Sewage to suds? German company uses treated wastewater to make beer.

There are four main ingredients in the production of beer: malt, hops, yeast and... sewage? That last one might not sound like the most intuitive choice, but it's the one that's already being made - with sewage water, of course, having gone through a total of four purification stages.

The first three treatment stages are mechanical, biological and chemical. The mechanical treatment stage includes a screening plant, a grit chamber and two primary clarifiers. In the biological treatment stage, billions of microorganisms help to convert the dissolved substances in the wastewater into solid, settleable substances through their metabolic activity. The chemical treatment stage removes phosphorus from the wastewater.

The fourth stage is unique to the Weissenburg treatment plant. It involves ozonizing the water by mixing it with ozone via a feed system, using ozone produced on site using oxygen and a generator. The ozonization of the waste water in the reactor produces by-products that can be harmful to the aquatic environment, so this process is followed by filtration. The two-stage filtration system consists of a biological activated carbon filter, which is being trialed for the first time on an industrial scale, and a sand filter. This fourth purification stage removes up to 80% of anthropogenic trace substances.

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Yet, this water is still not safe to drink, said Tobias Fruehauf, operations manager at Weissenburg's wastewater treatment plant. So, the water has to be treated further.

"This makes the water cleaner than the drinking water quality law actually requires it. It even includes partial demineralization," explained Uwe Huebner of Xylem Water Solutions.

State-of-the-art technology makes it economical and efficient to use sewage water to brew beer. The "Reuse Brew" is a collaboration between the Chair of Brewery and Beverage Technology at Technical University of Munich (TUM), the Chair of Urban Water Systems Engineering at TUM, the city of Weissenburg and Xylem.

The Reuse Brew is not yet available for purchase. Its main purpose is to demonstrate the possibilities of modern water treatment and how water can be used sustainably. It's also one of the ways to combat climate change.

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"We are currently experiencing very frequent water shortages due to climate change," said Huebner. "And one way to counteract this is to reuse treated wastewater."

All these purification efforts culminate in satisfied beer lovers. "It's delicious," said Nadine Krogull after tasting the beer at a trade fair in Munich. "You don't realize that it's waste water."

"I don't notice any difference to a normal beer. It's really good," agreed Sebastian Beck.