Work out filter loading rate instantly with clear inputs, formula shown and shareable results.
Filtration rate is flow divided by the area of filters actually in service, expressed in cubic metres per square metre per hour, which is numerically the same as metres per hour. Rapid gravity sand filters run 5-12 m/h, and the design must check the rate when the largest filter is out for backwash.
Filtration rate
Rate (m/h) = flow (m3/day) / (24 x effective area)
Effective area
Effective area = (filters - filters in backwash) x area per filter
Because the remaining filters must carry the whole flow. With four filters and one washing, the rate rises by a third, and if that pushes past the design maximum, turbidity breakthrough follows.
Media size and depth, floc strength and head available. Higher rates drive floc deeper into the bed, shortening runs and risking breakthrough; deeper, coarser dual media beds allow higher rates.