Carien Spagnuolo, general manager for ZebraTube, the proudly South African manufacturer of geotextile dewatering tubes for wastewater treatment works and mine tailings and process ponds, talks about the advantages of this technology compared to other dewatering technologies.
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ZebraTube is a proudly South African manufacturer of geotextile dewatering bags and tubes, offering a flexible and cost-effective alternative to conventional and more capital intensive dewatering methods such as belt filters and filter presses. “Our geotextile dewatering bags are widely used in South Africa for the dewatering of dredged material from sludge lagoons or waste stabilisation ponds at municipal wastewater treatment works, and for waste slurries from the minerals processing plants at mines,” says Carien Spagnuolo, general manager for ZebraTube.
“When rapid urbanisation or development occurs in a specific area, one commonly finds that the incoming feed load exceeds the production capacity of the area’s wastewater treatment works,” she suggests. “This typically leads to drying beds becoming overloaded or waste stabilisation ponds silting up with sludge.”
Desludging of these waste ponds is required in order to re-establish dam capacity. At wastewater treatment works, this is typically done using an auger suction dredge, which enables dredging whilst the pond remains in operation.
ZebraTube’s geotextile dewatering bags can be used to efficiently and cost-effectively dewater the dredged sludge. Sediment or sludge is dredged or pumped from the pond and fed into to the geotextile dewatering tubes. As the bags begin to fill, the slurry in contact with the surface forms a thin ‘caked’ layer of relatively dry solids on the fabric surface, creating a very efficient filter for the fines. “We can retain particulate down to 10 µm because of this filter cake effect,” Spagnuolo says.
“When full capacity has been reached after several fill cycles, the feed line is removed and the bag simply left to drain, which can take several weeks, depending on how dry the solids needs to be,” she adds. “Given sufficient space, some operators simply leave the bags in place or, if removal is required, the bag is broken open and the dry solids loaded into trucks for safe and easy disposal or re-use.”
ZebraTube’s dewatering bags were recently utilised for the desludging of sludge lagoons at a large wastewater treatment works in the Durban area. “This is the second time in the past four years that ZebraTube has been involved in the desludging of sludge lagoons at this specific wastewater treatment works,” says Spagnuolo. “For this specific project, a flocculant was required in order to agglomerate the solids and enable efficient settling and dewatering within the tubes. Flocculant addition is commonly required for the dewatering of bio-solids,” she notes, adding that the flocculant is injected in-line, downstream from the dredger. “The agglomerated sludge particles settle inside the tube, causing a filter cake to form on the surface of the geotextile, enhancing filtration efficiency and allowing clear filtrate to percolate through the geotextile.
“For the Durban treatment project a total dredged volume of 40 000 m3 was contained in ZebraTube geotextile dewatering tubes. The available laydown area was limited, which meant dewatering tubes needed to be stacked in two layers to enable optimum use of the limited laydown area. The dewatering tubes were placed on an HDPE liner, allowing filtrate to be channelled back into the pond. The project was completed within two and half months,” she relates.
ZebraTube geotextile tubes can also be utilised to supplement drying capacity in existing drying beds at wastewater treatment works, especially during the wet season when drying beds do not perform to full capacity. Geotextile tubes enable much more rapid dewatering of large sludge volumes within a short timeframe and offer the ability to easily scale the dewatering process in line with dredging volumes. Furthermore, the stackability of tubes enables efficient use of laydown area, reducing the overall footprint required.
“ZebraTube is a proudly South African business and we pride ourselves on our ability to service our customers with rapid delivery, in-house engineering support, customised designs and technical guidance throughout each project’s life-cycle,” Spagnuolo says.
Recognising the need for continued customer interaction and industry engagement, ZebraTube regularly hosts educational webinars, with the latest being an overview of municipal wastewater sludge management, which was delivered by Zutari’s Daniel Petri.
