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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.
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Influence of electrolysis on the degradation of dye water solutions
Olexová, Barbora ; Možíšková, Petra (referee) ; Kozáková, Zdenka (advisor)
The basic subject of this thesis is to investigate the influence of electrolysis on degradation of organic dyes in aqueous solutions. Electrolysis is a physically-chemical process, during which - under the influence of direct current - chemical reactions proceed inside the system. By choosing efficient conditions it is possible to achieve fundamental changes in the structure of organic compound’s molecules and on the basis of that for example their gradual degradation. This effect can be used in the process of wastewater treatment. The main task of the thesis is to analyse the influence of variously chosen chemical and physical conditions on the rate of degradation of azo dyes, which is the largest group of organic dyes used in industry and from this reason in great amounts contained both in mill residues and sewage water. Azo dyes have been selected for this experiment for their good solubility in water. Other advantage is that their degradation is accompanied by visible decoloration of the solution and their concentration in solution can be easily determined by UV-VIS spectrometry. Concretely two direct azo dyes - C.I. Direct Blue 106 and C.I. Direct Red 79 - have been chosen. The experiment was carried out in a simple reactor consisted of a bath with a stirrer into which two electrodes were installed and attached to the source of direct voltage. Every series of measurement proceeded at constant current which values were varied in range from 100 mA to 1 000 mA. The electric voltage ranged from 7 V to 22 V. Several samples were taken away from the solution during the experiment and the decrease of dye concentration was evaluated in every series. This evaluation validated the hypothesis that the dyes contained in the solution really degraded. This process was also connected to the expected bleaching of the solution. Decoloration of aqueous solution of dye is caused by disruptions in the structure of the dye molecule which is loosing its characteristic sections that cause colourfulness (a conjugate system of double bonds and presence of appropriate substitutes). A total amount of measured series was 16 with various input conditions (Fe and Pt electrodes, electrolytes NaCl, Na2SO4, and NaNO3 and their different concentrations, different current values) which more or less influenced the rate of degradation of investigated substances. It was found out that the blue dye is more likely to be electrolytically degraded. Chemical structure of its molecules, which is smaller and less branched than molecules of the used red dye, could be the source of that. The greatest degradation of the blue one proceeded at two chosen maximum values of constant current 800 mA and 1 000 mA. It could be assumed that current enhancement through the system induces higher dye concentration decrease. Degradation of the blue dye proceeded faster by using electrodes made of stainless steel than the platinum electrodes. The most suitable electrolyte was shown to be sodium chloride. When higher concentration (or conductivity) of electrolyte was used higher efficiency of degradation process was observed.
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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.
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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 %.
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Spectroscopy of VOC degradation by surface discharge catalyzed by TiO2
Veverková, Radka ; Slavíček, Pavel (referee) ; Kozáková, Zdenka (advisor)
Bachelor thesis is focused on the study of degradation of volatile organic compounds in surface discharge catalysed by TiO2. Volatile organic compounds are dangerous both for human beings and the environment. Therefore it is necessary to eliminate volatile organic compounds. Plasma technology is one of the options how to reach their efficient removal. The experiment was carried out in the plasma reactor with electrodes for surface discharge. One or two layers of TiO2 catalyst were deposited on one of the electrodes. Nitrogen was used as a carrier gas and it was mixed with air before entering the reactor. The radiation emitted by the discharge during the degradation of VOC was transmitted via optical fibre to the optical emission spectrometer Jobin Yvon TRIAX 550. Toluene, hexane, cyklohexane and xylene were used as model VOCs. During the experiment the impact of input power on catalysed or non-catalysed degradation of VOC by the discharge has been monitored. Using optical emission spectrometry it is possible to determine some important parameters of surface discharge, such as rotation and vibration temperature. The values were determined for each measurement in the range from 650 to 1050 K for rotation temperature and from 1600 to 1950 K for vibration temperature. The average error of determination was 100 K for rotation temperature and 120 K for vibration temperature. It was found, that the catalyst is without effect on the rotation and vibration temperature. In contrast, change of discharge input power significantly influenced both rotation and vibration temperature. Significantly different values of rotation and vibration temperature were obtained in the presence of particular compound for lower input power, while these values were similar for higher input power. Further, the spectral bands of nitrogen, oxygen and NO were identified from emission spectra. The obtained results may be used as a fundament for further study of volatile organic compounds decomposition in surface discharge.
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Diagnostics of diaphragm discharge in liquids
Dřímalková, Lucie ; Krčma, František (referee) ; Kozáková, Zdenka (advisor)
The main goal of this thesis is the diagnostics of the diaphragm discharge generated in liquids. Although many applications of electric discharge in liquids have been developed during the last years, the exact mechanism of the discharge ignition is not sufficiently known up to now. Based on this reason, this work focused on the investigation of processes before the discharge ignition, breakdown parameters and the discharge itself both in the irregular and stable regime. Using two kinds of inorganic salt solutions the work studied the influence of conductivity and electrolyte kind on the diaphragm discharge and its static current-voltage characteristics. The last task of the work investigated the emission spectra produced by the discharge. The theoretical part of the work presents mechanisms of the discharge generation in gases including the description of particular kinds of known discharges. The base theories of the discharge ignition in liquids are mentioned as well. Experiments were carried out in the reactor divided by the dielectric barrier (diaphragm) with a central pin-hole into two electrode spaces. Diaphragm was made of PET and the pin-hole initial diameter was 0.4 mm. Stainless steel electrodes were installed in the same distance of 2 cm from the barrier and symmetrically with respect to the diaphragm. Time resolved characteristics of current and voltage were recorded using two-channel oscilloscope which detected their output values. Parameters were measured by the constantly increasing DC voltage with a step of 50 V. When the regular discharge was ignited voltage had been gradually decreased. Used solutions contained sodium sulphate or sodium phosphate electrolyte at six different conductivities. Radiation emitted by the discharge was recorded by the spectrometer Jobin Yvon TRIAX 550. Emission spectra were investigated for one electrolyte at two different conductivities. The part with results presents all dependencies that were achieved during the measurements and all obtained data are compared. Recorded time resolved characteristics determine breakdown moment and describe current and voltage in particular parts within the static current-voltage curve. The work compares the influence of conductivity change on current-voltage characteristics as well as the effect of inorganic salt kind. By the conductivity enhancement the measured curve moves towards lower voltage which means that the breakdown voltage is decreased. Changing the inorganic salt the change of voltage related to the creation of bubbles in the diaphragm surroundings is observed. However, the change of electrolyte does not induce any significant change of the breakdown voltage. The last part of the work was focused on the optical emission spectroscopy of the discharge. Typical line system of OH radicals was identified in measured spectra which intensity was not dependent on the salt concentration. The work show particular processes taking place in the diaphragm surroundings when DC voltage is applied on the electrodes in electrolyte up to the diaphragm discharge ignition. Further, results describing the influence of conductivity and electrolyte changes on the processes are presented. The breakdown moment of the discharge and its dependence on the solution conductivity was determined. Optical emission spectroscopy revealed the contents of radiation emitted by the discharge.
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Study of sterilization effect of diaphragm discharge in liquids
Holíková, Lenka ; Slámová, Jitka (referee) ; Kozáková, Zdenka (advisor)
The main objective of this thesis is to study the sterilizing effect of diaphragm discharge in liquids. Sterilization is a process, which can eliminate all forms of life. Generally, sterilization is divided into physical and chemical methods. Plasma sterilization is ranked among physical methods although the action of chemical processes participates in the decontamination as well. Effects of UV radiation, free radicals and temperature are utilized in these methods. Fungi spores of Aspergillus niger F8189 and bacteria spores of Bacillus subtilis are selected as model organisms. Aspergillus niger microorganism is suitable for its resistance to changes in pH and it is viable in a wide range of pH values. Bacillus subtilis is chosen because of a good heat resistance. Diaphragm discharge is one of the possible types of electrical discharges in generated liquids. It is a low-temperature plasma, which is generated using a high DC voltage. In the created plasma streamers various physical and chemical processes rise. The chemical processes are mainly the generation of active species and particles that initiate subsequent chemical reactions and attack mould spores and bacteria in liquids. The physical processes include shock waves, strong electric field and ultraviolet radiation. Experiments were conducted in a reactor with separate cathode and anode space. In the dielectric barrier PET diaphragm with a pin-hole (initial diameter of 0.4 mm) was attached. Enlargement of the hole was observed as a result of degradation of material at the edge of holes due to the discharge. Degradation of spores was observed, depending on the time and on the input power. Other parameters measured were pH, conductivity and temperature. Experiments did not show any difference of discharge activity in the cathode and anode area. The main factor in the removal of spores Aspergillus niger was probably the temperature because no demonstrable effect of sterilization by the diaphragm discharge operation had been observed when heat resistant Bacillus subtilis was used. Also, it was made an attempt, which has been studied only the temperature effect of the fungi spores of Aspergillus niger. The samples were placed in a thermoregulator, where it was simulated the same temperature increase as at the discharge. The experiment had a similar course as an attempt at the discharge.
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Isolation of fulvic acids from soil origin and fluorescence study
Rubínková, Eva ; Kozáková, Zdenka (referee) ; Fasurová, Naděžda (advisor)
Aim of this bachelor thesis was to find the optimal procedure and evaluation of soil fulvic acid (FA) isolation (soil type Eutric Cambisol, locality Vatín). Soil Cambisol contained higher amount of fulvic acid than humic acid (37,5%). Isolation and purifying of fulvic acid was made with 0,3 % yield. Fluorescence measurement by synchronous mode was used and compared with spectra of FA standard Elliot II. SFS spectra were similar. The main fluorophore of FA sample at excitation 358 and emission 448 nm from SFS spectra was determined.
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Study of influence of organic dye structure on their decomposition in the diaphragm discharge in liquids
Pajurková, Jana ; Fasurová, Naděžda (referee) ; Kozáková, Zdenka (advisor)
The main goal of presented thesis is to study the influence of organic dyes structure on its degradation in diaphragm discharge in liquids. Diaphragm discharge is a kind of non-thermal plasma that can be generated in liquids by the application of high voltage. In plasma channels (so-called streamers), many physical and chemical processes are formed. High electrical field, shock waves and last but not least emission of electromagnetic waves in the range of visible and ultra-violet radiation appear among physical processes. The most important chemical process is generation of active species. These species initiate chemical reactions and could attack molecules of organic compounds contained in water solution. The reason why organic dyes were chosen in this study is its visible destruction, because it is related to its decolouration. Further, UV-VIS spectroscopy for the determination of concentration during the experiment can be used. Organic dyes are good models of organic substance often contained in waste water and for which removal classical biological, chemical and physical methods aren’t sufficient. Selected dyes were mostly from the group of azo-dyes: Acid Red 14, Acid Red 18, Acid Yellow 23, Direct Blue 53, Direct Red 79, Direct Red 80, Direct Yellow 29, Food Yellow 3 and further, Acid Blue 74 (indigotic dye) and Direct Blue 106 (oxazine dye). Experiments were carried out in a special batch discharge reactor with the anode and the cathode spaces divided by a non-conductive barrier, where the diaphragm with a pin-hole was placed. Measurement showed different removal in the anode and cathode space. We have supposed it was caused by different streamers features and energetic conditions. Dyes were decomposed with higher efficiency in the anode space where the final concentration reached 40 % of the initial concentration while it remained about 90 % in the cathode space. In this thesis the influence of dyes structure on the dye decomposition by electrical discharge was investigated. Dyes consisted of small molecules and dyes with many substitutes bounded on aromatic ring were decomposed more easily than dyes consisted of big molecules. The shift of characteristic wavelength on both directions (to shorter as well as longer wavelength) was observed during the experiments especially when the Direct dyes were decomposed. This phenomenon was probably due to the formation of intermediate product, which have different characteristic wavelength than the primary compound. In general, colourfulness is given by long conjugated systems of double bonds with substitutes bounded on an aromatic ring. Each change in the molecule structure provides the colour change and this could be the possible reason of the shift of characteristic wavelength. The other task was the comparison of degradation process efficiency by the mean of electrolysis and diaphragm discharge. Results showed that electrolysis (30 W) was more convenient for degradation of dyes consisted of small molecules while diaphragm discharge (130170 W) suited for complex molecules. For degradation of small molecules, oxidation on the anode assumed to be the most effective process that is initiated by electrolysis. For degradation of big molecules, attack of active species produced by the discharge is necessary.
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Study of electrolytic influence on organic dye decomposition in the diaphragm discharge in liquids
Davidová, Jaroslava ; Rašková, Zuzana (referee) ; Kozáková, Zdenka (advisor)
This Bachelor thesis is focused on study of chemical and physical influences which are proceed in diaphragm discharge in water solution. These processes could be used in water treatment. If DC non-pulsed voltage is applied, a significant influence of electrolysis must be taken into account. The main goal of this thesis is the estimation of electrolytic contribution to processes in the discharge. Theoretical part describes basic theory about creation of electrical discharges in water and electrolysis with emphasis on processes leading to destruction of organic compounds. Production of reactive particles (radicals, hydrogen peroxide, ozone, etc.) and electrochemical reactions on electrodes mainly belongs among these processes. This part describes analytical method (UV-VIS spectroscopy) which was used for determination of organic dyes concentration as well. Experimental part is oriented to experiment procedure which was carried out in an apparatus with separated anode and cathode area. Separation was made by dielectric diaphragm with a pinhole in the centre. Its initial diameter was 0.25 mm. Electrolytic decomposition was carried out at constant current of 30 mA and supplied power was about 14–32 W. Two Saturn dyes (Direct Blue 106 and Direct Red 79) were selected for experiments. As the decomposition was related to decoloration of the solution, UV-VIS spectroscopy in the range of 350–700 nm was used for determination of dye concentration. Next part focused on results presents various factors which had remarkable effect on decomposition of organic dyes. These factors were: various polarities of electrodes, conductivity and pH of solution, applied power, kind of electrolyte and structure of organic dye. The electrolysis had the significant influence on decomposition of small organic molecules. Decomposition was running mainly in the anode area where so called negative discharge was created. Optimal conditions were set by NaCl electrolyte with concentration providing initial conductivity of 500 S·cm-1. By the NaNO3 electrolyte half decomposition efficiency was achieved and in Na3PO4 electrolyte, the decomposition even didn’t run. The decomposition in the anode area was stimulated by the low pH value, which was decreasing during electrolysis. Generally, higher decomposition was achieved by the discharge than by pure electrolysis but the electrolysis had higher efficiency. In pure electrolysis, high rate of removal can be achieved by the application of a relatively low power. When bigger organic molecules were decomposed, the efficiency was higher by applying the discharge.
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