The rate of filtration in slow sand filters in million litres per day per hectare is about

Slow sand filters operate at a very low filtration rate because the purification mainly occurs through biological action in the schmutzdecke layer formed on top of the sand.

The typical rate of filtration for slow sand filters is 0.1 to 0.2 m³/m²/hr, which when converted equals approximately 50 to 60 million litres per day per hectare (MLD/ha).

Thus, the correct filtration rate range matches Option A.