MCQ
21. The time of contact for chlorination should be at least-
5 minutes
20 minutes
1 hour
2 hours
22. The minimum size of a fire hydrant is--
5cm
10cm
15cm
20cm
23. By lime soda process, hardness can be reduced to less than
50 ppm
75 ppm
150 ppm
100 ppm
24. The minimum diameter of a manhole cover should be-
25cm
50cm
75cm
100cm
25. The cross-section recommended for separate system of sewerage is--
circular
rectangular
egg-shaped
none of these
26. Rapid sand filter can remove bacteria upto an extent of-
60 to 70%
70 to 80%
80 to 90%
90 to 99%
27. The internal diameter of the sewer should not be less than-
15cm
25cm
50cm
75cm
28. The detention time for an ordinary plain sedimentation tank is-
1 to 2 hours
6 to 8 hours
2 to 4 hours
20 to 24 hours
29. Cleaning period for a rapid sand filter is taken as-
2 to 3 hours
2 to 3 days
2 to 3 weeks
2 to 3 months
30. The amount of chlorine used for plain b chlorination of water is about-
0.2 ppm
0.3 ppm
0.4 ppm
0.5 ppm
31. Rapid sand filter can remove turbidity from water upto an extent of-
15 to 25 ppm
25 to 35 ppm
35 to 40 ppm
40 to 50 ppm
32. The percentage of chlorine in fresh bleaching powder is-
20 to 25%
25 to 30%
30 to 35%
35 to 40%
33. The coefficient of uniformity for slow sand filters is-
1.35
1.75
1.55
2.05
34. The velocity of flow in any sedimentation tank should not exceed-
0.05mm/s
5mm/s
0.5mm/s
50mm/s
35. The human excreta is a ---waste.
dry
liquid
semi-liquid
solid
36. The water from kitchens, bathrooms, wash basins is called-
sewage
raw sewage
sullage
none of this
37. The effective size of sand particles for slow sand filters varies from- 0.3 to 0.35mm 0.35 to 0.5mm 0.5 to 0.65mm 0.65 to 0.75mm
0.3 to 0.35mm
0.35 to 0.5mm
0.5 to 0.65mm
0.65 to 0.75mm
38. The process of killing pathogenic bacterias from water is called-
sedimentation
coagulation
filteration
disinfection
39. The aeration of water is done to remove--
colour
taste
odour
all of these
40. Slow sand filter is more efficient for the removal of-
bacteria
turbidity
odour
all of these