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

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:

51) Air binding phenomena in rapid sand filters occur due to

52) The percentage of filtered water, which is used for backwashing in rapid sand filters, is about

53) Period of cleaning of slow sand filters is about