|
|
Influence of humidity on total sterilisation effect of dielectric barrier discharge
Kramárová, Petra ; Bartlová, Milada (referee) ; Kozáková, Zdenka (advisor)
The main subject of this diploma thesis is the study of the effect of humidity on the total sterilization effect of the dielectric barrier discharge. Sterilization is a process which can eliminate all forms of life. The plasma sterilization is one of the methods that are suitable for sterilization of temperature and chemical sensitive materials. This sterilization method was proved to be effective on the wide spectrum of procaryotic and eucaryotic microorganisms. Basically, the main inactivation factors for cells exposed to plasma are heat, UV radiation and various reactive species. Dielectric barrier discharge (DBD) operating at atmospheric pressure was used for the sterilization of the samples. The discharge was generated in dry air and in humid air. The plasma power densities were 2 160 mW.cm-3, 2 279 mW.cm-3 and 2 760 mW.cm-3 (dry air) or 2 326 mW.cm-3 and 2 850 mW.cm-3 (humid air). Humidity of air was achieved using a wash bottle filled with water through which air flowed into the DBD reactor. Fungi spores of Aspergillus niger were used as model microorganisms. Whatman paper No. 1 was used as the carrying medium. When comparing sterilization efficiency of humid and dry air operating at the same conditions, the higher sterilization effect was observed in humid air. The sterilization effect of the DBD generated in air was compared with results obtained during plasma generation in argon and nitrogen. At the same conditions, the highest sterilization effect was observed in argon, followed by humid air, nitrogen and dry air. It was found out that in our experimental setup the active species are probably the main inactivation mechanism. The influence of temperature on the inactivation of microorganisms was completely negligible. The discharge parameters were studied by means of the optical emission spectroscopy (OES). Plasma treated samples were analyzed employing scanning electron microscopy (SEM). Damage of the microorganisms due to the effect of plasma as well as plasma effect on the structure of the carrying medium was evaluated.
|
|
|
Study of elementary inactivation processes acting during sterilization of procaryotic systems in dielectric barrier discharge
Bittnerová, Zuzana ; Sťahel, Pavel (referee) ; Kozáková, Zdenka (advisor)
Presented master’s thesis is focused on the study of the elementary inactivation processes acting during sterilization of procaryotic systems in dielectric barrier discharge (DBD). Sterilization is an important biomedical and food-industry application and plasma sterilization is one of the methods, which are suitable for sterilization of heat and chemical sensitive materials. Biologically contaminated samples were treated in dielectric barrier discharge operated at atmospheric pressure. The discharge was generated in argon and in nitrogen. The plasma power density was 2725,93 mW cm–3 in argon and 2325,93 mW cm–3 in nitrogen. Gram positive bacteria Bacillus subtilis and gram negative bacteria Escherichia coli were used as a bioindicator. Bacteria were spread onto the surface of Whatman No.1 filtration paper. The influence of UV radiation, reactive species, heat and plasma discharge where the synergistic function of all of the agents was studied. Effects of UV radiation and temperature were studied separately. In order to separate the effect of UV radiation generated by DBD the quartz glass transmitting UV radiation was employed. During the plasma exposition selected samples were covered with the quartz window while other samples were directly exposed to the plasma. Covered samples were exposed to UV radiation and temperature (which cannot be eliminated), samples without quartz window were directly plasma exposed (treated). Results show that for covered samples the lower inactivation was reached than by the samples directly exposed to plasma. When studying the effect of temperature, the temperature between the DBD electrodes was measured by means of a thermocouple. Afterwards the samples were placed in an oven and exposed to the same temperature as was measured between the electrodes. By comparing the results of heat treated samples and plasma treated samples it can be assumed that the influence of the temperature during the sterilization process in DBD is very low. The discharge parameters were studied by means of the Optical Emission Spectroscopy. Plasma treated samples were assessed employing Scanning Electron Microscopy (SEM). Damage of Bacillus subtilis cell wall due to the effect of plasma was observed while no effect of plasma on the structure of filtration paper was detected.
|
|
|
Study of elementary inactivation processes acting during sterilization of eucaryotic systems in dielectric barrier discharge
Vojkovská, Hana ; Machala, Zdenko (referee) ; Kozáková, Zdenka (advisor)
This diploma thesis is focused on studying of the effect of the dielectric barrier discharge (DBD) on eucaryotic microorganisms. Plasma sterilization is considered to be an alternative method to conventional sterilization processes. Contrary to standard decontamination methods it doesn´t stress exposed material by heat, pressure and chemicals. Plasma acts on eucaryotic and procaryotic systems by means of synergy of three inactivation mechanisms. They are various reactive species, UV radiation and heat. The Aspergillus niger has been chosen as a bio-indicator enabling to evaluate the effect of plasma assisted microbial inactivation. Plasma was generated in dielectric barrier discharge (DBD) at atmospheric pressure. Nitrogen and argon were used as working gases, paper and PET foil were used as carrying media. The influence of various working conditions on the sterilization effect was studied. Namely it was the influence of plasma exposition time, plasma power density, the type of operating gas and type of supporting medium. The effect of UV radiation in combination with temperature, temperature and direct plasma were studied separately. According to our results the efficiency of DBD increases with plasma power density, resp. plasma exposition time. When comparing sterilization efficiency of nitrogen and argon operating at the same conditions, the higher sterilization effect was observed in argon. The influence of the carrying medium on sterilization effectiveness was proved. It was caused by the different structure of surface. It was found out, that in our experimental setup the active species are probably the main inactivation mechanism. The influence of temperature on inactivation of microorganisms was negligible. The combination of UV radiation and temperature reached the decontamination level about 2 orders. The discharge parameters were studied by means of optical emmision spectroscopy. Scanning electron microscopy enabled to evaluate possible damage of exposed materials through DBD.
|
|
|
Study of the sterilization effect of temperature and UV light present in dielectric barrier discharge
Kramárová, Petra ; Grossmannová, Hana (referee) ; Kozáková, Zdenka (advisor)
The main theme of this bachelor thesis is to study the effect of temperature and UV radiation to the total sterilizing effect of dielectric barrier discharge. Sterilization is a process, which can eliminate all forms of life. The presented bachelor thesis discusses plasma sterilization, which is one of the method, which are suitable for sterilization of heat and chemical sensitive materials. This sterilization method is effective on the wide spektrum of procaryotic and eucaryotic microorganisms. Basically, the main inactivation factors for cells exposed to plasma are heat, UV radiation and various reactive species. In my thesis a dielectric barrier discharge (DBD) operating at atmospheric pressure was used for the sterilization of the samples. Plasma was generated in argon and nitrogen. According to the previous measurement the best sterilization results were observed using plasma power input 2 562,96 mW•cm-3 (argon) a 2 044,44 mW•cm-3 (nitrogen), therefore the same plasma power input was applied during our measurement. Fungi spores of Aspergillus niger were used as model organisms. Whatman paper No. 1st was used as the carrying medium. Each sample series was exposed to plasma for 5, 10, 20, 40, 60, 120 and 180 s. In order to separate the effect of UV radiation generated by DBD the quartz glass transmitting UV radiation was used. During the plasma exposition one of the sample was covered with the quartz window and the other sample was directly exposed to the plasma, afterwards the results were compared. The microbial abatement observed for the samples covered by quartz window was much lower than for the the samples directly exposed to the plasma. In first case the UV radiation and temperature is the main inactivation mechanism, while in the latter one the synergistic effect of UV radiation, temperature and active species is employed. Furthermore the effect of plasma sterilization increases with increasing the plasma exposition time. While comparing results observed for the argon and nitrogen, better results were achieved in argon. Effects of UV radiation and temperature were studied separately. The temperature between the DBD electrodes was measured by means of thermocouple. Afterwards the samples were placed in an oven and exposed to the same temperature as was measured between the electrodes. By comparing the results of heat treated samples and plasma treated samples it can be assumed that the influence of the temperature during the sterilization process in DBD was negligeable. The discharge parameters were studied by means of the optical emission spectroscopy.
|
|
|
Study of sterilization effect of dielectric barrier discharge on eucaryotic microorganisms
Vojkovská, Hana ; Ing.Hana Grossmannová, Ph.D. (referee) ; Kozáková, Zdenka (advisor)
Nowadays the wide spectrum of decontamination methods are used for the inactivation of microorganism on various materials and subjects. The serious disadvantage of the conventional decontaminations methods is stressing of the exposed material by heat or chemicals. The presented bachelor thesis discusses plasma sterilization, which is more friendly and more effective on the wide spectrum of procaryotic and eucaryotic microorganisms. Basically, the main inactivation factors for cells exposed to plasma are heat, UV radiation and various reactive species The work was focused on studying of the effect of the dielectric barrier discharge (DBD) operating at atmospheric pressure on bioindicator Aspergillus niger. Plasma was generated in nitrogen and argon. Paper and PET-foil wer used as the carrying medium. The influence of various working conditions on the efficiency of plasma sterilization was studied. Namely it was the influence of plasma exposition time, plasma power density, the type of operating gas and type of the medium supporting the microorganism. According to our results the efficiency of the plasma sterilization increases with increasing plasma power density, resp. the plasma exposition time. When comparing the results observed for the same conditions in argon and nitrogen the higher sterilization effect was reached in argon. The sterilization time was 40 – 120 second in dependence to plasma power density, gas and carrying medium. Furthermore the influence of the carrying medium on the sterilization efficiency was prooved. It was shown, that porous materials have a ”shadowing effect” for microorganisms. The microorganism may penetrate into the paper material and embed in pits and cavities. Such penetration could preclude the interaction of plasma with the microorganism, thereby decreasing the efficiency of spore inactivation. Additionaly paper porosity complicates the detachment of spores into solution, so it is reached less microorganisms as from the PET-foil. The discharge parameters were studied by means of the optical emission spectroscopy.
|
|
|
Study of sterilization effect of dielectric barrier discharge on procaryotic microorganisms
Bittnerová, Zuzana ; Ing.Hana Grossmannová, Ph.D. (referee) ; Kozáková, Zdenka (advisor)
Presented bachelor thesis is focused on sterilization effect of dielectric barrier discharge on procaryotic microorganisms. Sterilization is important biomedical and food-industry application and plasma sterilization is one of the method, which are suitable for sterilization of heat and chemical sensitive materials. Biologicaly contaminated samples were treated in dielectric barrier discharge operated at atmospheric pressure. The discharge was generated in argon and in nitrogen. Gram positive bacteria Bacillus subtilis was used as a bioindicator. Bacteria was spread onto the surface of paper and PET material. Efficiency of sterilization was evaluated according to exposure time, plasma power density and process gas. The positive effect of DBD on inactivation of microorganism was observed. The efficiency of the plasma sterilization increases with increasing treatment time. As regards plasma power density, the higher density was used the more effective the sterilization was and time necessary for inactivation of all microorganisms was shorter. Sterility was observed within 60 s while using plasma power density 2,37 W/cm, when using plasma power density of 1,78 W/cm longer treatment time is neccesary. The sterilization was more effective if argon was used as a process gas. Time necessary for the most reduction of microorganisms in argon was 10 s, while using nitrogen the reduction was only 50 %.
|
guest ::
