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Closed water cycles

Water is the source of all life – today, Audi already uses this valuable resource very sparingly at its Ingolstadt site. In the future, the use of a membrane bioreactor (MBR) will further optimize water-conserving processes.

The plant in Ingolstadt utilizes water of two different qualities. Drinking water is only used if absolutely necessary, such as in showering facilities for employees. For all other purposes, process water is used. Audi gets its water primarily from sources that are unsuitable for drinking water, but production of this water is limited. Another portion of process water comes directly from the sky – rain water is collected on the 450,000 m2 (111.20 acres) surface area of the roof and parking areas and is routed to five retention basins and two overflow storage channels. It can be drawn from this storage as needed.

In order to reuse a portion of the process water, it is purified in a water treatment system. “We want to attain the best possible quality,” stresses Gerhard Scharrer, who is responsible for water and wastewater analysis at the Ingolstadt production site. The graduate engineer monitors all water circulation system processes. First, dirt particles are removed from the used process water in multiple stages, and then the pH value is adjusted. Afterwards, the water is reintroduced into production via a pumping station. “Then the circulation process begins anew. We treat our process water around the clock,” says Scharrer.

Innovative system: the membrane bioreactor

The next step Audi is taking is to set up what is known as a membrane bioreactor (MBR) at the plant site. In the future, it will be used to treat the wastewater in two stages. In the first step, bacteria clean the water; they break down substances such as paint solvents, while they bind hazardous inorganic materials like heavy metals – e.g. nickel and zinc – to their surfaces, removing them from the water. In the second step, membranes prevent the bacteria from entering the output water.

“Conventional water treatment systems lack this ultrafiltration method. We are utilizing membranes whose permeability lies below the micron range. The membranes are so fine that they form an absolute barrier to bacteria and viruses,” explains Dr. Antje Arnold from the Company’s Environmental Protection department. “This gives the treated wastewater very good quality and lets us re-use it as process water.”
MBR technology reduces the annual fresh water requirements for Ingolstadt production by up to 40 percent, which represents 500 million liters (132.09 million US gallons); the goal is to reduce disposal of wastewater by up to 50 percent. This is a clear competitive advantage for Audi: “No other carmaker in the world has a membrane bioreactor for re-using process water in recirculation,” stresses Arnold. Initial tests with a small test system have already been running successfully for several months now; startup of the large system is scheduled for the end of 2014.

Using this new technology, Audi is systematically advancing its energy efficiency and conservation expertise in handling water resources – from Antje Arnold’s point of view the outlook is very good: “We are already handling our water resources very efficiently and sustainably. The membrane bioreactor represents our next big step towards wastewater-free production.”