Question 33 For a rapid sand filter the filter bed porosity

Question 33 For a rapid sand filter, the filter bed porosity or void fraction is best described as o Greater during normal filtration runs than during filter media cleaning operations O Greater during filter media cleaning operations than during normal filtration runs O A property of the media so constant and equal in both filtration runs and media cleaning operations None of the above answers are accurate

Solution

Option A is correct. It is greater during normal filtraion and during filter media cleaning operations( Back washing) , it is less. For back washing porosity is less because, to kept the velocity low inorder not to escape of the bed particles from the filter.