Assertion (A): Slow sand filters are less efficient in the removal of bacteria than rapid sand filter.
Reason (R): The sand used in slow sand filter is finer than in the rapid sand filters
A is false but R is true
Assertion (A) is FALSE: Slow sand filters are actually more efficient at removing bacteria (98% to 99% efficiency) than
rapid sand filters (80% to 90% efficiency). This high efficiency is due to the formation of a biological layer (Schmutzdecke)
and a lower filtration rate.
Reason (R) is TRUE: The sand used in slow sand filters is finer. It has an effective size D10 of 0.2 to 0.35 mm, whereas
rapid sand filters use coarser sand with an effective size of 0.45 to 0.7 mm.
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