MCQ
21. The human excreta is a ---waste.
dry
liquid
semi-liquid
solid
22. 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
23. 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
24. By lime soda process, hardness can be reduced to less than
50 ppm
75 ppm
150 ppm
100 ppm
25. Rapid sand filter can remove bacteria upto an extent of-
60 to 70%
70 to 80%
80 to 90%
90 to 99%
26. The percentage of chlorine in fresh bleaching powder is-
20 to 25%
25 to 30%
30 to 35%
35 to 40%
27. The coefficient of uniformity for slow sand filters is-
1.35
1.75
1.55
2.05
28. The aeration of water is done to remove--
colour
taste
odour
all of these
29. The cross-section recommended for separate system of sewerage is--
circular
rectangular
egg-shaped
none of these
30. 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
31. The process of killing pathogenic bacterias from water is called-
sedimentation
coagulation
filteration
disinfection
32. The time of contact for chlorination should be at least-
5 minutes
20 minutes
1 hour
2 hours
33. The internal diameter of the sewer should not be less than-
15cm
25cm
50cm
75cm
34. The minimum size of a fire hydrant is--
5cm
10cm
15cm
20cm
35. 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
36. 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
37. Slow sand filter is more efficient for the removal of-
bacteria
turbidity
odour
all of these
38. Biochemical Oxygen Demand (BOD) of safe drinking water must be-
0
50
10
100
39. The water from kitchens, bathrooms, wash basins is called-
sewage
raw sewage
sullage
none of this
40. The velocity of flow in any sedimentation tank should not exceed-
0.05mm/s
5mm/s
0.5mm/s
50mm/s