Filter Area for a Target Loading Rate
The inverse of the filter-loading tile: the filter area needed for a target loading rate at the design flow, area = flow / target loading. 800 GPM at 4 gpm/ft^2 needs 200 ft^2 of media; the backwash flow that area draws (15 gpm/ft^2 default) is reported and the loading band named. Answers 'how big a filter' instead of the rate from one area. AWWA general practice; the operator of record and the state primacy agency govern.
Formula and source
Required filter area (ft²) = design_flow / target_loading. Backwash flow = backwash_rate × area. Bands: rapid sand 2-5 gpm/ft², high-rate 4-8 gpm/ft².
Ten States Standards (Recommended Standards for Water Works), Great Lakes - Upper Mississippi River Board of State and Provincial Public Health and Environmental Managers, current edition by name. AWWA B100 / B130 (filter media) by name.
Audience
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