Water and Wastewater Engineering MCQ
1 For a continuous flow type of sedimentation tanks
(A) Width of the tank is normally kept about 6 m
(B) Length of the tank is normally kept 4 to 5 times the width
(C) ) Maximum horizontal flow velocity is limited to 0.3 m/minute
(D) All the above
Ans. D
2 The asbestos cement sewers are
(A) Light in weight
(B) Not structurally strong to bear large compressive stress
(C) Susceptible to corrosion by sulphuric acid
(D) All the above
Ans. D
3 For efficient working of a sewer, it must be ensured that
(A) Minimum velocity of 0.45 m/sec, is maintained at its minimum flow
(B) A maximum velocity of 0.90 m/sec, is maintained at its maximum flow
(C) Both (a) and (b)
(D) Neither (a) nor (b)
Ans. C
4 Bottom openings 15 cm × 15 cm in the standing baffle wall are provided
(A) 15 cm c/c
(B) 22.5 cm c/c
(C) 30 cm c/c
(D) 50 cm c/c
Ans. B
5 For drainage pipes in buildings the test applied before putting them to use, is
(A) Water test
(B) Smoke test
(C) Straightness test
(D) All the above
Ans. B
6 The pressure exerted by
(A) The sewage when running full from inside, is called internal pressure
(B) The internal pressure if any, causes tensile stress in the pipe material
(C) Pressure sewers are designed to be safe in tension
(D) All the above
Ans. D
7 No treatment of the sewage is given if dilution factor is
(A) Less than 150
(B) Between 150 to 200
(C) Between 200 to 300
(D) More than 500
Ans. D
8 Which of the following pumps in used to pump sewage solids with liquid sewage without clogging the pump is?
(A) Centrifugal pump
(B) Pneumatic ejector
(C) Reciprocating pump
(D) None of these
Ans. A
9 Acid regression stage of sludge digestion at a temperature 21°C extends over a period of
(A) 15 days
(B) 30 days
(C) ) 60 days
(D) 90 days
Ans. D
10 The coagulant which is generally not used for treating the sewage, is
(A) Alum
(B) Ferric chloride
(C) Ferric sulphate
(D) Chlorinated copperas
Ans. A
11 The layers of vegetable wastes and night soil alternatively piled above the ground to form a mound, is called
(A) A heap
(B) Plateau
(C) Windrow
(D) None of these
Ans. D
12 If the flame of a miner’s safety lamp in the upper layers of the sewer forms an explosive, the sewer certainly contains
(A) Hydrogen sulphide
(B) Carbon dioxide
(C) Methane
(D) Oxygen
Ans. C
13 The gas which may cause explosion in sewers, is
(A) Carbondioxide
(B) Methane
(C) Ammonia
(D) Carbon monoxide
Ans. B
14 Pick up the incorrect statement from the following:
(A) The process of decomposing the organic matter under controlled anaerobic conditions, is called sludge digestion
(B) Sludge digestion is carried out in sludge tank
(C) The gases produced in sludge digestion process, contain 75% carbon dioxide
(D) The gases produced in sludge digestion process, contain 75% methane
Ans. C
15 The sewer pipes
(A) Carry sewage as gravity conduits
(B) Are designed for generating self-cleansing velocities at different discharge
(C) Should resist the wear and tear caused due to abrasion
(D) All the above
Ans. D
16 The settling velocity of the particles larger than 0.06 mm in a settling tank of depth 2.4 is 0.33 m per sec. The detention period recommended for the tank, is
(A) 30 minutes
(B) 1 hour
(C) 1 hour and 30 minutes
(D) 2 hours
Ans. D
17 The Chezy’s constant C in the formula V = C ???????? depends upon
(A) Size of the sewer
(B) Shape of the sewer
(C) Roughness of sewer surface
(D) All the above
Ans. D
18 To prevent settling down of sewage both at the bottom and on the sides of a large sewer, selfcleaning velocity recommended for Indian conditions, is
(A) 0.50 m/sec
(B) 0.60 m/sec
(C) 0.70 m/sec
(D) 0.75 m/sec
Ans. D
19 Assertion (A): The determination of pH value of sewerage is important.
Reason (R): The efficiency of certain treatment methods depends upon the availability of pH value.
(A) Both A and R are true and R is the correct explanation of A
(B) Both A and R are true but R is not a correct explanation of A
(C) A is true but R is false
(D) A is false but R is true
Ans. A
20 The normal values of over flow rates for sedimentation tanks using coagulant, ranges between
(A) 25,000 to 35,000 litres/sqm/day
(B) 40,000 to 50,000 litres/sqm/day
(C) 50,000 to 60,000 litres/sqm/day
(D) 80,000 to 100,000 litres/sqm/day
Ans. C
21 The sewer that unloads the sewage at the point of treatment is called
(A) Main sewer
(B) Outfall sewer
(C) Branch sewer
(D) House sewer
Ans.
22 During preliminary treatment of a sewage
(A) Oil and grease are removed from skimming tanks
(B) Floating materials are removed by screening
(C) Girt and sand are removed by girt chambers
(D) All the above
Ans. D
23 Dry weather flow is:
(A) Average daily rate of flow
(B) Average monthly rate of flow
(C) Average annual rate of flow
(D) Water supply allowance per capita
Ans. D
24 If q is the average sewage flow from a city of population P, the maximum sewage flow
(A) Q = [(4 + ???? )/(18 + ???? )] q
(B) Q = [(18 +p )/(4 + ???? )] q
(C) Q = [(18 + ???? )/(4 + ???? )] q
(D) Q = [(5 + ???? )/(15 + ???? )] q
Ans. D
25 If the flame of a miner’s safety lamp in a manhole extinguishes within 5 minutes, the sewer certainly contains
(A) Hydrogen sulphide
(B) Carbon dioxide
(C) Methane
(D) Oxygen
Ans. B
26 Hydraulic mean radius is
(A) Mean radius of sewer
(B) Difference in heads between two points in circular pipes
(C) Mean of radii in a pipe line of varying cross-sections
(D) Cross-sectional area/wetted perimeter
Ans. D
27 If the depth of flow in a circular sewer is 1/4th of its diameter D, the wetted perimeter is
(A) ????????????
(B) ????????????
(C) ????????????
(D)????????
Ans. C
28 At the junction of sewers
(A) Top of smaller sewer is kept lower
(B) Top of larger sewer is kept lower
(C) Tops of both the sewers are at the same level
(D) None of these
Ans. D
29 The sewage treatment units in which anaerobic decomposition of organic matter is used, are called
(A) Imhoff tanks
(B) Trickling filters
(C) Sludge sedimentation tanks
(D) None of these
Ans. B
30 The sewer which received discharge from two or more main sewers, is known as
(A) A trunk sewer
(B) An outfall sewer
(C) A main sewer
(D) An intercepting sewer
Ans. A
31 The grit and silt of the grit chambers, may not be used for
(A) Raising low lying areas by dumping
(B) Concreting
(C) Both (a) and (b)
(D) Neither (a) nor (b)
Ans. B
32 For treating the sewage of a large city, you will recommend
(A) A sedimentation tank and an activated sludge treatment plant
(B) A plant consisting of Imhoff tanks with low rate trickling filters
(C) Sedimentation tanks with high rate trickling filters
(D) None of these
Ans. A
33 Imhoff cone is used to measure
(A) Total organic solids
(B) Total solids
(C) Total in organic solids
(D) Settleable solids
Ans. D
34 1000 kg of sewage contains
(A) 0.112 kg in suspension
(B) 0.112 kg in solution
(C) 0.225 kg in solution
(D) Both (a) and (c) of above
Ans. D
35 For the COD test of sewage, organic matter is oxidised by K2 Cr2O7 in the presence of
(A) H2SO4
(B) HNO3
(C) HCl
(D) None of these
Ans. A
36 The sludge does not contain waste water from
(A) Bath rooms
(B) Wash basins
(C) Kitchen sinks
(D) Toilets
Ans. D
37 In sewers the velocity of flow should not be
(A) More than the self-cleansing velocity
(B) Less than the self-cleansing velocity
(C) Less than 10 m/sec
(D) More than 20 m/sec
Ans. B
38 In sewers the effect of scouring is more on
(A) Top side
(B) Bottom side
(C) Horizontal side
(D) All sides
Ans. B
39 The sewer which resists sulphide corrosion, is
(A) Brick sewer
(B) Cast iron sewer
(C) R.C.C. sewer
(D) Lead sewer
Ans. D
40 In a sedimentation tank (length L, width B, depth D) the settling velocity of a particle for a discharge Q, is
(A) Q/(B × D)
(B) Q/(L × D)
(C) Q/L
(D) Q/(B × L)
Ans. D
41 The formula which accepts the value of rugosity coefficient n = 0.012 to be used in Manning’s formula, is given by
(A) Bazin
(B) Crimp and Bruges
(C) William-Hazen
(D) Kutter
Ans. B
42 The amount of oxygen consumed by the aerobic bacterias which cause the aerobic biological decomposition of sewage, is known
(A) Bio-Chemical Oxygen Demand (B.O.D.)
(B) Dissolved Oxygen (D.O.)
(C) Chemical Oxygen Demand (C.O.D.)
(D) None of these
Ans. B
43 Water content of sewage is about
(A) 90 %
(B) 95 %
(C) 99 %
(D) 9.9 %
Ans. D
44 Skimming tanks are
(A) Used to remove the grease and oil
(B) Those from which sludge is skimmed out
(C) Tanks provided with self-cleansing screens
(D) Improved version of grit chambers
Ans. A
45 The most efficient cross-section of sewers in a combined sewerage system is
(A) ) Parabolic
(B) Circular
(C) Rectangular
(D) New egged
Ans. B
46 The detention period for plain sedimentation water tanks, is usually
(A) 4 to 8 hours
(B) 8 to 16 hours
(C) 16 to 24 hours
(D) 24 to 36 hours
Ans. A
47 The factor responsible for purification of sewage in river is
(A) Hydrology
(B) Dissolved oxygen in water
(C) Temperature
(D) All the above
Ans. D
48 Hume steel pipes are
(A) Steel pipes
(B) Steel shell coated from inside with cement mortar
(C) Steel shell coated from outside with cement mortar
(D) Both (B) and (C)
Ans. D
49 To maintain aerobic biological activity, the moisture content of the compost mass should be about
(A) 45 %
(B) 50 %
(C) 55 %
(D) 60 %
Ans. C
50 Pick up the correct statement from the following:
(A) The larger the sewer in size, more will be
(B) The smaller the sewer in size, less will be velocity
(C) The larger the sewer in size, no deposition will take place
(D) The larger the sewer in size, deposition will take place
Ans. D
