41.The detention period and overflow rate respectively for plain sedimentation as
compared to sedimentation with coagulation are generally more and less
42. The amount of coagulant needed for coagulation of water increases with
increase in turbidity of water,decrease in temperature of water
43. Alum as a coagulant is found to be most effective when pH range of water is
6 to 8
44. The detention period in coagulation tanks is usually kept as 2 to 6 hour
45. The alum, when added as a coagulant in water decreases pH value of water
46. The chemical most commonly used to increase speed of sedimentation of sewage is lime
47. In water treatment, rapid gravity filters are adopted to remove bacteria and colloidal solids
48. The rate of filtration in slow sand filters in million litres per day per hectare is
about 50 to 60
49. The effective size of sand particles used in slow sand filters is 0.25 to 0.35mm
50. As compared to rapid sand filters, slow sand filters give slower filtration rate,higher efficiency in removal of bacteria
51.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
52. Air binding phenomena in rapid sand filters occur due to excessive negative head
53. The percentage of filtered water, which is used for backwashing in rapid sand filters, is about 2 to 4
54. Period of cleaning of slow sand filters is about 2-3 month
55. The rate of Alteration of pressure filters is greater than that of rapid sand filters
56. Double filtration is used to increase the filtration capacity of slow sand filters
57. Cleaning is done by scraping and removal in slow sand filters,back washing in rapid sand filters
58. Disinfection of water results in killing of disease bacteria
59. The disinfection efficiency of chlorine increases by increasing the temperature of water
60. Chlorine demand of water is equal to difference of applied and residual
chlorine
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