2.2.01 Dams as a source of drinking water – the benefits of the membrane procedure

Pressure-driven membrane procedures are gaining importance in the field of treating water. After several years of pilot testing, one of the world’s largest ultrafiltration membrane facilities was commissioned in 2005 in the North Eifel region to turn the water from dams into drinking water. The expectations of this facility have been met in full. The preliminary tests were financed by the Federal Ministry of Education and Research.

The hygienic requirements of treating surface water for use as drinking water have increased considerably over the last few years. Membrane procedures are a solution with a great deal of development potential in order to meet these requirements: they can filter out dissolved substances and also serve as a barrier for particles and microorganisms. The universal application potential in removing salt from seawater, treating wastewater and producing process and drinking water provides the backing for the growth potential of pressure-driven micro, ultra and nanofiltration membrane procedures and also reverse osmosis.

The potential fields of application for the membrane filtration procedure depend on the impurities to be removed from the untreated water. Reverse osmosisThe process of osmosis involves the diffusion (movement) of a solvent (e.g. water) through a semi-permeable membrane (i.e. permeable only to the solvent). The solvent moves from the area with the lower concentration of the dissolved substance to that with the higher concentration. In the case of reverse osmosis, the natural osmosis process is reversed through the application of pressure. The salts are retained by the membrane and discharged in the form of concentrate. for desalination has long been the technology of choice for treating brackish water and seawater for use as drinking water. The main methods used for processing untreated water inland are the ultra and microfiltration low-pressure membrane procedures as well as nanofiltration. Wide-scale elimination of parasites and viruses has recently become a core interest. Both micro and ultrafiltration are used to remove most of these particles dissolved in the water (with microfiltration removing virtually all parasites, but ultrafiltration possibly not removing all the viruses). Processes using denser membranes are required to remove inorganic dissolved matter, e.g. nanofiltration or reverse osmosis.

Good combination potential

The success of the membrane procedure is in the way it can be combined with conventional water treatment procedures and techniques (e.g. flocculationA procedure used in drinking water purification to reduce existing turbidity; insoluble substances are removed from the water in the form of large particles (flocs) through the addition of flocculants such as aluminium and iron salts in the form of chlorides and sulphates. The flocs are then separated by sedimentation, for example.). Other benefits are the greatly reduced price of membranes and the considerable reduction in energy requirements through low-pressure membranes and intelligent energy recovery.

Wassergewinnungs- und -aufbereitungsgesellschaft Nordeifel (WAG) has been operating a membrane facility in Roetgen since the end of 2005, treating water obtained from dams for use as drinking water. The facility supplies around 500,000 people in the Aachen region with drinking water. With a capacity of up to 7,000 cubic metres an hour, the facility is one of the world’s top-performing ultrafiltration membrane facilities producing drinking water from dam water. Even when the dam water is heavily contaminated (e.g. after heavy rain), it eliminates almost 100% of the parasites and viruses present.

Several years of preliminary testing

Before the facility was commissioned, WAG and the IWW Water Centre (Rheinisch-Westfälisches Institut für Wasserforschung) spent four years working together with the chair for water technology at the University of Duisburg- Essen carrying out tests: they used multiple test facilities with capacities of around ten cubic metres an hour and a pilot facility with a much higher treatment output (approx. 150 m3/h). At the same time, pilot tests were performed using an immersed suction membrane to produce drinking water and to treat the flushing water for the membrane facility. The BMBF funded these tests as part of the research project entitled “Hochleistungs-Membrantechnologie” (high-performance membrane technology). Wetzel + Partner Ingenieurgesellschaft mbH (Moers) was able to use the results of these tests to plan the industrial- scale facility in Roetgen, with scientific support from the IWW.

The facility in Roetgen combines flocculation and direct ultrafiltration. This reduces the amount of sedimentation on the filter membrane and thus the associated, irreversible drop in efficiency. The flakes collect on the surface of the membrane and stabilise filtration operation. Optimised membrane backwashing then enables the impurities to be removed from the surface of the membrane together with the flakes. Another feature of the facility is that the sludgy backwash from the membrane facility is treated during a second membrane stage. The resultant permeate – water cleaned through particulate filtration – is then mixed with the untreated waterWater before it has been purified or cleaned, e.g. to produce drinking water. in the first stage. This increases the yield of the overall process to over 99%. The second stage has a treatment capacity of 630 cubic metres an hour, meaning it is also one of the world’s largest facilities of its type.

Expectations met in full

The stable operation and outstanding quality of the water produced meet all expectations. The costs for material use and debt service (including the new buildings) amount to less than EUR 0.10 per cubic metre of drinking water.

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2.2.02 Detecting water impurities

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2.2 Hygiene and Health