A rapid sand filter is to be provided in a water treatment plant to processes the water for a town with a population of 4,00,000. The peak water demand is 220 litre/ capita/ day .

The rate of filtration is 20 m^3/m^2/hr .

Allow 5 % of filtered water for storage to meet the backwash requirements.

Each backwashing period is 30 minutes .

No . Of filters required including one as a stand by unit is

Assume available surface area configuration of one filter unit is 70 m^2 .

THANKS IN ADVANCE .