Which of the following is the performance efficiency of slow sand filter?
1. It removes about 98 to 99% bacteria.
2. It removes turbidity to the extent of 50 PPM.
3. It does not remove color of raw water.
4. It removes about 95% colloidal matter.

Correct option is C

→ Efficiency of slow sand filter for removal of organic matter and micro-organisms is 98-99%.
→ Efficiency of Rapid sand filter for removal of organic matter and bacteria is about 80- 90 %
→ Slow sand filter removes turbidity to the extent of about 50 ppm. For the water having turbidity more then 60 PPM then preliminary treatment is required,
→ Frequency of cleaning for slow sand filters is 1-3 months
→ Frequency of cleaning for rapid sand filters 24 to 48 hrs.