11 of 18 WATR 048 - Fall 2021 Practice Exam 2 - Solution Shabbir Basrai 71. The proper operation of an aerated grit removal process will: a. Cause material with a specic gravity of greater than 1.0 to settle. b. Cause sand and other non-organics to settle and keep organic material in suspension. c. Help to freshen stale or septic wastewater. *d. b and c 72. The major purpose of an inlet bae in a settling tank is to: *a. Reduce velocity and disperse the ow b. Increase velocity to prevent excessive settling near the inlet c. Remove scum from the wastewater d. Protect the scrapping mechanism from damage by excessive velocities. 73. Primary treatment units are designed to remove settleable solids from the wastewater stream by: a. biological treatment b. chemical addition c. bioltration *d. gravity sedimentation e. comminuting devices 74. Raw sludge pumping cycles that are too short will *a. Cause wastestream going to secondary treatment to turn dark. b. Decrease return and waste sludge suspended solids. c. Increase amount of grit in raw sludge. d. Increase rags in raw sludge. 75. Which of the following is not a characteristic of hydrogen sulde? a. Foul odors *b. Lighter than air c. Toxic d. Corrosiveness e. Explosiveness Page 12 of 18 WATR 048 - Fall 2021 Practice Exam 2 - Solution Shabbir Basrai 76. Improper handling, storing or preparing solutions of chemicals can cause a. Burns b. Explosions c. Loss of eye sight *d. All of the above 77. A problem associated with trickling lters is a. Bulking b. Protozoans *c. Ponding d. Liquefaction 78. The primary organisms responsible for treating wastewater in the trickling lter process are: a. Anaerobic bacteria b. Anoxic bacteria c. Facultative bacteria *d. Aerobic bacteria 79. Sloughing from a trickling lter refers to a. A process whereby wastewater is recirculated over the lter. b. Bypassing of the lter. c. The breaking of the lter stone as a result of weathering and the sluicing of small stone particles to the nal settling tank. *d. The periodic discharge of large quantities of slime growth with the lter euent. 80. Sludge with a sludge density of 7%would have a solids concentration of a. 7 mg/l b. 700 mg/l c. 7000 mg/l *d. 70,000 mg/l Page 13 of 18 WATR 048 - Fall 2021 Practice Exam 2 - Solution Shabbir Basrai Math Problems - 4 points each 81. What is the surface area of a cylindrical tank 80 feet in diameter and 25 feet in height. Cylindrical part surface area only. Disregard the oor and roof areas. a. 125,600 sq. ft *b. 6,280 sq. ft c. 1,570 sq. ft d. 502,400 sq. ft Solution: Diameter (D)=80' Cylinder Surface Area= π ∗ D ∗ h Height (h) = 25' Surf ace area of cylinder = π ∗ D ∗ h = 3.14 ∗ 80 ∗ 25 = 6, 280f t2 82. Calculate the VS loading to the digester in lbs/day if 10,000 cu. ft of sludge containing 4.8% TS with and an average VS content of 82% a. 42,756 lbs/day *b. 24,554 lbs/day c. 30,987 lbs/day d. 3,256 lbs/day Solution: Digester VS loading (lbs/day) = 10, 000f t3 sludge 7.48 gal 8.34lbs sludge 0.048 ∗ 0.82lbsV S ∗ ∗ ∗ = 24, 554lbs sludge per day day f t3 gal lb sludge Page 14 of 18 WATR 048 - Fall 2021 Practice Exam 2 - Solution Shabbir Basrai 83. Calculate the detention time for a sedimentation tank that is 48 feet wide, 210 feet long and 9 feet deep with a ow of 5 MGD. *a. 3.25 hours. b. 3.63 hours. c. 5.65 hours. d. 5.82 hours. Solution: Clarif ier volume(cu.f t or gal) Inf luent f low (cu.f t or gal)/hr) (48 ∗ 210 ∗ 9) f t3 = 3.25hrs Clarif ier detention time (hr) = 6 3    gal 5 M G 10  day f t   ∗ ∗  ∗   24hrs day M G 7.48 gal  Clarif ier detention time (hr) = 84. Calculate the weir loading for a sedimentation tank that has an outlet weir 480 ft long and a ow of 5 MGD. a. 9,220 gpd/ ft b. 9,600 gpd/ ft c. 9,920 gpd/ ft *d. 10,420 gpd/ft Solution: W eir overf low rate  gpd  ft 5 M G 106 gal ∗  day M G = = 10, 417gpd/f t 480f t 85. How many pounds of solids are pumped to a digester each day if the digester receives 10,000 gpd of sludge at 5% density a. 417 lbs/day b. 1,479 lbs/day c. 2,337 lbs/day d. 3,273 lbs/day *e. 4,170 lbs/day Solution: lbs T S 10, 000gal sludge (8.34 ∗ 0.05lbsT S) lbs T S = ∗ = 4, 170 day day gal sludge day Page 15 of 18 WATR 048 - Fall 2021 Practice Exam 2 - Solution Shabbir Basrai 86. A 90 feet diameter trickling lter treats a 540,000 gpd primary euent ow. If the recirculated ow to the trickling lter is 120,000 gpd, what is the hydraulic loading on the trickling lter in gpd/ft2. *a. 104 gpd/ft2 b. 2 gpd/ft2 c. 3 gpd/ft2 d. 4 gpd/ft2 Solution: Hydraulic loading : gpd (540, 000 + 120, 000)gpd gpd gpd =⇒ Hydraulic loading = = 104 2 f t2 f t2 (0.785 ∗ 902 )f t2 ft 87. A 40 acre wastewater treatment pond receives a ow of 0.6 MGD. If the pond is operated at a depth of 4ft. What is the detention time of this pond? a. 22 days, b. 52 days *c. 87 days d. 97 days e. 16 days Solution: P ond detention time = V olume = F low (40 ∗ 4)acre − f t = 87 days gal f t3 acre − f t 0.6 ∗ 106 ∗ ∗ day 7.48gal 43, 560f t3 88. Chlorine is being fed at the rate of 200 pounds per day. Plant ow is 4 MGD. The chlorine residual is measured and found to be 3 mg/L Calculate chlorine demand. *a. 3 mg/L b. 2 mg/L c. 16 mg/L d. 9 mg/L Solution: Chlorine dosage(lbs/day) = conc.(mg/l) ∗ f low(M GD) ∗ 8.34 lbs/day 200 =⇒ chlorine dosage conc.(mg/l) = = = 6mg/l f low(M GD) ∗ 8.34 4 ∗ 8.34 Chlorine dosage = chlorine demand + chlorine residual =⇒ chlorine demand = chlorine dosage − chlorine residual = 6 − 3 = 3mg/l Page 16 of 18 WATR 048 - Fall 2021 Practice Exam 2 - Solution Shabbir Basrai 89. A sludge settleability test shows a reading 220 ml after 30 minutes of settling in a one liter graduated cylinder. Lab testing on this mixed liquor shows a MLSS concentration of 1850 mg/L and a MLVSS concentration of 1440 mg/L. Calculate SVI for this mixed liquor sample. *a. 119 b. 108 c. 153 d. 138 Solution: SVI (ml/g)= SVI= mg Settled sludge volume in ml/l af ter 30 min ∗ 1000 M LSS mg/l g mg 220ml/l ∗ 1000 = 119ml/g 1, 850mg/l g 90. On an average, 2 inches of grit is collected and removed every day in a 2.2 feet wide, 205 feet long grit channel. Knowing the average ow through that grit channel is 3 MGD calculate the rate of grit collection in cu.ft/MG. *a. 25 b. 301 c. 345 d. 32 Solution: 3 Grit volume accumulated: Page 17 of 18 2 75.16f t f t ∗ (2.2 ∗ 205)f t2 = 12 day Grit Collection: 75.16f t3  f t3 day  = 7.5 10M G MG  day  WATR 048 - Fall 2021 Practice Exam 2 - Solution Shabbir Basrai BLANK PAGE Page 18 of 18 WATR 048 - Fall 2021