MechChem Africa visited the ZebraTube stand at Electra Mining Africa and talked to Tshepang Dolamo, the company’s technical sales engineer, about the significant difference ZebraTube geotextile dewatering tubes and bags can make in preventing sewage and mine-impacted wastewater from contaminating freshwater ecosystems.
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With a Bachelor of Technology degree in chemical engineering from the University of Johannesburg, Tshepang Dolamo began her career as a water treatment process engineer on the goldmines in the Carletonville area. “I have a background as a process engineer looking after the plants treating mine-impacted water to potable or environmental discharge quality levels,” she tells MechChem Africa.
“I worked on a Crystalactor® plant with a treatment capacity of 5.0 Mℓ per day for removing hardness ions and heavy metals, including uranium and arsenic, for example. The system consists of a vessel filled with small sand pebbles. The contaminated mine water is dosed with chemicals that trigger precipitation and introduced from the sides of the vessel. The heavy metals come out of solution and attach themselves to the pebbles, while near potable water is taken off the top. The only thing other thing we had to adjust was the pH, adding a little acid if the pH was too high or alkaline chemicals if we needed to increase the pH,” Dolamo explains.
“We also ran a dual-stage ion exchange plant, which was able to remove water hardness elements using ion exchange resins to produce potable water,” she says, adding that she was involved in managing a 40 Mℓ/day settler plant in the Carletonville area.
Dolamo resigned from her job as a process engineer to join ZebraTube because she felt her skills and personality were better suited to technical sales. “With my background in water treatment, I thought I could add more value to the wastewater sector if I were out talking to people and helping them to implement new projects. So, I am now the technical sales engineer for ZebraTube, out in the field looking for opportunities to use our geotextile tubes and bags to help people better meet their dewatering needs and manage their solid waste,” she informs MechChem Africa.
Describing a more unusual project on the West Coast, Dolamo says that ZebraTube has supplied large low-flow tubular geotextile bags to a diamond processing plant close to the shore. “We put our tubes along the beach front at low tide and went as far as we possibly could, effectively building a berm wall to enable the processing plant to be moved closer to the shore,” she says.
To fill the bags, sea sand was pumped from 50 to 100 m offshore using slurry pumps. The water immediately begins to drain out, leaving behind a very efficient retaining wall about
1.8 m high to keep the Cape’s stormy seas at bay.
A core focus for ZebraTube in South Africa, though, is for emergency dewatering applications for mine impacted water or municipal wastewater. “We have started to assist wastewater plants along the Vaal River. For example, a client in Sebokeng is filling six of our high flow tubes every month to reduce the amount of effluent overflow entering the Vaal river,” she tells MechChem Africa.
“Areas along the Vaal near the wastewater plants are pitch black, and this is clearly visible on Google Earth. Overwhelmed wastewater treatment plants are having to release raw sewage into the river and people from the surrounding communities are getting sick,” she adds.
Dolamo says there is a huge need to empty out the accumulated sludge from these facilities so the pumps can be fixed. “We've been supplying our large tubular ZebraTube bags to enable plants to take the sludge out of the bottom of their clarifiers for dewatering and storage nearby.
“We are trying to provide a safe and environmentally friendly solution, and while using plastic is not ideal, it offers much better containment for sludge and is a far better solution than simply pumping it into a hole or allowing it to flow into the river. The tubes also help with odour control, because all the solids are contained,” she says.
ZebraTube has quoted on similar sludge containment projects in Cape Town as well as Potchefstroom, but take up is still very slow.
Also under discussion is a clean-up project for the Vaal river. “The next step of the Vaal project is to take a couple of metres of sludge from the contaminated areas of the river. Just as we did in Kwazulu-Natal, we can pump this sludge into geotextile tubes on the banks of the river. Once dewatered, the bags can be broken open and the dry solids safely transported to disposal sites,” explains Tshepang Dolamo. This will need to be done for several kilometres downstream of each contamination point, she adds.
North of the border, ZebraTube is supplying its high-flow geotextile bags for use in a mineral sands operation in Kenya. “Here we are using our small square bags, which can contain about 1.0 m3 of material. The operation was using regular bulk bags, but there were complaints that they were exporting water. Once they realised ZebraTube bags were designed for dewatering, they could simply fill the bags, leave them to drain for a day or so before closing them up and loading them into a shipping container using a forklift truck. It makes the whole operation much more manageable and cost effective.
“We have customised these bags for dewatering, transportation and lifting purposes. It’s actually a little bit less than one cube in volume, but we have modified the stitching to double the amount of webbing on every corner. This makes the bags stronger and easier to handle during transportation,” says Dolamo.
“This is typical of our fit-for-purpose approach. We are able to determine the real needs of an application then try and match the geotextile material and the stitching requirements to best suit that need.
As well as the high-flow range of products for dewatering sludge and sand, ZebraTube can offer low-flow geotextiles for dewatering fine slurries with particle sizes down to 10 µm. “We have also recently patented ZebraTex, a composite-lined geotextile solution for
retaining and dewatering slurries in the sub-10 µm range – without the need for flocculants,” she notes.
“We are willing and able to develop customised solutions for any dewatering task, be it for the reparation of the municipal wastewater infrastructure in South Africa, assisting in the clean up our contaminated rivers, assisting with emergency dredging of flooded slime dams or helping to dewater and transport valuable minerals or waste solids,” Tshepang Dolamo concludes.
