The long-term solution for water purification from harmful microorganisms or dangerous pharmaceutical residues is a current topic in modern society. A scientific team from the Brno University of Technology, the Department of Biology of the CAS, and the Department of Plasma Physics and Technology of Masaryk University developed a new technology that enables cheap and effective water treatment.
Ridding water of harmful substances is not easy, let alone cheap, on an industrial scale. It is a very subtle and final step of water treatment. Current sewage and wastewater treatment plants, especially the small ones, cannot deal with this pollution effectively. The impact of human activity on surface waters and the aquatic organisms living in them is increasing every year. It is not only with the amount of waste produced but, even more worryingly, with our ability to effectively detect even small amounts of pollutants and their significant impacts on our ecosystem, particularly when it comes to substances that act even with small quantities, such as hormones or toxic substances.
The initial idea for plasma as the new water treatment technology dates to 2018. Electrical discharges can be easily ignited in a gaseous environment, e.g., by discharging static electricity. However, the efficient transfer of the obtained reactive particles from gas to liquid is a challenging process. Thus, scientists have been thinking about efficiently generating a gaseous environment in a liquid where the discharges ignite easily. At the same time, there should also be efficient transfer of the generated reactive particles to the surrounding liquid.
Hydrodynamic cavitation in a fast-flowing liquid was a promising starting point. Still, the critical issue was finding a way to generate plasma in this environment. The researchers found a solution and subsequently filed a patent application in 2019. As a result, as of 2020, the plasma water treatment technology (named CaviPlasma) is protected by a national patent, and in 2023 the first of the international patents filed was also granted, in Israel.
CaviPlasma technology
CaviPlasma came into being as a natural, but not apparent, consequence of a successful collaboration that had aimed to develop a patented and proven technology for waste air purification. The earlier successful collaboration brought together teams of scientists from the Faculty of Science of Masaryk University (Applied Plasmochemistry research group), the Faculty of Mechanical Engineering of Brno University of Technology (group of Assoc. Prof. Pavel Rudolf), and the group of Prof. Maršálek from the Institute of Botany, CAS. It is thanks to this unique multidisciplinary overlap that the researchers managed to fundamentally innovate the method of water purification and shift the volumetric efficiency of plasma water treatment by 2-3 orders of magnitude compared to existing technologies.
The newly developed plasma unit combines advanced technologies of fluid and plasma engineering and enables plasma treatment of water of several cubic meters of water per hour at operating costs of a few CZK per cubic meter. The technology combining the worlds of fluid engineering and plasma physics has been named CaviPlasma. Thanks to the innovative approach of scientists from MU, BUT and the CAS, an industrially attractive technology with huge application potential for its deployment has been created, with unprecedented energy efficiency.
The outstanding properties of the new plasma source are based on the unique combination of hydromechanical and plasma chemical effects in a single device. The process of hydrodynamic cavitation produces a large number of tiny cavities (bubbles) containing water vapor in the flowing liquid. When such cavities collapse, they exert significant mechanical effects on the liquid and its surroundings. This phenomenon causes undesirable erosion of the turbine blades. However, these cavities are necessary for the efficient operation of the CaviPlasma unit. In the so-called cavitation cloud, the conditions are very favorable for the ignition of an electrical discharge. The cavities are formed by vapors of liquid (water) at a pressure much lower than atmospheric pressure. In the discharge, the water molecules in the cavities dissociated easily. After the cavities collapse, resulting reactive particles enter the liquid volume. And it is these reactive particles that cleanse the liquid of unwanted chemicals.
CaviPlasma technology does not only offer purification of chemically polluted water. Another significant application is protection against dangerous microorganisms. CaviPlasma uniquely combines the mechanical, electrical, plasma chemical, and UV radiation effects. Together, they have a significant biocidal effect on harmful microorganisms such as cyanobacteria or multi-resistant strains of bacteria. And not only that. Even the water itself, treated with CaviPlasma technology, has been shown to have significant biological effects. This so-called "plasma treated water" (PTW) has proven to be very effective, e.g. for suppressing the growth of cyanobacteria and algae (DOI), as well as human and animal pathogens. The application potential of CaviPlasma extends to a wide range of other fields. In preliminary trials, the technology was successfully tested in aquaponic crop production in an agricultural production environment. It is this direction of application potential of CaviPlasma that Dr. Jan Čech focused on.
Technology that works
So far, the research results have generated positive responses in the professional community, both at international conferences in the field of basic and applied plasma research (e.g., HAKONE XVII, CESPC-9, FSO 2023) and also at conferences dedicated to protection against hazardous substances (HAZMAT PROTECT 2022) or CBRN PROTECT 2023).
The scientists have published two scientific papers and are preparing others. One was evaluated as the "editor's choice" of the Water (DOI) journal. The recognition of the significant commercial potential of this technology towards real applications is also evidenced by winning the finals of the "Transfera Technology Day 2020", where an expert jury selected it as one of two projects from Brno (see Transfera.cz). In 2021, the CaviPlasma technology won the Gold Medal at the International Engineering Fair in Brno.
However, the development of CaviPlasma technology would not be possible without systematic research – both basic and applied. Scientists from the Applied Plasmochemistry group are working on the plasma-physical aspects and diagnostics of CaviPlasma for a deeper understanding of its mechanisms, which will allow tuning the operational parameters of the discharge and the actual design, which they are working on together with experts at the BUT. Colleagues at the Institute of Botany of the CAS are characterizing and improving decontamination efficiency and destruction of microorganisms or chemical agents. Scientists have focused mainly on finding the most suitable applications in recent years. Research has been and continues to be conducted under several grant projects.
The ongoing project GA22-11456S, funded by the Grant Agency of the Czech Republic, focuses on basic research. In this project, Assoc. Prof. Pavel Sťahel, as the principal investigator, aims to understand the basic mechanisms of CaviPlasma to enhance its effects. The already completed project SS01020006, supported by the Technology Agency of the Czech Republic under the Environment for Life program, was aimed at using CaviPlasma technology for wastewater treatment. In 2022, Dr. Jan Čech worked on a Proof of Concept project, MUNI/31/06202105/2021, supported by the GAMA program of the Technology Agency of the Czech Republic, in which he investigated the potential of CaviPlasma technology for use in agriculture.
The results are the best evidence of the success of this research in multidisciplinary collaboration. The invented and successfully patented technology has a high potential for environmentally and economically friendly treatment of polluted waters. International patent proceedings and negotiations with interested parties for industrial licenses are ongoing. So far, Czech, Canadian, and Israeli patents have been granted, the first two licensing agreements have been concluded, and one can look forward to the first commercial tests.
For student readers, you can also contribute to the CaviPlasma research. You are welcome to join the team. Contact directly Assoc. Prof. Pavel Sťahel.
Let us mention that the CaviPlasma technology has already received media attention. Already in 2021, the BUT wrote about the research successes here. In January 2022, CaviPlasma was discussed by Assoc. Prof. Pavel Sťahel, Assoc. Prof. Pavel Rudolf and Prof. Blahoslav Maršálek in the Good Morning program of Czech Televison (here). In February 2022, in an interview with Pavel Rudolf for Technický denik here.
Ondřej Caha from the Department of Condensed Matter Physics and Jaroslav Hnilica from the Department of Plasma Physics and Technology as new associate professors ceremonially received their appointment decrees. The MU Rector Martin Bareš personally handed them the decrees in the refectory of the Augustinian Abbey on Mendel Square.
The leader of the Plasma Nanotechnologies and Bioapplications research group, Dušan Kováčik visits Laval Université in Québec, Canada. His trip aims to support the developing scientific cooperation with Prof. Gaetan Laroche's research group.
