"Currently, water contamination is a big problem, whether we are talking about wastewater, utility water or drinking water. Waters may contain, for example, pathogenic microorganisms, typically cyanobacteria in surface waters, while sewage may be contaminated with drug residues or oestrogens from contraception. Wastewater treatment plants use a biological treatment process and it cannot eliminate everything," Pavel Rudolf from the Faculty of Mechanical Engineering at BUT outlined the problem.

Rudolf and his team have been researching the possibilities of water purification for 15 years using so-called hydrodynamic cavitation, a physical phenomenon in which, by reducing the pressure, steam bubbles can begin to appear in the water, similar to boiling. When the bubbles turn back into a liquid, it is such a dramatic collapse that the radiated pressure wave is able to rupture some microorganisms and thus neutralize them. In addition, during the phenomenon the chemical composition of the liquid temporarily changes and hydrogen peroxide is formed, which acts as a disinfectant. These effects are known and are used, for example, in laboratories for water purification. "The problem is that cavitation alone is not very effective. It is used only in the laboratory, for volumes in the order of millilitres or units of litters. In addition, the liquid must go through a cavitation cycle, even a hundred times. This is, of course, unusable in industrial practice,” Rudolf explains.

From units of litres to ten thousand

Therefore, the scientists from the Faculty of Mechanical Engineering joined forces with Pavel Sťahel's team at Masaryk University and added cavitation to the low-temperature plasma discharge. It worked. "It's surprising how efficiently liquids can be treated with this technology. After testing the cavitation plasma nozzle at flow rates of around a thousand litres per hour, including the efficiency of the treatment, tests for ten times larger fluid flows followed, and the device still worked well. At present, we have managed to expand the zone where the plasma discharge is generated tenfold, which has made the plasma treatment of liquids even more efficient. When we realize that so far the technologies have worked in plasma treatments with flow rates in the order of at most units of litres per hour, we consider this invention a real success," Pavel Sťahel from the Faculty of Science of Masaryk University praises.

It was clear that the device was physically working. In order to verify how effectively it eliminates contaminants in water, experts from the Institute of Botany of the Academy of Sciences of the Czech Republic contributed to the research. The samples prepared by them were decontaminated in a new device and returned for evaluation at the Academy of Sciences. "Our team is still involved in the development of this method towards the purification of water from psychotropic drugs, pesticides, but also from bacteria, fungi, algae and currently also viruses, which has real potential for use in pre-treatment and wastewater treatment, laundry and treatment plant technologies such as for hospitals where infectious contamination is expected, in plants producing pharmaceuticals and pesticides, where they can decompose contamination in production and recycle large volumes of water, wherever there is a need to reduce contamination to meet the possibility of discharging wastewater into sewers and the like. The latest results show that if drinking water passes through cavitation and plasma equipment, microorganisms do not grow in this water even after six months, which is practically usable in many areas of energy, heating, spa, swimming pools or wellness," Blahoslav Maršálek from the Institute of Botany of Academy of Sciences of the Czech Republic believes.

An investor is being sought

In addition to high efficiency, the performance of the new technology is also important. “We have built three of these devices of different sizes. All of them have been tested and we have confirmed that our principle works equally well on a small and large scale, which is essential for the use in practice. We currently manage tens of cubic meters of water per hour, which is no longer just an academic matter, but an industrially usable device,” Rudolf adds.

An investor is now being sought who would like to turn the technology into a product and launch it on the market. According to Rudolf, the operation of the equipment is relatively cheap and production costs could be in the order of tens to hundreds of thousands of crowns, depending on the size, so the technology would be relatively affordable for customers.

The invention has been protected by a Czech patent since last September, and an international patent application is being prepared. This should allow the future manufacturer to protect the technology in countries whose markets it considers to be key. In December, the invention was announced the best Transfera Technology Day 2020 project, organized by the Transfera.cz association in cooperation with the CzechInvest agency with the aim of connecting Czech science and the business environment.