UFC 3-280-04
17 DEC 2003
and manufacturer's catalogs and examples of manufacturer's literature. Because this
UFC focuses on package unit applications, manufacturer's catalogs and literature will
provide invaluable assistance. Each reference source used should be properly refer-
enced with the date, title, issue, or other pertinent information to completely identify it.
8-3.1.4 In addition to reference and design data from the design analysis report, tele-
phone conversations to equipment suppliers and manufacturers and regulatory agen-
cies may also be used for the design calculations.
8-3.2
Granular Media Filters. Multiple filter units are used to permit continuous op-
eration during backwashing or maintenance of another unit. The number of units must
be sufficient to avoid excessive backwash flow and to properly accommodate flow,
unless flow can be interrupted during backwashing. The total filter surface area is de-
fined as:
Filter area [m2 (ft2)] = plant flow [L/s (gpm)] / filter rate [L/ m2 s (gpm/ft2)].
8-3.2.1 The total filter area required may then be used to determine the filter bed size.
Using rectangular units, referring to standard manufacturer filter bed widths, the de-
signer may determine the filter length by:
Filter length [ft (m)] = required area [m2 (ft2)] / standard width [m (ft)]
This total length should be divided where multiple units are desired. Similarly, for circu-
lar filters, the minimum diameter can be solved and the nearest standard manufacturer
filter bed diameter used.
8-3.2.2 Filtered effluent is generally used for backwashing filters. As such, the abso-
lute minimum influent is limited to the backwash flow rates required during the cleaning
cycle. The minimum influent flow must exceed the backwash flow rate so that sufficient
effluent will be available for backwashing. Refer to vendor data to determine the back-
wash flow rates.
8-3.2.3
Solids loading is determined by the equation:
Solids loading [kg/m2d] = suspended solids [mg/L] / 1,000,000 mg/kg flow rate [L/m2s]
86,400 s/d
Solids loading [(lb/ft2)/day] = flow rate [gpm/ft2] 0.01199 lb/gal. ppm suspended solids [ppm]
8-3.2.4 Backwash frequency will depend on the types of solids, the solids loading
rate, the filter length, and the acceptable head loss. Each filter within a system should
have the capability of operating separately from other filter units.
8-3.3
Gravity Granular Media Filters. Typical operation of a filter includes piping
and valves for influent, effluent, washwater supply, washwater drain, surface wash and
filter-to-waste lines. The influent to the filter bed should not agitate the surface of the
8-3
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