11.The settling velocity of a particle in a sedimentation tank increases if

12.Percentage of bacterial load that can be removed from water by the process of plain sedimentation is about

13.The dissolved oxygen level in natural unpolluted waters at normal temperature is found to be of the order of

14.For a given discharge, the efficiency of sedimentation tank can be increased by

15.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