Vital layer in slow-sand filter is of:

Correct option is C

Answer: (c) Schmutzdecke
Sol.
In slow-sand filtration, the Schmutzdecke is the vital layer that plays a crucial role in the filtration process. It is a layer of biological film that forms on the surface of the sand bed. This layer contains microorganisms that help in the removal of pathogens and impurities from the water.
· (a) Alum - Hoc: This is incorrect. Alum is used as a coagulating agent in water treatment, but it is not the vital layer in slow-sand filtration.
· (b) Sand bed: While the sand bed is important, it is the Schmutzdecke (the biological layer) that is the most active part in removing contaminants.
· (c) Schmutzdecke: Correct. The Schmutzdecke is a thin layer of microorganisms and biological matter on top of the sand bed that is essential for filtering pathogens and particles from the water.
· (d) Under drainage: Under drainage refers to the system used to collect the filtered water, but it is not the vital filtering layer.
Conclusion:
The correct answer is (c) Schmutzdecke, as it is the vital layer responsible for the filtration process in a slow-sand filter.