26. Turbidity is measured on
a) standard silica scale
b) standard cobalt scale
c) standard platinum scale
d) platinum cobalt scale
Ans:a
27. On standard silica scale, the turbidity in drinking water should be limited to
a) 10 ppm
b) 20 ppm
c) 30 ppm
d) 50 ppm
Ans:a
28. Residual chlorine in water is determined by
a) starch iodide method
b) orthotolidine method
c) both (a) and (b)
d) none of the above
Ans:c
29. Orthotolidine test is used for determination of
a) dissolved oxygen
b) residual chlorine
c) biochemical oxygen demand
d) dose of coagulant
Ans:b
30. If the total hardness of water is greater than its total alkalinity, the carbonate hardness will be equal to
a) total alkalinity
b) total hardness
c) total hardness – total alkalinity
d) non carbonate hardness
Ans:a
31. The amount of residual chlorine left in public water supply for safety against pathogenic bacteria is about
a) 0.01 to 0.05 ppm
b) 0.05 to 0.5 ppm
c) 0.5 to 1.0 ppm
d) 1.0 to 5.0 ppm
Ans:b
32. The dissolved oxygen level in natural unpolluted waters at normal temperature is found to be of the order of
a) 1 mg/litre
b) 10 mg/litre
c) 100 mg/litre
d) 1000 mg/litre
Ans:b
33. The velocity of flow of water in a sedimentation tank is about
a) 5 to 10 cm/sec.
b) 15 to 30 cm/sec.
c) 15 to 30 cm/minute
d) 15 to 30 cm/hour
Ans:c
34. The length of rectangular sedimentation tank should not be more than
a) B
b) 2B
c) 4B
d) 8B
where B is the width of the tank
Ans:c
35. The overflow rate for plain sedimentation tanks is about
a) 500 to 750 litres/hour/ m2
b) 1000 to 1250 litres/hour/ m2
c) 1250 to 1500 litres/hour/m2
d) 1500 to 2000 litres/hour/m2
Ans:a
36. Percentage of bacterial load that can be removed from water by the process of plain sedimentation is about
a) 10 to 25
b) 50
c) 75
d) 100
Ans:c
37. The settling velocity of a particle in a sedimentation tank depends on
a) depth of tank
b) surface area of tank
c) both depth and surface area of tank
d) none of the above
Ans:b
38. The settling velocity of a particle in a sedimentation tank increases if
a) particle size is decreased
b) the surface area of tank is increased
c) the depth of tank is decreased
d) none of the above
Ans:d
39. For a given discharge, the efficiency of sedimentation tank can be increased by
a) increasing the depth of tank
b) decreasing the depth of tank
c) increasing the surface area of tank
d) decreasing the surface area of tank
Ans:c
40. The detention period and overflow rate respectively for plain sedimentation as compared to sedimentation with coagulation are generally
a) less and more
b) less and less
c) more and less
d) more and more
Ans:c
41. The amount of coagulant needed for coagulation of water increases with
i) increase in turbidity of water
ii) decrease in turbidity of water
iii) increase in temperature of water
iv) decrease in temperature of water
The correct answer is
a) (i) and (ii)
b) (i)and(iv)
c) (ii) and (iii)
d) (ii) and (iv)
Ans:b
42. Alum as a coagulant is found to be most effective when pH range of water is
a) 2 to 4
b) 4 to 6
c) 6 to 8
d) 8 to 10
Ans:c
43. The detention period in coagulation tanks is usually kept as
a) 1 to 2 minutes
b) 30 to 45 minutes
c) 2 to 6 hours
d) 2 to 6 days
Ans:c
44. The alum, when added as a coagulant in water
a) does not require alkalinity in water for flocculation
b) does not affect pH value of water
c) increases pH value of water
d) decreases pH value of water
Ans:d
45. The chemical most commonly used to increase speed of sedimentation of sewage is
a) sulphuric acid
b) copper sulphate
c) lime
d) sodium permanganate
Ans:c
46. In water treatment, rapid gravity filters are adopted to remove
a) dissolved organic substances
b) dissolved solids and dissolved gases
c) floating solids and dissolved inorganic solids
d) bacteria and colloidal solids
Ans:d
47. The rate of filtration in slow sand filters in million litres per day per hectare is about
a) 50 to 60
b) 100 to 150
c) 500 to 600
d) 1400 to 1500
Ans:a
48. The effective size of sand particles used in slow sand filters is
a) 0.25 to 0.35 mm
b) 0.35 to 0.60 mm
c) 0.60 to 1.00 mm
d) 1.00 to 1.80 mm
Ans:a
49. As compared to rapid sand filters, slow sand filters give
i) slower filtration rate
ii) higher filtration rate
iii) lesser efficiency in removal of bacteria
iv) higher efficiency in removal of bacteria
The correct answer is
a) (i) and (ii)
b) (ii) and (iii)
c) (i) and (iv)
d) (ii) and (iv)
Ans:c
50. Assertion A: Slow sand filters are more efficient in removal of bacteria than rapid sand filters.
Reason R : The sand used in slow sand filters is finer than that in rapid sand filters.
Select your answer based on the coding system given below:
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 the correct explanation of A.
c) A is true but R is false.
d) A is false but R is true.
Ans:a