41. The amount of residual chlorine left in public water supply for safety against pathogenic bacteria is about
42. Which of the following retards the self purification of stream?
43. 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
(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
44. 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
(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
45. Cleaning is done by
(i) Scraping and removal in filters slow sand
(ii) Back washing in slow sand filters
(iii) Scraping and removal in filters rapid sand
(iv) Back washing in rapid sand filters
The correct answer is
(i) Scraping and removal in filters slow sand
(ii) Back washing in slow sand filters
(iii) Scraping and removal in filters rapid sand
(iv) Back washing in rapid sand filters
The correct answer is
46. Sludge volume index is defined as the ratio of
47. The maximum permissible limit for fluoride in drinking water is
48. Facultative bacteria are able to work in
49. The minimum dissolved oxygen which should always be present in water in order to save the aquatic life is
50. The dissolved oxygen level in natural unpolluted waters at normal temperature is found to be of the order of
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