Roetgen, Germany


Reservoir water


Potable water production


WAG Nordeifel

Xiga 40 performs beyond expectation in biggest German membrane-based drinking water plant. When treating surface water to produce drinking water in large quantities, the highest priority is public health and the certain removal of microorganisms, bacteria and viruses.

Next priority is typically to do this as cost-efficiently as possible. In the German town of Roetgen, membranes are doing the job very well. X-Flow’s Xiga 40 membrane modules are currently being replaced in three stages. They served for twelve years in continuous operation, where only eight were expected.


Roetgen is a small municipality in the northern Eifel region, situated on the border with Belgium. Behind a 35-metre high dam, the local stream Dreilägerbach has formed a large reservoir for the production of drinking water. If water were not constantly flowing in, this reservoir would ensure the supply of water for about one month. The Roetgen water treatment plant is operated by the Water Collection and Preparation Company Nordeifel (WAG). 

The company produces drinking water for the greater Aachen region, the town of Düren, and even the municipality of Vaals and the town of Kerkrade in the Netherlands.


The water from the reservoir is sent through various piping systems into the Roetgen treatment plant. Whereas in some parts of the world membrane technology is playing an important role in the supply of drinking water, this is not yet the case in Germany. “Our ultrafiltration membrane plant is one of the largest and most advanced in Europe, and by far the largest in Germany”, says Walter Dautzenberg, Technical Director at WAG Nordeifel. ‘Every year we supply around 35 million cubic meters of drinking water to more than 600,000 people. The raw water comes exclusively from dams in the Eifel. We treat this raw water at two sites to produce drinking water; about 26 million cubic meters here in Roetgen, and about 9 million cubic meters at the Wehebach dam.”

Membranes are increasingly important in drinking water production as hygiene regulations often require the complete removal of microorganisms. The main advantages of membrane technology  are the low energy use and the removal of turbidity and microbiology. Adding  chemicals such as chlorine is usually not necessary at all, as pathogenic germs are retained by the membranes. Increasingly small pore sizes serve different goals in drinking water production: microfiltration and ultrafiltration for particle removal, nanofiltration and reverse osmosis for softening and desalination.

Xiga Membrane Elements

Economics and performance

In Roetgen, the decision to build a membrane-based water treatment plant was based on economics and performance. Dautzenberg: ‘Our plant started operating in December 2005. Before that we had a normal, two-stage open rapid filtration plant, a classic sand filtration operation as is typically used in Germany to produce drinking water from reservoir water. At the time our plant had already been in operation for over 30 years, and we were considering how best to renew it. When the planning calculations with conventional and membrane technology showed about the same economics, we decided in favour of membrane technology because it appeared to be more future-proof and because the cleaning performance is significantly better”. The Dreilägerbach reservoir is not the only one the Roetgen water plant can depend on.

Every year, millions of cubic metres of raw water come from up to four other reservoirs. An ingenious system system of tunnels, pumping stations,transfer and bypass pipes allows WAG Nordeifel to choose from which storage lake to take water. The water quality in an open reservoir can be compromised, for example by weather effects, or an oil or fuel spill from a road accident. In order to keep the plant running and the region supplied with drinking water at all times,the filter systems can be divided and a reservoir can be taken “offline” if it needs time to recover. Compared to traditional systems, membrane-based treatment is also much better able to deal with variations in raw water quality, making operations much more stable and reliable.

Exceeded expectations

According to Dautzenberg, the Xiga 40 membranes have far exceeded expectations. “We wanted a skid designin which you could use membranes fromdifferent manufacturers. The idea was to keep our options open in case there are developments in price and quality, and to retain the ability to make the best choice when the time for replacement has come. Meanwhile it has become clear that the service life of the Xiga 40 is much better than we had expected. We counted on eight years, we hoped for ten years, and they have worked well for over twelve years. We have never used chlorine to clean the membranes, which contributes to a longer life. The number of leaks in the membranes was also much lower than expected, averaging four per month”.

From WAG Nordeifel’s point of view, there is not much to say about energy consumption, production and quality. The system works with dam pressure, so onlythe backwashing requires energy input. Production follows demand and quality is prescribed by the German Drinking Water Ordinance. Walter Dautzenberg: “The filtrate quality in the microbiological sense was always inconspicuous, which was not always the case with sand filtration in the past. This plant has significantly improved the stability of the treatment process and particle retention. We have therefore recommended membrane technology in general and these membranes in particular to colleagues who also treat dam water. We also feel well looked after by Pentair’s customer service over the years. Together we were able to determine the right time to replace the membranes.”

scope of supply

12 blocks with Xiga 40.

UF membrane elements installed in December 2005 and replaced in 2018-2019.

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