The generally accepted maximum filtration rate for a single-media rapid sand filter is approximately what?

• A. 1-2 gpm/ft^2
• B. 3-4 gpm/ft^2
• C. 2-3 gpm/ft^2
• D. 4-5 gpm/ft^2

Answer: (C)

Filtration rate through a single-media rapid sand filter is the pace at which water is allowed to pass through the bed, which directly affects how long particles stay in contact with the media and how effectively they are removed. The commonly accepted upper limit for this type of filter is about 2 to 3 gallons per minute per square foot of filter area. Staying within this range helps maintain good removal of suspended solids and keeps head loss at a manageable level, making backwashing workable and the effluent quality consistent. If the rate goes much higher, particles aren’t captured as efficiently, effluent turbidity can rise, head loss increases, and backwashing becomes more frequent and less effective. Multi-media filters can tolerate higher rates because the different media sizes provide additional capture capacity, but single-media beds rely on a lower rate to achieve reliable performance.