Cold Plasma Sterilization of Liquids and Surfaces
Development of New High-Effective Sterilization Methods of Liquids and Surfaces by Cold Plasma at Atmospheric Pressure
Tech Area / Field
- PHY-PLS/Plasma Physics/Physics
- BIO-SFS/Biosafety and BioSecurity/Biotechnology
- ENV-RED/Remediation and Decontamination/Environment
3 Approved without Funding
TRINITI, Russia, Moscow reg., Troitsk
- State Research Center for Applied Microbiology, Russia, Moscow reg., Obolensk
- Universiteit Gent / Department of Applied Physics, Belgium, Gent\nTexas A&M University / Department of Civil Engineering, USA, TX, College Station\nLos Alamos National Laboratory / Plasma Physics Group, USA, NM, Los-Alamos\nErnst Moritz Arndt Universitat Greifswald / Institut fur Physik, Germany, Greifswald\nUniversity of Minnesota / Department of Mechanical Engineering, USA, MN, Minneapolis\nEuropean Commission / Joint Research Center / Institute for Health and Consumer Protection, Italy, Ispra\nABB Corporate Research Ltd, Switzerland, Baden\nUniversity of Montreal, Canada, QC, Montreal\nPrinceton University / School of Engineering and Applied Science / Department of Mechanical and Aerospace Engineering, USA, NJ, Princeton
Project summaryImproving life quality is one of challenges for modern society stimulating new developments and their implementation. Life quality has many aspects, among which most important are a standard of public medical service and biologically safe environment. In this connection, an actual problem of modern medicine/biology and environment protection is development of effective and energy efficient methods for destruction of biologically harmful pollutants (pathogens and toxic chemicals) in gases, liquids and on surface of bodies.
Sterilization of objects consists of destruction or removal processes of microorganisms, including vegetative cells, spores and viruses. Traditional sterilization and disinfection methods used heating in dry and humid environment, filtration, radiation and chemicals (biocydes). These methods are labor and time consuming and expensive. Besides, using of biocydes does not provide environmental safety. Introduction into medical practice new materials based on usage of polymers demands that non-destructive (non-thermal), fast, safe and cheap sterilization methods must be developed.
One more siding with sterilization problem is protection of different industrial materials, equipment, electronic devices etc. from bio-corrosion and biodegradability. It is known that corrosion of metals speeds up hundreds times when induced by thin films of microorganisms. Usually, microorganisms forming films are very resistive against traditional sterilization methods. This necessitates development of new and more effective sterilization methods of surfaces subject to biodegradation and bio-corrosion.
In this respect, application of cold atmospheric pressure plasmas, created just in treated liquids or gases or nearby sterilized surface looks very promising. Non-thermal plasma can generate in economical way many active particles, and interaction of these particles with harmful chemicals or microorganisms results in their destruction.
Non-thermal methods of sterilization in medicine/biology  and off-gases and liquids cleanup in industry  started to be developed from 90-s in the last century. Despite some progress achieved in lab-scale tests, cold plasma treatment at atmospheric pressure has not got wide distribution in practice. A primary reason for that lies in the fact that scaling of developed sources of cold plasma to parameters attractive for modern consumers is technically complicated and economically inefficient. One more and very important reason is that existing methods of plasma production are based on using of non-homogeneous discharges composed of many high-intensive thin current filaments (streamers), and they therefore do not give a firm guarantee that no local damage of object takes place when plasma contacted the treated surface. Two new methods of atmospheric pressure cold plasma production suggested by the project authors are free of pointed above drawbacks. These methods are original, simple in implementation, easy scalable and effective in their action on treated objects.
The first method assigned for treatment of both hard and soft objects is based on usage of a special discharge composed of many low-intensive streamers, widely covering the surface of the treated object. Widely spread discharge is maintained in electro-positive gas by applying low amplitude alternating voltage. This form of discharge provides effective treatment of objects at low energy density released at the treated surface. The last factor is a key for absence of local damages of the surface. The second method assigned for treatment of liquid objects is based on usage of a unique electric discharge in a liquid with gas bubbles. This discharge realized by authors can be operated under specific conditions in a mode, which may be called “cold boiling”. In this mode, initially existing big gas bubbles are broken up and form numerous small bubbles with cold plasma inside. Strong fining of gas bubbles and intense mixing of them by discharge (“boiling”) provide a good efficiency of transportation of active species produced by plasma from bubbles to the liquid. This form of discharge requires steady voltage of 25 kV by magnitude. This is an important advantage of the discharge over existing lab-scale sources of cold plasma in liquids, employing expensive high-current and high-voltage pulse-periodical power supplies [3,4]. Another great merit of the second method is insensitivity of the discharge in bubbles to the electric properties of liquids. This ensures versatility of the proposed method because in reality the electric properties of liquids to be sterilized vary over wide range. At last, the sterilization method proposed is much simpler in comparison with the bacterial decontamination by virtue of electroporation , which requires ultrashort (@ 0.1-1 ms) high-voltage pulses to provide high electric field (@ 104 V/cm) in liquids. Besides, such a field can be imposed not upon every liquid, and this restricts the limits of applicability of electroporation.
To this moment, an essential base exists to perform project studies. Earlier performed work on the ISTC project #439 results in development of expandable data banks for processes being of interest for present studies and in development of numerical codes including the 2D code for modeling corona dynamics. At present project participants have created research samples of plasmachemical reactors, and trial experiments have been performed on sterilization of such tough and die-hard microbiological objects as bacteria spores.
It was shown that the discharge in a liquid with gas bubbles and the discharge over agar surface, both, killed almost 100% of very tough and die-hard spores of Bacillus after a few of tens of seconds treatment. Besides, the widely spread over surface discharge was successfully applied to cold treatment of thin polymer films . Absence of local damages of soft materials after plasma treatment opens new possibilities for sterilization and disinfection of different polymer and paper pieces. This is of a big interest in connection with protection against bio-terrorism. In summary, the preliminary results of project participants convince that execution of the project may result in appearance of new very effective sterilization methods of liquids and solid surfaces based on proposed cold atmospheric pressure plasma sources.
It is planned in this project to develop not only new sterilization methods, but also to prove new methods of control of environmental safety of gases effluent from sterilization plants. Nowadays, environmental safety of flue gases is controlled by methods of physics and chemistry, which are laborious, expensive and not versatile. Control of gas toxicity with bio-tests should be more effective, because it demonstrated integral action of all harmful species (which may be identified or not identified by physical and chemical diagnostics) in effluent gas. These tests give a direct evidence of gas toxicity for environment. For bio-testing it is assumed to use photo-bacteria and micro-algae in combination with methods of electro-orientation and osmose-optics. Thus, the project reveals a comprehensive approach to development of new sterilization methods, which provides high efficiency and environmental safety of designed facilities for plasma treatment of liquids and solid surfaces.
1. Study experimentally and theoretically key processes involved in formation of cold atmospheric pressure plasma near surface of sterilized objects in discharges with widely spread over surface streamers and in gas bubbles in liquids.
2. Study experimentally and theoretically interaction of cold plasma in dense gases and liquids with microorganisms, spores, viruses and microorganism bio-films resulting in their killing.
3. Develop the bio-test methods applicable to control biological safety of gases effluent from sterilization plants.
4. Develop non-specific application prototypes of gas and liquid sterilization plants based on usage of proposed discharges to prove novel approaches in sterilization of liquids and surfaces, providing fast, energy-saving and environmentally safe sterilization of treated objects keeping them in their entity.
A number of problems should be solved to achieve the project goals:
– study dynamics of the discharge with widely spread over surface low-current streamers and the discharge in a liquid with gas bubbles for different compositions of gases and liquids and electric circuit parameters;
– determine, what active species are formed in cold atmospheric pressure plasma, produced by novel discharge forms;
– study inactivation processes of microorganisms, spores, viruses and bio-films of microorganisms by cold plasma at surfaces and in liquids and find out plasma parameter ranges providing an effective sterilization;
– develop diagnostic systems for measurements parameters of cold atmospheric pressure plasma produced by novel type discharges at/near surface and in gas bubbles in liquids;
– elaborate an optimum design of electrodes and sterilization plants providing strong interaction of plasma with sterilized objects and hence a high sterilization efficiency for novel discharge forms.
Expected basic results:
1. Experimental and theoretical data describing properties of novel types of discharges (the discharge in a liquid with gas bubbles and the discharge at/near surface of sterilized objects), including parameters of cold plasma produced by these discharges for different conditions of their maintenance.
2. Experimental and theoretical data about mechanisms and destruction efficacy of microorganisms, spores, viruses and bio-films of microorganisms by novel discharge types for different gas and liquid compositions, parameters of electric circuits and treatment doses.
3. Experimental and theoretical data about survival of different microorganisms in gases effluent from sterilization plants activated with novel discharge types.
4. Significant progress in insight into the character of processes regulating cold plasma dynamics in dense gases and liquids and interaction of this plasma at atmospheric pressure with microorganisms.
Expected application-specific results:
1. Elaboration of novel effective methods to produce atmospheric-pressure cold plasma in gases, liquids and on surfaces of different objects.
2. Development of cost- and energy-effective methods for sterilization of liquids and surfaces at atmospheric pressure exploiting proposed discharges.
3. Selection of specific bio-tests to control biological safety of gas streams, effluent from sterilizators.
4. Development of methods of diagnostics/description of processes controlling cold plasma dynamics in dense gases and liquids and interaction of plasma with microorganisms.
Applicability of the obtained results will not be restricted by the field of cold plasma sterilization. Novel cold plasma reactors developed are easy scalable and do not require expensive high-voltage pulsed technique. They can be successfully applied in the following areas, progress in which will improve life quality of the modern society:
– Protection of industrial materials and products from bio-damage and bio-corrosion (benefit: significant extension of life duration for materials and products, operated in difficult of access locations or in extreme cases);
– Cleaning sanitary or manufacturing water from harmful microorganisms (benefit: treatment of water by bubbles filled with cold plasma will reduce or eliminate use of chlorine for disinfection and sterilization, and hence formation of carcinogenic chlorine-organic substance in water will be slowed down or stopped);
– Treatment of foodstuffs and edible raw material (benefit: more safe in comparison with radicidation);
– Cold plasma treatment of soft surfaces at atmospheric pressure including coating by protective films, treatment of fabrics, polymer films, as well as mail envelopes, banknotes and plastic cards as a measure against bio-terrorism, etc. (benefit: atmospheric pressure plasma treatment is less expensive than at low gas pressure, because there is no need in expensive vacuum equipment, and is more environmentally safe than chemical treatment).
Bio-tests can be applied to environmental safety control including exhaust gas monitoring in motor transport and waste gas and liquids in industry (benefit: bio-test gives a result from an integral action of all harmful pollutants, and hence is more adequate for evaluation of environmental safety of waste streams).
Project participants have a high skill and more than 20-year experience in research and development work in fields of plasma physics and technology and microbiology. A number of ISTC projects were successfully completed (№ 199, № 439, № 1344), as well as of RFBR project (№ 97-02-17888), and results of the work serve as a basis and stimulus for preparing the present project. To perform basic and applied researches planned and prove novel sterilization methods, project participants will comply with the technical approach and methodology, which are world over used in science and engineering practice. It means that comprehensive experimental research carried out with usage of different and complementary diagnostics will be combined with theoretical and numerical modeling of phenomena studied.
The proposed project completely conforms to the ISTC purposes. An important merit is the fact that it is inter-disciplinary one in nature and combines efforts of experts in different scientific fields earlier engaged in an activity connected with development of mass-destruction weapon and defensive means. The project is aimed to perform fundamental and applied researches on plasma physics and microbiology to develop new and effective technologies for environmental safety and health care. The project objective is improvement of life quality of modern society, therefore it is urgent for all advanced countries. This will assist to involvement of project participants in international scientific society. Effective sterilization methods are needed in medicine/biology and in industry, transportation engineering, agriculture and many others, as well (trade, tourism, hotel business and so on). Thus and so, the technologies to be developed possess a high commercial potential and respond to Russian programs in transition to market economies.
Foreign collaborators will exchange by information and data resulting from project execution, do joint research on project topics, provide comments to the annual technical reports submitted by project participants to the ISTC, conduction of joint seminars, and help in dissemination of project results and search of partners for further implementation of developed by authors technologies. Project participants have a long-standing alliance with expected collaborator Professor C. Leys established during performing of our former project #439 supported by the ISTC. Due to our common efforts, lab-scale non-thermal plasma reactor based on glow discharge at atmospheric pressure is occurred in the laboratory of Professor C. Leys. At present, this reactor is used for experiments on cleanup of exhausted gases by non-thermal plasma at atmospheric pressure. In future, this reactor can be used for cross-checks of results obtained in the course of project implementation.
1. T. Montie, K. Kelly-Wintenberg, and R. Roth, IEEE Trans. Plasma Sci., 28(2000), 41-50.
2. Non-Thermal Plasma Techniques for Pollution Control (1992: Cambridge, England), NATO ASI Series G: Ecological Sciences, Vol. 34, Parts A and B, Edited by B. Penetrante and S. Schultheis.
3. A. Anpilov, E. Barkhudarov, Yu. Bark et al, J. Phys. D: Appl. Phys., 34(2001), 993-999.
4. C. Yamabe, T. Miichi, S. Ihara, N. Hayashi, and S. Satoh, Proc. XIII Int. Conf. G D -2000, Vol. 2, 684-687.
5. K. Schoenbach, R.Joshi, R.Stark, F.Dobbs, S.Beebe, IEEE Trans. Diel. Electr. Insulat., 7(2000), 637-645.
6. Y.Akishev, S.Kroepke, J.Behnisch, A.Hollander et al, HAKONE-VII, Greifswald, Germany, 2000, Vol. 2, 481-485.