MIL-HDBK-1005/9A
Usually, carbon columns are designed with hydraulic
loadings of 2 to 10 gpm/ft2 (81.5 to 407.5 L/min⋅m2) for carbon beds
10 to 30 feet (3.05 to 9.1 m) high. Bed height-to-diameter ratio
varies from 1:1 to as high as 4:1. The higher rations are needed
for columns operating without flow distribution systems.
3.10.8
Sludge Dewatering and Disposal. The solids that settle
to the bottom of the LETs, gravity separators, and DAF/IAF must be
removed periodically. In addition, the scum that accumulates at
the surface in the DAF/IAF must also be disposed. Oily sludges
may contain considerable quantities of heavy metals and organic
toxic chemicals. Inorganic coagulants such as lime and alum used
in wastewater treatment also increase sludge generation. These
sludges may be classified as toxic wastes and must be dewatered
(regardless of toxicity) to minimize transportation and disposal
costs and comply with typical disposal site criteria. Sludge
drying beds or mechanical dewatering equipment are the preferred
method of sludge dewatering.
The efficiency of dewatering can be improved by sludge
conditioning prior to dewatering. The common processes include
chemical and thermal conditioning. Chemical conditioning by
polyelectrolytes is more suitable for oily waste plants as it
requires less capital and O&M costs and the process hardware is
less complex as compared to thermal conditioning. However,
chemical conditioning requires an investigation to select the type
and feed rates of chemicals. Inorganic conditioning chemicals are
also considered effective, but they increase the quantity of
sludge and increase disposal cost as compared to organic
polyelectrolytes.
The water fraction from dewatering oily sludges is to be
transferred to the LETs.
3.10.8.1 Sludge Drying Beds. Sludge drying beds are the
preferred alternative if the treatment facility is located in a
suitable climate. Sludge drying beds are considerably less
expensive to design, construct, operate, and maintain as compared
to mechanical dewatering devices. Their performance is not
affected by variable solids/moisture content in sludges.
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