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Q: Select the correct statement with respect to a slow sand filter :
  • A. The filtering medium has effective size 0.45 to 0.7, multiple graded layers of sand with bacteria and odour removal.
  • B. The rate of filtration is in the range of 100-150 m³/m²/day.
  • C. The effective size of sand particles shall be 0.15 to 0.3 mm, and their uniformity coefficient shall be preferably below 3.
  • D. Backwashing daily or on alternate days is necessary for cleaning.
Correct Answer: Option C - Slow sand filter– The effective size of sand particles shall be 0.15 to 0.3 mm, and their uniformity coefficient shall be preferably below 3. • Rate of filtration in SSF = 100-200 l/m2/hr • Bacteria removal = 98-99% • Design period = 10 years.
C. Slow sand filter– The effective size of sand particles shall be 0.15 to 0.3 mm, and their uniformity coefficient shall be preferably below 3. • Rate of filtration in SSF = 100-200 l/m2/hr • Bacteria removal = 98-99% • Design period = 10 years.

Explanations:

Slow sand filter– The effective size of sand particles shall be 0.15 to 0.3 mm, and their uniformity coefficient shall be preferably below 3. • Rate of filtration in SSF = 100-200 l/m2/hr • Bacteria removal = 98-99% • Design period = 10 years.