Sugars, acetic acid, ethanol. You would find these and other substances in the wastewater that is produced in wineries during the processing of grapes and the production of the world's favourite beverage. Nevertheless, conventional wastewater treatment plants find it challenging to handle such polluted water. Winemakers therefore have to look for an alternative method of water disposal, which is complicated and expensive. They could be helped by a new technology developed by experts from the Institute of Process Engineering of the Brno University of Technology.

When visiting the Laboratory of Energy-Intensive Processes at the Faculty of Mechanical Engineering, it would be really hard for you to find any small device. The room is full of large devices designed to bring research as close as possible to industrial use. Part of the laboratory's equipment is used to develop new technology that could be a helper not only for South Moravian winemakers.

"Wineries currently have no convenient way of how to dispose of their wastewater which, especially during the time of the harvest, contains extreme levels of organic pollution," says researcher Václav Miklas. While for municipal wastewater the normal level of chemical oxygen demand, which serves as an indicator of organic pollution, is around 500 milligrams per litre, values in the tens of thousands of milligrams are not uncommon for wastewater produced by wineries.

"A conventional wastewater treatment plant often cannot cope with such polluted water. And what is worse, this water can even damage it, because microorganisms in treatment plants do not really "make friends" with low pH and high concentrations of ethanol. Both alternative solutions – i.e. transporting the water for disposal to a specialized company or building an own facility – are extremely expensive," Miklas adds. That is why, from time to time, the Czech Environmental Inspectorate happens to "catch" and fine a winemaker who gets rid of their wastewater in an inappropriate way.

At the same time, the amount of wastewater produced during wine production is not small at all. "It is estimated that amount of one to four litres of wastewater is generated per litre of wine," Miklas explains. Just to give you an idea: the average wine production in the Czech Republic amounts around 550 thousand hectolitres per year.

The idea of how to help winemakers solve this problem came from the domestic company Hutira who invited process engineers of the Brno University of Technology to help develop it. "The important thing is that we are not just interested in cleaning the water, which could then be "discharged into the sewer system" in layman's terms. From the beginning, we wanted to recycle water, i.e. process it so that it could be reused. And ideally, to extract valuable substances from it, in this case ethanol," explains researcher Michal Touš.

Wastewater from wineries is typically generated when tanks, pipes and other winemaking equipment gets rinsed. It is polluted with sugars, which are a natural part of wine grapes, as well as with ethanol, i.e. residual alcohol. Due to the presence of sugar, the wastewater can naturally continue to ferment, which later produces acetic acid. Plus, substances and chemicals rinsed from the mentioned devices add to the final “cocktail“, which, however, can be reused to a large extent.

"Our goal is to integrate two processes, namely evaporation and so-called stripping. During evaporation, water and ethanol enter the gaseous phase, in which they get separated from the rest of the solution, leaving us with about a tenth of the original amount, which is, however, heavily polluted. We see here the possibility of using this residue, for example, in biogas plants, because the sugars contained in the remaining concentrate contain a lot of energy," explains Marek Vondra, another member of the research team, adding that he and his colleagues in the research plan intend to further address the issue of using the residual solution.

"After evaporation, we have ninety percent of the original volume, which is a mixture of water and ethanol. These are then separated from each other by so-called stripping. Thanks to this process, we get clean water that can be used for technological purposes and concentrated ethanol that can be reused or sold," adds Vondra.

In addition, researchers are working to make the energy-intensive process as efficient as possible. However, it is already clear that the technology would pay off for winemakers both in terms of investment and operating costs. "We plan to make the whole process even more efficient. Yet another big advantage is that our technology is relatively compact and takes up a fraction of the space in the winery compared to what would be necessary, for example, for a biological treatment plant," says Vondra. The bottom line: this technology should be competitive. And there would be a market for it, there are 17,000 hectares of vineyards in South Moravia alone, which are managed by a total of 16,000 wine growers.

The idea of circular water management runs through the whole research like a red thread. Circularity is favoured both by the Hutira company and the process engineers from the Brno University of Technology. "In our laboratory, we focus a lot on industrial wastewater in general. We try to apply the principle of minimum liquid discharge, where industrial plants recycle water to the maximum extent possible and further use valuable substances contained in wastewater. Unfortunately, the laws are not yet ready for water recycling. For example, the water we purified from the winery cannot be reused to rinse the containers during wine production, as the law requires use of drinking water. However, we believe that legislation will also be directed towards the use of recycled water and its use will soon be given the green light for purposes where it makes sense," concludes Touš.