A slow sand filter has the ability to filter out bacteria. Which of the following components of the filter is responsible for providing bacteria free water?
The vital layer is layer of slimy gelatinous material which covers the surface of the sand bed after a few days. It consists of thread like algae, plankton, diatoms and bacteria. When fully formed it extends for 2 - 3 cm into the top poion of the sand bed. It removes organic material, holds back bacteria and oxidises ammoniacal nitrogen into nitrates and helps in yielding a bacteria free water. Ref: Park, Edition 21, Page - 654
Sand bed
Filter control valves
Vital layer
Under drainage system