Literature Review & Summary Report Design Basis Memorandum
BCI Project No. 19-15089 September 2007
St. Johns River Water Management District Contract # SK940AA
RAPID DEWATERING TECHNOLOGY ADVANTAGES AND DISADVANTAGES
The following section presents information on the advantages and disadvantages associated with the different rapid dewatering technologies. One advantage that is shared by the various methods discussed in this report is the ability to dewater dredged slurries in a limited amount of space. The space needed varies with each technique, but it is generally significantly less that is needed for passive dewatering. The reduced time required for the consolidation of solids is also a primary advantage of these methods.
Disadvantages center around the complex nature of the processes and the operation and maintenance of the equipment needed in most of the techniques. Another disadvantage is the sensitivity of the processes to temporal variation in the quality of the dredge material delivered to the processing facilities. As dredges move both vertically and horizontally in a lake, large differences in solids content and sediment characteristics can affect the dewatering efficiency of the rapid dewatering process. For this reason, some methods will include a mixing/storage tank at the process headworks to provide a more uniform feed of dredge material to the processing unit.
Table 3 provides a summary of the advantages and disadvantages of each process. A more detailed discussion of these features is providing the subsequent narrative.
Geotextile Tubes Advantages: Geotextile tubes are comprised of high-strength polypropylene fabric and are fabricated
to the project’s requirements. With the addition of a polymer flocculation agent, excess water drains from the container through the geotextile resulting in effluent that is suitable for reuse, and volume reduction within the container typically allows for repeated filling. Following the final cycle of filling and dewatering, the solids may be removed from the tube when dryness goals are met.
Geotextile tubes require much less dewatering equipment, less labor and operator effort, and provide effective containment. The tubes are a basic low tech operation requiring less labor and operator effort than more conventional approaches. Geotextile tubes are noted as typically the least expensive dewatering approach and provide effective containment.
Geotextile tubes typically require expensive polymer addition to pre-condition sludge. Tube solids are not as dry as filter press, belt press or centrifuge cake; therefore, much less waste volume reduction is gained. It is noted also that geotextile tubes do not meet the required PFT and/or dryness and compaction specs on many sludge streams.