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SPECIAL PUBLICATION SJ2008-SP11 - page 17 / 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 9

Sediments may be removed by truck for reuse as drying occurs, followed by reclamation of the disposal area.

    • 2.2


      • 2.2.1

        Process Type – Polymer

The use of polymers for the rapid dewatering of lake dredge sediments has been successfully demonstrated in recent years. Polymers are used in dredging projects to improve solids capture, increase cake solids and enhance the dewatering characteristics of the solids.

Thickening with polymers concentrates suspended solids by flocculation and improves the capture in all thickening equipment including gravity, mechanical and passive dewatering systems. Additionally, enhanced solids thickening increases the efficiency of any downstream equipment. Polymers can improve the settling rate of solids in both conventional settling basins and up-flow solids clarifiers.

Typical Applications include:

  • Thickening of dredged sediments by polymer injected directly in hopper dredgers to obtain a clear overflow.

  • In settlement ponds, the addition of polymers decreases the settlement time, reducing the number of ponds necessary. The overflow is typically clear after the first pond.

  • Dewatering of thickened sludge with either geo-textile tubes, centrifuges, belt filter presses or screw presses. Polymers have been proven to be very efficient in the dewatering of sludge from municipal and industrial lagoons, ponds, and lake clean- out projects.

  • In the case of contaminated sediment, polymers are able to enhance the attachment of the contaminants to the large flocculated sediment particles, thus leaving cleaner sediment behind. Therefore reducing the amount of contaminated sediment that will need to be properly disposed or contained.

Laboratory jar testing is used to establish the correct product and dosage which will optimize performance to achieve the highest solids concentration and greatest solids capture.

    • 2.3


      • 2.3.1

        Equipment Type - Solid Bowl Centrifuge Flocculated sludge is pumped into the feed port of the centrifuge where it is immediately

subjected to high centrifugal forces (in excess of 2800 G’s). The high “g” force takes advantage of the difference in specific gravity and thus separates the solids from the liquids. The solids collect and dry out on the elongated area of the bowl until they are augured to the solids discharge port. The liquids collect close to the interior of the unit (in effect “on top” of the solids) and are discharged from the liquid port. Dry centrifuge cake (solid phase) and clear

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