AWWA JAW50183

The weight of media per unit of filter area cannot be directly measured in a full-scale filter bed as it can be in a pilot-scale filter column. This the porosity of a full-scale bed of filter media cannot be readily calculated, and determinations of the porosity in full-scale filters are rarely reported. In this study the porosity of one full-scale monomedia filter bed was estimated by comparing the head loss in a full-scale filter with the head loss in a pilot-scale filter, when both used the same anthracite media. The full-scale filter contained uniform anthracite media with an effective size of 1.5 mm loaded to a depth of 6 ft (1.8 m). The gradual termination of the backwash flow produced more consistent porosities in pilot-scale filter beds. The porosity of the full-scale filter bed was about 48 percent, somewhat lower than that expected in pilot-scale columns. Thus, full-scale designs based on pilot data may underestimate clean-bed head loss. Includes 10 references, tables, figures.