WASTEWATER
33 pumps supplied to Zandvliet Netzsch Southern Africa supplied a range of pumps (via its Western Cape distributor, Dune Engineering) to Zandvliet Wastewater Treatment Works (WWTW) for polymer dosing, primary and secondary sludges, and dewatered sludge – with flow rates varying between 0.5 m3 and 130 m3.
A
long working history with PCI AFRICA (nationally) and the City of Cape Town, as well as a proven track record of providing quality engineered products that meet all tender specifications and client requirements, were among the reasons why Netzsch Pumps supplied Zandvliet WWTW with 33 pumps. “The dewatered sludge flow map was tough, and the pumps had to meet the specified flow requirements of the changing viscosities of both the primary and secondary sludge. Furthermore, the pumps had to be designed for the plant’s current capacity (after the expansion) of 90 Mℓ/day, as well as 140 Mℓ/day should it be further upgraded,” explains Eden McGee, managing director at Netzsch Southern Africa. Reduced downtime McGee adds that pumping dewatered sludge in WWTWs is a difficult process. “Netzsch Southern Africa has an STP
Eden McGee, managing director at Netzsch Southern Africa
2 System in place to protect from dry running. Our progressive cavity pumps are designed to handle complex fluids that are dry with high viscosity. But if there is no product within the pump for an extended period of time, there is a high likelihood of an increase in heat because of the friction between the metal rotor at the rubber stator. Netzsch has developed a system where a signal is sent to the motor control unit and the pump shuts down. This prevents any damage to the stator and rotor.” The dewatered sludge pumps are also fitted with an ABP® Module. This is a patented system that comprises a top hopper with two spoked wheels attached to its internal sides. The wheels sit deep inside the hopper and are very close to the walls. This largely prevents bridging. Bridging is an issue in sewage sludge handling applications and occurs when thick and dry dewatered sludge cakes bridge together across a hopper. Once the sludge sticks together, bridges between
Netzsch Southern Africa provided certification to confirm that the pumps performed according to specifications. PCI AFRICA was also given the opportunity to witness the testing of the pumps at the Netzsch factory in Germany
the side walls form as sludge falls into the hopper of a pump and starts to stick to the side walls above the pump auger. These bridges can prevent additional sludge from falling into the pump by blocking off the opening, thereby ceasing pump operation. As the sludge piles up on top of the bridge, it backs up the process until eventually it overflows out of the hopper or triggers an alarm, at which point the portion of the plant in question must shut down until the maintenance crew can break down the bridge over the pump auger, clean up any overflowed sludge, reset alarms, and pump the overflow sludge manually until the sludge feed is back within normal operating parameters. Depending on the plant setup and failure modes, the above delay to plant operation can last anywhere between an hour and a whole day. “The Zandvliet WWTW contract was a complex, interesting project and it is promising to see investment in the sector. Off the back of projects like Zandvliet, and growth over the past few years, Netzsch Southern Africa has recently set up an assembly plant in South Africa in order to meet the Department of Trade and Industry’s requirements for local content. We are now able to deliver pumps within shorter time frames, and give improved local support,” concludes McGee. M AY / J U NE 2021
37
