Clean and soft water

Article of 31 august 2018 

Treatment of drinking water with pneumatic drives

Drinking, cooking, washing and lots more – it is impossible to imagine life without water. So that fresh and clean water comes out of the tap when turned, sea, river and groundwater are extracted and treated in waterworks. Pneumatic drives help with the cleaning and decalcification process.

Simply turn on the tap and get as much high-quality water as you need – something that is taken for granted in Germany. However, before the groundwater flows through the tap at home in drinking-water quality, it must be treated at waterworks.

In Germany, there are around 6,000 waterworks – one of which is the facility in Langenau. It supplies 250 towns and communities in Baden-Württemberg with around 90 million cubic metres of drinking water a year. It comes from the Donauried, one of the largest groundwater basins in Germany. First it is taken from 204 springs and then piped to the waterworks.

As one of the largest waterworks in Europe, Langenau supplies three million people with high quality drinking water.
As one of the largest waterworks in Europe, Langenau supplies three million people with high quality drinking water.

Decarbonisation and filtration of the groundwater

Having arrived at the waterworks, the groundwater passes through a decarbonisation facility. Here the lime content is reduced, which would otherwise lead to unwanted deposits in pipes, household appliances and industrial facilities. The facility consists of seven reactors, which are ten metres high and have a diameter of four metres. Lime water and lime grains are added to the water for the lime to accumulate on these. Once the grains reach a certain weight, they sink to the bottom. The ‘soft’ water with a much reduced lime content flows off. The lime pellets left behind can also be reused – among other things in the glass, animal feed and plastics industries.

The decarbonisation facility at the Langenau waterworks extracts the lime from the water and thus reduces its hardness.
The decarbonisation facility at the Langenau waterworks extracts the lime from the water and thus reduces its hardness.

After the decarbonisation process, the ground water is filtered to remove organic cloudy and suspended particles. The water is fed to seven filter basins. Here, multilayer filters composed of sand and active carbon layers ensure the water is thoroughly cleaned. The water then flows through a 775-kilometre-long pipe network to the towns and communities.

Controlling the facility valves with pneumatic drives

Pneumatic semi-rotary drives support both the decarbonisation and filtration processes. In the decarbonisation facility, they move the valves that control the inflow and outflow of the water. In the case of the filter basins, they help the cleaning process: from time to time, the basins must be cleared of dirt particles. To do so, they are rinsed with fresh water and air. The drives move the butterfly valves that prevent groundwater from being let in during the rinsing process.

DAPS semi-rotary drives produced by Festo
DAPS semi-rotary drives produced by Festo contribute to stable processes at the waterworks.

The semi-rotary drives consists of two pistons and a shaft. They are activated by a valve or valve terminal. When the valve opens, air enters the drives and the pistons move the shaft. The screwed-on butterfly valves pick up the movement of the shaft and the valves open. If the air is removed again, the movement reduces and the valves close. The rotation angle of the butterfly valves is between 0°, when fully closed, and 90°, when the valve is fully open.

The advantage of pneumatic drive technology is that it is very clean – essential when dealing with drinking water. The drives are also reliable and can be operated for a very long time. That is extremely important at the waterworks because the operating time of the facilities in Langenau runs to several decades. It can therefore be guaranteed that the supply of high quality drinking water will not run out in Baden-Württemberg.