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

33) The velocity of flow of water in a sedimentation tank is about

34) The length of rectangular sedimentation tank should not be more than [where B is the width of the tank]

35) The overflow rate for plain sedimentation tanks is about

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