UFC 3-280-03
23 JULY 2003
2-4.8.2 Sludge Cake Storage. The overall size and use of cake storage devices is
based on the frequency and quantity of sludge cake generated and the ultimate dis-
posal method. For example, for smaller applications, material may be directly dis-
charged to a drum or dumpster. However, for larger applications, the material may be
discharged to a roll-off box that can be directly loaded onto a truck for offsite disposal or
discharged onto a conveyor for further treatment. Typical types and sizes of disposal
receptacles range from chute disposal systems equipped with 210-L (55-gallon) drums
to 0.7-m3 (25-cubic yard) roll-off boxes that can loaded directly onto trucks for further
disposal.
Design considerations for the storage of sludge cake include both discharge
into and removal from storage containers. Sludge cake has thixotropic characteristics
that can change the material from a firm cake into gelatinous discrete masses that, if
allowed to settle, will recompact with time. Therefore, the overall characteristics of the
cake that is removed from storage is typically different from the sludge cake discharged
into storage. A design concern with any type of cake handling and storage is bridging,
or buildup of sludge cake, which prevents removal of the cake. To avoid bridging,
sludge cake storage bins should be constructed with steep side walls (greater than 5
vertical to 1 horizontal). In addition, if further processing or treatment is required, a "live
bottom" (i.e., conveyor or screw auger) should be used over the full bottom length of the
bin. For this application, a chain and flight conveyor mechanism or gauged helical
screws with a minimum clearance to the outside of the bin should be used to minimize
bridging effects. A variable-speed control device should also be used in conjunction with
the live-bottom mechanism to achieve the desired loading rate to subsequent process
or treatment units.
In addition to designing for discharge and removal of sludge cake from
storage containers, housekeeping should also be considered in the design of sludge
cake discharge systems. Housekeeping includes the use of optional features and
equipment to reduce the amount of liquid sludge and potential for "splashing" or
"slopping" upon sludge cake discharge from the press to the storage receptacle or
transport equipment. To reduce the amount of liquid leakage into the sludge storage
receptacle during the filtration cycle, optional equipment such as drip trays and bombay
doors could be used, as described in Subparagraph 2-4.5.6.3. To reduce the amount of
liquid sludge present before sludge cake discharge, optional features could be used,
such as air or core blowing, as described in Subparagraph 2-4.3.4. In addition to options
available before sludge discharge, sludge cake handling equipment, such as drum
platforms and chutes for smaller presses and direct disposal chutes into roll-off boxes or
directly onto conveyor systems for larger presses, as described in Subparagraph 2-
4.8.1, could also be used.
2-4.8.3 Standby Capabilities. A critical factor that should not be overlooked is the
standby capability of the sludge dewatering system. The standby system is an auxiliary
sludge cake handling capability. This equipment is necessary in the event of a
breakdown of the primary cake handling or disposal equipment. Although most multiple-
unit filter press sludge dewatering systems are equipped with adequate dual auxiliary
sludge conditioning, pumping, and filter press backup capability, standby capability for
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