Dredging system helps rescue Gauteng sewage works

Local pump and dredging company IPR recently dredged the emergency water dams at a Gauteng wastewater treatment facility, using its SlurrySucker dredging system.

IPR business development manager Warren Spann explains that the emergency dams had filled with sludge over time, and were presenting an operational risk to the plant. Dredging the dams with hydraulic excavators was not effective for a number of reasons, and the manual removal of sludge in trucks caused environmental challenges. The dams are vital sources of additional water for the treatment plant during times when insufficient volumes are flowing into the facility.

“IPR was contracted to conduct the dredging of these emergency water dams, and we put our new generation SlurrySucker Maxi onto the job,” says Spann. “This powerful dredging system is equipped with three Toyo K30 heavy-duty submersible slurry pumps, and was able to remove 50 dry tonnes per hour.”

The specialised heavy duty 22 kW Toyo pumps are designed to deal with the variety of solids that accompany wastewater to plants including rags, nappies and even pillows. The pumps’ capacity allowed the sludge to be pumped through 450 m of pipeline, without the need for inline boosting.

Mounted on a purpose-designed pontoon, the SlurrySucker Maxi was drawn from across the 250-m-long dams using ropes and a winching system. The operation was managed by a trained technician using a remote control system.

“There were also two Atlas Copco WEDA D70H jetting pumps on the pontoon, to help stir up the sediment in the dams,” he says. “The first pump jets water down to the dredge head to agitate compacted sludge on the bottom of the dam, while the second pump jets water into sludge that is near – or even protruding from – the surface of the water. The latter is necessary as the pontoon needs 350 to 400 mm of water on which to float.”

To ensure that the discharge from the dredging activity complied with environmental standards, the dredged material was pumped into large dewatering bags. Each bag held 25 000 t of material, measured 30 m in circumference and was 60 m long.

These bags allowed water to weep out into a catchment pond, and IPR added a flocculant to the pipeline to help the solid materials to settle out. This helped the wastewater plant to conserve water, as the filtrate was pumped back to the plant for re-use. The added flocculant in the filtrate assisted the plant further by contributing to the levels of flocculant that the plant would be adding as part of its normal process.

Lime was used to reduce the odour from the dewatering bags, giving the customer various options related to removing the material later, including the provision of activated sludge to the agricultural sector.

“An added advantage of our dredging technique is that all our equipment is electrically powered, so it operates with hardly any noise,” says Spann. “This is in stark contrast to heavy mechanical equipment, and meant that we did not disturb the neighbouring residential estate.”

He adds that IPR’s advanced control panels on the SlurrySucker ensured that the power would trip if any oversize material threatened to damage the pumps. The panels convey an error message to the operators, so they can resolve the issue and return the system to work without risking any further harm to the equipment.