Module 3 - Practice Exam 1 Solutions.pdf
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WATR 048 - Fall 2021 Practice Exam 1 - Solution Shabbir Basrai 1. Acre-Ft is a unit of volume *a. True b. False 2. As a rule of thumb, the velocity in a gravity sewer should be at least 2 cubic feet per second to ensure that the solids do not settle out in the sewer lines *a. True b. False 3. V...
WATR 048 - Fall 2021 Practice Exam 1 - Solution Shabbir Basrai 1. Acre-Ft is a unit of volume *a. True b. False 2. As a rule of thumb, the velocity in a gravity sewer should be at least 2 cubic feet per second to ensure that the solids do not settle out in the sewer lines *a. True b. False 3. Volatile solids removal e ciency of a digester is most commonly monitored utilizing the BOD test a. True *b. False 4. Chlorine demand is a good indicator of eective disinfection a. True *b. False 5. Prior to working in a drained anaerobic digester, con ned space entry permits must be prepared. *a. True b. False 6. Vents in a chlorine storage room are located at the ground level as chlorine is lighter than air a. True *b. False 7. In ow is storm water entering into the sewer system *a. True b. False 8. Hypochlorite solution is a more eective disinfectant than gas chlorine and is much less expensive. a. True *b. False 9. The F in the F to M ratio refers to the pounds of mixed liquor volatile suspended solids under aeration in an activated sludge plant. a. True *b. False 10. A wastewater sample with a pH of 7.2 is slightly acidic. a. True *b. False Page 1 of 16 Practice Exam 1 - Solution Shabbir Basrai 11. BOD5 and SS are both used to measure the strength of wastewater *a. True b. False 12. Septic sludge has a low pH *a. True b. False 13. Total wastewater solids is the sum of total dissolved solids and suspended solids *a. True b. False 14. Algae produce oxygen in a facultative pond. *a. True b. False 15. In a facultative pond, the bottom layer of the pond will generally contain more dissolved oxygen than the surface layer. a. True *b. False 16. In a facultative pond, the pH falls when carbon dioxide produced by the aerobic bacteria is consumed by the algae a. True *b. False 17. The best time of the year to initiate operation of a new facultative pond is during the coldest months of the year. a. True *b. False 18. SVI is a measure of the sludge volume that needs to be wasted a. True *b. False 19. Organic loading to a stabilization pond is always calculated by knowing the pounds of BOD applied per 1.000 cubic feet of pond volume per day. a. True *b. False Page 2 of 16 WATR 048 - Fall 2021 Practice Exam 1 - Solution Shabbir Basrai 20. Chlorine dosage is the dierence between the amount of chlorine added to wastewater and the amount of residual chlorine remaining after a given contact time. a. True *b. False 21. Facultative ponds are anaerobic on the bottom and aerobic near the surface. *a. True b. False 22. The solids in primary sludge contain both volatile and xed parts. *a. True b. False 23. It is recommended to start up a pond in the coldest months of the year in order to avoid odor problems and to take advantage of the increased solubility of oxygen in cold water. a. True *b. False 24. A high rate anaerobic digester is always heated and mixed. *a. True b. False 25. Tertiary (polishing) ponds typically receive raw (untreated wastewater) as the feed stream a. True *b. False 26. Grit is composed mostly of inorganic material. *a. True b. False 27. A Venturi meter measures the amount of electricity used and should be read when there is a high electrical demand. a. True *b. False 28. A weir can be also be used for measuring ows *a. True b. False Page 3 of 16 WATR 048 - Fall 2021 Practice Exam 1 - Solution Shabbir Basrai 29. Activated sludge is an anaerobic process a. True *b. False 30. The process of pre-aeration in no way in uences the degree of settling in a primary clari er a. True *b. False 31. Barmunitor and comminutor are devices used for cutting up or shredding material normally present in raw wastewater *a. True b. False 32. The only function of ights in a rectangular sedimentation tank is to push the settled sludge towards the hopper a. True *b. False @ ights also skim the scum towards the scum trough 33. Hydrogen sul de in addition to creating an odor nuisance can be an explosion hazard when mixed with air in certain concentrations. *a. True b. False 34. Gas bubbles rising to the surface in a primary clari er are normally an indication that the sludge in the unit is undergoing proper settling a. True *b. False 35. Presence of hydrogen sul de cannot always be detected by its characteristic odor *a. True b. False 36. The trickling lter recirculation ratio is calculated as Qi/Qr where Qi is the in uent ow and Qr is the recirculated ow. a. True *b. False Page 4 of 16 WATR 048 - Fall 2021 Practice Exam 1 - Solution Shabbir Basrai 37. MCRT refers to the average number of days that a cell remains in an activated sludge system. *a. True b. False 38. The advantage of trickling lter over the activated sludge lies in its BOD removal e ciency a. True *b. False 39. Volatile solids removal e ciency of a digester is most commonly monitored utilizing the BOD test a. True *b. False 40. Series operation of trickling lter is the preferred mode during very low temperature conditions during winter a. True *b. False 41. BOD is a measure of the organic content of wastewater *a. True b. False 42. An inadequate detention time in a primary clari er would result in increased solids pumping to digesters a. True *b. False 43. Ba es ahead of outlet weirs in primary tanks serve as a physical barrier to inhibit the loss of oating solids and grease. *a. True b. False 44. If a shear pin for a particular installation is constantly bending, it would be proper and advisable to replace it with a pin of greater shear strength. a. True *b. False 45. It is common for primary clari ers to remove 80-85% of the BOD and 90-95% of the TSS. a. True *b. False 46. Coliform testing is typically conducted on a grab sample Page 5 of 16 WATR 048 - Fall 2021 Practice Exam 1 - Solution Shabbir Basrai *a. True b. False 47. An Imho cone is often used to measure the eectiveness of primary sedimentation. a. True *b. False 48. Conductivity is a very useful test for assessing sea water intrusion into sewer lines *a. True b. False 49. Grab or composite samples may be used interchangeable, whichever is most convenient and safest for all laboratory tests. a. True *b. False 50. Samples collected for the analysis of COD, BOD, and pH should be acidi ed for preservation. a. True *b. False 51. A 30 minute settleability test MLSS sample should be collected: a. At the primary clari er e uent b. In the return sludge line c. Where the return sludge mixes with the aeration basin contents d. At the aeration basin in uent *e. At the aeration basin outlet 52. Sludge wasting from secondary clari ers, are normally required in order to control a. E uent BOD. b. E uent suspended solids. c. Aerator mixed liquor solids. *d. Sludge settleability 53. The basic objective in the activated sludge process is to maintain balanced conditions in the aeration basin, this balance is called: a. Endogenous respiration *b. Food/microorganism ratio c. Equilibrium status d. Mass balance ratio 54. A good reason to run a trickling lter in the series mode of operation is: Page 6 of 16 WATR 048 - Fall 2021 Practice Exam 1 - Solution Shabbir Basrai a. During cold weather to prevent ice formation b. When the in uent BOD loading is low *c. When the in uent BOD loading is high d. When the weather is warm 55. Most common trickling lter operational control method is: a. Sloughing control *b. Recirculation c. Sludge removal d. Distributor arm speed 56. Ponding of a trickling lter means a. Flooding the lter. b. Hosing the growth from the rocks with a high pressure hose. *c. Blockage in the media that s prevents water to ow through. d. Running the trickling lter e uent to a wastewater pond. 57. Algae in a stabilization pond is most likely to: a. consume oxygen during daylight hours. b. decrease e uent TSS during the day. *c. change the pH throughout the day. d. increase oxygen at night. e. None of the above. 58. At what time of day is the dissolved oxygen content highest in a lagoon? a. 3 a.m. b. 7 a.m. c. 9 a.m. *d. 3 p.m. 59. Hydraulic loading to a facultative pond equals: a. Volume (MG) divided by Flow (MGD) *b. Depth (inches) divided by Detention Time (days) c. Volume (acre-feet) divided by Flow (acre-inches/day) d. Flow ( gallons/day) divided by Area (acres) e. Area (acres) divided by Flow (acre-inches/day) Page 7 of 16 WATR 048 - Fall 2021 Practice Exam 1 - Solution Shabbir Basrai 60. It is important to completely mix and aerate the following type of pond: *a. aerobic. b. facultative. c. anaerobic. d. All of the above. e. None of the above. 61. A device called an Imho cone is commonly used to measure settleable solids in: a. Percent *b. mL/L c. mg/L d. ppm e. SVI units 62. An e cient primary clari er is expected to remove what percent of the in uent settleable solids? a. 2 to 6 % b. 20 to 40 % c. 40 to 50 % d. 60 to 75 % *e. 90 % or better 63. A primary clari er does not have adequate detention time. Which of the following would result? a. Decreased organic leading on secondary unit b. Overloading of collector or ight drive motor c. Increased solids pumped to digester *d. Low BOD removal e. Reduced suspended solids in aeration tank. 64. A treatment plant process using sedimentation after screening and grit removal and before aerobic treatment is known as: a. preliminary treatment. *b. primary treatment. c. secondary treatment. d. RBC treatment. e. advanced wastewater treatment. Page 8 of 16 WATR 048 - Fall 2021 Practice Exam 1 - Solution Shabbir Basrai 65. 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. In ow and in ltration are frequently problems in older collection systems. d. High concentrations of hydrogen sul de in a sewer can lead to corrosion of concrete. e. Scouring can be a problem if wastewater is owing too fast. 66. A sewer system designed to transport only wastewater from homes, industries, institutions and businesses is called: a. Combined sewer *b. Sanitary sewer c. Service sewer d. Building sewer 67. A is used in the wastewater treatment plant to remove debris such as large rocks, branches, pieces of lumber, leaves, paper, tree roots, etc. from the in uent. a. Comminutor *b. Bar Screen c. Belt lter d. Grit chamber 68. Carryover of grit from the grit chamber may indicate the need to: *a. Increase rate of settled grit removal from the grit chamber. b. Decrease the operational depth of the channel. c. Increase the ow to the primary clari er. d. Increase the air input to an aerated grit chamber. 69. Grit is composed mostly of which of the following substances? a. Grease b. Colloidal solids c. Rubber goods *d. Inorganics e. Plastics 70. Proportional weirs usually are located at: a. A magnetic ow meter b. Stilling wells c. Aerobic digester scum boxes *d. Grit chambers e. Water treatment plants Page 9 of 16 WATR 048 - Fall 2021 Practice Exam 1 - Solution Shabbir Basrai 71. Anaerobic digester gas is composed mostly of: a. Carbon dioxide and hydrogen sul de *b. Methane and carbon dioxide c. Methane and hydrogen sul de d. Methane and carbon monoxide e. Methane and ammonia 72. When feeding an aerobic digester, the operator can control within certain limits: a. Amount of air available for stabilization b. Solids concentration c. Frequency of feeding d. Organic concentration e. b and d *f. b and c 73. A chlorine cylinder valve is thought to be leaking. If ammonia vapor is passed over the valve, the presence of a leak is indicated by a. A hissing noise. *b. A white cloud. c. An odor of hydrogen sul de. d. Red smoke 74. An operator should never enter a room containing a high concentration of chlorine gas without a. Staying low on the oor. b. Holding breath and have help standing by. *c. Having self-contained air or oxygen supply and help standing by. d. Covering nose and mouth with a wet handkerchief. 75. "Chlorine residual" refers to: a. the amount of chlorine remaining in the ton cylinder after use. b. the amount of chlorine consumed during disinfection. *c. the chlorine remaining after disinfection. d. the chlorine that displays no disinfection power. e. the residue left after the evaporation of chlorine gas. 76. Which of the following are factors that may in uence the eectiveness of chlorine? a. Chlorine dose rate b. Contact time c. Suspended solids concentration of the wastewater being disinfected. *d. Only (a) and (b) e. (a), (b), and (c) Page 10 of 16 WATR 048 - Fall 2021 Practice Exam 1 - Solution Shabbir Basrai 77. A composite sample will provide a(an) a. Even color. b. High pH. c. Low solids sample. *d. Representative sample. 78. Bacteria which cause diseases in man are generally called: a. Mesophilic b. Facultative *c. Pathogenic d. Coliforms 79. Hazardous conditions in a manhole, wetwell or other similar type of structure may not be always be detected by the presence of odor because: a. some toxic gases have no detectable odor b. the environment may be oxygen de cient c. some gases may deaden the sense of smell d. not all explosive gases have detectable odor *e. all of the above 80. An operator should not enter an enclosed structure if the percentage of oxygen in the air is less than: *a. 19.5% b. 23.5% c. 27.2% d. 32.5% Page 11 of 16 WATR 048 - Fall 2021 Practice Exam 1 - Solution Shabbir Basrai 81. At an activated sludge wastewater treatment plant receiving 3.25 MGD, the nal e uent suspended solids concentration averages 21.2 mg/L. What would the calculated MCRT value be when the aeration basin carries 2,050 mg/L MLSS and wastes 0.0550 MGD. The waste activated sludge has a concentration of 7,980 mg/L. The aeration tank has a volume of 1.00 MG and the secondary clari er has an operational volume of 0.250 MG. a. 2.5 days *b. 5.0 days c. 7.5 days d. 15 days e. 42 days Solution: M CRT (days) = M LSS in aeration tank (lbs) + M LSS in clarif ier (lbs) SS ef f luent (lbs/day) + SS W AS (lbs/day) M LSS in aeration tank (lbs) = 1 ∗ 2050 ∗ 8.34 = 17, 097lbs M LSS in clarif ier (lbs) = 0.25 ∗ 2050 ∗ 8.34 = 4, 274.3lbs SS ef f luent (lbs/day) = 3.25M GD ∗ 21.2mg/l ∗ 8.34 = 574.6lbs/day SS W AS (lbs/day) = 0.055M GD ∗ 7, 980mg/l ∗ 8.34 = 3, 660.4lbs/day Plugging in the values calculated above: M CRT (days) = 17, 097.6 + 4, 274.3 = 4.8 = 5 days 574.6 + 3, 660.4 82. How many gallons of wastewater would 600 feet of 6-inch diameter pipe hold, approximately? a. 740. *b. 880. c. 900. d. 930. Solution: Diameter=6" Length=600' V olume = 6 2 gallons π 2 D ∗ L = 0.785 ∗ ∗ 600 f t3 ∗ 7.48 = 881 gallons 4 12 f t3 Page 12 of 16 WATR 048 - Fall 2021 Practice Exam 1 - Solution Shabbir Basrai 83. Calculate the volatile solids reduction in an anaerobic digester given the following information: Raw sludge feed to digester: 73.7 % VS and digested sludge: 57.2 %VS *a. 52.3% b. 64% c. 16.5% d. 42% Solution: The VS reduction of the digester is provided by the Van Kleeck equation Digester V S reduction(%) = V Sin − V Sout ∗ 100 V Sin − V Sin ∗ V Sout Digester V S reduction(%) = 0.737 − 0.572 ∗ 100 = 52.3% 0.737 − 0.737 ∗ 0.572 84. The desired trickling lter recirculation ratio is 1.4. If the primary e uent ow is 4.4 MGD what is the trickling lter e uent ow that needs to be recirculated. a. 3.1 MGD *b. 6.2 MGD c. 1.9 MGD d. 4.7 MGD Solution: RR = QR QR =⇒ QR = 1.4 ∗ 4.4 = 6.2M GD =⇒ 1.4 = QI 4.4 85. The chlorine demand is 4.8 mg/l and a chlorine residual is 0.75 mg/l is desired. For a ow of 2.8 MGD, how many pounds per day should the chlorinator be set to deliver. *a. 130 b. 116 c. 112 d. 18 e. 16 Solution: Chlorine dosage = chlorine demand + chlorine residual chlorine dosage = 4.8 + 0.75 = 5.55mg/l To calculate pounds per day, applying the pounds formula: lbs/day = conc.(mg/l) ∗ f low(M GD) ∗ 8.34 = 2.8 ∗ 5.55 ∗ 8.34 = 130 Page 13 of 16 lbs day WATR 048 - Fall 2021 Practice Exam 1 - Solution Shabbir Basrai 86. What is the velocity (ft/s) of a 3 MGD ow in a 12 in. diameter pipe. Assume the pipe is owing full. *a. 5.9 ft/s b. 0.3 ft/s c. 2.5 ft/s d. 4 ft/s Solution: Q=V ∗A =⇒ V = Q =⇒ V A ft s 3 M G 1, 000, 000 gal f t3 day ∗ ∗ ∗ ft 1440 ∗ 60s day MG 7.48gal = = 5.9 12 2 s 0.785 ∗ f t2 12 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 f t3 acre − f t gal ∗ ∗ 0.6 ∗ 106 day 7.48gal 43, 560f t3 88. What is the grit production rate (cu. ft/MG) if 46 cu. ft of grit is removed every ve days and the daily plant ow averages 2 MGD. a. 12 cu. ft/MG b. 23 cu. ft/MG *c. 4.6 cu. ft/MG d. 9.2 cu. ft/MG Solution: f t3 46 f t3 day f t3 Grit P roduction Rate = ∗ = 4.6 MG 5days 2 M G MG Page 14 of 16 WATR 048 - Fall 2021 Practice Exam 1 - Solution Shabbir Basrai 89. At a 2.5 MGD wastewater treatment plant the primary clari er has a detention time of 2 hours. How many gallons does this clari er hold? a. 104,000 gallons *b. 208,000 gallons c. 250,000 gallons d. 500,000 gallons e. 5,000,000 gallons Solution: Clarif ier detention time (hr) = Clarif ier volume(gal) Inf luent f low (gal/hr) =⇒ Clarif ier volume(gal) = Clarif ier detention time (hr) ∗ Inf luent f low (gal/hr) gal day = 208, 333 gals ∗ =⇒ Clarif ier volume(gal) = 2 hrs ∗ 2.5 ∗ 106 day 24 hrs 90. How long will it take to pump down 25 feet of water in a 110 ft diameter cylindrical tank when using a 1,420 gpm pump. a. 20 hours and 85 minutes *b. 20 hours and 51 minutes c. 2 hours and 47 minutes d. 12 hours and 36 minutes Diameter=110' Height=25' T ime = T otal volume to be pumped P ump f low rate 7.48 gal 3 f t = 20.847hrs =⇒ 20 hrs + 0.847 ∗ 60 minutes = 20hrs 51min 60 min (0.785 ∗ 1102 ∗ 25) f t3 ∗ =⇒ Page 15 of 16 1420 gal ∗ min hr WATR 048 - Fall 2021 Practice Exam 1 - Solution Shabbir Basrai BLANK PAGE Page 16 of 16 WATR 048 - Fall 2021
