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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 24

Geotextile tubes are susceptible to cloth blinding by many sludge streams (oil and/or high biological content are most difficult), and require a large area. Additionally, tubes require a long period of time to dewater and can be adversely impacted by local climate conditions (high humidity/rain). Finally, the geotextile tubes are not feasible for hazardous sludge streams and require extensive preparation and construction of tube lay-down and drainage systems.

4.1.2

Confined Disposal Area

Advantages

Placement of sediments in a confined disposal area offers several advantages. Foremost is the elimination of mechanical dewatering equipment necessitated by an accelerated process approach. Sediments are pumped directly from the dredge to a disposal area and are allowed to

passively dewater requirements and technology.

while supernatant operator expertise

is decanted and

returned to the

lake.

are minimal as

the approach is

basic

Maintenance with limited

Disadvantages:

Confined disposal areas can require vast acreages to provide sufficient storage.

In

addition, engineered dams may be required, with the associated construction logistics are to be considered with the generally increased distance, and as with

costs. Pumping most dewatering

technologies, chemical treatment is necessary to enhance settlement. Consideration must given to sludge reuse timing as drying cannot occur until compartment filling is complete supernatant is removed.

also be and the

    • 4.2

      Chemical Aids

      • 4.2.1

        Polymer

Advantages:

Polymer technology, as an approach to enhanced settling of suspended sediments, is in continual development with tailoring to specific industries; including dredging and dewatering applications. The polymer (coagulant and flocculent) market is expanding due to shrinking disposal sites and an increase in dredging projects.

Studies confirm that tailor-made products enhance the efficiency of the dredging application and reduce overall costs for the contractor. Polymers applied in both thickening and de-watering processes improve the speed and efficiency of water separation thus saving time and disposal costs.

Polymers are typically used as pre-treatment aids in dewatering sludge when using geo- textile tubes, centrifuges, belt filter presses, screw presses, and thickeners. Specific advantages include:

  • Increasing the concentration of solids in the sludge blanket

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