A large vortex around the smallest particles

The Dreilägerbachtalsperre reservoir on the German-Belgian border near Roetgen has been supplying water to the district of Aachen since 1911, and takes advantage of water resources in the mountains of the nearby Eifel. From 2004, the connected drinking water treatment plant has routed raw water from the reservoir to a membrane filtration system. The ultrafiltration membranes have such small pores that they allow pure water to flow through, but retain all other substances in the water such as bacteria, viruses and proteins.

The project: Flushing pumps for drinking water ultrafiltration

The membrane filtration system comprises 12 units, each with 36 pressure pipes of 6 m length. Together, the membranes inside the pipes form a membrane surface of approx. 70,000 m2 which is capable of handling a considerable 6,000 m3 of drinking water per hour. This makes it one of the world’s largest and most modern ultrafiltration systems. 

However, the filtration process cannot be performed indefinitely. Each unit must be flushed once an hour using KSB pumps to remove the substances retained in the membranes and filter bed, ensuring that the comprehensive filtration process can continue.

The customer: WAG Wassergewinnungs- und -aufbereitungsgesellschaft Nordeifel

WAG Nordeifel is a subsidiary of enwor and STAWAG. It stores water in two of its own reservoirs and uses other reservoirs of the Eifel-Rur water association in Düren. It also has six of its own groundwater works in the region. WAG additionally operates eight modern drinking water treatment plants which process extracted water to supply high-quality drinking water. One of these is the Roetgen drinking water treatment plant (TWA, Trinkwasseraufbereitungsanlage)

Grey Omega pump with pipes in the drinking water treatment plant

One of the two Omega pumps for backwashing

The challenge: High frequency of pump starts

Membrane filtration is a relatively new process for purifying water. Its large-scale application in the treatment of drinking water from reservoirs was preceded by several years of research at the TWA Roetgen, whose results still had to prove themselves in practical operation.

The filter membranes are cleaned by backwashing. With the addition of compressed air, flushing water is pressed through the filter material from bottom to top by the pumps, thereby releasing the deposited residues from the walls and flushing them out of the capillary.

For the pumps used for backwashing, this type of application represents an enormous challenge. Pumps are essentially designed for continuous operation. In this case, however, operation and standstill alternate continuously. As each of the total of 12 units requires flushing once per hour, the pump starts up 12 times per hour and is then switched off again. Switching on and off places a heavy load for both the motor and the bearings.

The solution: Omega pumps with frequency inverters

KSB’s Omega pump is the perfect solution for this flushing job. It stands for first-class performance in water transport, is versatile and at the same time ensures the highest possible energy savings as required by the drinking water treatment plant. The combination of solid bearing brackets, a short, rigid shaft and spring-loaded, maintenance-free bearings ensures low vibrations and smooth running, minimised loads and thus a long service life for the bearings, seals and coupling.

In this case, the Omega pump is operated with a frequency inverter which allows the speed to be reduced or increased so that the pump can be started up from standstill within a few seconds before reaching synchronous speed and developing its full performance. It is worth noting that the frequency inverter actually comes from a different manufacturer, but this does not stop the two components working together perfectly. Proof once again that while KSB offers technologically formidable stand-alone solutions, these can always be seamlessly integrated into existing installations and systems.

In retrospect, the choice of Omega proved to be spot on: Despite strenuous intermittent operation, the pump bearings have only been replaced once since 2004.

Figures I Data I Facts

System: Flushing pumps for drinking water ultrafiltration
End user: WAG Wassergewinnungs- und -aufbereitungsgesellschaft Nordeifel

Project data: 2x Omega 350-360 B, year of construction 2004 (5-L61-717-750) 1600 m³/h 25m, 1485 m³/h