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SPECIAL PUBLICATION SJ2008-SP11 - page 29 / 48





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Literature Review & Summary Report Design Basis Memorandum

BCI Project No. 19-15089 September 2007

St. Johns River Water Management District Contract # SK940AA

Page 21

Comparisons were based on a sediment in situ volume of 1,000,000 cubic yards at 45% organic content and 0.1 grams/cm3. Storage requirements in acres are based on processed solids shown in Table 2. Disposal site area was based on a final fill height of 5 feet.

Post process solids ranged from an estimated low of 15% using confined area disposal placement to a high of 40% when using one of the integrated process systems. Based on this range of solids and the selected stack height, storage area requirements ranged from 70 to 200 acres for the one million yards of lake sediments removed.

Column six of Table 2 is labeled ‘Processing Rates to Truckable Solids (+25%)’. To clarify; these rates are reflective of the tons per hour (tph) of cake solids, on a dry basis, produced by each process. However, while dry-basis tons are shown in the table, final solids content varies with the process type. Two process parameters were looked at for each rapid dewatering option, which were rate (tph) and process continuity (batch/continuous). Dredging rates and discharge solids were held constant for all investigations.

Since the dewatering process output must match the dredging process input, all rapid dewatering options have effectively the same capacity, and all recover a calculated + 40 tph of sediment (with the +200 mesh fraction removed). Once each system of dewatering alternatives is charged with slurry and has reached operational equilibrium, the sole difference becomes the

final sediment solids. alternatives involves the

The second fundamental nature of feed slurry entry

difference among the various dewatering and removal from the system component(s).

The halt

two types in periodically

this investigation are classified as batch to discharge the thickened cake and

and continuous. A batch reload with feed slurry,

system must creating an

interruption in the process flow. ‘dump’ area, for process feeds product at the same rate as feed steady-state.

This potentially leads to the need for a temporary storage, or somewhere in the system. A continuous system discharges is introduced; thus, no interruptions occur and the process runs

Each of the rapid dewatering alternatives is preceded by cycloning to remove associated sand. Using cyclones, however, to directly fill a confined disposal area results in effectively the same thickening timing as pumping directly to the disposal area. As previously noted, Table 2 differentiates between the two process types for each rapid dewatering alternative.

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