MIL-HDBK-1005/9A
Design and use of drying beds are influenced by: (1)
meteorological and geological conditions; (2) sludge
characteristics; and (3) use of sludge conditioning aids.
Climatic conditions are the most important. The amount and rate
of precipitation, percentage of sunshine, air temperature,
relative humidity, and wind velocity are factors that determine
the effectiveness of air drying.
The following general design characteristics are
recommended for drying beds:
a) Basis of Sizing. Provide at least 1.5 sq. ft (0.14
sq. m) of drying bed per 1,000 gpd (3785 L/d) of oily waste flow.
Provide duplicate units for 100 percent redundancy. Individual
bed area should not exceed 2,000 sq. ft (186 sq. m). If more than
2,000 sq. ft (186 sq. m) is required, provide two beds each with
50 percent of the required design area and two equally sized beds
for redundancy requirement.
b) Bed Characteristics. If available land is limited,
consider use of premolded, polypropylene screen modules to replace
sand bottom. These beds require 1/6 to 1/10 the area of sand
beds. Alternatively, consider vacuum assist or solar assisted
drying for conventional sand bottom beds.
Drying beds usually consist of 10 to 30 cm of sand that
is placed over 20 to 50 cm of graded gravel or stone. A recent
study indicates 40 cm of sand to be preferred for mechanically
cleared beds. The sand typically has an effective size of 0.3 to
1.2 mm and a uniformity coefficient of less than 5.0. Gravel is
normally graded from up to 2 cm.
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