Consider the following statements in respect of sand filters of water purification.
P. Quality-wise, SSF is more efficient than RSF.
Q. RSF is more efficient in removal of color compared to SSF.
R. SSF flow rate is higher than RSF.
S. SSF needs periodic back washing.
The correct statements are
Slow sand filters utilize a naturally forming biological layer at the surface known as the Schmutzdecke. This active layer
is highly effective at biological purification, removing up to 98% to 99% of bacteria. RSF relies entirely on mechanical
straining and chemical pretreatments, resulting in a lower independent bacterial removal efficiency.
Rapid sand filtration systems are invariably paired with upstream chemical coagulation and flocculation processes.
These chemical coagulants bind to dissolved organic matter and colloidal pigments, allowing RSF to remove complex
color compounds that pass right through an un-coagulated SSF
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