Geosystems For Dewatering

TenCate Geotube® technology can be used to treat dredged contaminated sediments in two different ways. First, it can be used for the onshore dewatering of dredged contaminated sediment slurries. Second, it can be used for the offshore contained disposal of dredged contaminated sediments.

Onshore Geotube® dewatering of contaminated sediments
Geotube® containers provide a simple, low cost means of dewatering contaminated sediments. They enable the efficient dewatering of sediment slurries while at the same time ensure good effluent water quality. Further, the required Geotube® container numbers can be scaled easily depending on the size of the dewatering operation.

There are a number of steps involved in the Geotube® dewatering process. These are:

1. The dredged in-coming contaminated sediment slurry is dosed with a chemical dewatering accelerant to enhance the rate of dewatering and to trap contaminants within the structure of the contained dewatered solids. The use of the correct accelerant and its dosage rate is critical to dewatering efficiency.
2. The sediment slurry then enters the Geotube® dewatering containers. The slurry water passes out as effluent through the permeable skin of the Geotube® containers while the contaminated sediment solids remain inside the containers. It is normal practice for the containers to undergo several filling and drawdown cycles before the dewatering operation is complete.
3. The effluent water drains from the containers to a specific location in the dewatering facility and, if clean enough, may be returned directly to the natural environment, or alternatively, may undergo further treatment in order to meet specific water quality standards.
4. Once the dewatering process has been completed the dewatered solids may be transported to a designated offsite disposal facility, may be capped insitu, or put to beneficial reuse. Geotube® dewatering is noramally carried out in a designed dewatering facility. When dealing with contaminated sediments the facility is normally lined with a geomembrane to prevent leakage into the surrounding environment. Also, a drainage layer is placed across the top of the geomembrane prior to installation of the Geotube® containers. The drainage layer enables the effluent water from the dewatering containers to be drained to a specific location in the dewatering facility.

Offshore Geotube® contained disposal of contaminated sediments
Where limited land area exists for the onshore treatment and disposal of contaminated sediments offshore contained disposal has been carried out. This has involved the use of Geotube® containers to prevent the dispersal of the contaminated sediments while they are being dropped through the water column from split- bottom barges at designated offshore dumping sites.