### Civil Engineering - Waste Water Engineering MCQs Part 4

1. A nuisance is experienced in diluting water if dilution factor is less than

A.
100
B.
60
C.
40
D.
20
E.
10

2. Traps

A.
are water seals which prevent the entry of foul gases
B.
are used to trap the rats entering sewers
C.
dissolve the foul gases
D.
create syphonic action to increase the quick disposal of sewerage.

3. For estimating the peak run off the rational formula Q = 0.0278 KpA was evolved by

A.
Kinchling
B.
Lloyd Davis
C.
Frubling
D.
all the above.

4. Pick up the correct statement from the following :

A.
Inlets are provided on the road surface at the lowest point for draining rain water
B.
Inlets are generally provided at an interval of 30 m to 60 m along straight roads
C.
Inlets having vertical openings, are called curb inlets
D.
Inlets having horizontal openings, are called horizontal inlets
E.
All the above.

5. Pick up the correct statement from the following :

A.
The boning rod is used for checking the levels of the sewer inverts
B.
Manhole covers are made circular for the convenience of the cleaning staff
C.
A manhole is classified as deep manhole if its depth is more than 1.5 m
D.
A manhole is classified as shallow manhole if its depth is. less than 0.9 m
E.
All the above.

6. 3.0 ml of raw sewage is diluted to 300 ml. The D.O. concentration of the diluted sample at the beginning of the test was 8 mg/l. After 5 day-incubation at 20°C, the DO. concentration was 5 mg/l. The BOD of raw sewerage is

A. 100 mg/l
B. 200 mg/l
C. 300 mg/l
D. 400 mg/l.

7. The arrangement made for passing the sewer line below an obstruction below the hydraulic gradient lines called

A. inverted syphon
B. depressed sewer
C. sag pipe
D. all of these.

8. The angle subtended by the surface of sewer water with partial flow, at sewer centre is 120°, the depth of sewerage is

A. 20 cm
B. 25 cm
C. 40 cm
D. 50 cm
E. 60 cm.

9. Imhoff cone is used to determine

A. settlable solids
B. suspended solids
C. dissolved solids
D. none of these.

10. The sewage discharge in a detritus tank of a treatment plant is 576 litres/sec with flow velocity of 0.2 m/sec. If the ratio of width to depth is 2, the depth is

A. 100 cm
B. 110 cm
C. 120 cm
D. 150 cm.

11. 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.

12. A well oxidized sewage contains nitrogen mainly as

A. nitrates
B. nitrites
C. free ammonia
D. none of these.

13. A safety lamp when inserted in the upper portion of a manhole causes flames. It indicates the presence of

A. Carbondioxide gas
B. Hydrogen sulphide gas
C. Methane gas
D. Petrol vapours.

14. Assertion (A) : A free board of 0.3 m is provided above the top sewage line in septic tanks. Reason (R) : It helps to accommodate the scum in the septic tank.

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.

15. If D is the diameter of upper circular portion, the area of cross-section of a standard egg shaped sewer, is

A.
B.
C.
D.

16. Drop manholes at the junctions of sewer lines, are provided if

A. invert level of a branch sewer is more than 60 cm that of the main sewer
B. sewer line runs along a main road
C. ordinary manhole cannot be built
D. two sewer lines intersect.

17. The most effective arrangement for diverting excess storm water into a natural drainage, is

A. leaping weir
B. overflow weir
C. siphon spill way
D. none of these.

18. Large diameter sewers subjected to external pressure alone, are reinforced

A. near the inner surface of the pipe
B. near the outer surface of the pipe
C. both (a) and (b)
D. with elliptical cage
E. none of these.

19. Pick up the correct statement from the following :

A. The ratio of the quantity of the diluting water to that of the sewage, is known as dilution factor
B. The automatic purification of polluted water, is known self purification phenomenon
C. The photosynthesis is carried out in the presence of sun light
D. Grab sample is generally obtained from the surface where turbulence mixes the sewage particles
E. All the above.

20. In sewage, the solids in mg per litre is

A. 100 to 500
B. 500 to 1000
C. 1000 to 1500
D. 1500 to 2000

21. In a residential colony, sewers of diameters 100 mm, 150 mm and 225 mm were laid with a gradient 1 in 120. Which portion of the sewage system does not choke in due course of time

A. 100 mm dia.
B. 150 mm dia.
C. 225 mm dia.
D. all of these.

22. If D is the diameter of upper circular portion, the overall depth of New Egg shaped sewer section, is

A. 1.250 D
B. 1.350 D
C. 1.425 D
D. 1.625 D.

23. During putrifaction process of sewage the gas given off, is

A. carbon dioxide
B. hydrogen
C. ammonia
D. methane
E. all the above.

24. A circular sewer section is preferred to because

A. it is cheaper in construction
B. it provides maximum area for a given perimeter
C. it provides maximum hydraulic mean depth
D. all the above.

25. Assertion (A) : The minimum self cleansing velocity in the sewer, at least once a day, must be generated. Reason (R) : If certain deposition takes place and is not removed, it obstructs free flow and causes further deposition leading to complete blocking of the sewer.

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.

26. If the grit in grit chambers is 4.5 million litres per day, its cleaning is done

A. manually
B. mechanically
C. hydraulically
D. electrically.

27. The gas evolved in sewers is

A. Carbondioxide
B. Hydrogen sulphide
C. Methane
D. All of these.

28. The maximum depth of sedimentation tanks, is kept

A. 3 m
B. 3.5 m
C. 4 m
D. 4.5 m.

29. The reduced levels of the string at the consecutive sight rails A and B are 203.575 m, 203.475 m respectively. If the difference of their R.D.s is 10 m, the gradient of the sewer line is

A. 1 in 100 upward
B. 1 in 500 upward
C. 1 in 100 downward
D. 1 in 503 upward.

30. The detention time (t) of a settling tank, may be defined as the time required for

A. a particle to travel along its length
B. a particle to travel from top surface to bottom sludge zone
C. the flow of sewage to fill the tank
D. none of these.

31. Discrete or granular particles change their

A. size
B. shape
C. weight
D. none of these.

32. For a peak discharge of 0.0157 cumec, with a velocity of 0.9 m/sec, the diameter of the sewer main, is

A. 10 cm
B. 12 cm
C. 15 cm
D. 18 cm
E. 20 cm.

33. For design of sewers, percentage of sewage discharge is assumed

A. 65 to 70%
B. 70 to 75%
C. 75 to 80%
D. 85%.

34. In case of sewer lines

A. water test is carried out to check water tightness of the joints
B. test for straightness is carried out with the help of a lamp and mirror
C. obstruction test is carried out with the. help of smooth ball of diameter 13 mm
D. all the above.

35. The sewerage system originates from

A. house sewers
B. lateral sewers
C. branch sewers
D. main sewers
E. out fall sewers.

36. 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.

37. If D is the diameter of a circular sewer and D' is the top horizontal diameter of an equivalent egg shaped section, the relationship which holds good, is

A. D' = 0.64 D
B. D' = 0.74 D
C. D' = 0.84 D
D. D' = 0.94 D.

38. If a paper moistened with lead acetate for five minutes when placed in manhole turns black. The sewer certainly contains

A. Hydrogen sulphide
B. Carbon dioxide
C. Methane
D. Oxygen
E. None of these.

39. The design period of sewage treatment works in normally

A. 5 - 10 years
B. 15 - 20 years
C. 30 - 40 years
D. 40 - 50 years.

40. The porosity of sediments in sewer pipes, is usually taken as

A. 0.010
B. 0.011
C. 0.012
D. 0.013
E. 0.020

41. In septic tanks, decomposition of organic bacteria, is done by

A. anaerobic bacteria
B. aerobic bacteria
C. both types of bacterias
D. none of these.

42. The stone ware sewers

A. are used for carrying sewage and drainage from houses
B. are manufactured from clays and shales
C. after casting are dried and burnt at temperature 150°C, 700°C and 1200°C
D. are generally provided with a water proof cover by vaporising sodium chloride
E. all the above.

43. 'Cowl' is provided at

A. lower end of ventilating column
B. upper end of ventilating column
C. upper end of the manhole
D. first step in manhole.

44. The sewer which transports the sewage to the point of treatment, is called

A. house sewer
B. out-fall sewer
C. branch sewer
D. lateral
E. main sewer.

45. Kjedahl nitrogen is a mixture of

A. ammonia and nitrogen
B. nitrogen and organic nitrogen
C. organic nitrogen and ammonia
D. all the above.

46. 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.

47. Pick up the correct statement from the following :

A. The circular section of sewers provides maximum hydraulic mean depth
B. The circular sewers are provided for separate sewerage system
C. The circular sewers work efficiently if the sections run at least half full
D. Two sewers of different shapes are said to be hydraulically equivalent if they discharge at the same rate while running full on the same grade
E. All the above.

48. You are asked to design sewer pipes of diameters 0.4 m to 0.9 m at maximum flow, you will assume the sewer flow running at

A. full depth
B. half full
C. two third full
D. three fourth full.

49. The ratio of depths at partial flow with central angle α and at full flow of a sewer, is

A.
B.
C.
D.
E.

50. For sewer mains of 0.5 to 1 m diameter, the ratio of maximum daily sewage flow to the average daily sewage flow is assumed

A. 1.5
B. 2.0
C. 2.5
D. 3.0