The BMW Group has announced a waste-water treatment and re-use process at its engine plant in Steyr, Austria, that is so effective the mains drainage could be disconnected.

Using a new combination of various membrane technologies, all manufacturing waste water in the plant is treated and fed back into the production system. The mains drainage connection for operating waste water from the production area was closed at the end of 2006, which means that around 30 million litres of water will be saved each year.

Water is used in engine production to create an emulsion with coolants for milling and turning, and for washing or rinsing during the finishing of cylinder heads, crank cases, crank shafts and connecting rods. A waste water treatment system using nanofiltration technology was introduced at Steyr in 2003.

‘This system produced such convincing results that we decided on the ambitious objective of further improving our waste water treatment so that in the future we would be able to introduce a completely enclosed water cycle for production’, said Franz Hornbachner, who is responsible for planning fluid technology.

This objective became a reality at the beginning of the year. Through a combination of ultrafiltration, nanofiltration, reverse osmosis and evaporator systems, waste water is transformed back into valuable process water using purely physical methods, without the addition of any chemicals.

The waste water goes through three stages. Firstly, oil residues are removed from the waste water by ultrafiltration. Then heavy metals and low-volatility surfactants are removed from the water by nanofiltration. In the third stage of the waste water treatment, dissolved salts and short-chain organic compounds are removed by reverse osmosis.

The BMW Group has invested around €1.5m in these technologies over the last three years. The largest engine plant in the BMW Group will save 30 million litres of water a year altogether through the new technology, which is the same amount of water used on average each year by a village of 750 inhabitants. The BMW plant in Steyr is not only easing the burden on the environment, but is also saving a considerable amount on sewerage charges.

According to the BMW Group, the Steyr water cycle is an example of the company’s Clean Production, which aims always to implement sustainable production methods at each site. Since 2000, the use of process water in the group has fallen by a quarter for each vehicle produced.