Wastewater Treatment Works
Dam Dredging and Dewatering

40000 m3 total dredged volume


Zebratube® has its origins in the manufacturing of large dewatering bags for the deepest mines in the world. We have more than two decades of experience in retaining solids and percolating liquids through our woven geotextile bags.

Zebratube® products are designed and manufactured in South Africa. Our geotextiles are produced and woven locally by experienced weavers and thereafter converted to dewatering bags. Our complete control over the manufacturing process allows for design flexibility and speed of delivery. We cater for both large and small projects and our ease of deployment means Zebratube® is ideal for emergency dewatering projects.

Each roll of geotextile goes through a comprehensive set of tests at our factory to ensure absolute quality and traceability. Extruded strands are tested before weaving for tensile strength and, once woven, each roll of geotextile is tested for tensile strength and permeability.



When rapid urbanisation or development occurs in a specific area one would commonly find that the incoming feed load exceeds the production capacity of the area’s wastewater treatment plant. This would typically lead to drying beds becoming overloaded or waste stabilisation ponds silting up with sludge. Desludging of these wastewater ponds are required in order to regain dam capacity. Desludging at wastewater treatment works are typically done using an auger suction dredge, which enables dredging whilst the pond remains in operation.


Desludging and Dewatering

Geotextile dewatering tubes can be used to efficiently and cost-effectively dewater the dredged sludge

Sediment or sludge is dredged from the pond and fed to the geotextile dewatering tubes. For this specific project, a flocculant was required in order to agglomerate the solids, enabling efficiently settling and dewatering within the tubes. Flocculant addition is commonly required for the dewatering of bio-solids. Flocculant is injected in-line, downstream from the dredger. The agglomerated sludge particles settle inside the tube, allowing for the formation of a filter cake on the surface of the geotextile. The filter cake enhances filtration efficiency, allowing clear filtrate to percolate through the geotextile. Once the tube is filled and allowed to drain completely, the contained material is dry enough to be handled with an excavator for easy disposal or re-use. Figure 1 shows a filled dewatering tube being opened up for solids disposal.

Figure 1: Dewatering tube broken open to retrieve dry material for removal


For this project, 9 m circumference x 25 m length dewatering tubes were used. The filled dimensions of the tube is shown in Figure 2. The in-situ solids concentration contained within the pond was relatively low, which means a total of 40 tubes were used to dewater and contain a dredged volume of 40000 m3. The available laydown area was limited, which meant that dewatering tubes needed to be stacked in two layers to enable optimum usage of the available space. The dewatering tubes are placed on an HDPE liner, allowing filtrate to be channeled back into the pond. The project was completed within 2.5 months.


Figure 2: Dimension of the dewatering tubes used when filled to maximum capacity


Desludging and Dewatering

  • Rapid dewatering of large sludge volumes within a short period.
  • The ability to easily scale the dewatering process in line with dredging volumes.
  • Minimal skilled labour required.
  • Stackability of tubes enable efficient usage of the laydown area, reducing the overall footprint required.
  • Permanent containment of the dewatered material is possible, whilst removal and disposal of the dewatered material is easy and cost-effective.
  • Filtrate can be captured, allowing for containment, recycling and re-use.


Figure 3: Dewatering tubes were stacked in two layers to allow for optimum utilisation of the available laydown area.