What are the design criteria for a rapid sand filter?

Rapid sand filters operate at 4-6 m3/m2/hr (vs 0.1-0.2 for slow sand filters). Design criteria: sand size 0.45-0.7mm with uniformity coefficient 1.3-1.7, bed depth 60-75cm over 40-60cm gravel support. Under-drain system collects filtered water and distributes backwash. Backwashing at 36-48 m3/m2/hr for 5-10 minutes removes accumulated solids. Include surface wash or air scour. Head loss builds from 0.3m (clean) to 2.5m (terminal). Multiple units allow continuous operation during backwash.